The Songshugou ophiolite, located in the northern Qinling belt, consists mainly of metamorphosed mafic and ultramafic rocks recording details of deformation and metamorphism that occurred during subduction, accretion, and collision along the Shangdan suture in the Qinling orogenic belt. Electron backscatter diffraction measurements revealed that the harzburgites are dominated by olivine C-type crystal preferred orientations (CPOs), which were possibly induced by high pressure during slab subduction. Olivine A-type CPOs were also observed in some harzburgites, representing the remnants of the original fabric in oceanic mantle rocks formed in the spreading center of the Shangdan ocean. Coarse-grained dunites are characterized by B-type CPOs, which may have been caused by melt-rock reactions and/or high water contents in a suprasubduction-zone setting during exhumation. Fine-grained dunites are also dominated by B-type CPOs, suggesting that grain-size reduction related to mylonitization did not result in fabric variations. Combined with the mineral assemblages, application of geothermometry suggested that the Songshugou ophiolite has experienced metamorphism and deformation under amphibolite-facies conditions. Zircons from garnet-bearing amphibole schist are characterized by flat heavy rare earth element (HREE) patterns and low Th/U ratios and yielded a mass spectrometry U-Pb age of 500.5 ± 8.8 Ma, representing the peak metamorphic age of the metamafic rocks. Other zircons displayed relative HREE enrichment and a clearly negative Eu anomaly and gave an age of 492.5 ± 3.0 Ma, constraining the time of the exhumation of the ophiolite. Integrated with all the available regional geology, our new fabric, geochemical, and geochronological data suggest that the tectonic evolution of the Songshugou ophiolite can be proximately constrained as subduction at ca. 500 Ma and exhumation at ca. 492 Ma.

The Qinling orogenic belt, situated in the middle part of the Central China orogenic system, connects the Dabie orogen to the east and the Qilian and Kunlun orogens to the west (Fig. 1). It has been well documented that the Qinling orogenic belt was formed by polyphase collision between the North China block and the South China block (e.g., Mattauer et al., 1985; Zhang et al., 1995a, 1995b, 2001; Ames et al., 1996; Dong et al., 1998, 2003, 2011a, 2011b; Hacker et al., 1998; Zhai et al., 1998; Ratschbacher et al., 2003, 2006; Bader et al., 2013; Dong and Santosh, 2016; Liu et al., 2016; Tang et al., 2016). Two Paleozoic ophiolitic mélange zones, from north to south, the Erlangping and Shangdan sutures, have been revealed in the Qinling orogenic belt, constraining Paleozoic subduction and collision between the North China block and South China block (Zhang et al., 1995a, 1995b, 2001; Dong et al., 2011a, 2011b; Dong and Santosh, 2016). Although some authors have suggested that the Qinling orogenic belt was formed by southward subduction and collision along the Erlangping suture (Xue et al., 1996; Faure et al., 2001; Wang et al., 2011), most researchers have argued that the Qinling orogenic belt represents the northward subduction of Shangdan oceanic crust between the North China and South China blocks and subsequent collision along the Shangdan suture zone, while the Erlangping suture represents the related back-arc basin (Zhang, 1988; Zhang et al., 1995a; Li et al., 1996; Zhu, 2001; Xu et al., 2002; Dong et al., 2011a, 2011b; Dong and Santosh, 2016). Previous investigations of the geochemistry and geochronology of the ophiolites (Zhang et al., 1995, 2004; Dong et al., 2011b) and magmatic and metamorphic rocks (Liu et al., 1995; Wang et al., 2011), as well as sedimentary assemblages (Meng et al., 1994; Yan et al., 2006; Dong et al., 2013), have constrained the tectonic framework and evolutionary history between the North China and South China blocks; however, the detailed tectonic evolution and processes from subduction to collision along the Shangdan suture zone are still under debate. Ophiolites are the remnants of ancient oceanic crust and upper mantle formed at mid-ocean ridges or suprasubduction zones that were subsequently tectonically emplaced onto continental margins (Pearce, 2008, 2014; Dilek and Furnes, 2011, 2014). Therefore, the structure and fabric of the ophiolite from the Shangdan suture zone may preserve detailed records of deformation responding to tectonic processes ranging from rifting to subduction to collision between the North China and South China blocks.

Figure 1.

(A) Location map, (B) simplified tectonic map, and (C) cross section of the Qinling orogenic belt (modified from Dong et al., 2011a, 2018). Abbreviations: NCB—North China block; S-NCB—southern sector of the North China block; NQB—North Qinling belt; SQB—South Qinling belt; N-/S-SQB—northern/southern parts of South Qinling belt; SCB—South China block; LWF—Lushan-Wuyang fault; LLF—Luonan-Luanchuan fault; SDS—Shangdan suture; MLS—Mianlue suture; MBXF—Mianlue-Bashan-Xiangguang fault; TLF—Tanlu fault.

Figure 1.

(A) Location map, (B) simplified tectonic map, and (C) cross section of the Qinling orogenic belt (modified from Dong et al., 2011a, 2018). Abbreviations: NCB—North China block; S-NCB—southern sector of the North China block; NQB—North Qinling belt; SQB—South Qinling belt; N-/S-SQB—northern/southern parts of South Qinling belt; SCB—South China block; LWF—Lushan-Wuyang fault; LLF—Luonan-Luanchuan fault; SDS—Shangdan suture; MLS—Mianlue suture; MBXF—Mianlue-Bashan-Xiangguang fault; TLF—Tanlu fault.

In this study, we conducted new investigations on the microstructure, crystal preferred orientations (CPOs), mineral geochemistry, and zircon U-Pb ages of the mafic and ultramafic rocks in the Songshugou ophiolite. Our new results provide an opportunity to elucidate the detailed deformation that occurred in response to the subduction of the Shangdan ocean and collision along the Shangdan suture zone, as well as the exhumation of the Songshugou ophiolite on the northern side of the Shangdan suture zone, which may help to better understand the tectonic history of the Qinling orogenic belt.

Geological Setting

The Qinling orogenic belt is currently bounded by the Lingbao-Lushan-Wuyang fault to the north and the Mianlue-Bashan-Xiangguang fault to the south (Zhang et al., 2000; Dong and Santosh, 2016). Separated by the Luonan-Luanchuan fault, the Shangdan suture, and the Mianlue suture/Mianlue-Bashan-Xiangguang fault, the Qinling orogenic belt can be divided into four tectonic belts, from north to south, including the southern sector of the North China block, the North Qinling belt, the South Qinling belt, and the northern sector of the South China block (Fig. 1; Dong et al., 2011a, 2013; Dong and Santosh, 2016).

The southern sector of the North China block was overthrust toward the north onto the Paleozoic–Jurassic successions in the North China block along the Lingbao-Lushan-Wuyang fault (Fig. 1C). The basement is constituted by the Neoarchean–Paleoproterozoic Taihua and Tietonggou Complexes, which are composed dominantly of amphibolite and gneiss. The basement is unconformably overlain by the Mesoproterozoic Xiong’er Group, which consists of low-grade metamorphosed volcanic rocks and minor clastic rocks (Zhang et al., 2001; Dong and Santosh, 2016). The continuous Mesoproterozoic Gaoshanhe and Neoproterozoic Luonan Groups, which, respectively, consist of clastic and carbonate rocks, unconformably overlie the Xiong’er Group. The Luonan Group is occasionally overlain by late Neoproterozoic tillites and Cambrian limestones. In addition, scattered Ordovician, Permian, and Mesozoic strata discontinuously outcrop in the southern sector of the North China block.

The North Qinling belt, located between the Luonan-Luanchuan fault and the Shangdan suture, includes the Kuanping Complex, the Erlangping Group, and the Qinling Complex, from north to south, which are separated from each other by thrust faults or ductile shear zones (Figs. 1B and 1C). The Kuanping Complex includes a Mesoproterozoic to Neoproterozoic ophiolite unit and Neoproterozoic terrestrial clastic sediments (Zhang and Zhang, 1995; Dong et al., 2011b, 2014). The Erlangping Group mainly represents back-arc basin ophiolite related to early Paleozoic northward subduction along the Shangdan suture zone (Sun et al., 1996; Dong et al., 2011a, 2011b). The Qinling Complex chiefly consists of highly deformed and metamorphosed Paleoproterozoic to Mesoproterozoic gneisses, amphibolites, and marbles, which were intruded by voluminous Neoproterozoic and early Paleozoic granitoids, and the complex underwent two-phase amphibolite-facies metamorphism in the Neoproterozoic and early Paleozoic (Dong et al., 2011a). The high-grade basement of the North Qinling belt represents a discrete Precambrian terrane separated from the North China block by the Kuanping Ocean (Dong et al., 2014).

The South Qinling belt was overthrust toward the south onto the South China block along the Mianlue-Bashan-Xiangguang fault during the Middle–Late Triassic and Late Jurassic–Early Cretaceous (Fig. 1C; Zhang et al., 1995b; Dong et al., 2011a, 2015). It is characterized by thin-skinned structures indicating a south-vergent imbricated fold-and-thrust system, and it is composed of pre-Sinian basement overlain by Sinian to Triassic sedimentary successions (Zhang et al., 2001; Dong et al., 2011a, 2015, 2016). In the eastern South Qinling belt, the basement consists of the Mesoproterozoic to Neoproterozoic Wudang and Yaolinghe Groups with volcanic-sedimentary assemblages (Ling et al., 2008) metamorphosed under greenschist-facies conditions (Zhang et al., 2000), while the basement is predominantly composed of Archean–Paleoproterozoic plutonic-metamorphic rocks in the Tongbai-Dabie area (Zhang et al., 2000). The sedimentary cover chiefly includes Sinian clastic and carbonate rocks, Cambrian–Ordovician limestones, Silurian shales, Devonian to Carboniferous clastic rocks with interlayered limestones, and Permian–Early Triassic limestones interlayered with minor sandstones (Dong et al., 2011a, 2013).

The northern sector of the South China block, the foreland fold-and-thrust belt, is separated from the South Qinling belt by the Mianlue-Bashan-Xiangguang fault (Figs. 1B and 1C), and it progressively grades into the undeformed Jurassic to Cretaceous sequences within the Sichuan and Jianghan Basins in the main domain of the South China block. It consists of highly metamorphosed Neoarchean–Paleoproterozoic basement, greenschist-facies metamorphosed Mesoproterozoic/Neoproterozoic transitional basement, and a nonmetamorphosed cover sequence (Zhang et al., 1995a, 2001). Both basement units are exposed in the Huangling and Hannan-Micangshan massifs and are intruded by voluminous Neoproterozoic gabbroic and granitic intrusions (Dong et al., 2011c, 2012). The cover sequence mainly consists of uppermost Neoproterozoic clastic and carbonate rocks, Cambrian–Ordovician limestones, Silurian shales, and Permian–Middle Triassic limestones, which are unconformably covered by Upper Triassic molasses to Cretaceous terrestrial conglomerates and sandstones (Dong et al., 2011a, 2013, 2016).

The Songshugou ophiolite was tectonically emplaced to the northern side of the Shangdan suture zone and thrust into the Qinling Complex of the North Qinling belt (Fig. 2). Together with a series of early Paleozoic ophiolites and subduction-related volcanic and sedimentary rocks along the Shangdan suture zone, the Songshugou ophiolite marks the main tectonic boundary between the North Qinling belt and South Qinling belt (Zhang et al., 1995a, 1995b, 2001; Sun et al., 1996, 2002; Dong et al., 2011a, 2011b). It occurs as a NW-SE lenticular block ∼27 km long and ∼3 km wide (Fig. 2). This tectonic block is bounded by the Jieling ductile shear zone to the north, and it is separated from the Qinling Complex and the Fushui gabbroic intrusion by the Xigou shear zone to the south. The ophiolite consists chiefly of metamorphosed ultramafic and mafic rocks.

Figure 2.

Geological map of the Songshugou ophiolite, Qinling orogenic belt (modified from Dong et al., 2008).

Figure 2.

Geological map of the Songshugou ophiolite, Qinling orogenic belt (modified from Dong et al., 2008).

The ultramafic rocks occur as tens of rootless blocks tectonically emplaced within the metamorphosed mafic rocks. The largest lenticular outcrop is ∼18 km long and ∼2 km wide, and it is mainly composed of fine- to coarse-grained dunites and harzburgites with minor diopside veins (Figs. 2 and 3). The ultramafic rocks display continuous foliations (Fig. 3A) dipping SW (∼280°–300°) at high angles (∼70°–80°), aligning subparallel to the strike of the massif. Layered and podiform chromites predominantly occur in the coarse-grained dunites (Fig. 3B). Mylonitic deformation is superimposed on the dunites along the margin of the outcrop. Moreover, the dunites have been intruded by numerous diopside veins (Fig. 3C), which have been sinistrally sheared (Fig. 3D) or highly folded (Fig. 3E). Our previous geochemistry and in situ oxygen isotope investigations suggested that the Songshugou ophiolite was probably formed in a mid-ocean-ridge setting (Dong et al., 2008; Sun et al., 2019).

Figure 3.

Photographs of the ultramafic and mafic rocks of the Songshugou ophiolite. (A) Dunite with distinct foliations. (B) Dunite sample with layered chromite. (C) Diopside veins concordant with the foliations of ultramafic rocks. (D) Sheared diopside veins intruded into the dunites. (E) Highly deformed diopside veins intruded into the dunites. (F) Tight folding of amphibolite. (G) Quartz veins in amphibolite. (H) Sample of garnet amphibolite. The coin is RMB 50 cents (20.5 mm in diameter).

Figure 3.

Photographs of the ultramafic and mafic rocks of the Songshugou ophiolite. (A) Dunite with distinct foliations. (B) Dunite sample with layered chromite. (C) Diopside veins concordant with the foliations of ultramafic rocks. (D) Sheared diopside veins intruded into the dunites. (E) Highly deformed diopside veins intruded into the dunites. (F) Tight folding of amphibolite. (G) Quartz veins in amphibolite. (H) Sample of garnet amphibolite. The coin is RMB 50 cents (20.5 mm in diameter).

The mafic rocks are mainly of amphibolite, garnet amphibolite, and amphibole schist (Figs. 2 and 3). A few garnet amphibolites occur as discontinuous lenses within the amphibolites. The amphibole schists predominantly crop out as the outer part of the mafic rocks. Strong deformation led to the formation of an intensive foliation and lineation defined by strongly oriented amphiboles and plagioclases. These foliations and lineations are generally parallel to the tectonic contacts between the ultramafic rocks, the mafic rocks, and the Qinling Complex. Some tight folds of foliations (Fig. 3F) were also observed in the amphibole schists near the boundary faults. Several quartz veins occur parallel to the foliation (Fig. 3G). Geochemical investigations suggested that the mafic rocks were derived from a mantle source with a Dupal isotope anomaly (Dong et al., 2008). The garnet amphibolites (Fig. 3H), which occur as discontinuous lenses around the biggest ultramafic slice, were documented as retrograded eclogites (Figs. 2 and 3; Liu et al., 1995; Chen et al., 2015). Some high-pressure (HP) mafic granulites (retrograde metamorphosed eclogites) also crop out within the amphibolites, while a few of the felsic granulites are exposed in the Xigou shear zone (Liu et al., 1996). The formation of the garnet-amphibolites and HP metamorphic rocks was considered to have been associated with the oceanic subduction and emplacement of the Songshugou ophiolite (Liu et al., 1995, 2016; Dong et al., 2008; Chen et al., 2015; Tang et al., 2016).

The formation age of the Songshugou ophiolite has been constrained by maximum Re depletion model ages (TRD) of 1.0–0.8 Ga from the ultramafic rocks (Nie et al., 2017; Yu et al., 2017; Sun et al., 2019), zircon U-Pb ages of 973–729 Ma from the mafic rocks (Liu et al., 2004; Qian et al., 2013; Li et al., 2014; Chen et al., 2015; Yu et al., 2016), and a 40Ar-39Ar age of 848 ± 4 Ma from the diopside vein (Chen et al., 2002).

Representative samples of the ultramafic and mafic rocks were collected from the two sections in the Songshugou valley and the Tu’ao area (Fig. 2), and a subset was selected for electron microprobe analyses (EMPA), electron backscatter diffraction (EBSD) measurements, and zircon U-Pb dating.

The ultramafic rocks mainly included harzburgites and coarse-grained and fine-grained dunites (Table 1). The harzburgites were predominantly composed of olivine (∼80%) and orthopyroxene (∼10%), with minor clinopyroxene (0%–3%), chromite (0%–4%), and serpentine (0%–5%). They were mainly characterized by porphyroclastic texture with coarse-grained (up to 2–3 mm) olivine and pyroxene porphyroclasts. The olivine porphyroclasts generally displayed elongated shapes with aspect rations >2 and exhibited high-temperature plastic deformation features, such as undulose extinction, subgrain boundaries, and 120° triple junctions. Some orthopyroxene gains were elongated and displayed kink bands (Fig. 4A); subgrain boundaries were also observed (Fig. 4B). The foliations and lineations were defined by shape preferred orientations (SPOs) of olivines and/or orthopyroxenes (Figs. 4A and 4B).

TABLE 1.

LITHOLOGY, MICROSTRUCTURE, AND FABRIC OF THE SONGSHUGOU ULTRAMAFIC SAMPLES

Figure 4.

Microphotographs of dunite samples from the Songshugou ophiolite taken under cross-polarized light. The thin sections are 40 µm thick. Dashed lines denote the lineation defined by the shape preferred orientations or layering of olivine grains. (A) Elongated orthopyroxene displaying curved cleavage (SSG08). (B) Orthopyroxene phenocryst displaying subgrain boundary and corroded grain shape, surrounded by olivine neoblasts (SSG08). (C) Olivine porphyroclast showing undulose extinction (SSG19–7). (D) Olivine porphyroclast showing subgrain boundaries (SSG19–7). (E) Lineation in fine-grained dunite sample X4. (F) Lineation in fine-grained harzburgite sample X6. Ol—olivine; Opx—orthopyroxene.

Figure 4.

Microphotographs of dunite samples from the Songshugou ophiolite taken under cross-polarized light. The thin sections are 40 µm thick. Dashed lines denote the lineation defined by the shape preferred orientations or layering of olivine grains. (A) Elongated orthopyroxene displaying curved cleavage (SSG08). (B) Orthopyroxene phenocryst displaying subgrain boundary and corroded grain shape, surrounded by olivine neoblasts (SSG08). (C) Olivine porphyroclast showing undulose extinction (SSG19–7). (D) Olivine porphyroclast showing subgrain boundaries (SSG19–7). (E) Lineation in fine-grained dunite sample X4. (F) Lineation in fine-grained harzburgite sample X6. Ol—olivine; Opx—orthopyroxene.

The medium- to coarse-grained dunites were mainly composed of olivine (>90%), with minor pyroxene (0%–5%), chromite (0%–3%), and serpentine (0%–2%). They were of equigranular (∼0.2–0.5 mm) or porphyroclastic texture, and frequently serpentinized. Dislocation indicators such as undulose extinction and subgrain boundaries of olivines were commonly observed (Figs. 4C and 4D). The foliations and lineations were defined by SPOs of olivines as observed in the field (Figs. 3A–3D). Some dunites were composed of chromite-rich layers, which were parallel to the foliations (Fig. 3B). In addition, the diopside veins were commonly concordant with the foliation of dunites (Figs. 3C–3E). Moreover, orthopyroxene grains were generally in corroded shape and surrounded by fine-grained olivine neoblasts and sparse spinels, suggesting the rocks may have resulted from reaction of orthopyroxene = olivine + SiO2-rich melt between peridotite and boninitic melt, which led to dissolution of pyroxene and precipitation of olivine (Kelemen et al., 1995; Malpas et al., 2003; Tommasi et al., 2004; Sun et al., 2019).

The fined-grained dunites or mylonitic dunites were characterized by intensive ductile deformation showing elongated or fine-grained fabric, with grain size of 0.1–0.2 mm, suggesting that the ophiolite experienced high-temperature plastic deformation. Olivine porphyroclasts occasionally were observed, displaying undulose extinction and/or subgrain boundaries. The foliation and lineations were distinct in these samples, defined by SPOs of olivine and chromite (Figs. 4E–4F). The lineation was cut by anthophyllite and tremolite crystals (Fig. 5). Anthophyllite and tremolite are amphibolite minerals, which are mostly formed by fluid-rock reactions of orthopyroxene + H2O = anthophyllite + olivine, and orthopyroxene + clinopyroxene + H2O = tremolite + olivine, respectively (Cao et al., 2016).

Figure 5.

(A) Tremolite crystals cutting olivine grains and being cut by meshed serpentines (SSG17–6). (B) Anthophyllite crystals cutting talc and olivine grains (SSG-X3). (C) Petrogenetic grid for water-saturated ultramafic rocks in the system CaO-MgO-SiO2-H2O (modified from Winter, 2001). The thin sections are 40 µm thick. Atg—antigorite; Ath—anthophyllite; Di—diopside; En—enstatite; Fo—forsterite; Qtz—quartz; Tlc—talc; Tr—tremolite.

Figure 5.

(A) Tremolite crystals cutting olivine grains and being cut by meshed serpentines (SSG17–6). (B) Anthophyllite crystals cutting talc and olivine grains (SSG-X3). (C) Petrogenetic grid for water-saturated ultramafic rocks in the system CaO-MgO-SiO2-H2O (modified from Winter, 2001). The thin sections are 40 µm thick. Atg—antigorite; Ath—anthophyllite; Di—diopside; En—enstatite; Fo—forsterite; Qtz—quartz; Tlc—talc; Tr—tremolite.

The mafic samples are represented by garnet-bearing amphibole schist, which chiefly consisted of amphibole (45%–55%), plagioclase (20%–40%), and garnet (0%–10%), with minor quartz, apatite, ilmenite, and epidote (Figs. 6A–6C). The garnet grains were partly or totally replaced by neocrystals of plagioclase. A typical retrograde fabric was characterized by fine-grained new crystals of plagioclase surrounding garnet (Fig. 6C), which probably resulted from reaction of garnet + quartz + H2O = Ca-amphibole + plagioclase. The amphibole grains were brownish and bluish in color and exhibited a strong SPO parallel to the foliation and regional structural orientation. Plastic deformation features, which are rarely reported in experimentally or naturally deformed amphiboles (Nyman et al., 1992; Shelley, 1994; Berger and Stünitz, 1996; Imon et al., 2004; Aspiroz et al., 2007), were also not observed in the amphiboles of our samples. Quartz exhibited undulose extinction and bulging dynamic recrystallization behaviors, indicating low-temperature plastic deformation (Fig. 6D; Passchier and Trouw, 2005; Law, 2014).

Figure 6.

Microphotographs of mafic samples from the Songshugou ophiolite taken under cross-polarized (A, D) and plane-polarized (B, C) light. The thin sections are 40 µm thick. (A) Oriented amphibole grains define the foliation of amphibolite (sample SSG22–5). (B) Garnet grains are partly or totally replaced by plagioclase in sample SSG06. (C) Plagioclase grains occur around garnet core, suggesting a typical retrograde texture. (D) Undulose extinction of quartz in sample SSG22–4. Amp—amphibole; Grt—garnet; Pl—plagioclase; Qz—quartz.

Figure 6.

Microphotographs of mafic samples from the Songshugou ophiolite taken under cross-polarized (A, D) and plane-polarized (B, C) light. The thin sections are 40 µm thick. (A) Oriented amphibole grains define the foliation of amphibolite (sample SSG22–5). (B) Garnet grains are partly or totally replaced by plagioclase in sample SSG06. (C) Plagioclase grains occur around garnet core, suggesting a typical retrograde texture. (D) Undulose extinction of quartz in sample SSG22–4. Amp—amphibole; Grt—garnet; Pl—plagioclase; Qz—quartz.

Mineral Geochemistry

The major-element compositions of minerals were analyzed using an electron probe microanalyzer (EPMA; JEOL JXA-8230) at the State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China. Operating conditions were: accelerating voltage of 15 kV, beam current of 10 nA, and beam diameter of 1 mm. Microprobe standards of natural and synthetic phases were supplied by SPI Company (West Chester, Pennsylvania, USA): diopside for Si, olivine for Mg, hematite for Fe, almandine for Al, Cr2O3 for Cr, diopside for Ca, jadeite for Na, K-feldspar for K, rhodonite for Mn, rutile for Ti, NiSi for Ni, and SrSO4 for Sr.

EBSD Measurements

The mineral CPOs were measured using a scanning electron microscope (JEOL JSM-6490) equipped with an electron backscatter diffraction system (Oxford Nordlys S with HKL Channel 5) at the State Key Laboratory for Mineral Deposition Research, Nanjing University, Nanjing, China. Operating conditions were as follows: 20 kV accelerating voltage, 17–23 mm working distance, and 70° specimen tilt. About 200–300 grains were measured for olivine, plagioclase, and amphibole per thin section, and the computerized indexation of the diffraction pattern was manually checked for each orientation. All index data were determined with a mean angular deviation of <1°.

The CPO strength is described by the J-index, corresponding to a volume-averaged integral of the squared orientation densities. The J-index has a value of 1 for random fabric and infinity for a single crystal (Michibayashi and Mainprice, 2004), and most natural deformed peridotites yield values between 2 and 20 (Ben Ismaïl and Mainprice, 1998). The pfJ index, describing distribution density, equals 1 for random distribution and has a maximum value of ∼60 and 280 for single crystals of olivine and amphibole, respectively (Michibayashi et al., 2006; Barberini et al., 2007). Both the J-index and pfJ-index were calculated for each sample to constrain the CPO data (Mainprice et al., 2000; Michibayashi and Mainprice, 2004; Skemer et al., 2006).

Zircon U-Pb Dating

The U-Th-Pb measurements were obtained using the laser ablation–inductively coupled plasma–mass spectrometer (LA-ICP-MS) at the State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China, following the methodology described in Liu et al. (2007). Zircons were extracted from a garnet-bearing amphibole schist sample (SSG04) using standard heavy-liquid and magnetic separation methods and then purified by handpicking under a binocular microscope. A random population of zircons was mounted on adhesive tape, enclosed in epoxy resin, and polished to expose the interior. The internal texture of zircons was observed using cathodoluminescence (CL) images prior to the analysis. The laser-ablation system was a GeoLas 200 M equipped with a 193 nm ArF-excimer laser, and a homogenizing and imaging optical system (MicroLas, Göttingen, Germany). Analyses were performed on the ELAN 6100 ICP-MS from Perkin Elmer/SCIEX (Canada) with a dynamic reaction cell (DRC). The laser-ablation spot size was ∼30 μm, with a rate of 10 Hz and energy of up to 90 mJ. The 207Pb/206Pb, 206Pb/238U, 207Pb/235U, and 208Pb/232Th ratios were calculated using GLITTER 4.0 (Macquarie University) and were corrected for both instrumental mass bias and depth-dependent elemental and isotopic fractionation using Harvard zircon 91500 as the external standard. The ages were calculated using Isoplot 3 (Ludwig, 2003). Common Pb corrections were made following the method of Andersen (2002). Age uncertainties are quoted at the 95% confidence level.

Mineral Chemistry and Geothermometry

The geochemical compositions of individual minerals in harzburgite (samples SSG09–2, SSG11, SSG13–3, SSG17–2, SSG17–3, and SSG19–1), dunite (samples SSG10, SSG12, SSG18–3, and SSG19–4), and amphibolite (samples SSG22–1, SSG22–4, SSG22–5, and SSG06) samples were analyzed by EMPA, and the results are listed in Table DR1 in the GSA Data Repository.1

The olivines were characterized by high forsterite (Fo) contents, ranging from 0.90 to 0.91 (Fig. 7A). The spinels are chromites, as illustrated in the Fe3+-Cr-Al ternary diagram (Fig. 7B). These chromite grains showed a large variation in both Mg# [= Mg/(Mg + Fe2+) atomic ratio] and Cr# [ = Cr/(Cr + Al) atomic ratio], ranging from 0.11 to 0.34 and from 0.65 to 0.97, respectively (Fig. 7C). The TiO2 content of spinel varied in the range of 0–0.288 wt% (Fig. 7D). Together with the microstructure (Fig. 4), the high Cr# and low TiO2 in the spinel, and the high Fo in olivine (Fig. 7) suggest that these samples were associated with boninitic melt in a suprasubduction zone (Dick and Bullen, 1984; Arai, 1994a, 194b; Tamura and Arai, 2006), which was also found in our previous study (Sun et al., 2019). Reaction between mantle peridotites and boninitic melt resulted in the dissolution of pyroxene and precipitation of olivine, forming lenticular dunites (Berger and Vannier, 1984; Kelemen et al., 1995; Malpas et al., 2003; Tommasi et al., 2004). This is also supported by the texture and chemical characteristics of multiphase mineral inclusions in the Songshugou ultramafic rocks (Cao et al., 2016). In addition, EPMA analyses revealed that orthopyroxenes have compositions of enstatite (En) 0.90–0.91, and clinopyroxenes are diopsides. In the amphibolite samples, plagioclase compositions were in the range An 0.36–0.48, while amphiboles were typical hornblende.

Figure 7.

Chemical characteristics of olivine and spinel in ultramafic samples from Songshugou ophiolite. (A) Compositional relationship between spinel Cr# and olivine Fo content, plotted on olivine-spinel mantle array (OSMA) diagram of Arai (1994a, 1994b). (B) Spinel compositions on Fe3+-Cr-Al ternary diagram. Light and dark shading represent 90% of the entire terrestrial spinel data points and 90% of the entire spinel data points from boninite, respectively (Barnes and Roger, 2001). (C) Compositional relationship between Mg# and Cr# for spinel. Fields for mid-ocean-ridge (MOR) peridotite, suprasubduction-zone (SSZ) peridotite, and boninite were taken from Dick and Bullen (1984), Ishii et al. (1992), and van der Laan et al. (1992), respectively. (D) Compositional relationship between TiO2 content and Cr# for spinel. Dashed lines indicate the spinel compositions in Mg-rich magmas that originated from different tectonic settings (Arai, 1992). MORB—mid-ocean-ridge basalt.

Figure 7.

Chemical characteristics of olivine and spinel in ultramafic samples from Songshugou ophiolite. (A) Compositional relationship between spinel Cr# and olivine Fo content, plotted on olivine-spinel mantle array (OSMA) diagram of Arai (1994a, 1994b). (B) Spinel compositions on Fe3+-Cr-Al ternary diagram. Light and dark shading represent 90% of the entire terrestrial spinel data points and 90% of the entire spinel data points from boninite, respectively (Barnes and Roger, 2001). (C) Compositional relationship between Mg# and Cr# for spinel. Fields for mid-ocean-ridge (MOR) peridotite, suprasubduction-zone (SSZ) peridotite, and boninite were taken from Dick and Bullen (1984), Ishii et al. (1992), and van der Laan et al. (1992), respectively. (D) Compositional relationship between TiO2 content and Cr# for spinel. Dashed lines indicate the spinel compositions in Mg-rich magmas that originated from different tectonic settings (Arai, 1992). MORB—mid-ocean-ridge basalt.

The equilibrium temperatures of the dunite samples were estimated using the olivine-spinel thermometer (Ol-SplBal91) based on Fe2+-Mg exchange (Ballhaus et al., 1991), the orthopyroxene thermometer (OpxWS91) based on Al and Cr contents (Witt-Eickschen and Seck, 1991), the orthopyroxene thermometer (OpxBK90) based on Ca contents (Brey and Köhler, 1990), and the clinopyroxene-orthopyroxene thermometer (Cpx-OpxBK90) based on Fe-Mg exchange (Brey and Köhler, 1990). For amphibolite, the hornblende-plagioclase thermometer (Hb-PlHB94) based on nonideal interactions (Holland and Blundy, 1994) was applied to calculate the equilibrium temperatures. Assuming a pressure of 1.5 GPa, which corresponds to equilibration in the spinel stability field and the stability of the peak assemblage in the garnet amphibolite (Tang et al., 2016), the results of the calculation of the equilibrium temperatures are listed in Table 2.

TABLE 2.

GEOTHERMOMETERS OF DUNITE AND AMPHIBOLITE FROM THE SONGSHUGOU OPHIOLITE

For the dunites, the Ol-SplBal91 thermometer yielded temperatures between 604 ± 6 °C and 640 ± 15 °C, which obviously underestimate the equilibrium temperatures, because the Ol-SplBal91 thermometer gives reasonable results for temperatures higher than 800 °C in spinel peridotite (Ballhaus et al., 1991). The OpxWS91 and OpxBK90 thermometers gave temperatures of 751 ± 17 °C and 813 ± 49 °C for the dunite sample SSG10, respectively. For the harzburgite sample SSG13–3, the application of OpxWS91, OpxBK90, and Cpx-OpxBK90 thermometers yielded equilibrium temperatures of 812 ± 30 °C, 807 ± 30 °C, and 772 ± 15 °C, respectively. For the samples of amphibolite, assuming a pressure of 1.0 GPa, the temperatures estimated using the Hb-PlHB94 thermometer varied from 631 ± 28 °C to 695 ± 18 °C.

Crystal Preferred Orientations

The CPO data from the olivines in harzburgite (Fig. 8) and the coarse-grained (Fig. 9) and fine-grained (Fig. 10) dunite, as well as those of amphiboles and plagioclases in amphibolite (Fig. 11), are presented on equal-area, lower-hemisphere projections in the structural (x-z) reference frame, in which the foliation (x-y plane) is vertical and the lineation (x) is horizontal.

Figure 8.

Crystal preferred orientations of olivine for harzburgite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 8.

Crystal preferred orientations of olivine for harzburgite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 9.

Crystal preferred orientations of olivine for coarse-grained dunite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 9.

Crystal preferred orientations of olivine for coarse-grained dunite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 10.

Crystal preferred orientations of olivine for fine-grained dunite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 10.

Crystal preferred orientations of olivine for fine-grained dunite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; D—density.

Figure 11.

Crystal preferred orientations of amphibole and plagioclase in the amphibolite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; MD—maximum density.

Figure 11.

Crystal preferred orientations of amphibole and plagioclase in the amphibolite samples from the Songshugou ophiolite in equal-area, lower-hemisphere projections. Contours are multiples of uniform distribution. Foliation is shown by horizontal straight line, and lineation is E-W. N—number of measured grains; J and pfJ—indices of fabric intensity; MD—maximum density.

In general, the CPOs of olivine can be mainly classified into five types according to their different slip systems: (010)[100] for A-type, (010)[001] for B-type, (100)[001] for C-type, {0kl}[100] for D-type, and (001)[100] for E-type olivines, respectively (Jung and Karato, 2001; Katayama et al., 2004; Jung et al., 2006; Raterron et al., 2009, 2012; Michibayashi and Oohara, 2013; Hansen et al., 2014; Sun et al., 2016).

The harzburgites dominantly display a C-type olivine CPO (samples SSG08, SSG09–2, SSG17–3, SSG19–1, and SSG19–2), which is characterized by [001] axis concentrations close to the lineation (x direction), [100] axis concentrations normal to the foliation (z direction), and [010] axis concentrations perpendicular to the lineation on the foliation plane (y direction; Fig. 8). The J-index values for these samples were high, varying from 5.38 (SSG08) to 19.64 (SSG19–1), while the pfJ-index values for the [100], [010], and [001] axes were similar for each sample, varying from 1.41 to 4.74. However, some coarse-grained (samples SSG11, SSG13–3, and SSG17–2) and fine-grained (SSG-L5 and SSG-X6) harzburgite samples displayed A-type fabric, defined by the point maxima of [100] axes subparallel to the lineation and [010] axes normal to the foliation (Fig. 8).

The olivines from coarse-grained dunites (samples SSG10, SSG17–6, SSG18–3, SSG19–4, and SSG19–7) showed a preferential alignment of [001] axes parallel to the lineation and [010] axes normal to the foliation, suggesting B-type CPO. Their J-index and pfJ-index values varied from 5.96 to 19.50, and from 1.44 to 4.40, respectively. The fine-grained dunites (samples SSG-L1, SSG-L3, SSG-L8, and SSG-X4) displayed B-type fabric as well (Fig. 10), although some of the CPOs were not strong (e.g., sample SSG-L1).

In the metamafic rocks (samples SSG02–1, SSG06, SSG22–4, and SSG22–5), the amphibole crystals in the amphibole schists displayed strong and consistent CPO patterns (Fig. 11), which were characterized by [001] axis concentrations close to the lineation (x direction), and (100) pole concentrations perpendicular to the foliation (z direction). The distribution of (010) poles was more complicated, with a single concentration at y (SSG02–1), a partial girdle parallel to the foliation with the maximum concentration at y (SSG06), in the middle between y and z (SSG22–4), or a partial girdle perpendicular to x with the maximum concentration at y (SSG22–5). The J-index varied from 10.64 to 12.95. The pfJ-index, varying respectively from 1.71 to 3.43 for (100) and from 1.59 to 3.02 for [001], was higher than that for (010), which varied from 1.36 to1.54. These features suggest that the CPO strengths of amphibole (100) and [001] axes were stronger than (010). However, the plagioclases in the amphibolite samples displayed almost random CPOs, as shown in Figure 11, and their pfJ-index values for each principal crystallographic axis were consistently lower than 1.4.

Zircon U-Pb Geochronology

The zircon grains from the garnet-bearing amphibole schist (sample SSG04) can be classified into two groups according to their CL morphology and Th/U ratios. Group I zircons, including seven representative grains (Fig. 12), were anhedral to subhedral and 50–200 μm long with aspect-ratios of 1–2. These zircon gains were inhomogeneous and gray in color, and some of them showed distinct cores and thin outer rims in the CL images (Fig. 12A). Their Th and U contents varied from 0.028 to 0.544 ppm and 3.68–28.8 ppm, respectively, with very low Th/U ratios of 0.01–0.03 (Table DR2), suggesting their metamorphic origin. This conclusion is also supported by their very low rare earth element (REE) contents (Table DR3). Except one zircon (SSG04–09N) that showed enrichment of heavy (H) REEs, the other six zircons exhibited flat HREE patterns (Fig. 12B). All seven analyses plotted on or near the concordia tight cluster (Fig. 12C), yielding a weighted mean 206Pb/238U age of 500.5 ± 8.8 Ma (mean square of weighted deviates [MSWD] = 0.60; Fig. 12D). Taking together all the CL images, flat HREE distribution patterns, and low Th/U ratios (0.01–0.03), this age can be interpreted as the metamorphic age of the garnet-bearing amphibole schist in the Songshugou ophiolite.

Figure 12.

(A) Cathodoluminescence (CL) images, (B) chondrite-normalized rare earth element (REE) patterns, (C) U-Pb concordia diagram, and (D) weighted mean ages of group I zircons from sample SSG04. Smaller circles in A show laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) dating spots. Normalization values are from Sun and McDonough (1989). MSWD—mean square of weighted deviates.

Figure 12.

(A) Cathodoluminescence (CL) images, (B) chondrite-normalized rare earth element (REE) patterns, (C) U-Pb concordia diagram, and (D) weighted mean ages of group I zircons from sample SSG04. Smaller circles in A show laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) dating spots. Normalization values are from Sun and McDonough (1989). MSWD—mean square of weighted deviates.

Group II zircons showed distinctive morphology in CL images and Th/U ratios from those of group I zircons. This group included 20 grains, dark in color and mostly homogeneous in CL images (Fig. 13A). Twenty spots were analyzed on different grains, which displayed Th/U ratios ranging from 0.11 to 1.34, and Th and U contents varying from 102 to 1213 ppm and from 240 to 1282 ppm, respectively (Table DR2). In addition, group II zircons exhibited enrichment of HREEs with a negative Eu anomaly (Fig. 13B; Table DR3), which are different from the features of group I zircons. Twenty analyses displayed concordia 206Pb/238U ages varying from 505 Ma to 480 Ma (Table DR2), giving a weighted mean 206Pb/238U age of 492.5 ± 3.0 Ma (MSWD = 1.4; Fig. 13D).

Figure 13.

(A) Cathodoluminescence (CL) images, (B) chondrite-normalized rare earth element (REE) patterns, (C) U-Pb concordia diagram, and (D) weighted mean ages of group II zircons from sample SSG04. Smaller circles in A show laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) dating spots. Normalization values are from Sun and McDonough (1989).

Figure 13.

(A) Cathodoluminescence (CL) images, (B) chondrite-normalized rare earth element (REE) patterns, (C) U-Pb concordia diagram, and (D) weighted mean ages of group II zircons from sample SSG04. Smaller circles in A show laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) dating spots. Normalization values are from Sun and McDonough (1989).

Deformation Fabrics

Based on investigations of experimentally and natural deformed samples, A, B, C, D, and E types of olivine CPOs have been distinguished and documented during the past two decades (Jung and Karato, 2001; Katayama et al., 2004; Raterron et al., 2009, 2012; Michibayashi and Oohara, 2013; Sun et al., 2016). The development of these five fabric types depends mainly on the roles of temperature, pressure, stress, water content, strain rate, etc. (Jung and Karato, 2001; Jung et al., 2006; Katayama and Karato, 2006; Michibayashi and Oohara, 2013). The CPOs may be continuously modified by changing physical conditions until frozen at low temperatures (Carter and Avé Lallemant, 1970; Jung and Karato, 2001; Katayama et al., 2004).

The medium- to coarse-grained harzburgite samples are dominated by olivine C-type fabric (samples SSG08, SSG09–2, SSG17–3, SSG19–1, and SSG19–2). C-type CPO is related to dislocation of the (100)[001] slip system, resulting in the maximum concentrations of [100], [010], and [001] axes aligned parallel to the z, y, and x direction, respectively. This olivine CPO is relatively rare in natural samples and poorly understood (Ben Ismaïl and Mainprice, 1998; Mainprice, 2007; Wang et al., 2013). It has been suggested that C-type fabric could be induced by plastic flow under low temperatures and a high strain rate (Carter and Avé Lallemant, 1970), or high water content (Jung and Karato, 2001; Frese et al., 2003), or flow under high pressure (Couvy et al., 2004; Raterron et al., 2007). C-type fabrics have been reported in some orogenic garnet peridotite from ultrahigh-pressure (UHP) metamorphic terranes, such as the Sulu terrane (Xu et al., 2006) and the North Qaidam terrane (Jung et al., 2013) in China and the Western Gneiss Region, Norway (Katayama et al., 2005; Wang et al., 2013), considered as an indicator of UHP and low geothermal gradient (Xu et al., 2006; Wang et al., 2013). In the Songshugou ophiolite, the C-type CPOs observed in the coarse-grained harzburgites were inferred to be induced from the high pressure during subduction of Shangdan oceanic lithosphere, which is consistent with the occurrence of HP and UHP rocks in the surrounding mafic massif (Liu et al., 1995, 2016; Chen et al., 2015; Tang et al., 2016).

Three medium- to coarse-grained (samples SSG11, SSG13–3, and SSG17–2) and two fine-grained (SSG-L5 and SSG-X6) harzburgites are characterized by A-type fabric, which is characterized by [100], [010], and [001] axis concentrations close to the x, z, and y direction, respectively (Fig. 8). The A-type CPO is most common in the normal upper mantle (Mainprice and Silver, 1993; Ji et al., 1994; Jung et al., 2006), which has been widely reported in mantle xenoliths from kimberlites and basalts (Nicolas and Christensen, 1987; Mainprice and Silver, 1993; Ji et al., 1996; Saruwatari et al., 2001; Ohuchi and Irifune, 2014), and it is broadly used to explain seismic data observed in the upper mantle (e.g., Silver, 1996; Savage, 1999). The observation of A-type CPO is also consistent with the geochemistry and O isotope investigations, which suggested that the Songshugou peridotites represent a segment of mid-ocean-ridge mantle (Zhang, 1995; Dong et al., 2008; Lee et al., 2010; Sun et al., 2019). Therefore, the A-type CPOs in some harzburgites probably represent the remnant of original CPOs that were formed in the spreading center of an oceanic upper mantle. The original fabric can be progressively modified at different physical conditions, and the C-type CPOs in the harzburgite probably represent the more intense fabric replacing the A-type CPOs.

The coarse-gained dunites (samples SSG10, SSG17–6, SSG18–3, SSG19–4, SSG19–7) are dominated by B-type CPOs (Fig. 9), which are characterized by the maximum concentrations of olivine [100], [010], and [001] axes aligned parallel to the y, z, and x direction, respectively (Fig. 9). The B-type fabric was previously considered to exist in upper-mantle regions with extremely high water content and high differential stress (Jung and Karato, 2001; Jung et al., 2006; Karato et al., 2008). Recent experimental studies revealed that B-type CPOs may also be induced by high pressure in low water content (Palasse et al., 2012; Lee and Jung, 2015) or completely dry environments (Raterron et al., 2007; Jung et al., 2009; Sundberg and Cooper, 2008). Therefore, B-type CPOs in natural rocks may have two origins: water-induced and pressure-induced origins. The former, induced by high H2O fugacity at low pressure, is likely to be present in the forearc mantle wedge (Kneller et al., 2005, 2007, 2008; Katayama and Karato, 2006), where large volumes of water are released from dehydration reactions in the subducting slab. It agrees with the seismic anisotropy pattern in some mantle wedges, such as Kamchatka, NE Japan, Tonga, and Ryukyu (Mizukami et al., 2004; Nakajima and Hasegawa, 2004; Katayama and Karato, 2006; Long and van der Hilst, 2006; Tasaka et al., 2008; Huang et al., 2011). The latter, induced by high pressure, possibly exists beneath the downgoing plate in subduction zones (Jung et al., 2009). In this case, the observed trench-parallel shear-wave splitting below the subducting slab will be easier to interpret based on trench-perpendicular rather than trench-parallel mantle flow (Russo and Silver, 1994; Peyton et al., 2001; Long and Silver, 2008). In the Songshugou ophiolite, the B-type CPOs were restricted in the dunites, which resulted from the reaction between boninitic melt and harzburgites in a suprasubduction-zone setting (Cao et al., 2016; Sun et al., 2019). Therefore, we suggest that the olivine B-type CPOs were most likely to be formed due to the high water content in the suprasubduction-zone setting. This is also supported by the melt-induced B-type CPO reported in experimental samples (Holtzman et al., 2003).

The fine-grained dunites are dominated by B-type CPOs (samples SSG-L1, SSG-L3, SSG-L8, SSG-X4), which were probably induced by the melt-rock reactions occurring in the same suprasubduction-zone setting as those fabrics in coarse-grained dunites. However, this grain-size reduction was inferred to occur at relatively low temperatures and pressures, which did not result in olivine fabric weakening or fabric variation. This is also consistent with the A-type fabric observed in both fine-grained and coarse-grained harzburgites.

The CPOs of amphibole in our samples are characterized by the [001] axis and (100) pole concentrations close to the x and z directions, respectively, which are consistent with those measured previously in middle- to high-grade metamorphic rocks (Christensen, 1965; Siegesmund et al., 1989; Imon et al., 2004; Barberini et al., 2007; Tatham et al., 2008; Ji et al., 2013). The formation of amphibole CPO is interpreted by either [001] slip along the (100) or (110) plane (Dollinger and Blacic, 1975; Biermann and Van Roermund, 1983; Reynard et al., 1989; Barruol and Kern, 1996) or anisotropic growth (grain boundary migration) and passive rigid-body rotation under various different stresses (Ji et al., 1993; Shelley, 1994; Díaz Aspiroz et al., 2007; Tatham et al., 2008). At present, it is generally accepted that amphibole is one of the strongest and least plastic common rock-forming minerals during deformation (e.g., Shelley, 1994). Because few plastic features such as subgrains, dynamically recrystallized grains, or undulose extinction were observed in the samples, the CPO of amphiboles may have resulted from anisotropic growth or rigid-body rotation, rather than intracrystalline plasticity, which occurs at temperatures higher than amphibolite facies or 700 °C (Nyman et al., 1992; Lafrance and Vernon, 1993; Berger and Stünitz, 1996; Imon et al., 2004). It is also possible that the CPO of amphiboles in retrograde eclogites occurred through mimetic growth after a preexisting CPO of omphacites (McNamara et al., 2012; Heidelbach and Terry, 2013). Similarly, plagioclase grains that were formed during retrograde processes show random crystal orientations. Although the mafic rocks of the Songshugou ophiolite display strong foliation and lineation, it seems that they have not developed dislocation slip–induced fabrics since retrogression from eclogite to amphibolite.

Deformation Conditions

According to the mineral compositions, the deformation temperature was estimated by geothermometry. Assuming pressure (P) = 1.5 GPa, which characterizes the spinel stability field, the application of the OpxWS91, OpxBK90, and Cpx-OpxBK90 thermometers for ultramafic samples yielded temperatures ranging from 751 °C to 813 °C, indicating the equilibrium temperature during the melt-rock reaction that dissolved orthopyroxenes and formed olivine neoblasts. This temperature range is also supported by the metamorphic mineral assemblages. For instance, anthophyllite and tremolite crystals, which are formed by fluid-rock reactions, were observed in fine-grained dunite (Fig. 5A). As illustrated in Figure 5B, anthophyllite is stable at pressures lower than 1 GPa and temperatures of 650–800 °C, while tremolite could be stable at temperatures <900 °C. The coexistence of olivine, tremolite, anthophyllite, and talc in the ultramafic samples may indicate pressure-temperature (P-T) conditions of amphibolite-facies metamorphism (Winter, 2001; Bucher and Grapes, 2011). This is consistent with those in the metamafic rocks.

For mafic samples, the temperatures estimated using the Hb-PlHB94 thermometer varied in the range of 631 °C to 695 °C, i.e., slightly lower than those of the ultramafic samples. This temperature may reflect the retrogression of equilibrium temperatures, as the garnet grains were partly or totally replaced by plagioclase (Fig. 4C). According to the clockwise P-T path and characteristic retrograde textures reported by Tang et al. (2016), the mafic rocks experienced a rapid decompression and cooling history after the peak metamorphism, and the garnets were replaced by plagioclase at ∼<730 °C, agreeing with our data.

Timing of Deformation

The timing of metamorphism and deformation could be revealed by the U-Pb ages of the two groups of zircons separated from the garnet-bearing amphibole schist. Group I zircons are mainly characterized by flat HREE patterns (Fig. 12B), which probably resulted from the coexistence with garnet, because the growth of garnet could progressively deplete the limited HREE reservoir in a closed system (Rubatto, 2002; Whitehouse and Platt, 2003; Wu and Zheng, 2004). Together with the very low Th/U ratios (0.01–0.03), group I zircons are considered to be metamorphic zircons. Therefore, the weighted mean 206Pb/238U age of 500.5 ± 8.8 Ma most likely constrains the peak metamorphic age of the mafic rocks in the Songshugou ophiolite. This age is synchronous with the HP and UHP peak metamorphism in the North Qinling belt (Dong and Santosh, 2016; Liu et al., 2016), which has been well documented by the previously reported U-Pb zircon ages, such as 515 ± 12 Ma (Tang et al., 2016), 501 ± 9 Ma (Liao et al., 2016), 500 ± 8 Ma (Chen et al., 2015), 504 ± 7 Ma (Zhang et al., 2011), 510 ± 8 Ma (Liu et al., 2009), and 511 ± 35 Ma (Yang et al., 2003).

Group II zircons were most likely concentrated in the thin quartz veins paralleling the foliations of the amphibolite (Fig. 3G). Unlike the trace-element characteristics of group I, group II zircons display relative HREE enrichment and a clearly negative Eu anomaly (Fig. 13B). As the pressure decreases during the exhumation processes, garnets host significant HREEs in the mafic rocks and are unstable and progressively replaced by plagioclase, which is strongly enriched in Eu (Fig. 6C). Therefore, the metamorphic overgrowth group II zircons show HREE enrichment and a negative Eu anomaly. Furthermore, the high Th/U ratios of 0.11–1.34 suggest that group II zircons may have been crystallized from melt with a high Th/U ratio. This is coincident with the occurrence of quartz veins, which are parallel to the foliations and relate to metamorphic differentiation in the garnet amphibolites (Fig. 3G). According to their dark color, morphology in the CL images, enrichment of HREE, and high Th/U ratio (0.11–1.34) of the group II zircons, we interpret that 492.5 ± 3.0 Ma represents the crystallization age of the new generation of zircons that were related to fluids during the rapid exhumation of the Songshugou ophiolite. This age is close to the reported retrograde metamorphic ages in the North Qinling belt (Dong and Santosh, 2016; Liu et al., 2016), such as 470 Ma (Bader et al., 2013), 473 ± 4 Ma (Cheng et al., 2011), and 471 ± 8 Ma (Liao et al., 2016).

Tectonic Implications

As a fragment of oceanic lithosphere, the Songshugou ophiolite preserves a detailed record of the tectonic evolution of the Shangdan ocean between the North China block and South China block. Together with previous petrological and geochemical studies of the mafic rocks, the present investigations on the fabrics and geochronology of the deformed mafic and ultramafic rocks provided insights into the tectonic processes along the Shangdan suture zone between the North Qinling belt and South Qinling belt.

According to the geochemical and geochronological data from ophiolites in the North Qinling belt (Dong et al., 2011a; Dong and Santosh, 2016, and the references therein), the spreading of the Shangdan ocean between the North China and South China blocks has been well documented before ca. 534 Ma (Fig. 14A). Due to the extensional stress, the mantle flow in the oceanic lithosphere induced the olivine A-type fabric in the ultramafic rocks of the Songshugou ophiolite, which is the most prevalent fabric formed in normal mantle (Mainprice and Silver, 1993; Ji et al., 1994; Jung et al., 2006).

Figure 14.

Schematic cartoons showing the tectonic model for the Songshugou ophiolite. (A) Shangdan oceanic lithosphere is subducted toward the north beneath the North Qinling belt and generates olivine A-type fabric before ca. 534 Ma. (B) Deep subduction produces the high-pressure metamorphism and related olivine C-type fabric in the ultramafic rock at ca. 500 Ma. Possible break-off of the Songshugou oceanic slab generates the diapir of the Songshugou mafic-ultramafic complex. (C) Ongoing subduction and compression lead to the Songshugou mafic-ultramafic complex being thrusted and wedged into the North Qinling belt at ca. 492 Ma, accompanied by olivine B-type fabric. (D) Continuing compression induces the Songshugou mafic-ultramafic complex to thrust into the Qinling Complex and be exhumed along the Xigou and Jieling ductile shear zones during ca. 486–430 Ma.

Figure 14.

Schematic cartoons showing the tectonic model for the Songshugou ophiolite. (A) Shangdan oceanic lithosphere is subducted toward the north beneath the North Qinling belt and generates olivine A-type fabric before ca. 534 Ma. (B) Deep subduction produces the high-pressure metamorphism and related olivine C-type fabric in the ultramafic rock at ca. 500 Ma. Possible break-off of the Songshugou oceanic slab generates the diapir of the Songshugou mafic-ultramafic complex. (C) Ongoing subduction and compression lead to the Songshugou mafic-ultramafic complex being thrusted and wedged into the North Qinling belt at ca. 492 Ma, accompanied by olivine B-type fabric. (D) Continuing compression induces the Songshugou mafic-ultramafic complex to thrust into the Qinling Complex and be exhumed along the Xigou and Jieling ductile shear zones during ca. 486–430 Ma.

Up to ca. 500 Ma, deep subduction of the Shangdan oceanic lithosphere underneath the North Qinling belt is indicated by the peak metamorphic P-T conditions of 750–850 °C and 1.5–1.9 GPa (Tang et al., 2016), and a number of zircon U-Pb geochronological data points for the UHP rocks. Our group I metamorphic zircons from garnet amphibolite yielded a LA-ICP-MS U-Pb age of 500.5 ± 8.8 Ma, which is consistent with the U-Pb zircon ages around 500 Ma for the eclogite-facies metamorphism in the literature (Chen et al., 2004; Qian et al., 2013; Liu et al., 2016; Tang et al., 2016). Accordingly, the Songshugou ophiolite is proposed to have subducted underneath the North Qinling belt at ca. 500 Ma. During the subduction process, the increasing high pressure caused the olivine C-type CPO in the ultramafic rocks (Fig. 8). Due to the HP-UHP metamorphism and increasing density, a slab break-off of the subducted oceanic crust occurred, which generated the diapir of the Songshugou mafic-ultramafic complex (Fig. 14B).

At around 492 Ma, the ongoing subduction led to the Songshugou mafic-ultramafic complex thrusting and wedging into the North Qinling belt (Fig. 14C). Due to the pressure and temperature decrease, the eclogite evolved into retrograde metamorphism to form the garnet amphibolite (Fig. 6). The related equilibrium temperatures of retrogression is constrained within 631–695 °C by the application of Hb-PlHB94 thermometer. Our group II zircons from the quartz veins in the amphibole schist yielded a 206Pb/238U age of 492.5 ± 3.0 Ma, constraining the timing of this event. Several lines of geochemical (Fig. 7) and petrological evidence (Figs. 46) indicate that the ultramafic rocks of the Songshugou ophiolite had reacted with melt and fluid as they were exhumed to forearc mantle depth. The boninitic melt-rock reactions dissolved orthopyroxenes and formed olivine neoblasts (Fig. 4) at temperature of 751–813 °C, leading to dunitization. The subsequent fluid-rock reactions occurred at P < 1 GPa and T = 650–800 °C and resulted in the growth of tremolite, anthophyllite, and talc in the ultramafic rocks (Fig. 5). Because large volumes of water in the forearc mantle region were released from dehydration reactions in the subducting slab, the olivine B-type CPO in the dunites may have been induced by the high water content.

Finally, the continuing subduction of the Shangdan oceanic crust during ca. 486–430 Ma, which was constrained by the adjacent subduction-related I-type Huichizi granitoid (Dong and Santosh, 2016), led to the Songshugou mafic-ultramafic complex being thrust into the Qinling Complex and exhumed along the Xigou and Jieling ductile shear zones (Fig. 14D). Due to the intensive regional compression, the Qinling complex and a slice of the Songshugou ophiolite were highly sheared, leading to the mylonitization and foliations along the tectonic boundaries between the different units.

Together with regional geology, the fabric, geochemical, and geochronological data for the Songshugou ophiolite presented in this study lead to the following major conclusions.

  • (1) Mineral geochemistry and geothermometry investigations suggest that the ultramafic rocks of the Songshugou ophiolite have experienced boninitic melt-rock reactions at temperatures of 751–813 °C and that retrograde metamorphism of the mafic rocks occurred at 631–695 °C.

  • (2) The harzburgites are dominated by C-type CPOs, which may have resulted from high pressure during slab subduction. A-type CPOs are also observed in some harzburgites, representing a remnant of the original fabric formed in the spreading center of the Shangdan ocean. The B-type CPOs were predominantly developed in the dunites, probably induced by the high water content in the mantle wedge.

  • (3) Zircons from garnet-bearing amphibole schist are divided into two groups: group I zircons with flat HREE patterns and low Th/U ratios, which yielded LA-ICP-MS U-Pb ages of 500.5 ± 8.8 Ma, representing the peak metamorphic age, and group II zircons showing relative HREE enrichment and a clearly negative Eu anomaly, which gave an age of 492.5 ± 3.0 Ma, constraining the timing of exhumation.

  • (4) The Songshugou ophiolite had evolved into high-temperature ductile deformation in spreading center of the Shangdan ocean, subduction-related metamorphism, and ductile deformation with peak metamorphic conditions of 750–850 °C at ca. 500 Ma, and exhumation below 631–695 °C at ca. 492 Ma.

Financial support for this study was provided by the National Natural Science Foundation of China (grant nos. 41421002 and 41772208), the National Key Research and Development Program of China (no. 2016YFC0601003 and no. 2016YFC0600202), and the MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University. The crystal preferred orientation figures and calculations of the J-index were made using the programs of D. Mainprice. The critical and constructive reviews by R. Keppler and an anonymous reviewer are highly appreciated.

1GSA Data Repository Item 2019338, Table DR1: Geochemistry of Representative Minerals from Dunite and Amphibolite; Table DR2: LA-ICPMS U-Pb Data for Zircons from Garnet Bearing Amphibole Schist (SSG04); Table DR3: Rare Earth Element Compositions (PPM) of Zircons from Sample SSG04, is available at http://www.geosociety.org/datarepository/2019, or on request from editing@geosociety.org.
1.
Ames
,
L.
,
Zhou
,
G.
, and
Xiong
,
B.
,
1996
,
Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China
:
Tectonics
 , v.
15
, p.
472
489
.
2.
Andersen
,
T.
,
2002
,
Correction of common lead in U-Pb analyses that do not report 204Pb
:
Chemical Geology
 , v.
192
, p.
59
79
.
3.
Arai
,
S.
,
1992
,
Chemistry of chromian spinel in volcanic-rocks as a potential guide to magma chemistry
:
Mineralogical Magazine
 , v.
56
, p.
173
184
, https://doi.org/10.1180/minmag.1992.056.383.04.
4.
Arai
,
S.
,
1994a
,
Characterization of spinel peridotites by olivine-spinel compositional relationships: Review and interpretation
:
Chemical Geology
 , v.
113
, p.
191
204
, https://doi.org/10.1016/0009-2541(94)90066-3.
5.
Arai
,
S.
,
1994b
,
Compositional variation of olivine-chromian spinel in Mg-rich magmas as a guide to their residual spinel peridotites
:
Journal of Volcanology and Geothermal Research
 , v.
59
, p.
279
293
, https://doi.org/10.1016/0377-0273(94)90083-3.
6.
Aspiroz
,
M.D.
,
Lloyd
,
G.E.
, and
Fernandez
,
C.
,
2007
,
Development of lattice preferred orientation in clinoamphiboles deformed under low-pressure metamorphic conditions: A SEM/EBSD study of metabasites from the Aracena metamorphic belt (SW Spain)
:
Journal of Structural Geology
 , v.
29
, p.
629
645
, https://doi.org/10.1016/j.jsg.2006.10.010.
7.
Bader
,
T.
,
Franz
,
L.
,
Ratschbacher
,
L.
,
de Captitani
,
C.
,
Webb
,
A.A.G.
,
Yang
,
Z.
,
Pfänder
,
J.A.
,
Hofmann
,
M.
, and
Linnemann
,
U.
,
2013
,
The Heart of China revisited: II Early Paleozoic (ultra)high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage
:
Tectonics
 , v.
32
, p.
922
947
.
8.
Ballhaus
,
C.
,
Berry
,
R.F.
, and
Green
,
D.H.
,
1991
,
High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: Implications for the oxidation state of the upper mantle
:
Contributions to Mineralogy and Petrology
 , v.
107
, p.
27
40
, https://doi.org/10.1007/BF00311183.
9.
Barberini
,
V.
,
Burlini
,
L.
, and
Zappone
,
A.
,
2007
,
Elastic properties, fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity
:
Tectonophysics
 , v.
445
, p.
227
244
, https://doi.org/10.1016/j.tecto.2007.08.017.
10.
Barnes
,
S.J.
, and
Roger
,
P.L.
,
2001
,
The range of spinel compositions in terrestrial mafic and ultramafic rocks
:
Journal of Petrology
 , v.
42
, p.
2279
2302
, https://doi.org/10.1093/petrology/42.12.2279.
11.
Barruol
,
G.
, and
Kern
,
H.
,
1996
,
Seismic anisotropy and shear-wave splitting in lower-crustal and upper-mantle rocks from the Ivrea zone—Experimental and calculated data
:
Physics of the Earth and Planetary Interiors
 , v.
95
, p.
175
194
, https://doi.org/10.1016/0031-9201(95)03124-3.
12.
Ben Ismaïl
,
W.
, and
Mainprice
,
D.
,
1998
,
An olivine fabric database: An overview of upper mantle fabrics and seismic anisotropy
:
Tectonophysics
 , v.
296
, p.
145
157
, https://doi.org/10.1016/S0040-1951(98)00141-3.
13.
Berger
,
A.
, and
Stünitz
,
H.
,
1996
,
Deformation mechanisms and reaction of hornblende: Examples from the Bergell tonalite (central Alps)
:
Tectonophysics
 , v.
257
, p.
149
174
, https://doi.org/10.1016/0040-1951(95)00125-5.
14.
Berger
,
E.T.
, and
Vannier
,
M.
,
1984
,
Les dunites en enclaves dans les basaltes alcalins des îles océaniques: Approche pétrologique
:
Bulletin de Minéralogie
 , v.
107
, p.
649
663
.
15.
Biermann
,
C.
, and
Van Roermund
,
H.L.M.
,
1983
,
Defect structures in naturally deformed clinoamphibole—A TEM study
:
Tectonophysics
 , v.
95
, p.
267
278
, https://doi.org/10.1016/0040-1951(83)90072-0.
16.
Brey
,
G.P.
, and
Köhler
,
T.
,
1990
,
Geothermobarometry in four-phase lherzolites II. New thermobarometers, and practical assessment of existing thermobarometers
:
Journal of Petrology
 , v.
31
, p.
1353
1378
, https://doi.org/10.1093/petrology/31.6.1353.
17.
Bucher
,
K.
, and
Grapes
,
R.
,
2011
,
Petrogenesis of Metamorphic Rocks
:
Berlin
,
Springer-Verlag
,
428
p., https://doi.org/10.1007/978-3-540-74169-5.
18.
Cao
,
Y.
,
Song
,
S.
,
Su
,
L.
,
Jung
,
H.
, and
Niu
,
Y.
,
2016
,
Highly refractory peridotites in Songshugou, Qinling orogen: Insights into partial melting and melt/fluid-rock reactions in forearc mantle
:
Lithos
 , v.
252
, p.
234
254
, https://doi.org/10.1016/j.lithos.2016.03.002.
19.
Carter
,
N.L.
, and
Avé Lallemant
,
H.G.
,
1970
,
High temperature flow of dunite and peridotite
:
Geological Society of America Bulletin
 , v.
81
, p.
2181
2202
, https://doi.org/10.1130/0016-7606(1970)81[2181:HTFODA]2.0.CO;2.
20.
Chen
,
D.L.
,
Liu
,
L.
,
Zhou
,
D.W.
,
Luo
,
J.H.
, and
Sang
,
H.Q.
,
2002
,
Genesis and 40Ar-39Ar dating of clinopyroxene megacrysts in ultramafic terrain from Songshugou, east Qinling Mountain, and its geological implication
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
18
, no.
3
, p.
355
362
.
21.
Chen
,
D.L.
,
Liu
,
L.
,
Sun
,
Y.
,
Zhang
,
A.D.
,
Liu
,
X.M.
, and
Luo
,
J.H.
,
2004
,
LA-ICP-MS zircon U-Pb dating for high-pressure basic granulite from North Qinling and its geological significance
:
Chinese Science Bulletin
 , v.
49
, p.
2296
2304
, https://doi.org/10.1360/03wd0544.
22.
Chen
,
D.L.
,
Ren
,
Y.F.
,
Gong
,
X.G.
,
Liu
,
L.
, and
Gao
,
S.
,
2015
,
Identification and its geological significance of eclogite in Songshugou, the North Qinling
:
Acta Petrological Sinica (Yanshi Xuebao)
 , v.
31
, no.
7
, p.
1841
1854
[in Chinese with English abstract].
23.
Cheng
,
H.
,
Zhang
,
C.
,
Vervoort
,
J.D.
,
Li
,
X.H.
,
Li
,
Q.L.
,
Zheng
,
S.
, and
Cao
,
D.D.
,
2011
,
Geochronology of the transition of eclogite to amphibolite facies metamorphism in the North Qinling orogen of central China
:
Lithos
 , v.
125
, p.
969
983
, https://doi.org/10.1016/j.lithos.2011.05.010.
24.
Christensen
,
N.I.
,
1965
,
Compressional wave velocities in metamorphic rocks at pressures to 10 kilobars
:
Journal of Geophysical Research
 , v.
70
, p.
6147
6164
, https://doi.org/10.1029/JZ070i024p06147.
25.
Couvy
,
H.
,
Frost
,
D.J.
,
Heidelbach
,
F.
,
Nyilas
,
K.
,
Ungar
,
T.
,
Mackwell
,
S.
, and
Cordier
,
P.
,
2004
,
Shear deformation experiments of forsterite at 11 GPa-1400 °C in the multianvil apparatus
:
European Journal of Mineralogy
 , v.
16
, p.
877
889
, https://doi.org/10.1127/0935-1221/2004/0016-0877.
26.
Díaz Aspiroz
,
M.D.
,
Lloyd
,
G.E.
, and
Fernández
,
C.
,
2007
,
Development of lattice preferred orientation in clinoamphiboles deformed under low-pressure metamorphic conditions—An SEM/EBSD study of metabasites from the Aracena metamorphic belt (SW Spain)
:
Journal of Structural Geology
 , v.
29
, p.
629
645
, https://doi.org/10.1016/j.jsg.2006.10.010.
27.
Dick
,
H.J.B.
, and
Bullen
,
T.
,
1984
,
Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas
:
Contributions to Mineralogy and Petrology
 , v.
86
, p.
54
76
, https://doi.org/10.1007/BF00373711.
28.
Dilek
,
Y.
, and
Furnes
,
H.
,
2011
,
Ophiolite genesis and global tectonics: Geochemical and tectonic fingerprinting of ancient oceanic lithosphere
:
Geological Society of America Bulletin
 , v.
123
, p.
387
411
, https://doi.org/10.1130/B30446.1.
29.
Dilek
,
Y.
, and
Furnes
,
H.
,
2014
,
Ophiolites and their origins
:
Elements
 , v.
10
, p.
93
100
, https://doi.org/10.2113/gselements.10.2.93.
30.
Dollinger
,
G.
, and
Blacic
,
J.D.
,
1975
,
Deformation mechanisms in experimentally and naturally deformed amphiboles
:
Earth and Planetary Science Letters
 , v.
26
, p.
409
416
, https://doi.org/10.1016/0012-821X(75)90016-3.
31.
Dong
,
Y.P.
, and
Santosh
,
M.
,
2016
,
Tectonic architecture and multiple orogeny of the Qinling orogenic belt, central China
:
Gondwana Research
 , v.
29
, p.
1
40
, https://doi.org/10.1016/j.gr.2015.06.009.
32.
Dong
,
Y.P.
,
Zhou
,
D.W.
,
Zhang
,
G.W.
, and
Liu
,
X.M.
,
1998
,
Geochemistry of the Caledonian basic volcanic rocks in the south margin of Qinling orogenic belt and their tectonic implications
:
Geochimica
 , v.
27
, p.
432
441
[in Chinese with English abstract].
33.
Dong
,
Y.P.
,
Zhang
,
G.W.
, and
Zhu
,
B.Q.
,
2003
,
Proterozoic tectonics and evolutionary history of the North Qinling terrane
:
Acta Geoscientica Sinica (Diqiu Xuebao)
 , v.
24
, p.
3
10
[in Chinese with English abstract].
34.
Dong
,
Y.P.
,
Zhou
,
M.F.
,
Zhang
,
G.W.
,
Zhou
,
D.W.
,
Liu
,
L.
, and
Zhang
,
Q.
,
2008
,
The Grenvillian Songshugou ophiolite in the Qinling Mountains, central China: Implications for the tectonic evolution of the Qinling orogenic belt
:
Journal of Asian Earth Sciences
 , v.
32
, p.
325
335
, https://doi.org/10.1016/j.jseaes.2007.11.010.
35.
Dong
,
Y.P.
,
Zhang
,
G.W.
,
Neubauer
,
F.
,
Liu
,
X.M.
,
Genser
,
J.
, and
Hauzenberger
,
C.
,
2011a
,
Tectonic evolution of the Qinling orogen, China: Review and synthesis
:
Journal of Asian Earth Sciences
 , v.
41
, p.
213
237
, https://doi.org/10.1016/j.jseaes.2011.03.002.
36.
Dong
,
Y.P.
,
Zhang
,
G.W.
,
Hauzenberger
,
C.
,
Neubauer
,
F.
,
Yang
,
Z.
, and
Liu
,
X.M.
,
2011b
,
Palaeozoic tectonics and evolutionary history of the Qinling orogen: Evidence from geochemistry and geochronology of ophiolite and related volcanic rocks
:
Lithos
 , v.
122
, p.
39
56
, https://doi.org/10.1016/j.lithos.2010.11.011.
37.
Dong
,
Y.P.
,
Liu
,
X.M.
,
Santosh
,
M.
,
Zhang
,
X.N.
,
Chen
,
Q.
,
Yang
,
C.
, and
Yang
,
Z.
,
2011c
,
Neoproterozoic subduction tectonics of the northwestern Yangtze block in South China: Constraints from zircon U-Pb geochronology and geochemistry of mafic intrusions in the Hannan Massif
:
Precambrian Research
 , v.
189
, p.
66
90
, https://doi.org/10.1016/j.precamres.2011.05.002.
38.
Dong
,
Y.P.
,
Liu
,
X.M.
,
Santosh
,
M.
,
Chen
,
Q.
,
Zhang
,
X.N.
,
Li
,
W.
,
He
,
D.F.
, and
Zhang
,
G.W.
,
2012
,
Neoproterozoic accretionary tectonics along the northwestern margin of the Yangtze block, China: Constraints from zircon U-Pb geochronology and geochemistry
:
Precambrian Research
 , v.
196–197
, p.
247
274
, https://doi.org/10.1016/j.precamres.2011.12.007.
39.
Dong
,
Y.P.
,
Liu
,
X.M.
,
Neubauer
,
F.
,
Zhang
,
G.W.
,
Tao
,
N.
,
Zhang
,
Y.G.
,
Zhang
,
X.N.
, and
Li
,
W.
,
2013
,
Timing of Paleozoic amalgamation between the North China and South China blocks: Evidence from detrital zircon U-Pb ages
:
Tectonophysics
 , v.
586
, p.
173
191
, https://doi.org/10.1016/j.tecto.2012.11.018.
40.
Dong
,
Y.P.
,
Yang
,
Z.
,
Liu
,
X.M.
,
Zhang
,
X.N.
,
He
,
D.F.
,
Li
,
W.
,
Zhang
,
F.F.
,
Sun
,
S.S.
,
Zhang
,
H.F.
, and
Zhang
,
G.W.
,
2014
,
Neoproterozoic amalgamation of the Northern Qinling terrain to the North China craton: Constraints from geochemistry of the Kuanping ophiolite
:
Precambrian Research
 , v.
255
, p.
77
95
, https://doi.org/10.1016/j.precamres.2014.09.008.
41.
Dong
,
Y.P.
,
Zhang
,
X.N.
,
Liu
,
X.M.
,
Li
,
W.
,
Chen
,
Q.
,
Zhang
,
G.W.
,
Zhang
,
H.F.
,
Yang
,
Z.
,
Sun
,
S.S.
, and
Zhang
,
F.F.
,
2015
,
Propagation tectonics and multiple accretionary processes of the Qinling orogen
:
Journal of Asian Earth Sciences
 , v.
104
, p.
84
98
, https://doi.org/10.1016/j.jseaes.2014.10.007.
42.
Dong
,
Y.P.
,
Liu
,
X.M.
,
Li
,
W.
,
Yang
,
Z.
,
Sun
,
S.S.
,
Cheng
,
B.
,
Zhang
,
F.F.
,
Zhang
,
X.N.
,
He
,
D.F.
, and
Zhang
,
G.W.
,
2016
,
Mesozoic intracontinental orogeny in the Qinling Mountains, central China
:
Gondwana Research
 , v.
30
, p.
144
158
, https://doi.org/10.1016/j.gr.2015.05.004.
43.
Dong
,
Y.P.
,
Neubauer
,
F.
,
Genser
,
J.
,
Sun
,
S.S.
,
Yang
,
Z.
,
Zhang
,
F.F.
,
Cheng
,
B.
,
Liu
,
X.M.
, and
Zhang
,
G.W.
,
2018
,
Timing of orogenic exhumation processes of the Qinling orogen: Evidence from 40Ar/39Ar dating
:
Tectonics
 , v.
37
, p.
4037
4067
, https://doi.org/10.1029/2017TC004765.
44.
Faure
,
M.
,
Lin
,
W.
, and
Le Breton
,
N.
,
2001
,
Where is the North China–South China block boundary in eastern China
:
Geology
 , v.
29
, p.
119
122
, https://doi.org/10.1130/0091-7613(2001)029<0119:WITNCS>2.0.CO;2.
45.
Frese
,
K.
,
Trommsdorff
,
V.
, and
Kunze
,
K.
,
2003
,
Olivine [100] normal to foliation: Lattice preferred orientation in prograde garnet peridotite formed at high H2O activity, Cima di Gagnone (central Alps)
:
Contributions to Mineralogy and Petrology
 , v.
145
, p.
75
86
, https://doi.org/10.1007/s00410-002-0434-x.
46.
Hacker
,
B.R.
,
Ratschbacher
,
L.
,
Webb
,
L.
,
Ireland
,
T.
,
Walker
,
D.
, and
Dong
,
S.W.
,
1998
,
U/Pb zircon ages constrain the architecture of the ultrahigh-pressure Qinling-Dabie orogen, China
:
Earth and Planetary Science Letters
 , v.
161
, p.
215
230
, https://doi.org/10.1016/S0012-821X(98)00152-6.
47.
Hansen
,
L.N.
,
Zhao
,
Y.H.
,
Zimmerman
,
M.E.
, and
Kohlstedt
,
D.L.
,
2014
,
Protracted fabric evolution in olivine: Implications for the relationship among strain, crystallographic fabric, and seismic anisotropy
:
Earth and Planetary Science Letters
 , v.
387
, p.
157
168
, https://doi.org/10.1016/j.epsl.2013.11.009.
48.
Heidelbach
,
F.
, and
Terry
,
M.P.
,
2013
,
Inherited fabric in an omphacite symplectite: Reconstruction of plastic deformation under ultra-high pressure conditions
:
Microscopy and Microanalysis
 , v.
19
, p.
942
949
, https://doi.org/10.1017/S1431927613001451.
49.
Holland
,
T.J.B.
, and
Blundy
,
J.D.
,
1994
,
Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry
:
Contributions to Mineralogy and Petrology
 , v.
116
, p.
433
447
, https://doi.org/10.1007/BF00310910.
50.
Holtzman
,
B.K.
,
Kohlstedt
,
D.L.
,
Zimmerman
,
M.E.
,
Heidelbach
,
F.
,
Hiraga
,
T.
, and
Hustoft
,
J.
,
2003
,
Melt segregation and strain partitioning: Implications for seismic anisotropy and mantle flow
:
Science
 , v.
301
, p.
1227
1230
, https://doi.org/10.1126/science.1087132.
51.
Huang
,
Z.
,
Zhao
,
D.
, and
Wang
,
L.
,
2011
,
Shear wave anisotropy in the crust, mantle wedge, and subducting Pacific slab under northeast Japan
:
Geochemistry Geophysics Geosystems
 , v.
12
,
Q01002
, https://doi.org/10.1029/2010GC003343.
52.
Imon
,
R.
,
Okudaira
,
T.
, and
Kanagawa
,
K.
,
2004
,
Development of shape- and lattice preferred orientations of amphibole grains during initial cataclastic deformation and subsequent deformation by dissolution precipitation creep in amphibolites from the Ryoke metamorphic belt, SW Japan
:
Journal of Structural Geology
 , v.
26
, p.
793
805
, https://doi.org/10.1016/j.jsg.2003.09.004.
53.
Ishii
,
T.
,
Robinson
,
P.T.
,
Maekawa
,
H.
, and
Fiske
,
R.
,
1992
,
27
.
Petrological studies of peridotites from diapiric serpentinite sea mounts in the Izu-Ogasawara-Mariana forearc, Leg 125
, in
Fryer
,
P.
,
Pearce
,
J.A.
,
Stokking
,
L.B.
, et al
,
Proceedings of the Ocean Drilling Program, Scientific Results Volume 125
 :
College Station, Texas
,
Ocean Drilling Program
, p.
445
485
.
54.
Ji
,
S.
,
Salisbury
,
M.H.
, and
Hanmer
,
S.
,
1993
,
Petrofabric, P-wave anisotropy and seismic reflectivity of high-grade tectonites
:
Tectonophysics
 , v.
222
, p.
195
226
, https://doi.org/10.1016/0040-1951(93)90049-P.
55.
Ji
,
S.
,
Zhao
,
X.
, and
Francis
,
D.
,
1994
,
Calibration of shear-wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the Canadian Cordillera and Alaska
:
Tectonophysics
 , v.
239
, p.
1
27
, https://doi.org/10.1016/0040-1951(94)90104-X.
56.
Ji
,
S.
,
Shao
,
T.
,
Michibayashi
,
K.
,
Long
,
C.
,
Wang
,
Q.
,
Kondo
,
Y.
,
Zhao
,
W.
,
Wang
,
H.
, and
Salisbury
,
M.H.
,
2013
,
A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole-rich rocks
:
Journal of Geophysical Research–Solid Earth
 , v.
118
, p.
4699
4728
, https://doi.org/10.1002/jgrb.50352.
57.
Ji
,
S.C.
,
Rondenay
,
S.
,
Mareschal
,
M.
, and
Senechal
,
G.
,
1996
,
Obliquity between seismic and electrical anisotropies as an indicator of movement sense for ductile mantle shear zones
:
Geology
 , v.
24
, p.
1033
1036
, https://doi.org/10.1130/0091-7613(1996)024<1033:OBSAEA>2.3.CO;2.
58.
Jung
,
H.
, and
Karato
,
S.
,
2001
,
Water-induced fabric transitions in olivine
:
Science
 , v.
293
, p.
1460
1463
, https://doi.org/10.1126/science.1062235.
59.
Jung
,
H.
,
Katayama
,
I.
,
Jiang
,
Z.
,
Hiraga
,
T.
, and
Karato
,
S.
,
2006
,
Effect of water and stress on the lattice-preferred orientation of olivine
:
Tectonophysics
 , v.
421
, p.
1
22
, https://doi.org/10.1016/j.tecto.2006.02.011.
60.
Jung
,
H.
,
Mo
,
W.
, and
Green
,
H.W.
,
2009
,
Upper mantle seismic anisotropy resulting from pressure-induced slip transition in olivine
:
Nature Geoscience
 , v.
2
, p.
73
77
, https://doi.org/10.1038/ngeo389.
61.
Jung
,
H.
,
Lee
,
J.
,
Ko
,
B.
,
Jung
,
S.
,
Park
,
M.
,
Cao
,
Y.
, and
Song
,
S.
,
2013
,
Natural type-C olivine fabrics in garnet peridotites in North Qaidam UHP collision belt, NW China
:
Tectonophysics
 , v.
594
, p.
91
102
, https://doi.org/10.1016/j.tecto.2013.03.025.
62.
Karato
,
S.
,
Jung
,
H.
,
Katayama
,
I.
, and
Skemer
,
P.
,
2008
,
Geodynamic significance of seismic anisotropy of the upper mantle: New insights from laboratory studies
:
Annual Review of Earth and Planetary Sciences
 , v.
36
, p.
59
95
, https://doi.org/10.1146/annurev.earth.36.031207.124120.
63.
Katayama
,
I.
, and
Karato
,
S.
,
2006
,
Effects of temperature on the B- to C-type fabric transition in olivine
:
Physics of the Earth and Planetary Interiors
 , v.
157
, p.
33
45
, https://doi.org/10.1016/j.pepi.2006.03.005.
64.
Katayama
,
I.
,
Jung
,
H.
, and
Karato
,
S.
,
2004
,
New type of olivine fabric from deformation experiments at modest water content and low stress
:
Geology
 , v.
32
, p.
1045
1048
, https://doi.org/10.1130/G20805.1.
65.
Katayama
,
I.
,
Karato
,
S.
, and
Brandon
,
M.
,
2005
,
Evidence of high water content in the deep upper mantle inferred from deformation microstructures
:
Geology
 , v.
33
, p.
613
616
, https://doi.org/10.1130/G21332.1.
66.
Kelemen
,
P.B.
,
Shimizu
,
N.
, and
Salters
,
V.J.M.
,
1995
,
Extraction of midocean-ridge basalt from the upwelling mantle by focused flow of melt in dunite channels
:
Nature
 , v.
375
, p.
747
753
, https://doi.org/10.1038/375747a0.
67.
Kneller
,
E.A.
,
van Keken
,
P.E.
,
Karato
,
S.
, and
Park
,
J.
,
2005
,
B-type fabric in the mantle wedge: Insights from high-resolution non-Newtonian subduction zone models
:
Earth and Planetary Science Letters
 , v.
237
, p.
781
797
, https://doi.org/10.1016/j.epsl.2005.06.049.
68.
Kneller
,
E.A.
,
van Keken
,
P.E.
,
Katayama
,
I.
, and
Karato
,
S.
,
2007
,
Stress, strain, and B-type olivine fabric in the fore-arc mantle: Sensitivity tests using high-resolution steady-state subduction zone models
:
Journal of Geophysical Research
 , v.
112
,
B04406
, https://doi.org/10.1029/2006JB004544.
69.
Kneller
,
E.A.
,
Long
,
M.D.
, and
van Keken
,
P.E.
,
2008
,
Olivine fabric transitions and shear-wave anisotropy in the Ryukyu subduction system
:
Earth and Planetary Science Letters
 , v.
268
, p.
268
282
, https://doi.org/10.1016/j.epsl.2008.01.004.
70.
Lafrance
,
B.
, and
Vernon
,
R.H.
,
1993
,
Mass transfer and microfracturing in gabbroic mylonites of the Guadalupe igneous complex, California
, in
Boland
,
J.N.
, and
Fitz Gerald
,
J.D.
, eds.,
Defects and Processes in the Solid State: Geoscience Applications, the McLaren Volume
 :
Amsterdam, Netherlands
,
Elsevier
, Developments in Petrology 4, p.
151
167
.
71.
Law
,
R.D.
,
2014
,
Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures: A review
:
Journal of Structural Geology
 , v.
66
, p.
129
161
, https://doi.org/10.1016/j.jsg.2014.05.023.
72.
Lee
,
B.
,
Zhu
,
L.M.
,
Gong
,
H.J.
,
Guo
,
B.
,
Yang
,
T.
,
Wang
,
F.
,
Wang
,
W.
, and
Xu
,
A.
,
2010
,
Genetic relationship between peridotites and chromite deposit from Songshugou area of North Qinling
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
26
, p.
1487
1502
.
73.
Lee
,
J.
, and
Jung
,
H.
,
2015
,
Lattice-preferred orientation of olivine found in diamond-bearing garnet peridotites in Finsch, South Africa, and implications for seismic anisotropy
:
Journal of Structural Geology
 , v.
70
, p.
12
22
.
74.
Li
,
S.
,
Xiao
,
Y.
,
Liou
,
D.
,
Chen
,
Y.
,
Ge
,
N.
,
Zhang
,
Z.
,
Sun
,
S.
,
Cong
,
B.
,
Zhang
,
R.
,
Hart
,
S.R.
, and
Wang
,
S.
,
1993
,
Collision of the North China and Yangtse blocks and formation of coesite-bearing eclogites: Timing and processes
:
Chemical Geology
 , v.
109
, p.
89
111
.
75.
Li
,
S.G.
,
Sun
,
W.D.
, and
Zhang
,
G.W.
,
1996
,
Chronology and geochemistry of metavolcanic rocks from Heigouxia valley in Mian-Lue tectonic belt, South Qinling: Evidence for a Paleozoic oceanic basin and its closure time
:
Science in China, ser. D
 , v.
39
, p.
300
310
.
76.
Li
,
Y.
,
Zhou
,
H.W.
,
Li
,
Q.L.
,
Xiang
,
H.
,
Zhong
,
Z.Q.
, and
Brouwer
,
F.M.
,
2014
,
Palaeozoic polymetamorphism in the North Qinling orogenic belt, central China: Insights from petrology and in situ titanite and zircon U-Pb geochronology
:
Journal of Asian Earth Sciences
 , v.
92
, p.
77
91
, https://doi.org/10.1016/j.jseaes.2014.05.023.
77.
Liao
,
X.Y.
,
Liu
,
L.
,
Wang
,
Y.W.
,
Cao
,
Y.T.
, and
Chen
,
D.L.
,
2016
,
Multi-stage metamorphic evolution of retrogressed eclogites with a granulite-facies overprint in the North Qinling belt
:
Gondwana Research
 , v.
30
, p.
79
96
, https://doi.org/10.1016/j.gr.2015.09.012.
78.
Ling
,
W.L.
,
Ren
,
B.F.
,
Duan
,
R.C.
,
Liu
,
X.M.
,
Mao
,
X.W.
,
Peng
,
L.H.
,
Liu
,
Z.X.
,
Cheng
,
J.P.
, and
Yang
,
H.M.
,
2008
,
Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication
:
Chinese Science Bulletin
 , v.
53
, p.
2192
2199
.
79.
Liu
,
J.F.
,
Sun
,
Y.
, and
Sun
,
W.D.
,
2009
,
LA-ICP-MS zircon dating from the Lajimiao mafic complex in the Qinling orogenic belt
:
Acta Petrological Sinica
 , v.
25
, no.
2
, p.
320
330
[in Chinese with English abstract].
80.
Liu
,
L.
,
Zhou
,
D.W.
,
Dong
,
Y.P.
,
Zhang
,
H.F.
,
Liu
,
Y.J.
, and
Zhang
,
Z.J.
,
1995
,
High pressure metabasites and their retrograde metamorphic P-T-t path from Songshugou area, eastern Qinling Mountain
:
Acta Petrological Sinica
 , v.
11
, p.
127
136
[in Chinese with English abstract].
81.
Liu
,
L.
,
Zhou
,
D.W.
,
Wang
,
Y.
,
Chen
,
D.L.
, and
Liu
,
Y.
,
1996
,
Study and implication of the high-pressure felsic granulite in the Qinling complex of East Qinling
:
Science in China, ser. D
 , v.
39
, p.
60
68
.
82.
Liu
,
L.
,
Chen
,
D.L.
, and
Zhang
,
A.D.
,
2004
,
Geochemical characteristics and LA-ICP-MS zircon U-Pb dating of amphibolites in the Songshugou ophiolite in the eastern Qinling
:
Acta Geologica Sinica
 , v.
78
, p.
137
145
.
83.
Liu
,
L.
,
Liao
,
X.
,
Wang
,
Y.
,
Wang
,
C.
,
Santosh
,
M.
,
Yang
,
M.
,
Zhang
,
C.
, and
Chen
,
D.
,
2016
,
Early Paleozoic tectonic evolution of the North Qinling orogenic belt in central China: Insights on continental deep subduction and multiphase exhumation
:
Earth-Science Reviews
 , v.
159
, p.
58
81
, https://doi.org/10.1016/j.earscirev.2016.05.005.
84.
Liu
,
X.M.
,
Gao
,
S.
,
Diwu
,
C.R.
,
Yuan
,
H.L.
, and
Hu
,
Z.C.
,
2007
,
Simultaneous in-situ determination of U-Pb age and trace elements in zircon by LA-ICP-MS in 20 µm spot size
:
Chinese Science Bulletin
 , v.
52
, p.
1257
1264
, https://doi.org/10.1007/s11434-007-0160-x.
85.
Long
,
M.D.
, and
Silver
,
P.G.
,
2008
,
The subduction zone flow field from seismic anisotropy: A global view
:
Science
 , v.
319
, p.
315
318
, https://doi.org/10.1126/science.1150809.
86.
Long
,
M.D.
, and
van der Hilst
,
R.D.
,
2006
,
Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge
:
Physics of the Earth and Planetary Interiors
 , v.
155
, p.
300
312
, https://doi.org/10.1016/j.pepi.2006.01.003.
87.
Ludwig
,
K.R.
,
2003
,
User’s Manual for Isoplot/Ex v3.0: A Geochronology Toolkit for Microsoft Excel
:
Berkeley Geochronological Center Special Publication
4
, p.
25
31
.
88.
Mainprice
,
D.
,
2007
,
Seismic anisotropy of the deep Earth from a mineral and rock physics perspective
, in
Schubert
,
G.
, ed.,
Treatise on Geophysics, Volume 2: Mineral Physics
 :
Oxford, UK
,
Elsevier
, p.
437
491
, https://doi.org/10.1016/B978-044452748-6.00045-6.
89.
Mainprice
,
D.
, and
Silver
,
P.
,
1993
,
Interpretation of SKS-waves using samples from the sub-continental lithosphere
:
Physics of the Earth and Planetary Interiors
 , v.
78
, p.
257
280
, https://doi.org/10.1016/0031-9201(93)90160-B.
90.
Mainprice
,
D.
,
Barroul
,
G.
, and
Ben Ismaïl
,
W.
,
2000
,
The seismic anisotropy of the Earth’ s mantle: From single crystal to polycrystal
, in
Karato
,
S.
, ed.,
Earth’s Deep Interior
 :
Washington, D.C.
,
American Geophysical Union
, p.
237
264
.
91.
Malpas
,
J.
,
Zhou
,
M.F.
,
Robinson
,
P.T.
, and
Reynolds
,
P.
,
2003
,
Geochemical and geochronological constraints on the origin and emplacement of the Yarlung–Zangbo ophiolites, southern Tibet
, in
Dilek
,
Y.
, and
Robinson
,
P.T.
, eds.,
Ophiolites through Earth History
 :
Geological Society [London] Special Publication
218
, p.
191
206
, https://doi.org/10.1144/GSL.SP.2003.218.01.11.
92.
Mattauer
,
M.
,
Matte
,
P.
,
Malavieille
,
J.
,
Tapponnier
,
P.
,
Maluski
,
H.
,
Xu
,
Z.Q.
,
Lu
,
Y.L.
, and
Tang
,
Y.Q.
,
1985
,
Tectonics of Qinling belt: Build-up and evolution of eastern Asia
:
Nature
 , v.
317
, p.
496
500
, https://doi.org/10.1038/317496a0.
93.
McNamara
,
D.D.
,
Wheeler
,
J.
,
Pearce
,
M.
, and
Prior
,
D.J.
,
2012
,
Fabrics produced mimetically during static metamorphism in retrogressed eclogites from the Zermatt-Saas zone, western Italian Alps
:
Journal of Structural Geology
 , v.
44
, p.
167
178
, https://doi.org/10.1016/j.jsg.2012.08.006.
94.
Meng
,
Q.R.
,
Xue
,
F.
, and
Zhang
,
G.W.
,
1994
,
Conglomerate sedimentation and its tectonic implication, Heihe area within Shangdan zone of the Qinling
:
Acta Sedimentologica Sinica
 , v.
12
, p.
37
46
[in Chinese with English abstract].
95.
Michibayashi
,
K.
, and
Mainprice
,
D.
,
2004
,
The role of pre-existing mechanical anisotropy on shear zone development within oceanic mantle lithosphere: An example from the Oman ophiolite
:
Journal of Petrology
 , v.
45
, p.
405
414
, https://doi.org/10.1093/petrology/egg099.
96.
Michibayashi
,
K.
, and
Oohara
,
T.
,
2013
,
Olivine fabric evolution in a hydrated ductile shear zone at the Moho transition zone, Oman ophiolite
:
Earth and Planetary Science Letters
 , v.
377
, p.
299
310
, https://doi.org/10.1016/j.epsl.2013.07.009.
97.
Michibayashi
,
K.
,
Ina
,
T.
, and
Kanagawa
,
K.
,
2006
,
The effect of dynamic recrystallization on olivine fabric and seismic anisotropy: Insight from a ductile shear zone, Oman ophiolite
:
Earth and Planetary Science Letters
 , v.
244
, p.
695
708
, https://doi.org/10.1016/j.epsl.2006.02.019.
98.
Mizukami
,
T.
,
Wallis
,
S.R.
, and
Yamamoto
,
J.
,
2004
,
Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum
:
Nature
 , v.
427
, p.
432
436
, https://doi.org/10.1038/nature02179.
99.
Nakajima
,
J.
, and
Hasegawa
,
A.
,
2004
,
Shear-wave polarization anisotropy and subduction-induced flow in the mantle wedge of northern Japan
:
Earth and Planetary Science Letters
 , v.
225
, p.
365
377
, https://doi.org/10.1016/j.epsl.2004.06.011.
100.
Nicolas
,
A.
, and
Christensen
,
N.I.
,
1987
,
Formation of anisotropy in upper mantle peridotites—A review
, in
Fuchs
,
K.
, and
Froideoaux
,
C.
, eds.,
Composition, Structure and Dynamics of the Lithosphere-Asthenosphere System
 : American Geophysical Union Geodynamics Monograph 16, p.
111
123
, https://doi.org/10.1029/GD016p0111.
101.
Nie
,
H.
,
Yang
,
J.Z.
,
Zhou
,
G.Y.
,
Liu
,
C.Z.
,
Zheng
,
J.P.
,
Zhang
,
W.X.
,
Zhao
,
Y.J.
,
Wang
,
H.
, and
Wu
,
Y.B.
,
2017
,
Geochemical and Re-Os isotope constraints on the origin and age of the Songshugou peridotite massif in the Qinling orogen, central China
:
Lithos
 , v.
292
, p.
307
319
, https://doi.org/10.1016/j.lithos.2017.09.009.
102.
Nyman
,
M.W.
,
Law
,
R.D.
, and
Smelik
,
E.A.
,
1992
,
Cataclastic deformation mechanism for the development of core-mantle structure in amphibole
:
Geology
 , v.
20
, p.
455
458
, https://doi.org/10.1130/0091-7613(1992)020<0455:CDMFTD>2.3.CO;2.
103.
Ohuchi
,
T.
, and
Irifune
,
T.
,
2014
,
Crystallographic preferred orientation of olivine in the Earth’s deep upper mantle
:
Physics of the Earth and Planetary Interiors
 , v.
228
, p.
220
231
, https://doi.org/10.1016/j.pepi.2013.11.013.
104.
Palasse
,
L.N.
,
Vissers
,
R.L.M.
,
Paulssen
,
H.
,
Basu
,
A.R.
, and
Drury
,
M.R.
,
2012
,
Microstructural and seismic properties of the upper mantle underneath a rifted continental terrane (Baja California): An example of sub-crustal mechanical asthenosphere?
:
Earth and Planetary Science Letters
 , v.
345
, p.
60
71
, https://doi.org/10.1016/j.epsl.2012.06.042.
105.
Passchier
,
C.W.
, and
Trouw
,
R.
,
2005
,
Microtectonics
:
Berlin
,
Springer-Verlag
,
366
p.
106.
Pearce
,
J.A.
,
2008
,
Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust
:
Lithos
 , v.
100
, p.
14
48
, https://doi.org/10.1016/j.lithos.2007.06.016.
107.
Pearce
,
J.A.
,
2014
,
Immobile element fingerprinting of ophiolites
:
Elements
 , v.
10
, p.
101
108
, https://doi.org/10.2113/gselements.10.2.101.
108.
Peyton
,
V.V.
,
Levin
,
J.
,
Park
,
M.
,
Brandon
,
M.
,
Lees
,
J.
,
Gordeev
,
E.
, and
Ozerov
,
A.
,
2001
,
Mantle flow at a slab edge: Seismic anisotropy in the Kamchatka region
:
Journal of Geophysical Research
 , v.
28
, p.
379
382
, https://doi.org/10.1029/2000GL012200.
109.
Qian
,
J.H.
,
Yang
,
X.Q.
,
Liu
,
L.
,
Cao
,
Y.T.
,
Chen
,
D.L.
, and
Yang
,
W.Q.
,
2013
,
Zircon U-Pb dating, mineral inclusion, Lu-Hf isotopic data and their geological significance of garnet amphibolite from Songshugou, North Qinling
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
29
, no.
9
, p.
308
309
[in Chinese with English abstract].
110.
Raterron
,
P.
,
Chen
,
J.
,
Li
,
L.
,
Weidner
,
D.
, and
Cordier
,
P.
,
2007
,
Pressure-induced slip-system transition in forsterite: Single-crystal rheological properties at mantle pressure and temperature
:
The American Mineralogist
 , v.
92
, p.
1436
1445
, https://doi.org/10.2138/am.2007.2474.
111.
Raterron
,
P.
,
Amiguet
,
E.
,
Chen
,
J.
,
Li
,
L.
, and
Cordier
,
P.
,
2009
,
Experimental deformation of olivine single crystals at mantle pressures and temperatures
:
Physics of the Earth and Planetary Interiors
 , v.
172
, p.
74
83
, https://doi.org/10.1016/j.pepi.2008.07.026.
112.
Raterron
,
P.
,
Girard
,
J.
, and
Chen
,
J.
,
2012
,
Activities of olivine slip systems in the upper mantle
:
Physics of the Earth and Planetary Interiors
 , v.
200
, p.
105
112
, https://doi.org/10.1016/j.pepi.2012.04.006.
113.
Ratschbacher
,
L.
,
Hacker
,
B.R.
,
Calvert
,
A.
,
Webb
,
L.E.
,
Grimmer
,
J.C.
,
McWilliams
,
M.O.
,
Ireland
,
T.
,
Dong
,
S.W.
, and
Hu
,
J.M.
,
2003
,
Tectonics of the Qinling (central China): Tectonostratigraphy, geochronology, and deformation history
:
Tectonophysics
 , v.
366
, p.
1
53
, https://doi.org/10.1016/S0040-1951(03)00053-2.
114.
Ratschbacher
,
L.
,
Franz
,
L.
,
Enkelmann
,
E.
,
Jonckeere
,
R.
,
Poerschke
,
A.
,
Hacker
,
B.R.
,
Dong
,
S.W.
, and
Zhang
,
Y.Q.
,
2006
,
The Sino-Korean-Yangtze suture, the Huwan detachment, and the Paleozoic–Tertiary exhumation of (ultra)high-pressure rocks along the Tongbai-Xinxian–Dabie Mountains
, in
Hacker
,
B.R.
,
McClelland
,
W.C.
, and
Liou
,
J.G.
, eds.,
Ultrahigh-Pressure Metamorphism: Deep Continental Subduction
 :
Geological Society of America Special Publication
403
, p.
45
75
.
115.
Reynard
,
B.
,
Gillet
,
P.
, and
Willaime
,
C.
,
1989
,
Deformation mechanisms in naturally deformed glaucophanes: A TEM and HREM study
:
European Journal of Mineralogy
 , v.
1
, p.
611
624
, https://doi.org/10.1127/ejm/1/5/0611.
116.
Rubatto
,
D.
,
2002
,
Zircon trace element geochemistry: Partitioning with garnet and the link between U-Pb ages and metamorphism
:
Chemical Geology
 , v.
184
, p.
123
138
, https://doi.org/10.1016/S0009-2541(01)00355-2.
117.
Russo
,
R.M.
, and
Silver
,
P.G.
,
1994
,
Trench-parallel flow beneath the Nazca plate from seismic anisotropy
:
Science
 , v.
263
, p.
1105
1111
, https://doi.org/10.1126/science.263.5150.1105.
118.
Saruwatari
,
K.
,
Ji
,
S.
,
Long
,
C.
, and
Salisbury
,
M.H.
,
2001
,
Seismic anisotropy of mantle xenoliths and constraints on upper mantle structure beneath the southern Canadian Cordillera
:
Tectonophysics
 , v.
339
, p.
403
426
, https://doi.org/10.1016/S0040-1951(01)00136-6.
119.
Savage
,
M.K.
,
1999
,
Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting?
:
Reviews of Geophysics
 , v.
37
, p.
65
106
, https://doi.org/10.1029/98RG02075.
120.
Shelley
,
D.
,
1994
,
Spider texture and amphibolite preferred orientations
:
Journal of Structural Geology
 , v.
16
, p.
709
717
, https://doi.org/10.1016/0191-8141(94)90120-1.
121.
Siegesmund
,
S.
,
Takeshita
,
T.
, and
Kern
,
H.
,
1989
,
Anisotropy of Vp and Vs in an amphibolite of the deeper crust and its relationship to the mineralogical, microstructural and textural characteristics of the rock
:
Tectonophysics
 , v.
157
, p.
25
38
, https://doi.org/10.1016/0040-1951(89)90338-7.
122.
Silver
,
P.G.
,
1996
,
Seismic anisotropy beneath the continents: Probing the depths of geology
:
Annual Review of Earth and Planetary Sciences
 , v.
24
, p.
385
432
, https://doi.org/10.1146/annurev.earth.24.1.385.
123.
Skemer
,
P.
,
Katayama
,
I.
, and
Karato
,
S.
,
2006
,
Deformation fabrics of the Cima di Gagnone peridotite massif, central Alps, Switzerland: Evidence of deformation at low temperatures in the presence of water
:
Contributions to Mineralogy and Petrology
 , v.
152
, p.
43
51
, https://doi.org/10.1007/s00410-006-0093-4.
124.
Sun
,
S.S.
, and
McDonough
,
W.F.
,
1989
,
Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processed
, in
Saunders
,
A.D.
, and
Norry
,
M.J.
, eds.,
Magmatism in Ocean Basins
 :
Geological Society [London] Special Publication
42
, p.
313
345
, https://doi.org/10.1144/GSL.SP.1989.042.01.19.
125.
Sun
,
S.S.
,
Ji
,
S.C.
,
Michibayashi
,
K.
, and
Salisbury
,
M.
,
2016
,
Effects of olivine fabric, melt-rock reaction, and hydration on the seismic properties of peridotites: Insight from the Luobusha ophiolite in the Tibetan Plateau
:
Journal of Geophysical Research–Solid Earth
 , v.
121
, p.
3300
3323
, https://doi.org/10.1002/2015JB012579.
126.
Sun
,
S.S.
,
Dong
,
Y.P.
,
Sun
,
Y.L.
,
Cheng
,
C.
,
Huang
,
X.X.
, and
Liu
,
X.M.
,
2019
,
Re-Os geochronology, O isotopes and mineral geochemistry of the Neoproterozoic Songshugou ultramafic massif in the Qinling orogenic belt, China
:
Gondwana Research
 , v.
70
, p.
71
87
, https://doi.org/10.1016/j.gr.2018.12.016.
127.
Sun
,
W.D.
,
Li
,
S.G.
,
Sun
,
Y.
,
Zhang
,
G.W.
, and
Zhang
,
Z.Q.
,
1996
,
Chronology and geochemistry of a lava pillow in the Erlangping Group at Xixia in the northern Qinling Mountains
:
Geological Review (Dizhi Lunping)
 , v.
42
, p.
144
153
[in Chinese with English abstract].
128.
Sun
,
W.D.
,
Li
,
S.G.
,
Sun
,
Y.
,
Zhang
,
G.W.
, and
Li
,
Q.L.
,
2002
,
Mid-Paleozoic collision in the North Qinling: Sm-Nd, Rb-Sr and 40Ar/39Ar ages and their tectonic implications
:
Journal of Asian Earth Sciences
 , v.
21
, p.
69
76
, https://doi.org/10.1016/S1367-9120(02)00010-X.
129.
Sundberg
,
M.
, and
Cooper
,
R.F.
,
2008
,
Crystallographic preferred orientation produced by diffusional creep of harzburgite: Effects of chemical interactions among phases during plastic flow
:
Journal of Geophysical Research
 , v.
113
,
B12208
, https://doi.org/10.1029/2008JB005618.
130.
Tamura
,
A.
, and
Arai
,
S.
,
2006
,
Harzburgite-dunite-orthopyroxenite suite as a record of supra-subduction zone setting for the Oman ophiolite mantle
:
Lithos
 , v.
90
, p.
43
56
, https://doi.org/10.1016/j.lithos.2005.12.012.
131.
Tang
,
L.
,
Santosh
,
M.
,
Dong
,
Y.P.
,
Tsunogae
,
T.
,
Zhang
,
S.T.
, and
Cao
,
H.W.
,
2016
,
Early Paleozoic tectonic evolution of the North Qinling orogenic belt: Evidence from geochemistry, phase equilibrium modeling and geochronology of metamorphosed mafic rocks from the Songshugou ophiolite
:
Gondwana Research
 , v.
30
, p.
48
64
, https://doi.org/10.1016/j.gr.2014.10.006.
132.
Tasaka
,
M.
,
Michibayashi
,
K.
, and
Mainprice
,
D.
,
2008
,
B-type olivine fabrics developed in the fore-arc side of the mantle wedge along a subducting slab
:
Earth and Planetary Science Letters
 , v.
272
, p.
747
757
, https://doi.org/10.1016/j.epsl.2008.06.014.
133.
Tatham
,
D.J.
,
Lloyd
,
G.E.
,
Butler
,
R.W.H.
, and
Casey
,
M.
,
2008
,
Amphibole and lower crustal seismic properties
:
Earth and Planetary Science Letters
 , v.
267
, p.
118
128
, https://doi.org/10.1016/j.epsl.2007.11.042.
134.
Tommasi
,
A.
,
Godard
,
M.
,
Coromina
,
G.
,
Dautria
,
J.M.
, and
Barsczus
,
H.
,
2004
,
Seismic anisotropy and compositionally induced velocity anomalies in the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia
:
Earth and Planetary Science Letters
 , v.
227
, p.
539
556
, https://doi.org/10.1016/j.epsl.2004.09.019.
135.
van der Laan
,
S.R.
,
Arculus
,
R.J.
,
Pearce
,
J.A.
, and
Murton
,
B.J.
,
1992
,
Petrography, mineral chemistry, and phase relations of the basement boninite series of Site 786, Izu-Bonin forearc
, in
Fryer
,
P.
,
Pearce
,
J.A.
,
Stokking
,
L.B.
, et al
,
Proceedings of the Ocean Drilling Program, Scientific Results Volume 125
 :
College Station, Texas
,
Ocean Drilling Program
, p.
171
201
.
136.
Wang
,
H.
,
Wu
,
Y.B.
,
Gao
,
S.
,
Liu
,
X.C.
,
Gong
,
H.J.
,
Li
,
Q.L.
,
Li
,
X.H.
, and
Yuan
,
H.L.
,
2011
,
Eclogite origin and timings in the North Qinling terrane, and their bearing on the amalgamation of the South and North China blocks
:
Journal of Metamorphic Geology
 , v.
29
, p.
1019
1031
, https://doi.org/10.1111/j.1525-1314.2011.00955.x.
137.
Wang
,
Q.
,
Xia
,
Q.K.
,
O’Reilly
,
S.Y.
,
Griffin
,
W.L.
,
Beyer
,
E.E.
, and
Brueckner
,
H.K.
,
2013
,
Pressure- and stress-induced fabric transition in olivine from peridotites in the Western Gneiss Region (Norway): Implications for mantle seismic anisotropy
:
Journal of Metamorphic Geology
 , v.
31
, p.
93
111
, https://doi.org/10.1111/jmg.12011.
138.
Whitehouse
,
M.J.
, and
Platt
,
J.P.
,
2003
,
Dating high-grade metamorphism—Constraints from rare-earth elements in zircons and garnet
:
Contributions to Mineralogy and Petrology
 , v.
145
, p.
61
74
, https://doi.org/10.1007/s00410-002-0432-z.
139.
Winter
,
J.D.
,
2001
,
An Introduction to Igneous and Metamorphic Petrology
:
Englewood Cliffs, New Jersey
,
Prentice Hall
,
697
p.
140.
Witt-Eickschen
,
G.
, and
Seck
,
H.A.
,
1991
,
Solubility of Ca and Al in orthopyroxene from spinel peridotite: An improved version of an empirical geothermometer
:
Contributions to Mineralogy and Petrology
 , v.
106
, p.
431
439
, https://doi.org/10.1007/BF00321986.
141.
Wu
,
Y.
, and
Zheng
,
Y.
,
2004
,
Genesis of zircon and its constraints on interpretation of U-Pb age
:
Chinese Science Bulletin
 , v.
49
, p.
1554
1569
, https://doi.org/10.1007/BF03184122.
142.
Xu
,
J.F.
,
Castillo
,
P.R.
,
Li
,
X.H.
,
Yu
,
X.Y.
,
Zhang
,
B.R.
, and
Han
,
Y.W.
,
2002
,
MORB-type rocks from the Paleo-Tethyan Mian-Lueyang northern ophiolite in the Qinling Mountains, central China: Implications for the source of the low 206Pb/204Pb and high 143Nd/144Nd mantle component in the Indian Ocean
:
Earth and Planetary Science Letters
 , v.
198
, p.
323
337
, https://doi.org/10.1016/S0012-821X(02)00536-8.
143.
Xu
,
Z.
,
Wang
,
Q.
,
Ji
,
S.
,
Chen
,
J.
,
Zeng
,
L.
,
Yang
,
J.
,
Chen
,
F.
,
Liang
,
F.
, and
Wenk
,
H.
,
2006
,
Petrofabrics and seismic properties of garnet peridotite from the UHP Sulu terrane (China): Implications for olivine deformation mechanism in a cold and dry subducting continental slab
:
Tectonophysics
 , v.
421
, p.
111
127
, https://doi.org/10.1016/j.tecto.2006.04.010.
144.
Xue
,
F.
,
Lerch
,
M.F.
,
Kroner
,
A.
, and
Reischmann
,
T.
,
1996
,
Tectonic evolution of the east Qinling Mountains, China, in the Palaeozoic: A review and new tectonic model
:
Tectonophysics
 , v.
253
, p.
271
284
, https://doi.org/10.1016/0040-1951(95)00060-7.
145.
Yan
,
Z.
,
Wang
,
Z.Q.
,
Yan
,
Q.R.
,
Wang
,
T.
,
Xiao
,
W.J.
,
Li
,
J.L.
,
Han
,
F.L.
,
Chen
,
J.L.
, and
Yang
,
Y.C.
,
2006
,
Devonian sedimentary environments and provenances of the Qinling orogen: Constraints on late Paleozoic southward accretion of the North China craton
:
International Geology Review
 , v.
48
, p.
585
618
, https://doi.org/10.2747/0020-6814.48.7.585.
146.
Yang
,
J.S.
,
Liu
,
F.L.
,
Wu
,
C.L.
,
Wan
,
Y.S.
,
Zhang
,
J.X.
,
Shi
,
R.D.
, and
Chen
,
S.Y.
,
2003
,
Two ultrahigh pressure metamorphic events recognized in the Central orogenic belt of China: Evidence from the U-Pb dating of coesite-bearing zircons
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
77
, p.
463
477
[in Chinese with English abstract].
147.
Yu
,
H.
,
Zhang
,
H.F.
,
Li
,
X.H.
,
Zhang
,
J.
,
Santosh
,
M.
,
Yang
,
Y.H.
, and
Zhou
,
D.W.
,
2016
,
Tectonic evolution of the North Qinling orogen from subduction to collision and exhumation: Evidence from zircons in metamorphic rocks of the Qinling Group
:
Gondwana Research
 , v.
30
, p.
65
78
, https://doi.org/10.1016/j.gr.2015.07.003.
148.
Yu
,
H.
,
Zhang
,
H.F.
, and
Santosh
,
M.
,
2017
,
Mylonitized peridotites of Songshugou in the Qinling orogen, central China: A fragment of fossil oceanic lithosphere mantle
:
Gondwana Research
 , v.
52
, p.
1
17
, https://doi.org/10.1016/j.gr.2017.08.007.
149.
Zhai
,
X.
,
Day
,
H.W.
,
Hacker
,
B.R.
, and
You
,
Z.
,
1998
,
Paleozoic metamorphism in the Qinling orogen, Tongbai Mountains, central China
:
Geology
 , v.
26
, p.
371
374
, https://doi.org/10.1130/0091-7613(1998)026<0371:PMITQO>2.3.CO;2.
150.
Zhang
,
C.L.
,
Gao
,
S.
,
Zhang
,
G.
,
Guo
,
A.L.
, and
Yuan
,
H.L.
,
2004
,
Geochemistry of ophiolite cherts from the Qinling orogenic belt and implications for their tectonic settings
:
Science in China, ser. D
 , v.
47
, p.
329
337
, https://doi.org/10.1360/02YD0480.
151.
Zhang
,
G.W.
,
1988
,
Formation and Evolution of the Qinling Orogen
:
Xi’an, China
,
Northwest University Press
,
192
p. [in Chinese with English abstract].
152.
Zhang
,
G.W.
,
Meng
,
Q.R.
, and
Lai
,
S.C.
,
1995a
,
Structure and tectonics of the Qinling orogenic belt
:
Science in China, ser. D
 , v.
38
, p.
1379
1394
.
153.
Zhang
,
G.W.
,
Zhang
,
Z.Q.
, and
Dong
,
Y.P.
,
1995b
,
Nature of main tectono-lithostratigraphic units of the Qinling orogen: Implications for the tectonic evolution
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
11
, p.
101
114
[in Chinese with English abstract].
154.
Zhang
,
G.W.
,
Yu
,
Z.P.
,
Dong
,
Y.P.
, and
Yao
,
A.P.
,
2000
,
On Precambrian framework and evolution of the Qinling belt
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
16
, p.
11
21
.
155.
Zhang
,
G.W.
,
Zhang
,
B.R.
,
Yuan
,
X.C.
, and
Xiao
,
Q.H.
,
2001
,
Qinling Orogenic Belt and Continental Dynamics
:
Beijing
,
Science Press
,
855
p. [in Chinese with English abstract].
156.
Zhang
,
J.X.
,
Yu
,
S.Y.
, and
Meng
,
F.C.
,
2011
,
Polyphase early Paleozoic metamorphism in the northern Qinling orogenic belt
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
27
, no.
4
, p.
1179
1190
.
157.
Zhang
,
Q.
,
Zhang
,
Z.Q.
,
Sun
,
Y.
, and
Han
,
S.
,
1995
,
Trace element and isotopic geochemistry of metabasalts from Danfeng Group (DFG) in Shangxian-Danfeng area, Shaanxi Province
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
11
, p.
43
54
[in Chinese with English abstract].
158.
Zhang
,
Z.J.
,
1995
,
The genesis of dunites in the Songshugou ultramafic rock body, North Qinling
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
11
, p.
178
189
[in Chinese with English abstract].
159.
Zhang
,
Z.Q.
, and
Zhang
,
Q.
,
1995
,
Geochemistry of metamorphosed late Proterozoic Kuanping ophiolite in the northern Qinling, China
:
Acta Petrologica Sinica (Yanshi Xuebao)
 , v.
11
, supplement, p.
165
177
.
160.
Zhu
,
B.Q.
,
2001
,
Geochemical Province and Geochemical Steep Zone
:
Beijing
,
Science Press
,
118
p. [in Chinese with English abstract].
Gold Open Access: This paper is published under the terms of the CC-BY-NC license.