Abstract

The preservation of ultra-high-pressure and super-reducing phases in the Neotethyan Luobusa ophiolite in Tibet suggests their deep origin near the mantle transition zone. Dunite and harzburgite core samples from the Luobusa Scientific Drilling Project show supra-subduction zone geochemical signatures and equilibration temperatures of c. 950–1080°C. Olivine shows A-, B-, C- and E-type fabrics, and combinations of A- and E-type or B- and E-type fabrics. Transmission electron microscopy observations show straight dislocations and the activation of multiple slip systems [100](010), [001](010), [001](100) and [100](001) in olivine. The mean water content in olivine, orthopyroxene (Opx) and clinopyroxene (Cpx) from 24 peridotite samples was 16 ± 5, 90 ± 21 and 492 ± 64 ppm, respectively, which is different from the water content of hydrated peridotites above the mantle wedge. The trace element compositions of Cpx exclude significant metasomatism after melt extraction. The high hydrogen partition coefficient between Cpx and Opx (DHCpx/Opx = 5.56 ± 0.96) implies equilibrium at high pressures and rapid exhumation. Based on deformation experiments, the B- and C-type fabrics could be formed in a subduction zone at depths >200 km, whereas the A- and E-type fabrics were produced in the shallow mantle. In a process triggered by slab rollback, the Luobusa peridotites may have been rapidly exhumed within a subduction channel and mixed with the lithospheric mantle of the forearc.

Supplementary material: Major oxide contents in Opx, Cpx and spinel, trace element concentration in Cpx, micrographs and TEM images of peridotite are available at https://doi.org/10.6084/m9.figshare.c.4307828

Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection’ available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways

The fabrics of ophiolitic peridotites record thermodynamic processes from the mid-ocean ridge to the subduction zone, followed by their final emplacement at a convergent boundary (Dilek & Robinson 2003 and references cited therein). The lattice-preferred orientations (LPOs) of olivine and orthopyroxene (Opx) from both a fast-spreading ridge, such as the Oman ophiolite (Boudier & Nicolas 1995), and a slow-spreading ridge, such as the Lanzo massif in the Alps (Boudier 1978), indicate that dislocation creep is the dominant deformation mechanism in the oceanic lithosphere. The LPO of olivine in naturally deformed peridotites is generally characterized by the [100] axis parallel to the lineation and the (010) plane parallel to the foliation, i.e. the A-type fabric (Ben Ismaı̈l & Mainprice 1998; Tommasi & Vauchez 2015; Michibayashi et al. 2016; Tommasi et al. 2016), which can be attributed to the dominant activation of the slip system [100](010) at high temperatures and low strain rates under upper mantle conditions (e.g. Carter & Avé Lallemant 1970; Zhang et al. 2000; Hirth & Kohlstedt 2003). Because olivine is the most abundant mineral in the upper mantle, the A-type olivine fabric is used to infer the direction of mantle flow from seismic anisotropy (e.g. Blackman & Kendall 2002; Park & Levin 2002 ).

Deformation experiments investigating the effects of water, stress, pressure and temperature have found a number of different fabric types in olivine (e.g. Carter & Avé Lallemant 1970; Jung & Karato 2001; Jung et al. 2006; Ohuchi et al. 2011; Ohuchi & Irifune 2013). In addition to the A-type fabric, B- and E-type olivine fabrics, produced by the predominance of the [001](010) and [100](001) slip systems, respectively, have been observed in peridotites from supra-subduction zones (SSZ) – for example, the B-type fabric was seen in peridotites from the Sanbagawa metamorphic belt of SW Japan (Mizukami et al. 2004; Tasaka et al. 2008), the E-type fabric was seen in peridotites from the accreted Talkeetna arc in south-central Alaska (Mehl et al. 2003) and the Hidaka metamorphic belt in northern Japan (Sawaguchi 2004). It is still not clear whether the trench-parallel seismic anisotropy observed in forearc regions is caused by the B-type olivine fabric in the water-rich mantle wedge or the A-type olivine fabric resulting from trench-parallel flow (Long & Becker 2010).

Based on the water-induced fabric transition in olivine in deformation experiments (Jung & Karato 2001), the C-type fabric in garnet peridotites from ultra-high-pressure (UHP) metamorphic terranes is often attributed to ductile deformation in the hydrous deep mantle, e.g. the Cima Di Gagnone of the Central Alps (Frese et al. 2003; Skemer et al. 2006), the Norwegian Caledonides (Katayama et al. 2005) and the North Qaidam UHP belt (Jung et al. 2013). However, Xu et al. (2006) reported that the C-type fabric from the Zhimafang garnet peridotites in the Sulu UHP terrane was formed under 4–7 GPa, 750–950°C and water-poor conditions in a continental subduction zone. This interpretation was confirmed by the C-type fabric in water-poor olivine from the Xugou peridotites in the Sulu UHP terrane (Wang et al. 2013b). In addition, water-poor olivine from the Western Gneiss Region (Norway) has developed the B-type fabric in strongly sheared peridotites and the C-type fabric in garnet peridotites that had undergone UHP metamorphism at P > 6 GPa and 850–950°C, implying a water-independent fabric transition in a cold and dry continental subduction zone (Wang et al. 2013a).

The Luobusa ophiolite, located in the eastern part of the Yarlung–Zangbo Suture Zone (YZSZ) in southern Tibet, represents a remnant of the Neotethyan oceanic lithosphere in an SSZ environment (Zhou et al. 1996, 2005, 2014; Xu et al. 2015a; Dilek & Yang 2018). Different models, such as a mantle plume (Yang et al. 2014; Xiong et al. 2015), channelized mantle upwelling from the transition zone (Griffin et al. 2016) or slab rollback-induced channel flow from the transition zone (Dilek & Yang 2018) have been proposed to interpret the occurrence of UHP and super-reducing phases (e.g. in situ diamond, moissanite and native Fe) in the Luobusa peridotites and chromitites. Only the A-type olivine fabric has so far been observed in the Luobusa peridotites at outcrop and without measurements of the water content (Xu & Jin 2010; Sun et al. 2016), which casts doubt on the implications of the peridotite microstructure for the interpretation of deep mantle processes.

Here we present an integrated study of harzburgite and dunite samples from two boreholes of the Luobusa Scientific Drilling Project. The A-, B-, C- and E-type olivine fabrics, as well as different slip systems in olivine, were recognized in the core samples. Combined with the chemical composition and water content of olivine, Opx and clinopyroxene (Cpx), we propose that the Luobusha ophiolite presents a mixture of peridotites from different depths in a subduction channel. Channel flow from the transition zone to shallow depths induced by slab rollback provides an important pathway for the incorporation of subducted material into the oceanic lithosphere and a connection with plate tectonic processes.

Geological setting

As the tectonic boundary between the Eurasian and Indian plates, the nearly east–west-striking YZSZ extends for >2000 km and separates the Lhasa Terrane in the north from the Himalayan Orogen in the south (Fig. 1a). The onset of India–Asia continental collision has been constrained to 59 ± 1 Ma by stratigraphic dating (Hu et al. 2016). The Gangdese arc along the southern margin of the Lhasa Terrane is an Andean-type continental margin formed by northward subduction of the Neotethyan oceanic lithosphere from the Late Triassic to the Paleocene and has been overprinted by post-collisional magmatism in the thickened crust. The Gangdese batholith is mainly composed of gabbros, diorites, granodiorites, granites and leucogranites, with four discrete stages of magmatism at 205–152, 109–80, 65–41 and 33–13 Ma (e.g. Mo et al. 2007; Wen et al. 2008; Chung et al. 2009; Ji et al. 2009; Zhu et al. 2011; Zhang et al. 2014).

Fig. 1.

(a) Tectonic sketch of the Tibetan Plateau. (b) Simplified geological map of the Luobusa ophiolite in southern Tibet. (c) Lithological profile of the LBSD-1 and LBSD-2 boreholes and location of samples (modified from Xu et al. 2015a). EBSD, electron back-scattered diffraction.

Fig. 1.

(a) Tectonic sketch of the Tibetan Plateau. (b) Simplified geological map of the Luobusa ophiolite in southern Tibet. (c) Lithological profile of the LBSD-1 and LBSD-2 boreholes and location of samples (modified from Xu et al. 2015a). EBSD, electron back-scattered diffraction.

The ophiolite massifs and ophiolitic mélanges along the YZSZ preserve two age peaks of generation: 180–150 and 130–110 Ma (Hébert et al. 2012; Xu et al. 2015b). All the ophiolites show geochemical features of an SSZ environment, particularly arc and back-arc settings (Hébert et al. 2012). The Luobusa ophiolite in the eastern YZSZ is the largest chromite mine in China and extends c. 42 km along-strike and covers an area of c. 70 km2. It mainly consists of harzburgites, dunites, sparse podiform chromitites and mafic cumulates (Zhou et al. 1996; Xiong et al. 2015). The Luobusa ophiolite was formed at a mid-ocean ridge in the Mid-Jurassic, as constrained by a whole-rock Sm–Nd isochron age of 177 ± 31 Ma for gabbro dykes (Zhou et al. 2002) and a sensitive high-resolution ion microprobe U–Pb age of 163 ± 3 Ma for mid-ocean ridge basalt (MORB)-type diabase (Zhong et al. 2006). It was then re-fertilized by boninitic melts in a mantle wedge above the subduction zone at c. 126 Ma (Malpas et al. 2003; Zhou et al. 2005, 2014).

Bounded by two south-dipping thrust faults, the Luobusa ophiolite was thrust over the upper Oligocene–lower Miocene conglomerate of the Luobusa Formation to the north and is underlain by Upper Triassic flysch to the south (Fig. 1b) (Yamamoto et al. 2007; Liang et al 2011; Xu et al. 2015a). Although all the ultramafic rocks in the Luobusa ophiolite appear to have equilibrated at relatively shallow depths as spinel- or plagioclase-bearing peridotites (Hébert et al. 2003; Xiong et al. 2015), the occurrence of UHP (diamond, TiO2 II, coesite, stishovite pseudomorph, phase BMJ) and super-reducing phases (native elements, alloys, carbides, nitrides and moissanite) in the Luobusa peridotites and chromitites shows that they originated from the deep upper mantle or the mantle transition zone under conditions of very low oxygen fugacity (Bai et al. 1993; Robinson et al. 2004; Yang et al. 2007, 2014; Dobrzhinetskaya et al. 2009; Yamamoto et al. 2009; Xu et al. 2015b; Griffin et al. 2016; R.Y. Zhang et al. 2016). The abundant clinoenstatite lamellae in enstatite from lherzolite and harzburgite core samples of the Luobusa Scientific Drilling Project suggest that the Luobusa peridotites originated at P > 7 GPa (R.Y. Zhang et al. 2016). In addition, crustal minerals (e.g. zircon, quartz, corundum, K-feldspar, plagioclase, apatite and amphibole) have been found as mineral inclusions in the Luobusa peridotites and podiform chromitites (Robinson et al. 2015). These findings have initiated a heated debate about the formation mechanisms of the Luobusa ophiolite, as well as the recycling of the subducted continental and oceanic materials.

Sample description

To constrain the petrological and structural variations of the Luobusa ophiolite, the Luobusa Scientific Drilling Project drilled two boreholes (29° 13′ 24.19″ N, 92° 11′ 36.33″ E) at an altitude of 4378 m: the 1478.8 m deep LBSD-1 borehole and the 1853.8 m deep LBSD-2 borehole (Fig. 1b). Serpentinization is common in the Luobusa peridotites and some of the core samples are strongly serpentinized and fragile, which makes it difficult to identify the lineation and foliation of the peridotites.

We selected 17 relatively fresh harzburgite and seven relatively fresh dunite samples from the LBSD-1 and LBSD-2 boreholes (Fig. 1c; Table 1). Most of the samples show a degree of serpentinization <5%, although samples B186, B199, B281, B329, B137, B155, B226, B368 and B536 have a degree of serpentinization of 5–10%. The serpentine minerals are lizardite and/or chrysotile aggregates and appear along grain boundaries or fractures. Theses samples are coarse grained and show granoblastic or porphyroclastic textures.

Table 1.

Major oxide concentrations in olivine from peridotite core samples in the Luobusa ophiolite

SampleLithologyDepth (m)SiO2TiO2Al2O3FeOTMnOMgOCaONiOCr2O3TotalMg#
LBSD-1 borehole
 B98Hz16441.100.020.019.380.1048.380.010.340.0199.3490.2
 B106Hz18841.120.000.019.200.1148.730.010.340.0299.5390.4
 B143Hz28441.410.010.009.060.1048.700.020.370.0299.6990.6
 B153Hz30341.090.010.009.480.0948.520.010.320.0199.5390.1
 B169Hz34241.040.010.009.170.1148.820.010.400.0199.5690.5
 B180Hz36741.490.010.019.840.1548.170.010.280.0099.9889.7
 B186Hz37941.360.010.009.460.1048.470.010.410.0099.8290.1
 B199Hz40741.060.010.009.560.1448.490.020.360.0299.6590.0
 B245Hz52441.220.010.009.160.1148.870.020.400.0199.7990.5
 B256Dun55841.430.010.008.700.1048.880.020.330.0099.4590.9
 B281Hz62741.300.010.009.870.1348.470.020.420.01100.2389.7
 B300Dun68241.330.010.007.290.0950.150.070.350.0199.3192.5
 B329Hz79041.030.020.019.840.1146.310.020.360.2099.4989.7
 B520Dun137040.480.000.0011.610.1646.310.220.140.0198.9387.7
LBSD-2 borehole
 B120Hz31641.050.010.019.610.1148.720.020.360.0199.8890.0
 B137Hz35441.660.010.009.670.1548.270.000.260.01100.0689.9
 B155Dun39840.940.000.019.290.1149.140.010.330.0199.8390.4
 B196Hz50441.260.010.009.810.1048.570.020.390.01100.1689.8
 B226Hz57241.210.010.019.550.1348.320.020.350.0199.6290.0
 B269Dun67340.850.000.018.070.0949.880.020.350.0099.2791.7
 B368Hz89741.390.010.009.740.1348.130.020.390.0199.8189.8
 B512Dun137541.100.010.009.230.1148.850.130.250.0299.7090.4
 B536Dun145041.010.010.019.420.1548.560.190.250.0199.6190.2
SampleLithologyDepth (m)SiO2TiO2Al2O3FeOTMnOMgOCaONiOCr2O3TotalMg#
LBSD-1 borehole
 B98Hz16441.100.020.019.380.1048.380.010.340.0199.3490.2
 B106Hz18841.120.000.019.200.1148.730.010.340.0299.5390.4
 B143Hz28441.410.010.009.060.1048.700.020.370.0299.6990.6
 B153Hz30341.090.010.009.480.0948.520.010.320.0199.5390.1
 B169Hz34241.040.010.009.170.1148.820.010.400.0199.5690.5
 B180Hz36741.490.010.019.840.1548.170.010.280.0099.9889.7
 B186Hz37941.360.010.009.460.1048.470.010.410.0099.8290.1
 B199Hz40741.060.010.009.560.1448.490.020.360.0299.6590.0
 B245Hz52441.220.010.009.160.1148.870.020.400.0199.7990.5
 B256Dun55841.430.010.008.700.1048.880.020.330.0099.4590.9
 B281Hz62741.300.010.009.870.1348.470.020.420.01100.2389.7
 B300Dun68241.330.010.007.290.0950.150.070.350.0199.3192.5
 B329Hz79041.030.020.019.840.1146.310.020.360.2099.4989.7
 B520Dun137040.480.000.0011.610.1646.310.220.140.0198.9387.7
LBSD-2 borehole
 B120Hz31641.050.010.019.610.1148.720.020.360.0199.8890.0
 B137Hz35441.660.010.009.670.1548.270.000.260.01100.0689.9
 B155Dun39840.940.000.019.290.1149.140.010.330.0199.8390.4
 B196Hz50441.260.010.009.810.1048.570.020.390.01100.1689.8
 B226Hz57241.210.010.019.550.1348.320.020.350.0199.6290.0
 B269Dun67340.850.000.018.070.0949.880.020.350.0099.2791.7
 B368Hz89741.390.010.009.740.1348.130.020.390.0199.8189.8
 B512Dun137541.100.010.009.230.1148.850.130.250.0299.7090.4
 B536Dun145041.010.010.019.420.1548.560.190.250.0199.6190.2

Dun, dunite; Hz, harzburgite; FeOT, total Fe in FeO.

The harzburgite samples contain olivine (65–85 vol.%), Opx (10–28 vol.%) and Cpx (1–5 vol.%), with minor spinel and serpentine (Fig. S1). Cpx occurs as either small interstitial grains or exsolution lamellae in Opx grains. The dunite samples consist of 85–95 vol.% olivine, minor Opx, and interstitial Cpx and spinel. The grain size of olivine is usually 1–3 mm, although it sometimes reaches 8 mm. Both olivine and Opx show plastic deformation features, such as irregular grain boundaries (Fig. 2a), kink bands in olivine (Fig. 2b), the undulose extinction of coarse-grained olivine (Fig. 2c–d) and the dynamic recrystallization of fine-grained olivine (0.1–0.5 mm grain size) (Fig. 2e–f). We also observed abundant exsolution lamellae of Cpx in Opx grains (Fig. 2g–h), which has previously been reported in harzburgite core samples from the LBSD-1 borehole and attributed to the transformation of clinoenstatite from high-temperature Ca-bearing orthoenstatite at pressures >7 GPa (Zhang et al. 2017). Some harzburgite samples show coarsely vermicular symplectites of Opx + Cr–Al spinel ± Cpx (Fig. 3), which have been interpreted as the breakdown products of majoritic garnet, with estimated minimum pressures >13 GPa (Griffin et al. 2016).

Fig. 2.

Photomicrographs (cross-polarized light) of representative core samples. (a) Slight serpentinization of olivine in harzburgite. (b) Kink bands of olivine and Opx in Cpx-bearing harzburgite. (c, d) Undulose extinction of coarse-grained olivine in harzburgite and dunite. (e, f) Dynamic recrystallization of olivine in foliated harzburgites. (g, h) Exsolution lamellae of Cpx in Opx in harzburgites. Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene; Srp, serpentine.

Fig. 2.

Photomicrographs (cross-polarized light) of representative core samples. (a) Slight serpentinization of olivine in harzburgite. (b) Kink bands of olivine and Opx in Cpx-bearing harzburgite. (c, d) Undulose extinction of coarse-grained olivine in harzburgite and dunite. (e, f) Dynamic recrystallization of olivine in foliated harzburgites. (g, h) Exsolution lamellae of Cpx in Opx in harzburgites. Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene; Srp, serpentine.

Fig. 3.

Coarse symplectites of Cr–Al spinel and orthopyroxene from harzburgite samples: (a, c) plane polarized and (b, d) crossed-polarized photomicrographs. Ol, olivine; Opx, orthopyroxene; Spl, spinel.

Fig. 3.

Coarse symplectites of Cr–Al spinel and orthopyroxene from harzburgite samples: (a, c) plane polarized and (b, d) crossed-polarized photomicrographs. Ol, olivine; Opx, orthopyroxene; Spl, spinel.

Methods

Mineral composition analyses

The major element compositions of olivine, Opx, Cpx and spinel from 23 peridotite samples were determined using a Shimadzu EPMA1600 electron microprobe at the Chinese Academy of Sciences Key Laboratory of Crust–Mantle Materials and Environments at the University of Science and Technology of China and a JEOL JXA-8100 electron microprobe at the State Key Laboratory for Mineral Deposits Research at Nanjing University. The analytical conditions were a 20 nA beam current, a 15 kV accelerating voltage and a 1 µm spot diameter. For each sample, the major element concentrations in each mineral were the mean value of five to eight grains. The trace element concentrations in Cpx from 11 harzburgite samples was acquired using an Agilent 7700× laser ablation inductively coupled plasma mass spectrometer with an energy density of 10 J cm−2, a spot diameter of 44 µm, a frequency of 4 Hz and ablation time of 40 s. For each sample, four to ten Cpx grains were analysed to give a mean value.

Microstructural analyses

The LPOs of olivine and Opx from nine harzburgite samples were measured using the electron back-scattered diffraction (EBSD) technique. We used a JEOL JSM-6490 scanning electron microscope equipped with an Oxford Nordlys-S EBSD detector and Channel 5+ software at the State Key Laboratory for Mineral Deposits Research. The highly polished thin sections were tilted by 70° and we used an accelerating voltage of 20 kV, 200× magnification and a working distance of 14–23 mm. Samples B106 and B180 were measured by automatic mapping, whereas the other seven samples were measured by manual indexing. The grain size of Opx in harzburgite B143 was so large that we could not find enough grains for plotting. Excluding sample B143, at least 100 grains of olivine and 50 grains of Opx were analysed for each sample to ensure the reliability of the statistical analyses.

For samples without evident lineation and foliation, non-oriented thin sections were prepared for microstructural analyses. Despite variations in composition and water content, Opx in peridotites develops a stable LPO characterized by the [001] axis parallel to the lineation and the (100) plane parallel to the foliation (e.g. Manthilake et al. 2013; Bystricky et al. 2016; Soustelle & Manthilake 2017; Jung 2017). Therefore the [001](100) fabric of Opx was used as a coordinate reference to rotate the EBSD data, i.e. the point maxima of the [001] axis parallel to the X direction and the point maxima of the [100] axis parallel to the Z direction. The pole figures of olivine and Opx were plotted using the Petrophysics program of Mainprice (1990).

To examine the slip systems of olivine, we carried out transmission electron microscopy (TEM) observations of olivine at the Institute of Geology and Geophysics, Chinese Academy of Sciences. The samples for the TEM imaging were prepared by focused ion beam milling using a Carl Zeiss Auriga Compact system. The acceleration voltage was 0.1–30 kV and the beam current was 1 pA–50 nA. The resolution ratio was 5 nm (30 kV, 1 pA). Imaging and electron diffraction were performed on a JEOL JEM-2100 transmission electron microscope using an LaB6 electron shooter and an accelerating voltage of 200 kV.

Water content measurements

Fourier transform infrared spectrometry (FTIR) was used to determine the water content of olivine, Opx and Cpx from 17 harzburgites and seven dunites. A Vertex 70 spectrometer coupled with a Hyperion 2000 microscope at the State Key Laboratory for Mineral Deposits Research and a Nicolet 5700 spectrometer coupled with a Continuμm microscope at the School of Earth and Space Sciences, University of Science and Technology of China, were used for comparison. Both instruments have a KBr beam splitter and a mercury cadmium telluride detector cooled by liquid nitrogen. The thickness of the double-polished thin sections used for the water content measurements varied between 150 and 300 µm. Prior to analysis, the thin sections were placed in an oven at 120°C for at least 8 h to remove any free water from the surface and fractures. The unpolarized FTIR spectra were collected in the range 4000–2800 cm−1 at room temperature, with 128 or 256 scan times and a resolution of 8 cm−1. Depending on the grain size, apertures of 50 × 50 or 25 × 25 µm were used for optically clean, crack- and inclusion-free regions. For each sample, 4–27 grains of each mineral were measured to obtain the mean water content.

A modified form of the Beer–Lambert law was used to calculate the hydrogen concentration: 
CH2O=A/(I×t)
(1)
where CH2O is the content of hydrogen species in ppm H2O, A is the integrated area (cm−1) of the absorption bands in the region of interest, I is the integral specific absorption coefficient (ppm−1·cm−2) and t is the sample thickness (cm). The infrared spectra were integrated from 3325 to 3650 cm−1, the region dominated by the stretching vibrations of OH bonds. The integral specific coefficients were 14.84 ppm−1 cm−2 for Opx and 7.09 ppm−1·cm−2 for Cpx (Bell et al. 1995). For olivine, 1/0.188 ppm−1·cm−2 was adopted as the integral specific coefficient (Bell et al. 2003), which could be 3.5 times the concentration derived from the Paterson (1982) calibration for unpolarized samples.

Results

Mineral chemistry and equilibration temperatures

Table 1 lists the mean major element compositions of olivine from the Luobusa peridotite samples. The Mg# values, defined as the Mg/(Mg + Fe) atomic ratio, vary between 89.6 and 90.6 for olivine in the harzburgites and between 87.7 and 92.5 for olivine in the dunites. Except for dunite B520, with an Mg# for olivine as low as 87.7, the mean Mg# of olivine in the dunites is 91.0, higher than the mean value of 90.1 for the harzburgites (Fig. 4a). The Opx and Cpx grains fall into the composition ranges of enstatite and diopside, respectively (Table S1). The Mg# values of Opx are 89.8–90.8 in the harzburgite samples and 91.4–92.2 in the dunite samples, whereas those of Cpx are in the range 92.4–94.1 in the harzburgite samples and 94.2–95.0 in the dunite samples (Table S1). The Mg# values of Opx and Cpx in the harzburgites and dunites show a negative correlation with the Al2O3 content (Fig. 4b, c). The Cr# values in spinel, defined as the Cr/(Cr + Al) atomic ratio, are 20.4–37.1 for the harzburgite samples and 54.9–78.1 for the dunite samples (Table S1 and Fig. 4d). The spinel grains in the harzburgites are characterized by a higher Al2O3 content (35.56–48.65 wt%), a lower Cr2O3 content (18.57–31.29 wt%) and a higher MgO content (13.84–17.31 wt%) than those in the dunites (Table S2). The Mg# values in spinel are 25.3–46.9 for the harzburgite samples and 58.0–68.9 for the dunite samples.

Fig. 4.

Compositional relationships of (a) NiO content v. Mg# in olivine, Al2O3 content v. Mg# in (b) orthopyroxene and (c) clinopyroxene, and (d) TiO2 content v. Cr# in spinel for harzburgite and dunite samples from the LBSD-1 and LBSD-2 boreholes.

Fig. 4.

Compositional relationships of (a) NiO content v. Mg# in olivine, Al2O3 content v. Mg# in (b) orthopyroxene and (c) clinopyroxene, and (d) TiO2 content v. Cr# in spinel for harzburgite and dunite samples from the LBSD-1 and LBSD-2 boreholes.

The relationships between the Mg# in olivine and the Cr# in spinel (Fig. 5a) and between the Mg# and Cr# in spinel (Fig. 5b) indicate that the Luobusa harzburgites are abyssal peridotites subjected to 10–20% partial melting, whereas the more depleted dunites are SSZ peridotites that experienced a high degree of partial melting and were then modified by melt–rock interactions in a mantle wedge, as suggested by previous studies (Zhou et al. 1996, 2005; Xiong et al. 2015). The negative correlation between the Al2O3 content in Opx and the Cr# in spinel (Fig. 5c) confirms the different origins and different degrees of partial melting of the Luobusa harzburgites and dunites.

Fig. 5.

Chemical variations of olivine, spinel and orthopyroxene in harzburgite and dunite samples from the LBSD-1 and LBSD-2 boreholes. (a) Compositional relationship between Cr# in spinel and Mg# in olivine. Fields for abyssal peridotites (Dick & Bullen 1984) and supra-subduction zone peridotites (Pearce et al. 2000) are shown within dotted lines. Partial melting and fractional crystallization trend (Arai 1994) and the degree of partial melting (Jaques & Green 1980) are shown by black arrows. (b) Compositional variations of Cr# v. Mg# in spinel. (c) Compositional relationship of Al2O3 content in orthopyroxene v. Cr# in spinel. The fields for abyssal and supra-subduction zone peridotites are from Bonatti & Michael (1989). FMM, fertile mid-ocean ridge basalt mantle; OSMA, olivine–spinel mantle array, which is a spinel peridotite restite trend (Arai 1994).

Fig. 5.

Chemical variations of olivine, spinel and orthopyroxene in harzburgite and dunite samples from the LBSD-1 and LBSD-2 boreholes. (a) Compositional relationship between Cr# in spinel and Mg# in olivine. Fields for abyssal peridotites (Dick & Bullen 1984) and supra-subduction zone peridotites (Pearce et al. 2000) are shown within dotted lines. Partial melting and fractional crystallization trend (Arai 1994) and the degree of partial melting (Jaques & Green 1980) are shown by black arrows. (b) Compositional variations of Cr# v. Mg# in spinel. (c) Compositional relationship of Al2O3 content in orthopyroxene v. Cr# in spinel. The fields for abyssal and supra-subduction zone peridotites are from Bonatti & Michael (1989). FMM, fertile mid-ocean ridge basalt mantle; OSMA, olivine–spinel mantle array, which is a spinel peridotite restite trend (Arai 1994).

Assuming a pressure of 1.5 GPa, which corresponds to equilibration in the spinel stability field, the equilibration temperatures of our samples were calculated using the Ca-in-Opx thermometer (Brey & Köhler 1990), the Al-in-Opx thermometer (Witt-Eickschen & Seck 1991) and the two-pyroxene thermometer (Taylor 1998) (Table 2). There is no data for dunites B269, B512, B520 and B536 due to their lack of Opx porphyroblasts in thin section. Orthopyroxene porphyroblasts in the harzburgites and dunites are very uniform in their CaO content (0.44–1.11 wt%), but variable in their Al2O3 content (2.96–4.24 wt% for the harzburgites and 0.68–1.83 wt% for the dunites). For dunites B155 and B256, the Al-in-Opx thermometer yields equilibration temperatures of 776–896°C, c. 100–250°C lower than the values from the Ca-in-Opx and two-pyroxene thermometers (Table 2). The low-Al Opx in the Luobasa dunites has been attributed to the reaction of boninitic melts with the surrounding peridotites (Zhou et al. 2005). Given the better performance of the Taylor (1998) two-pyroxene thermometer for peridotites (Nimis & Grütter 2010), the equilibration temperatures of the studied harzburgites and dunites are c. 950–1080°C.

Table 2.

Estimated temperatures from peridotite core samples in the Luobusa ophiolite

SampleLithologyDepth (m)Temperatures (°C)Olivine fabrics
Ca-in-OpxAl-in-OpxTwo-pyroxene
B98Hz1649321034956B + E
B106Hz18810779681021B
B143Hz28410449931080A
B153Hz303113510281011E
B120Hz3169981035984
B169Hz34210419951059A
B137Hz3549409211061B + E
B180Hz36710328911022B + E
B186Hz3799711022999
B199Hz4078721024973
B196Hz504103910461012
B245Hz52411489901082C
B226Hz57291510201002
B281Hz62795710211052
B329Hz79010171051963
B368Hz8979901032982
B155Dun3891128896975
B256Dun5581067776987A + E
SampleLithologyDepth (m)Temperatures (°C)Olivine fabrics
Ca-in-OpxAl-in-OpxTwo-pyroxene
B98Hz1649321034956B + E
B106Hz18810779681021B
B143Hz28410449931080A
B153Hz303113510281011E
B120Hz3169981035984
B169Hz34210419951059A
B137Hz3549409211061B + E
B180Hz36710328911022B + E
B186Hz3799711022999
B199Hz4078721024973
B196Hz504103910461012
B245Hz52411489901082C
B226Hz57291510201002
B281Hz62795710211052
B329Hz79010171051963
B368Hz8979901032982
B155Dun3891128896975
B256Dun5581067776987A + E

Cpx, clinopyroxene; Dun, dunite; Hz, harzburgite; Opx, orthopyroxene.

Thermometers: Ca-in-Opx thermometer (Brey & Köhler 1990), Al-in-Opx thermometer (Witt-Eickschen & Seck 1991), two-pyroxene thermometer (Taylor 1998).

It is noteworthy that some Opx grains in the harzburgites have a very high CaO content, e.g. sample B120. Such samples show abundant exsolution lamellae of Cpx in Opx grains (Fig. 2h), which has been interpreted as the transformation of clinoenstatite from orthoenstatite at pressures >7 GPa (Zhang et al. 2017). The deep origin of sample B120 is consistent with the coarse vermicular symplectites of Opx + Cr–Al spinel ± Cpx (Fig. 3), which has been attributed to the breakdown of majoritic garnets in Luobusa harzburgites with estimated minimum pressures >13 GPa (Griffin et al. 2016). Therefore the calculated temperature, assuming P = 1.5 GPa, only yields constraints on the temperature of their last equilibrium stage at shallow mantle depths.

Trace element composition of Cpx

The Cpx from the 11 Luobusa harzburgites show consistent rare earth element (REE) patterns, with a slow decrease in heavy to medium REEs from Yb to Eu and a rapid decrease in light REEs from Sm to Ce (Fig. 6a). Cpx from the harzburgites contains extremely low concentrations of the more incompatible lithophile elements (Table S3) and has negative anomalies in Sr, Zr and Ce relative to neighbouring REEs in the trace element patterns (Fig. 6b). These features are similar to the Cpx found in abyssal peridotites (Johnson et al. 1990) and agree with previous studies of the Luobusa harzburgites (Zhou et al. 1996, 2005). Therefore the Luobusa harzburgites did not experience pervasive metasomatism after melt extraction.

Fig. 6.

(a) Chondrite-normalized rare earth element and (b) primitive mantle-normalized trace element patterns of clinopyroxene from the Luobusa harzburgites. Normalizing values taken from McDonough & Sun (1995). Cpx, clinopyroxene.

Fig. 6.

(a) Chondrite-normalized rare earth element and (b) primitive mantle-normalized trace element patterns of clinopyroxene from the Luobusa harzburgites. Normalizing values taken from McDonough & Sun (1995). Cpx, clinopyroxene.

Fabrics of olivine and pyroxene

After rotation of the EBSD data, Opx from eight harzburgite samples and one dunite sample show the concentration of grains with the [001] axis sub-parallel to the lineation and the (100) plane sub-parallel to the foliation (Fig. 7). This fabric pattern agrees with the typical LPO of Opx in peridotites (e.g. Tommasi et al. 2016; Jung 2017). Therefore the structural coordinate system is established with X parallel to the lineation, Z normal to the foliation and Y normal to the lineation in the foliation plane. The pole figures of olivine can be plotted using the rotated EBSD data.

Fig. 7.

Pole figures of orthopyroxene in the peridotite core samples from the Luobusa ophiolite. Crystallographic orientations are plotted as one point per grain in the lower hemisphere equal-area projection. J-index, fabric strength of orthopyroxene; n, number of grains analysed; pfJ, texture index for the fabric strength of each axis; X, parallel to the lineation; Z, normal to the foliation.

Fig. 7.

Pole figures of orthopyroxene in the peridotite core samples from the Luobusa ophiolite. Crystallographic orientations are plotted as one point per grain in the lower hemisphere equal-area projection. J-index, fabric strength of orthopyroxene; n, number of grains analysed; pfJ, texture index for the fabric strength of each axis; X, parallel to the lineation; Z, normal to the foliation.

The olivine in our samples shows complex fabrics (Fig. 8; Table 3). Harzburgites B143 and B169 have developed a typical A-type fabric with the maximum concentration of the [100], [010] and [001] axes sub-parallel to the X, Z and Y directions, respectively, implying dominant activation of the [100](010) slip system. By contrast, harzburgite B106 shows a B-type fabric characterized by the maximum concentration of the [001] axis parallel to the lineation and the [010] axis perpendicular to the foliation, suggesting the predominance of the [001](010) slip system. Harzburgite B153 has developed an E-type fabric due to the activation of the [100](001) slip system. Harzburgite B245 show a C-type fabric with the point maxima of the [001] axis parallel to the lineation and those of the [100] axis perpendicular to the foliation, reflecting the dominant activation of the [001](100) slip system.

Fig. 8.

Pole figures of olivine in the peridotite core samples from the Luobusa ophiolite. Crystallographic orientations are plotted as one point per grain in the lower hemisphere equal-area projection. J-index, fabric strength of orthopyroxene; n, number of grains analysed; pfJ, texture index for the fabric strength of each axis; X, parallel to the lineation; Z, normal to the foliation.

Fig. 8.

Pole figures of olivine in the peridotite core samples from the Luobusa ophiolite. Crystallographic orientations are plotted as one point per grain in the lower hemisphere equal-area projection. J-index, fabric strength of orthopyroxene; n, number of grains analysed; pfJ, texture index for the fabric strength of each axis; X, parallel to the lineation; Z, normal to the foliation.

Table 3.

Water contents of olivine, Opx and Cpx, and fabrics and slip systemts in olivine from the Luobusa peridotites

SampleDepth (m)LithologyOlivineOrthopyroxeneClinopyroxeneOlivine fabricsSlip systems
No. of grainsWater content (ppm)No. of grainsWater content (ppm)No. of grainsWater content (ppm)
B98164Hz101513114B + E[001](100), [001](010)
B106188Hz141925998563B[001](100)
B143284Hz131324774500A[100](010)
B153303Hz1023269481273E[001](100), [001](010)
B169342Hz11223296A[001](hk0), [100](021)
B180367Hz12131711110467B + E[100](010), [100](011)
B186379Hz8610560
B199407Hz1823228413373
B245524Hz1115377212507C[001](010), [001](100)
B252546Hz1315863
B256558Dun10212084A + E[100](001)
B281627Hz4151169
B300682Dun1418
B329790Hz9141275
B5201370Dun718
B120316Hz118209312479
B137354Hz92510141B + E[001](hk0), [001](010)
B155398Dun102319952557
B196504Hz1081170
B226572Hz7211090
B368897Hz71610122
B269673Dun313
B5121375Dun48
B5361450Dun1014
SampleDepth (m)LithologyOlivineOrthopyroxeneClinopyroxeneOlivine fabricsSlip systems
No. of grainsWater content (ppm)No. of grainsWater content (ppm)No. of grainsWater content (ppm)
B98164Hz101513114B + E[001](100), [001](010)
B106188Hz141925998563B[001](100)
B143284Hz131324774500A[100](010)
B153303Hz1023269481273E[001](100), [001](010)
B169342Hz11223296A[001](hk0), [100](021)
B180367Hz12131711110467B + E[100](010), [100](011)
B186379Hz8610560
B199407Hz1823228413373
B245524Hz1115377212507C[001](010), [001](100)
B252546Hz1315863
B256558Dun10212084A + E[100](001)
B281627Hz4151169
B300682Dun1418
B329790Hz9141275
B5201370Dun718
B120316Hz118209312479
B137354Hz92510141B + E[001](hk0), [001](010)
B155398Dun102319952557
B196504Hz1081170
B226572Hz7211090
B368897Hz71610122
B269673Dun313
B5121375Dun48
B5361450Dun1014

Water contents estimated using the calibration of Bell et al. (2003) for olivine and Bell et al. (1995) for orthopyroxene and clinopyroxene.

It is noteworthy that olivine from other samples shows maximum concentrations of the [100] axis and the [010] axis sub-parallel to the lineation and perpendicular to the foliation, respectively, but the [001] axis does not concentrate along the Y direction as in the typical A-type fabric. For dunite B256, the [001] axis of olivine concentrates sub-perpendicular to the foliation, suggesting the activation of both the [100](010) and [100](001) slip systems, i.e. a combination of A- and E-type fabrics. For harzburgites B98, B137 and B180, the [001] axis of olivine forms two-point maxima sub-parallel to the lineation and sub-perpendicular to the foliation, respectively. Given the orthorhombic crystallography of olivine, the asymmetrical pole figures allow us to distinguish the corresponding slip direction and the slip plane of olivine. For example, the two-point maxima of the olivine [001] axis from sample B98 are sub-parallel to those of the [100] and [010] axes, respectively, suggesting the activation of both the [001](010) and [100](001) slip systems. Therefore the three harzburgite samples record a combination of B- and E-type fabrics.

The bright-field TEM images of olivine grains were used to infer the dominant slip systems in olivine and compared with the EBSD-derived LPO of olivine (Fig. 9). The Burgers vectors were determined using the g · b = 0 and g · (b Ʌu) = 0 criteria, where b is the Burgers vector, g is the diffraction vector and u is a unit vector along the dislocation line. The dislocation direction was obtained through the corresponding selected-area electron diffraction (SAED) pattern. The index of the point in the SAED pattern represents the plane of the corresponding index in reciprocal space. Figure S2 shows the bright-field images of olivine and the corresponding SAED patterns of the studied samples. The observed slip systems in olivine grains from the Luobusa peridotites are summarized in Table 3.

Fig. 9.

Representative bright-field transmission electron microscopy images of olivine from the Luobusa peridotites and corresponding diffraction patterns (insets). (a) Straight dislocations in olivine from sample B106; dislocation loops are visible. (b) Short-line dislocations in olivine from sample B143. (c) Sub-grain boundaries and straight dislocations in olivine from sample B153. (d) Straight dislocations in the paper plane and dot-like dislocations normal to the paper plane in olivine from sample B245; dislocation tangle is visible.

Fig. 9.

Representative bright-field transmission electron microscopy images of olivine from the Luobusa peridotites and corresponding diffraction patterns (insets). (a) Straight dislocations in olivine from sample B106; dislocation loops are visible. (b) Short-line dislocations in olivine from sample B143. (c) Sub-grain boundaries and straight dislocations in olivine from sample B153. (d) Straight dislocations in the paper plane and dot-like dislocations normal to the paper plane in olivine from sample B245; dislocation tangle is visible.

Almost all the dislocations in the bright-field images of olivine from the Luobusa peridotites are straight (Fig. 9a–c), suggesting that the dominant deformation mechanism is dislocation creep at relatively low temperatures (either low temperature and low pressure, or high temperature and UHP). Dislocation loops (Fig. 9a), which are formed at high temperature or through dislocation cross-slipping (Raterron et al. 2007, 2009), are rare. The occasionally observed square-like figures (Fig. 9c) and dislocation tangles (Fig. 9d) are characteristic of low-temperature deformation at high pressure (Raterron et al. 2004). Dislocations are aligned along a particular direction and form sub-grain boundaries. The preservation of straight dislocations and sub-grains in olivine suggests that the Luobusa peridotites experienced limited annealing.

Water content

The representative FTIR spectra of olivine, Opx and Cpx from 17 harzburgite samples and seven dunite samples are given in Figure 10. The absorption bands of structural hydroxyl appear in the range 3400–3570 cm−1 for olivine (Fig. 10a). The infrared spectra of Opx are characterized by three hydroxyl absorption bands in the ranges 3410–3420, 3515–3525 and 3560–3570 cm−1, whereas those of Cpx are in the ranges 3450–3465, 3530–3535 and 3645–3648 cm−1 (Fig. 10b). The broad absorption band near 3400 cm−1 has been attributed to the inclusion of molecular water, whereas the absorption peaks near 3690 and 3717 cm−1 are caused by the OH stretching bands of serpentine. The absorption band at 3594 cm−1 matches the OH stretching bands of hydrous minerals, such as vermiculite group minerals (e.g. Khisina et al. 2001; Johnson et al. 2002; Beran & Libowitzky 2006; Aubaud et al. 2007). The very high absorptions between 3720 and 3750 cm−1 occur in some olivine grains (Fig. 10a) and may be caused by non-hydrogen-bonded OH, such as inclusions of a sheet silicate (Bell et al. 2003). The contribution of these extrinsic hydrogens was excluded in the baseline correction used to obtain the water content of olivine and pyroxene.

Fig. 10.

Representative Fourier transform infrared spectra and water content of (a) olivine and (b) orthopyroxene and clinopyroxene from the Luobusa peridotites. The water contents were obtained using the Bell et al. (2003) integral specific coefficient for olivine and the Bell et al. (1995) integral specific coefficient for orthopyroxene and clinopyroxene. The green lines represent the spectra after subtraction of the background. All spectra are normalized to 1 cm thickness and shifted vertically for clarity. Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene.

Fig. 10.

Representative Fourier transform infrared spectra and water content of (a) olivine and (b) orthopyroxene and clinopyroxene from the Luobusa peridotites. The water contents were obtained using the Bell et al. (2003) integral specific coefficient for olivine and the Bell et al. (1995) integral specific coefficient for orthopyroxene and clinopyroxene. The green lines represent the spectra after subtraction of the background. All spectra are normalized to 1 cm thickness and shifted vertically for clarity. Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene.

Table 3 shows that the water content of olivine is very low (6–25 ppm) with a mean of 16 ± 5 ppm. By contrast, both Opx and Cpx have high water contents. The water content of Opx is 56–141 ppm with a mean of 90 ± 21 ppm, whereas the water content of Cpx varies from 373 to 1273 ppm. If we exclude the extremely water-rich Cpx with 1273 ppm in harzburgite sample B153, the mean water content of Cpx is 492 ± 64 ppm.

Discussion

Implications of water content in Luobusa peridotites

Consistent with previous studies on the Luobusa ophiolite (Zhou et al. 1996, 2005; Dilek & Furnes 2011, 2014; Xiong et al. 2015), the studied harzburgites are abyssal peridotites subjected to 10–20% partial melting, whereas the more depleted dunites are SSZ peridotites that have been modified by melt–rock interactions in a mantle wedge (Fig. 5). The subducted oceanic lithosphere has lost most of its water at depths >200 km due to the continuous breakdown of hydrous minerals such as serpentine, talc and chlorite (Hacker et al. 2003). The mantle wedge above the subducted oceanic lithosphere generally has a high water content as a result of metasomatism and fluid infiltration, as evidenced by arc magmatism. However, olivine in 24 peridotite core samples from the Luobusa ophiolite is very poor in water, whereas Cpx is extremely rich in water relative to olivine and Opx (Table 3). The REE patterns of Cpx indicate that the Luobusa peridotites did not experience pervasive metasomatism after partial melting (Fig. 6).

Figure 11a shows that the diffusion of hydrogen in pyroxene is about 500 times slower than in olivine (Mackwell & Kohlstedt 1990; Ingrin et al. 1995; Stalder & Skogby 2003). Given the temperature dependence of hydrogen diffusion, the very low water content in olivine shows that widespread serpentinization of the Luobusa peridotites occurred at shallow depths. The combined δ13C and nitrogen data of microdiamonds from the Luobusa peridotites indicate that these microdiamonds were formed over a narrow and cold temperature range (<950°C) and were incorporated into the chromitites and peridotites near the mantle transition zone during a short residence time (i.e. within several million years) at high temperature in the deep mantle (Xu et al. 2018). Assuming 5 myr for the exhumation of microdiamonds and their host rocks from the transition zone to the shallow mantle depths, this implies a very fast exhumation rate of 6–8 cm a−1. Based on the hydrogen diffusion coefficients and fast exhumation rates, Cpx and Opx in the Luobusa peridotites have been subjected to limited hydrogen loss during exhumation, whereas olivine may have been subjected to significant hydrogen loss when temperatures exceeded 1000°C (Fig. 11b). This implies that olivine was strongly dehydrated when the peridotites were subducted to depths >200 km (i.e. the geothermal gradient is >5°C km−1) or when they entered the mantle transition zone.

Fig. 11.

(a) Arrhenius diagram of various hydrogen diffusivities and (b) the effective hydrogen diffusion distance in olivine, orthopyroxene and clinopyroxene for 1, 5 and 10 Ma using a grain size of 1 mm. Hydrogen diffusion along [100] is faster than that along [010] and [001] in olivine (Mackwell & Kohlstedt 1990). The effective diffusion distance of hydrogen in olivine takes into account both lattice diffusion along [100] (Mackwell & Kohlstedt 1990) and diffusion in grain boundaries assuming a grain size of 1 mm and a grain boundary width of 0.75 nm (Demouchy 2010, 2012). The hydrogen diffusion coefficients of pyroxene are from dehydration experiments (Ingrin et al. 1995; Stalder & Skogby 2003). Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene.

Fig. 11.

(a) Arrhenius diagram of various hydrogen diffusivities and (b) the effective hydrogen diffusion distance in olivine, orthopyroxene and clinopyroxene for 1, 5 and 10 Ma using a grain size of 1 mm. Hydrogen diffusion along [100] is faster than that along [010] and [001] in olivine (Mackwell & Kohlstedt 1990). The effective diffusion distance of hydrogen in olivine takes into account both lattice diffusion along [100] (Mackwell & Kohlstedt 1990) and diffusion in grain boundaries assuming a grain size of 1 mm and a grain boundary width of 0.75 nm (Demouchy 2010, 2012). The hydrogen diffusion coefficients of pyroxene are from dehydration experiments (Ingrin et al. 1995; Stalder & Skogby 2003). Cpx, clinopyroxene; Ol, olivine; Opx, orthopyroxene.

When the slab reaches the mantle transition zone, the melt–rock interactions could significantly dehydrate olivine given the partition coefficient of hydrogen between the melt and olivine (Hirschmann et al. 2009). The partition coefficient of hydrogen between Cpx and Opx (DHCpx/Opx) is 5.56 ± 0.96 for the Luobusa peridotites. This value is much higher than DHCpx/Opx of 1.2–3.5 from previous measurements on natural peridotites (Bell & Rossman 1992; Bell & Ihinger 2000; Peslier et al. 2002, 2007, 2008, 2010, 2012; Peslier & Luhr 2006; Grant et al. 2007; Li et al. 2008; Yang et al. 2008) (Fig. 12). The experiments on hydrogen partitioning in mantle minerals show a trend of increasing DHCpx/Opx with pressures up to 4 GPa (Aubaud et al. 2004; Hauri et al. 2006; Tenner et al. 2009; Kovács et al. 2012; Rosenthal et al. 2015; Demouchy et al. 2017). The abundant exsolution lamellae of Cpx in Opx grains (Fig. 2g, h) from the Luobusa peridotite core samples suggest an origin at P > 7 GPa (Zhang et al. 2017). This is consistent with the estimation of P > 13 GPa from the coarse vermicular symplectites of Opx + Cr–Al spinel ± Cpx as breakdown products of majoritic garnet in harzburgite samples (Fig. 3) (Griffin et al. 2016). Therefore the extremely high DHCpx/Opx in the Luobusa peridotites probably benefits from a higher DHCpx/Opx at pressures >7 GPa and less hydrogen loss in Cpx than in Opx during rapid exhumation. It is worth noting the high water content of high-pressure phases of olivine, i.e. wadsleyite and ringwoodite, from volatile-rich kimberlite xenoliths (Pearson et al. 2014). Given the localized non-equilibrium phases in the Luobusa peridotites and chromitites, the transition zone could be heterogeneous in both composition and water content (Dilek & Yang 2018). The high water content of Cpx and Opx from the Luobusa peridotites show that the subducted oceanic lithosphere can transport a lot of water into the mantle transition zone via pyroxene.

Fig. 12.

Water concentration in clinopyroxene v. water concentration in orthopyroxene in Luobusa peridotite core samples. The results from previous studies on natural peridotites (Bell & Rossman 1992; Bell & Ihinger 2000; Peslier et al. 2002, 2007, 2008, 2010, 2012; Peslier & Luhr 2006; Grant et al. 2007; Li et al. 2008; Yang et al. 2008) are shown as grey dots. The inset shows the correlation between DCpx/Opx (the partition coefficient of hydrogen between clinopyroxene and orthopyroxene) with pressure in experimental studies (Aubaud et al. 2004; Hauri et al. 2006; Tenner et al. 2009; Kovács et al. 2012; Rosenthal et al. 2015; Demouchy et al. 2017) (modified after Xia et al. 2017). Cpx, clinopyroxene; Opx, orthopyroxene.

Fig. 12.

Water concentration in clinopyroxene v. water concentration in orthopyroxene in Luobusa peridotite core samples. The results from previous studies on natural peridotites (Bell & Rossman 1992; Bell & Ihinger 2000; Peslier et al. 2002, 2007, 2008, 2010, 2012; Peslier & Luhr 2006; Grant et al. 2007; Li et al. 2008; Yang et al. 2008) are shown as grey dots. The inset shows the correlation between DCpx/Opx (the partition coefficient of hydrogen between clinopyroxene and orthopyroxene) with pressure in experimental studies (Aubaud et al. 2004; Hauri et al. 2006; Tenner et al. 2009; Kovács et al. 2012; Rosenthal et al. 2015; Demouchy et al. 2017) (modified after Xia et al. 2017). Cpx, clinopyroxene; Opx, orthopyroxene.

Exhumation of Luobusa peridotites in a subduction channel

It is still unclear how the UHP and super-reducing phases were formed and preserved in the Luobusa peridotites and chromitites, which are generally regarded as relicts of the Neotethyan oceanic lithosphere and are characterized by the geochemical signatures of an SSZ environment (Griffin et al. 2016; Dilek & Yang 2018 and references cited therein). Although the mantle plume model (Yang et al. 2007) and the rapid channelized mantle upwelling model (Griffin et al. 2016) can explain the coexistence of shallow pre-metamorphic chromitites and peridotites and their metamorphism in the mantle transition zone at pressures >13 GPa, it is difficult to explain the widespread straight dislocations and sub-grains in olivine and the complex olivine fabrics in the Luobusa peridotites, which are easily modified at high temperature of mantle upwelling. In addition, the preservation of crustal minerals (e.g. zircon, quartz, corundum and K-feldspar) in ophiolitic peridotites and chromitites suggests the mixing of subducted continental crustal materials with oceanic lithosphere in a subduction channel (Yang et al. 2014; Robinson et al. 2015; Dilek & Yang 2018).

All the studied peridotites are coarse grained with granoblastic or porphyroclastic textures, which excludes stress-induced B-type fabrics in mylonitic peridotites (Wang et al. 2013a) or E-type fabrics in a hydrated ductile shear zone at the Moho transition zone (Michibayashi & Oohara 2013). Deformation experiments on olivine aggregates show different fabric types with increasing temperature and pressure. Carter & Avé Lallemant (1970) deformed dunites and peridotites under conditions of 0.5–3 GPa and 300–1400°C in the presence or absence of water. They found that the predominant slip systems in olivine changed from [001]{110} at low temperatures to [100]{0kl}(D-type fabric) and then [100](010) (A-type fabric) with increasing temperatures. Their observations were confirmed by the A-type fabric of olivine aggregates in simple shear deformation experiments at 300 MPa and 1300°C (Zhang et al. 2000). However, deformation experiments on single crystals of forsterite using a multi-anvil apparatus showed that UHP will favour [001] slip in olivine at pressures >7 GPa temperatures of 1200–1400°C (Couvy et al. 2004; Raterron et al. 2007, 2009). More recent deformation experiments have found that the A-type fabric in dry olivine aggregates changes to a B-/C-type fabric at 7.6 GPa and 1400°C (Ohuchi et al. 2011). However, at 7.2–11.1 GPa and 1127–1500°C, olivine will develop A- and B-type fabrics under water-rich and moderately wet conditions, respectively, whereas the C-type fabric is dominant under water-poor conditions at pressure >9.6 GPa and 1400°C (Ohuchi & Irifune 2013). Although we cannot exclude the possibility that different water contents in olivine affected the development of fabrics during exhumation, the preservation of straight dislocations (Fig. 9) and the general consistency between olivine fabrics and slip systems (Table 3) suggest the deformation of olivine under water-poor and relatively low-temperature conditions because a high water content and high temperature will facilitate the modification of dislocations. Compared with deformation experiments (Couvy et al. 2004; Raterron et al. 2007, 2009; Ohuchi et al. 2011; Ohuchi & Irifune 2013), the B- and C-type olivine fabrics in the Luobusa peridotites could be formed at pressures >7.6 and >9.6 GPa, respectively, whereas the A- and E-type olivine fabrics could be formed by dynamic recrystallization in the shallow mantle.

The ophiolites along the YZSZ were first obducted onto the continental margin of proto-India or onto a series of intra-oceanic island arcs (Aitchison et al. 2007; Hébert et al. 2012). The Luobusa ophiolite was formed at a mid-ocean ridge in the Mid-Jurassic (Zhou et al. 2002; Zhong et al. 2006) and then re-fertilized by boninitic melts in a mantle wedge above the subduction zone at c. 126 Ma (Malpas et al. 2003; Zhou et al. 2005, 2014). The 40Ar/39Ar dating of amphiboles from the Luobusa amphibolites yields amphibolite facies metamorphism at 90–80 Ma, which was interpreted as the initial tectonic displacement of the Luobusa ophiolite (Malpas et al. 2003). By contrast, zircon U-Pb ages of gabbro and amphibolite from the Luobusa ophiolite yield 128–131 Ma (C. Zhang et al. 2016), comparable with the 40Ar/39Ar cooling ages of amphiboles at 127–124 Ma for strongly foliated amphibolites in the Xigaze ophiolite in the central YZSZ (Guilmette et al. 2009). This implies multiple emplacement events before the closure of the Neotethyan Ocean along this suture zone. Slab rollback and southwards trench migration at c. 130–120 Ma has been proposed to explain the accretion of the Neotethyan forearc lithosphere in Tibetan ophiolites (Xiong et al. 2016).

Based on these geochronological constraints and the multiple magmatic events of the Gangdese arc, we propose a model in which channel flow induced by slab rollback can be used to explain the mixture of peridotites with different olivine fabrics and UHP minerals in the Luobusa ophiolite. As shown in Figure 13a, the Luobusa ophiolite probably represents the remnants of forearc oceanic lithosphere above a north-dipping subduction zone. The Neotethyan oceanic lithosphere was subducted to the transition zone in the Early Cretaceous. The slab rollback at 130–120 Ma formed a new subduction system to the south of the original system and triggered very rapid exhumation of the Luobusa peridotites and chromitites along the subduction channel between the subducting oceanic crust and the big mantle wedge. The return flow in the oceanic subduction channel resulted in a mixture of peridotites with different origins and fabrics, including peridotites and chromitites derived from the transition zone, UHP phases bearing SSZ peridotites and chromitites from the big mantle wedge, and SSZ peridotites that had been trapped in the subduction channel at shallow depths (Fig. 13b). This scenario is comparable with the dual origin of the Dabie–Sulu peridotites (Liou et al. 2000) and the exhumation of UHP rocks in continental subduction zones (Zheng 2012), but the return depth of the subducted materials is deeper than expected.

Fig. 13.

(a) Model of channel flow triggered by slab rollback for the rapid exhumation of supra-subduction zone peridotites in a subduction channel. See text for description. (b) Structure of the subduction channel shown as the dashed black rectangle in part (a). SSZ, supra-subduction zone; UHP, ultra-high pressure.

Fig. 13.

(a) Model of channel flow triggered by slab rollback for the rapid exhumation of supra-subduction zone peridotites in a subduction channel. See text for description. (b) Structure of the subduction channel shown as the dashed black rectangle in part (a). SSZ, supra-subduction zone; UHP, ultra-high pressure.

Compared with the mantle plume model, the exhumation of peridotites and chromitites in an oceanic subduction channel occurred at relatively low temperatures and a high exhumation rate. This model allows the addition of crustal minerals to peridotites and chromitites, the preservation of fabrics and dislocations in olivine, and the preservation of the δ13C and N signatures of microdiamonds. The subduction channel provides an important pathway for the transportation of subducted oceanic and continental materials from the mantle transition zone to shallow depths. In addition, due to the very low water content in olivine and the lack of hydrous minerals at depths >200 km, the water released from the subduction channel to the mantle wedge was limited during exhumation of the UHP rocks, which explains the interruption of magmatism in the Gangdese arc between 130 and 120 Ma. Therefore our model supports the exhumation of diamonds and UHP minerals by channel flow driven by slab rollback in forearc settings (Dilek & Yang 2018).

In a similar manner to the different fabrics seen in water-poor olivine from peridotites in the Western Gneiss Region (Norway) (Wang et al. 2013a), the Luobusa peridotites provide evidence for the water-independent development of fabrics in a subduction channel. Given the recent discovery of microdiamonds and UHP minerals in other ophiolites (Yang et al. 2014; Dilek & Yang 2018), it appears that the oceanic lithosphere has a more complex deformation history than that predicted based on plate tectonics theory. Further investigations of microstructure of ophiolites from different tectonic settings is required to investigate the heterogeneity of the oceanic lithosphere and the recycling of material through subduction channels.

Conclusions

We studied the composition, microstructure and water content of dunite and harzburgite core samples from the Luobusa Scientific Drilling Project to explore the complex deformation history of the diamond-bearing Luobusa ophiolite. All the peridotite samples show an SSZ signature and equilibration temperatures at c. 950–1080°C. The development of A-, B-, C- and E-type fabrics of olivine and the preservation of straight dislocations in olivine suggest their deformation at relatively low temperatures. Olivine is water-poor, with a mean water content of 16 ± 5 ppm due to the loss of hydrogen, whereas Opx and Cpx preserve high water contents and high hydrogen partition coefficients (DHCpx/Opx = 5.56 ± 0.96). The REE patterns of Cpx exclude the possible hydration of the Luobusa peridotites by mantle metasomatism. The subducted oceanic lithosphere can therefore transport a lot of water into the mantle transition zone via pyroxene. The B- and C-type fabrics in water-poor olivine represent a fossil fabric formed at great depths, whereas the A- and E-type fabrics were formed at shallow depths during exhumation. Our results, combined with previous studies, we propose channel flow driven by slab rollback to explain the mixture of different olivine fabrics, the extremely high DHCpx/Opx, and the occurrence of UHP and super-reducing mineral inclusions in the Luobusa peridotites and chromitites.

Acknowledgements

We are grateful to Y. Dilek for his invitation and encouragement to submit this paper, and for discussions with Y. Dilek, R. Wirth, W.L. Griffin and S.Y.O'Reilly. Constructive comments from T. Tsujimori and an anonymous reviewer were very helpful in improving this paper.

Funding

This research was supported by the NSFC project (41590623) and the National Key R & D Plan of China (Grant No. 2017YFC0601406).

Scientific editing by Yildirim Dilek

References

Aitchison
,
J.C.
,
Ali
,
J.R.
&
Davis
,
A.M.
2007
.
When and where did India and Asia collide?
Journal of Geophysical Research
 ,
112
,
B05423
, https://doi.org/10.1029/2006JB004706
Arai
,
S.
1994
.
Characterization of spinel peridotites by olivine–spinel compositional relationships: review and interpretation
.
Chemical Geology
 ,
113
,
191
204
.
Aubaud
,
C.
,
Hauri
,
E.H.
&
Hirschmann
,
M.M.
2004
.
Hydrogen partition coefficients between nominally anhydrous minerals and basaltic melts
.
Geophysical Research Letters: Solid Earth
 ,
31
,
L20611
, https://doi.org/10.1029/2004GL021341
Aubaud
,
C.
,
Withers
,
A.C.
,
Hirschmann
,
M.M.
,
Guan
,
Y.
,
Leshin
,
L.A.
,
Mackwell
,
S.J.
&
Bell
,
D.R.
2007
.
Intercalibration of FTIR and SIMS for hydrogen measurements in glasses and nominally anhydrous minerals
.
American Mineralogist
 ,
92
,
811
828
, https://doi.org/10.2138/am.2007.2248
Bai
,
W.J.
,
Zhou
,
M.F.
&
Robinson
,
P.T.
1993
.
Possibly diamond-bearing mantle peridotites and podiform chromitites in the Luobusa and Donqiao ophiolites, Tibet
.
Canadian Journal of Earth Sciences
 ,
30
,
1650
1659
, https://doi.org/10.1139/e93-143
Bell
,
D.R.
&
Ihinger
,
P.D.
2000
.
The isotopic composition of hydrogen in nominally anhydrous mantle minerals
.
Geochimica et Cosmochimica Acta
 ,
64
,
2109
2118
, https://doi.org/10.1016/S0016-7037(99)00440-8
Bell
,
D.R.
&
Rossman
,
G.R.
1992
.
Water in Earth's mantle: the role of nominally anhydrous minerals
.
Science
 ,
255
,
1391
1397
, http://10.1126/science.255.5050.1391
Bell
,
D.R.
,
Ihinger
,
P.D.
&
Rossman
,
G.R.
1995
.
Quantitative analysis of trace OH in garnet and pyroxenes
.
American Mineralogist
 ,
80
,
465
474
, https://doi.org/10.2138/am-1995-5-608
Bell
,
D.R.
,
Rossman
,
G.R.
,
Maldener
,
J.
,
Endisch
,
D.
&
Rauch
,
F.
2003
.
Hydroxide in olivine: a quantitative determination of the absolute amount and calibration of the IR spectrum
.
Journal of Geophysical Research
 ,
108
,
2105
, https://doi.org/10.1029/2001JB000679
Ben Ismaı̈l
,
W.
&
Mainprice
,
D.
1998
.
An olivine fabric database: an overview of upper mantle fabrics and seismic anisotropy
.
Tectonophysics
 ,
296
,
145
157
, https://doi.org/10.1016/S0040-1951(98)00141-3
Beran
,
A.
&
Libowitzky
,
E.
2006
.
Water in natural mantle minerals II: olivine, garnet and accessory minerals
.
Reviews in Mineralogy and Geochemistry
 ,
62
,
169
191
, https://doi.org/10.2138/rmg.2006.62.8
Blackman
,
D.K.
&
Kendall
,
J.M.
2002
.
Seismic anisotropy in the upper mantle 2. Predictions for current plate boundary flow models
.
Geochemistry, Geophysics, Geosystems
 ,
3
,
8602
, https://doi.org/10.1029/2001GC000247
Bonatti
,
E.
&
Michael
,
P.J.
1989
.
Mantle peridotites from continental rifts to ocean basins to subduction zones
.
Earth and Planetary Science Letters
 ,
91
,
297
311
, https://doi.org/10.1016/0012-821X(89)90005-8
Boudier
,
F.
1978
.
Structure and petrology of Lanzo peridotite massif (Piedmont Alps)
.
Geological Society of America Bulletin
 ,
89
,
1574
1591
.
Boudier
,
F.
&
Nicolas
,
A.
1995
.
Nature of the Moho transition zone in the Oman Ophiolite
.
Journal of Petrology
 ,
36
,
777
796
, https://doi.org/10.1093/petrology/36.3.777
Brey
,
G.P.
&
Köhler
,
T.
1990
.
Geothermobarometry in four-phase lherzolites II. New thermobarometers, and practical assessment of existing thermobarometers
.
Journal of Petrology
 ,
31
,
1353
1378
, https://doi.org/10.1093/petrology/31.6.1353
Bystricky
,
M.
,
Lawlis
,
J.S.
,
Mackwell
,
S.
,
Heidelbach
,
F.
&
Raterron
,
P.
2016
.
High-temperature deformation of enstatite aggregates
.
Journal of Geophysical Research: Solid Earth
 ,
121
,
6384
6400
, https://doi.org/10.1002/2016JB013011
Carter
,
N.L.
&
Avé Lallemant
,
H.G.
1970
.
High temperature flow of dunite and peridotite
.
Geological Society of Ameraca Bulletin
 ,
81
,
2181
2202
, https://doi.org/10.1130/0016-7606(1970)81
Chung
,
S.L.
,
Chu
,
M.F.
et al. 
2009
.
The nature and timing of crustal thickening in Southern Tibet: geochemical and zircon Hf isotopic constraints from postcollisional adakites
.
Tectonophysics
 ,
477
,
36
48
, https://doi.org/10.1016/j.tecto.2009.08.008
Couvy
,
H.
,
Frost
,
D.J.
,
Heidelbach
,
F.
,
Nyilas
,
K.
,
Ungar
,
T.
,
Mackwell
,
S.
&
Cordier
,
P.
2004
.
Shear deformation experiments of forsterite at 11 GPa–1400°C in the multianvil apparatus
.
Europeran Journal of Mineralogists
 ,
16
,
877
889
.
Demouchy
,
S.
2010
.
Diffusion of hydrogen in olivine grain boundaries and implications for the survival of water-rich zones in the Earth's mantle
.
Earth and Planetary Science Letters
 ,
295
,
305
313
, https://doi.org/10.1016/j.epsl.2010.04.019
Demouchy
,
S.
2012
.
Erratum to ‘Diffusion of hydrogen in olivine grain boundaries and implications for the survival of water-rich zones in Earth's mantle’ [Earth Planet. Sci. Lett. 295 (2010) 305–313]
.
Earth and Planetary Science Letters
 ,
355–356
,
351
, https://doi.org/10.1016/j.epsl.2012.09.034
Demouchy
,
S.
,
Shcheka
,
S.
,
Denis
,
C.M.
&
Thoraval
,
C.
2017
.
Subsolidus hydrogen partitioning between nominally anhydrous minerals in garnet-bearing peridotite
.
American Mineralogist
 ,
102
,
1822
1831
, https://doi.org/10.2138/am-2017-6089
Dick
,
H.J.B.
&
Bullen
,
T.
1984
.
Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas
.
Contributions to Mineralogy and Petrology
 ,
86
,
54
76
.
Dilek
,
Y.
&
Furnes
,
H.
2011
.
Ophiolite genesis and global tectonics: geochemical and tectonic fingerprinting of ancient oceanic lithosphere
.
Geological Society of America Bulletin
 ,
123
,
387
411
, http://https://doi.org/0.1130/B30446.1
Dilek
,
Y.
&
Furnes
,
H.
2014
.
Ophiolites and their origins
.
Elements
 ,
10
,
93
100
, http://https://doi.org/10.2113/gselements.10.2.93
Dilek
,
Y.
&
Robinson
,
P.T.
2003
. Ophiolites in earth history: introduction. In: Dilek, Y.D. & Robinson, P.T. (eds)
Ophiolites in Earth History. Geological Society, London, Special Publications
,
218
,
1
18
, https://doi.org/10.1144/GSL.SP.2003.218.01.01
Dilek
,
Y.
&
Yang
,
J.S.
2018
.
Ophiolites, diamonds, and ultrahigh-pressure minerals: new discoveries and concepts on upper mantle petrogenesis
.
Lithosphere
 ,
10
,
3
13
.
Dobrzhinetskaya
,
L.F.
,
Wirth
,
R.
,
Yang
,
J.
,
Hutcheon
,
I.D.
,
Weber
,
P.K.
&
Nd
,
G.H.
2009
.
High-pressure highly reduced nitrides and oxides from chromitite of a Tibetan ophiolite
.
Proceedings of the National Academy of Sciences of the USA
 ,
106
,
19233
19238
, https://doi.org/10.1073/pnas.0905514106
Frese
,
K.
,
Trommsdorf
,
V.
&
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 Petrology
 ,
145
,
73
86
, https://doi.org/10.1007/s00410-002-0434-x
Grant
,
K.
,
Ingrin
,
J.
,
Lorand
,
J.P.
&
Dumas
,
P.
2007
.
Water partitioning between mantle minerals from peridotite xenoliths
.
Contributions to Mineralogy and Petrology
 ,
154
,
15
34
, http://10.1007/s00410-006-0177-1
Griffin
,
W.L.
,
Afonso
,
J.C.
et al. 
2016
.
Mantle recycling: transition zone metamorphism of Tibetan ophiolitic peridotites and its tectonic implications
.
Journal of Petrology
 ,
57
,
655
684
, https://doi.org/10.1093/petrology/egw011
Guilmette
,
C.
,
Hébert
,
R.
,
Wang
,
C.
&
Villeneuve
,
M.
2009
.
Geochemistry and geochronology of the metamorphic sole underlying the Xigaze Ophiolite, Yarlung Zangbo Suture Zone, South Tibet
.
Lithos
 ,
112
,
149
162
, https://doi.org/10.1016/j.lithos.2009.05.027
Hacker
,
B.R.
,
Abers
,
G.A.
&
Peacock
,
S.M.
2003
.
Subduction factory, 1. Theoretical mineralogy, densities, seismic wave speeds, and H2O contents
.
Journal of Geophysical Research
 ,
108
,
2029
, https://doi.org/10.1029/2001JB001127
Hauri
,
E.H.
,
Gaetani
,
G.A.
&
Green
,
T.H.
2006
.
Partitioning of water during melting of the Earth's upper mantle at H2O-undersaturated conditions
.
Earth and Planetary Science Letters
 ,
248
,
715
734
, https://doi.org/10.1016/j.epsl.2006.06.014
Hébert
,
R.
,
Huot
,
F.
,
Wang
,
C.
&
Liu
,
Z.
2003
.
Yarlung Zangbo ophiolites (Southern Tibet) revisited: geodynamic implications from the mineral record
. In: Dilek, Y.D. & Robinson, P.T. (eds)
Ophiolites in Earth History.
Geological Society, London, Special Publications
 ,
218
,
165
190
, https://doi.org/10.1144/GSL.SP.2003.218.01.10
Hébert
,
R.
,
Bezard
,
R.
,
Guilmette
,
C.
,
Dostal
,
J.
,
Wang
,
C.S.
&
Liu
,
Z.F.
2012
.
The Indus–Yarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syntaxes, southern Tibet: first synthesis of petrology, geochemistry, and geochronology with incidences on geodynamic reconstructions of Neo-Tethys
.
Gondwana Research
 ,
22
,
377
397
, https://doi.org/10.1016/j.gr.2011.10.013
Hirschmann
,
M.M.
,
Tenner
,
T.
,
Aubaud
,
C.
&
Withers
,
A.C.
2009
.
Dehydration melting of nominally anhydrous mantle: the primacy of partitioning
.
Physics of the Earth and Planetary Interiors
 ,
176
,
54
68
.
Hirth
,
G.
&
Kohlstedt
,
D.L.
2003
. Rheology of the upper mantle and the mantle wedge: a view from the experimentalists. In:
Eiler
,
J.
(ed.)
Inside the Subduction Factory. Geophysical Monograph Series,
 
138
.
American Geophysical Union
,
Washington, DC
,
83
105
, https://doi.org/10.1029/138GM06
Hu
,
X.M.
,
Garzanti
,
E.
,
Wang
,
J.
,
Huang
,
W.
,
An
,
W.
&
Webb
,
A.
2016
.
The timing of India–Asia collision onset – facts, theories, controversies
.
Earth-Science Reviews
 ,
160
,
264
299
, https://doi.org/10.1016/j.earscirev.2016.07.014
Ingrin
,
J.
,
Hercule
,
S.
&
Charton
,
T.
1995
.
Diffusion of hydrogen in diopside: results of dehydration experiments
.
Journal of Geophysical Research
 ,
100
,
15,489
15,499
.
Jaques
,
A.L.
&
Green
,
D.H.
1980
.
Anhydrous melting of peridotite at 0–15 kb pressure and the genesis of tholeiitic basalts
.
Contributions to Mineralogy and Petrology
 ,
73
,
287
310
.
Ji
,
W.Q.
,
Wu
,
F.Y.
,
Chung
,
S.L.
,
Li
,
J.X.
&
Liu
,
C.Z.
2009
.
Zircon U–Pb geochronology and Hf isotopic constraints on petrogenesis of the Gangdese batholith, southern Tibet
.
Chemical Geology
 ,
262
,
229
245
, https://doi.org/10.1016/j.chemgeo.2009.01.020
Johnson
,
E.A.
,
Rossman
,
G.R.
,
Dyar
,
M.D.
&
Valley
,
J.W.
2002
.
Correlation between OH concentration and oxygen isotope diffusion rate in diopsides from the Adirondack Mountains, New York
.
American Mineralogist
 ,
87
,
899
908
, https://doi.org/10.2138/am-2002-0713
Johnson
,
K.T.M.
,
Dick
,
H.J.B.
&
Shimizu
,
N.
1990
.
Melting in oceanic upper mantle: an ion microprobe study of diopsides in abyssal peridotites
.
Journal of Geophysical Research: Solid Earth
 ,
95
,
2661
2678
, https://doi.org/10.1029/JB095iB03p02661
Jung
,
H.
2017
.
Crystal preferred orientations of olivine, orthopyroxene, serpentine, chlorite, and amphibole, and implications for seismic anisotropy in subduction zones: a review
.
Geosciences Journal
 ,
21
,
985
1011
, https://doi.org/10.1007/s12303-018-0009-0
Jung
,
H.
&
Karato
,
S.I.
2001
.
Water-induced fabric transitions in olivine
.
Science
 ,
293
,
1460
1463
, https://doi.org/10.1126/science.1062235
Jung
,
H.
,
Katayama
,
I.
,
Jiang
,
Z.
,
Hiraga
,
T.
&
Karato
,
S.I.
2006
.
Effect of water and stress on the lattice-preferred orientation of olivine
.
Tectonophysics
 ,
421
,
1
22
, https://doi.org/10.1016/j.tecto.2006.02.011
Jung
,
H.
,
Lee
,
J.
,
Ko
,
B.
,
Jung
,
S.
,
Park
,
M.
,
Cao
,
Y.
&
Song
,
S.
2013
.
Natural type-C olivine fabrics in garnet peridotites in North Qaidam UHP collision belt, NW China
.
Tectonophysics
 ,
594
,
91
102
, https://doi.org/10.1016/j.tecto.2013.03.025
Katayama
,
I.
,
Karato
,
S.I.
&
Brandon
,
M.
2005
.
Evidence of high water content in the deep upper mantle inferred from deformation microstructures
.
Geology
 ,
33
,
613
616
, https://doi.org/10.1130/G21332.1
Khisina
,
N.R.
,
Wirth
,
R.
,
Andrut
,
M.
&
Ukhanov
,
A.V.
2001
.
Extrinsic and intrinsic mode of hydrogen occurrence in natural olivines: FTIR and TEM investigation
.
Physics and Chemistry of Minerals
 ,
28
,
291
301
, https://doi.org/10.1007/s002690100162
Kovács
,
I.
,
Green
,
D.H.
,
Rosenthal
,
A.
,
Hermann
,
J.
,
O'Neill
,
H.S.C.
,
Hibberson
,
W.O.
&
Udvardi
,
B.
2012
.
An experimental study of water in nominally anhydrous minerals in the upper mantle near the water-saturated solidus
.
Journal of Petrology
 ,
53
,
2067
2093
, https://doi.org/10.1093/petrology/egs044
Li
,
Z.X.A.
,
Lee
,
C.T.A.
,
Peslier
,
A.H.
,
Lenardic
,
A.
&
Mackwell
,
S.J.
2008
.
Water contents in mantle xenoliths from the Colorado Plateau and vicinity: implications for the mantle rheology and hydration-induced thinning of continental lithosphere
.
Journal of Geophysical Research
 ,
113
,
B09210
, https://doi.org/10.1029/2007JB005540
Liang
,
F.H.
,
Xu
,
Z.Q.
,
Ba
,
D.Z.
,
Xu
,
X.Z.
,
Liu
,
F.
,
Xiong
,
F.H.
&
Jia
,
Y.
2011
.
Tectonic occurrence and emplacement mechanism of ophiolites from Luobusha-Zedang, Tibet [in Chinese with Englshi abstract]
.
Acta Petrologica Sinica
 ,
27
,
3255
3268
.
Liou
,
J.G.
,
Hacker
,
B.R.
&
Zhang
,
R.Y.
2000
.
Into the forbidden zone
.
Science
 ,
287
,
1215
1216
.
Long
,
M.D.
&
Becker
,
T.W.
2010
.
Mantle dynamics and seismic anisotropy
.
Earth and Planetary Science Letters
 ,
297
,
341
354
.
Mackwell
,
S.J.
&
Kohlstedt
,
D.L.
1990
.
Diffusion of hydrogen in olivine: implications for water in the mantle
.
Journal of Geophysical Research
 ,
95
,
5079
5088
.
Mainprice
,
D.
1990
.
A FORTRAN program to calculate seismic anisotropy from the lattice preferred orientation of minerals
.
Computers & Geosciences
 ,
16
,
385
393
.
Malpas
,
J.
,
Zhou
,
M.F.
,
Robinson
,
P.T.
&
Reynolds
,
P.H.
2003
.
Geochemical and geochronological constraints on the origin and emplacement of the Yarlung Zangbo ophiolites, Southern Tibet
. In: Dilek, Y.D. & Robinson, P.T. (eds)
Ophiolites in Earth History.
Geological Society, London, Special Publications
 ,
218
,
191
206
, https://doi.org/10.1144/GSL.SP.2003.218.01.11
Manthilake
,
M.A.G.M.
,
Miyajima
,
N.
,
Heidelbach
,
F.
,
Soustelle
,
V.
&
Frost
,
D.J.
2013
.
The effect of aluminum and water on the development of deformation fabrics of orthopyroxene
.
Contributions to Mineralogy and Petrology
 ,
165
,
495
505
, https://doi.org/10.1007/s00410-012-0819-4
McDonough
,
W.F.
&
Sun
,
S.S.
1995
.
The composition of the Earth
.
Chemical Geology
 ,
120
,
223
253
, https://doi.org/10.1016/0009-2541(94)00140-4
Mehl
,
L.
,
Hacker
,
B.R.
,
Hirth
,
G.
&
Kelemen
,
P.B.
2003
.
Arc-parallel flow within the mantle wedge: evidence from the accreted Talkeetna arc, south central Alaska
.
Journal of Geophysical Research: Solid Earth
 ,
108
,
2375
, https://doi.org/10.1029/2002JB002233
Michibayashi
,
K.
&
Oohara
,
Y.
2013
.
Olivine fabric evolution in a hydrated ductile shear zone at the Moho Transition Zone, Oman Ophiolite
.
Earth and Planetary Science Letters
 ,
377–378
,
299
310
.
Michibayashi
,
K.
,
Mainprice
,
D.
et al. 
2016
.
Natural olivine crystal-fabrics in the western Pacific convergence region: a new method to identify fabric type
.
Earth and Planetary Science Letters
 ,
443
,
70
80
, https://doi.org/10.1016/j.epsl.2016.03.019
Mizukami
,
T.
,
Wallis
,
S.R.
&
Yamamoto
,
J.
2004
.
Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum
.
Nature
 ,
427
,
432
436
.
Mo
,
X.
,
Hou
,
Z.
,
Niu
,
Y.
,
Dong
,
G.
,
Qu
,
X.
,
Zhao
,
Z.
&
Yang
,
Z.
2007
.
Mantle contributions to crustal thickening during continental collision: evidence from Cenozoic igneous rocks in southern Tibet
.
Lithos
 ,
96
,
225
242
, https://doi.org/10.1016/j.lithos.2006.10.005
Nimis
,
P.
&
Grütter
,
H.
2010
.
Internally consistent geothermometers for garnet peridotites and pyroxenites
.
Contributions to Mineralogy and Petrology
 ,
159
,
411
427
, https://doi.org/10.1007/s00410-009-0464-8
Ohuchi
,
T.
&
Irifune
,
T.
2013
.
Development of A-type olivine fabric in water-rich deep upper mantle
.
Earth and Planetary Science Letters
 ,
362
,
20
30
, https://doi.org/10.1016/j.epsl.2012.11.029
Ohuchi
,
T.
,
Kawazoe
,
T.
,
Nishihara
,
Y.
,
Nishiyama
,
N.
&
Irifune
,
T.
2011
.
High pressure and temperature fabric transitions in olivine and variations in upper mantle seismic anisotropy
.
Earth and Planetary Science Letters
 ,
304
,
55
63
, https://doi.org/10.1016/j.epsl.2011.01.015
Park
,
J.
&
Levin
,
V.
2002
.
Seismic anisotropy: tracing plate dynamics in the mantle
.
Science
 ,
296
,
485
489
, https://doi.org/10.1126/science.1067319
Paterson
,
M.S.
1982
.
The determination of hydroxyl by infrared absorption in quartz, silicate glasses and similar materials
.
Bulletin of Mineralogy
 ,
105
,
20
29
.
Pearce
,
J.A.
,
Barker
,
P.F.
,
Edwards
,
S.J.
,
Parkinson
,
I.J.
&
Leat
,
P.T.
2000
.
Geochemistry and tectonic significance of peridotites from the South Sandwich arc–basin system, South Atlantic
.
Contributions to Mineralogy and Petrology
 ,
139
,
36
53
, https://doi.org/10.1007/s004100050572
Pearson
,
D.G.
,
Brenker
,
F.E.
,
Nestola
,
F.
et al. 
2014
.
Hydrous mantle transition zone indicated by ringwoodite included within diamond
.
Nature
 ,
507
,
221
224
.
Peslier
,
A.H.
&
Luhr
,
J.F.
2006
.
Hydrogen loss from olivines in mantle xenoliths from Simcoe (USA) and Mexico: mafic alkalic magma ascent rates and water budget of the sub-continental lithosphere
.
Earth and Planetary Science Letters
 ,
242
,
302
319
, https://doi.org/10.1016/j.epsl.2005.12.019
Peslier
,
A.H.
,
Luhr
,
J.F.
&
Post
,
J.
2002
.
Low water contents in pyroxenes from spinel-peridotites of the oxidized, sub-arc mantle wedge
.
Earth and Planetary Science Letters
 ,
201
,
69
86
, https://doi.org/10.1016/S0012-821X(02)00663-5
Peslier
,
A.H.
,
Snow
,
J.E.
,
Hellebrand
,
E.
&
Von Der Handt
,
A.
2007
.
Low water contents in minerals from Gakkel ridge abyssal peridotites, Arctic Ocean
.
Geochimica et Cosmochimica Acta
 ,
71
,
A779
.
Peslier
,
A.H.
,
Woodland
,
A.B.
&
Wolff
,
J.A.
2008
.
Fast kimberlite ascent rates estimated from hydrogen diffusion profiles in xenolithic olvines from southern Africa
.
Geochimica et Cosmochimica Acta
 ,
72
,
2711
2722
, https://doi.org/10.1016/j.gca.2008.03.019
Peslier
,
A.H.
,
Woodland
,
A.B.
,
Bell
,
D.R.
&
Lazarov
,
M.
2010
.
Olivine water contents in the continental lithosphere and the longevity of cratons
.
Nature
 ,
467
,
78
81
, https://doi.org/10.1038/nature09317
Peslier
,
A.H.
,
Woodland
,
A.B.
,
Bell
,
D.R.
,
Lazarov
,
M.
&
Lapen
,
T.J.
2012
.
Metasomatic control of water contents in the Kaapvaal cratonic mantle
.
Geochimica et Cosmochimica Acta
 ,
97
,
213
246
, https://doi.org/10.1016/j.gca.2012.08.028
Raterron
,
P.
,
Wu
,
Y.
,
Weidner
,
D.J.
&
Chen
,
J.
2004
.
Low-temperature olivine rheology at high pressure
.
Physics of the Earth and Planetary Interiors
 ,
145
,
149
159
, https://doi.org/10.1016/j.pepi.2004.03.007
Raterron
,
P.
,
Chen
,
J.
,
Li
,
L.
,
Weidner
,
D.
&
Cordier
,
P.
2007
.
Pressure-induced slip-system transition in forsterite: single-crystal rheological properties at mantle pressure and temperature
.
American Mineralogist
 ,
92
,
1436
1445
, https://doi.org/10.2138/am.2007.2474
Raterron
,
P.
,
Amiguet
,
E.
,
Chen
,
J.
,
Li
,
L.
&
Cordier
,
P.
2009
.
Experimental deformation of olivine single crystals at mantle pressures and temperatures
.
Physics of the Earth and Planetary Interiors
 ,
172
,
74
83
, https://doi.org/10.1016/j.pepi.2008.07.026
Robinson
,
P.T.
,
Bai
,
W.J.
et al. 
2004
.
Ultra-high pressure minerals in the Luobusa Ophiolite, Tibet, and their tectonic implications
. In:
Malpas
,
J.
,
Fletcher
,
C.J.N.
,
Ali
,
J.R.
&
Aitchison
,
J.C.
(eds)
Aspects of the Tectonic Evolution of China.
Geological Society, London, Special Publications
 ,
226
,
247
271
, https://doi.org/10.1144/GSL.SP.2004.226.01.14
Robinson
,
P.T.
,
Trumbull
,
R.B.
et al. 
2015
.
The origin and significance of crustal minerals in ophiolitic chromitites and peridotites
.
Gondwana Research
 ,
27
,
486
506
, https://doi.org/10.1016/j.gr.2014.06.003
Rosenthal
,
A.
,
Hauri
,
E.H.
&
Hirschmann
,
M.M.
2015
.
Experimental determination of C, F, and H partitioning between mantle minerals and carbonated basalt, CO2/Ba and CO2/Nb systematics of partial melting, and the CO2 contents of basaltic source regions
.
Earth and Planetary Science Letters
 ,
412
,
77
87
, https://doi.org/10.1016/j.epsl.2014.11.044
Sawaguchi
,
T.
2004
.
Deformation history and exhumation process of the Horoman Peridotite Complex, Hokkaido, Japan
.
Tectonophysics
 ,
379
,
109
126
, https://doi.org/10.1016/j.tecto.2003.10.011
Skemer
,
P.
,
Katayama
,
I.
&
Karato
,
S.I.
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 Petrology
 ,
152
,
43
51
, https://doi.org/10.1007/s00410-006-0093-4
Soustelle
,
V.
&
Manthilake
,
G.
2017
.
Deformation of olivine-orthopyroxene aggregates at high pressure and temperature: implications for the seismic properties of the asthenosphere
.
Tectonophysics
 ,
694
,
385
399
, https://doi.org/10.1016/j.tecto.2016.11.020
Stalder
,
R.
&
Skogby
,
H.
2003
.
Hydrogen diffusion in natural and synthetic orthopyroxene
.
Physics and Chemistry of Minerals
 ,
30
,
12
19
, https://doi.org/10.1007/s00269-002-0285-z
Sun
,
S.
,
Ji
,
S.
,
Michibayashi
,
K.
&
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
 ,
121
,
3300
3323
, https://doi.org/10.1002/2015JB012579
Tasaka
,
M.
,
Michibayashi
,
K.
&
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
 ,
272
,
747
757
, https://doi.org/10.1016/j.epsl.2008.06.014
Taylor
,
W.R.
1998
.
An experimental test of some geothermometer and geobarometer formulations for upper mantle peridotites with application to the thermobarometry of fertile lherzolites and garnet websterite
.
Neues Jahrbuch für Mineralogie Abhandlungen
 ,
172
,
381
408
.
Tenner
,
T.J.
,
Hirschmann
,
M.M.
,
Withers
,
A.C.
&
Hervig
,
R.L.
2009
.
Hydrogen partitioning between nominally anhydrous upper mantle minerals and melt between 3 and 5 GPa and applications to hydrous peridotite partial melting
.
Chemical Geology
 ,
262
,
42
56
, https://doi.org/10.1016/j.chemgeo.2008.12.006
Tommasi
,
A.
&
Vauchez
,
A.
2015
.
Heterogeneity and anisotropy in the lithospheric mantle
.
Tectonophysics
 ,
661
,
11
37
, https://doi.org/10.1016/j.tecto.2015.07.026
Tommasi
,
A.
,
Baptiste
,
V.
,
Vauchez
,
A.
&
Holtzman
,
B.
2016
.
Deformation, annealing, reactive melt percolation, and seismic anisotropy in the lithospheric mantle beneath the southeastern Ethiopian rift: constraints from mantle xenoliths from Mega
.
Tectonophysics
 ,
682
,
186
205
, https://doi.org/10.1016/j.tecto.2016.05.027
Wang
,
Q.
,
Xia
,
Q.K.
,
O'Reilly
,
S.Y.
,
Griffin
,
G.L.
,
Beyer
,
E.E.
&
Brueckner
,
H.K.
2013
a.
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
 ,
31
,
91
111
.
Wang
,
Y.F.
,
Zhang
,
J.
&
Shi
,
F.
2013
b.
The origin and geophysical implications of a weak C-type olivine fabric in the Xugou ultrahigh pressure garnet peridotite
.
Earth and Planetary Science Letters
 ,
376
,
63
73
, https://doi.org/10.1016/j.epsl.2013.06.017
Wen
,
D.R.
,
Liu
,
D.
et al. 
2008
.
Zircon SHRIMP U–Pb ages of the Gangdese Batholith and implications for Neotethyan subduction in southern Tibet
.
Chemical Geology
 ,
252
,
191
201
, https://doi.org/10.1016/j.chemgeo.2008.03.003
Witt-Eickschen
,
G.
&
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
 ,
106
,
431
439
.
Xia
,
Q.K.
,
Liu
,
J.
et al. 
2017
.
Water in the upper mantle and deep crust of eastern China: concentration, distribution and implications
.
National Science Review
 ,
nwx016
, https://doi.org/10.1093/nsr/nwx016
Xiong
,
F.
,
Yang
,
J.
et al. 
2015
.
Origin of podiform chromitite, a new model based on the Luobusa ophiolite, Tibet
.
Gondwana Research
 ,
27
,
525
542
, https://doi.org/10.1016/j.gr.2014.04.008
Xiong
,
Q.
,
Griffin
,
W.L.
,
Zheng
,
J.P.
,
O'Reilly
,
S.Y.
,
Pearson
,
N.J.
,
Xu
,
B.
&
Belousova
,
E.A.
2016
.
Southward trench migration at ∼130–120 Ma caused accretion of the Neo-Tethyan forearc lithosphere in Tibetan ophiolites
.
Earth and Planetary Science Letters
 ,
438
,
57
65
, https://doi.org/10.1016/j.epsl.2016.01.014
Xu
,
M.J.
&
Jin
,
Z.M.
2010
.
Deformation microstructures of mantle peridotite from Luobusha ophiolite, Tibet, China and its geological implication [in Chinese with English abstract]
.
Geological Bulletin of China
 ,
29
,
1795
1803
.
Xu
,
X.Z.
,
Yang
,
J.S.
,
Robinson
,
P.T.
,
Xiong
,
F.
,
Ba
,
D.
&
Guo
,
G.
2015
b.
Origin of ultrahigh pressure and highly reduced minerals in podiform chromitites and associated mantle peridotites of the Luobusa ophiolite, Tibet
.
Gondwana Research
 ,
27
,
686
700
, https://doi.org/10.1016/j.gr.2014.05.010
Xu
,
X.Z.
,
Cartigny
,
P.
,
Yang
,
J.-S.
,
Dilek
,
Y.
,
Xiong
,
F.
&
Guo
,
G.
2018
.
Fourier transform infrared spectroscopy data and carbon isotope characteristics of the ophiolitehosted diamonds from the Luobusa ophiolite, Tibet, and Ray-Iz ophiolite
,
Polar Urals. Lithosphere
 ,
10
,
156
169
, https://doi.org/10.1130/L625.1
Xu
,
Z.Q.
,
Wang
,
Q.
,
Ji
,
S.
,
Chen
,
J.
,
Zeng
,
L.
,
Yang
,
J.
&
Wenk
,
H.R.
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
 ,
421
,
111
127
, https://doi.org/10.1016/j.tecto.2006.04.010
Xu
,
Z.Q.
,
Dilek
,
Y.
et al. 
2015
a.
Crustal structure of the Indus–Tsangpo suture zone and its ophiolites in southern Tibet
.
Gondwana Research
 ,
27
,
507
524
, https://doi.org/10.1016/j.gr.2014.08.001
Yamamoto
,
H.
,
Yamamoto
,
S.
,
Kaneko
,
Y.
,
Terabayashi
,
M.
,
Komiya
,
T.
,
Katayama
,
I.
&
Iizuka
,
T.
2007
.
Imbricate structure of the Luobusa ophiolite and surrounding rock units, southern Tibet
.
Journal of Asian Earth Sciences
 ,
29
,
296
304
, https://doi.org/10.1016/j.jseaes.2006.04.004
Yamamoto
,
S.
,
Komiya
,
T.
,
Hirose
,
K.
&
Maruyama
,
S.
2009
.
Coesite and clinopyroxene exsolution lamellae in chromites: in-situ ultrahigh-pressure evidence from podiform chromitites in the Luobusa ophiolite, southern Tibet
.
Lithos
 ,
109
,
314
322
, https://doi.org/10.1016/j.lithos.2008.05.003
Yang
,
J.S.
,
Dobrzhinetskaya
,
L.
,
Bai
,
W.J.
,
Fang
,
Q.S.
,
Robinson
,
P.T.
,
Zhang
,
J.
&
Green
,
H.W.I.I.
2007
.
Diamond- and coesite-bearing chromitites from the Luobusa ophiolite, Tibet
.
Geology
 ,
35
,
875
878
, https://doi.org/10.1130/G23766A.1
Yang
,
J.S.
,
Robinson
,
P.T.
&
Dilek
,
Y.
2014
.
Diamonds in ophiolites
.
Elements
 ,
10
,
127
130
, https://doi.org/10.2113/gselements.10.2.127
Yang
,
X.Z.
,
Xia
,
Q.K.
,
Deloule
,
E.
,
Dallai
,
L.
,
Fan
,
Q.C.
&
Feng
,
M.
2008
.
Water in minerals of the continental lithospheric mantle and overlying lower crust: a comparative study of peridotite and granulite xenoliths from the North China Craton
.
Chemical Geology
 ,
256
,
33
45
, https://doi.org/10.1016/j.chemgeo.2008.07.020
Zhang
,
C.
,
Liu
,
C.Z.
,
Wu
,
W.Y.
,
Zhang
,
L.L.
&
Ji
,
W.Q.
2016
.
Geochemistry and geochronology of mafic rocks from the Luobusa ophiolite, South Tibet
.
Lithos
 ,
245
,
93
108
, https://doi.org/10.1016/j.lithos.2015.06.031
Zhang
,
R.Y.
,
Yang
,
J.S.
,
Ernst
,
W.G.
,
Jahn
,
B.M.
,
Iizuka
,
Y.
&
Guo
,
G.L.
2016
.
Discovery of in situ super-reducing, ultrahigh-pressure phases in the Luobusa ophiolitic chromitites, Tibet: new insights into the deep upper mantle and mantle transition zone
.
American Mineralogist
 ,
101
,
1245
1251
, https://doi.org/10.2138/am-2016-5436
Zhang
,
R.Y.
,
Shau
,
Y.H.
,
Yang
,
J.S.
&
Liou
,
J.G.
2017
.
Discovery of clinoenstatite in the Luobusa ophiolitic mantle peridotite recovered from a drill hole, Tibet
.
Journal of Asian Earth Sciences
 ,
145
,
605
612
.
Zhang
,
S.
,
Karato
,
S.I.
,
Gerald
,
J.F.
,
Faul
,
U.H.
&
Zhou
,
Y.
2000
.
Simple shear deformation of olivine aggregates
.
Tectonophysics
 ,
316
,
133
152
, https://doi.org/10.1016/S0040-1951(99)00229-2
Zhang
,
Z.
,
Dong
,
X.
,
Xiang
,
H.
,
He
,
Z.
&
Liou
,
J.G.
2014
.
Metagabbros of the Gangdese arc root, south Tibet: implications for the growth of continental crust
.
Geochimica et Cosmochimica Acta
 ,
143
,
268
284
, https://doi.org/10.1016/j.gca.2014.01.045
Zheng
,
Y.-F.
2012
.
Metamorphic chemical geodynamics in continental subduction zones
.
Chemical Geology
 ,
328
,
5
48
.
Zhong
,
L.F.
,
Xia
,
B.
,
Zhang
,
Y.Q.
,
Wang
,
R.
,
Wei
,
D.L.
&
Yang
,
Z.Q.
2006
.
SHRIMP age determination of the diabase in Luobusa ophiolite, southern Xizang (Tibet) [in Chinese with English abstract]
.
Geological Review
 ,
52
,
224
229
.
Zhou
,
M.F.
,
Robinson
,
P.T.
,
Malpas
,
J.
&
Li
,
Z.J.
1996
.
Podiform chromitites in the Luobusa ophiolite (Southern Tibet): implications for melt–rock interaction and chromite segregation in the upper mantle
.
Journal of Petrology
 ,
37
,
3
21
, https://doi.org/10.1093/petrology/37.1.3
Zhou
,
M.F.
,
Robinson
,
P.T.
,
Malpas
,
J.
,
Edwards
,
S.J.
&
Qi
,
L.
2005
.
REE and PGE geochemical constraints on the formation of dunites in the Luobusa ophiolite, Southern Tibet
.
Journal of Petrology
 ,
46
,
615
639
, https://doi.org/10.1093/petrology/egh091
Zhou
,
M.F.
,
Robinson
,
P.T.
,
Su
,
B.X.
,
Gao
,
J.F.
,
Li
,
J.W.
,
Yang
,
J.S.
&
Malpas
,
J.
2014
.
Compositions of chromite, associated minerals, and parental magmas of podiform chromite deposits: the role of slab contamination of asthenospheric melts in suprasubduction zone environments
.
Gondwana Research
 ,
26
,
262
283
, https://doi.org/10.1016/j.gr.2013.12.011
Zhou
,
S.
,
Mo
,
X.
,
Mahoney
,
J.J.
,
Zhang
,
S.
,
Guo
,
T.
&
Zhao
,
Z.
2002
.
Geochronology and Nd and Pb isotope characteristics of gabbro dikes in the Luobusha ophiolite, Tibet
.
Chinese Science Bulletin
 ,
47
,
143
146
.
Zhu
,
D.C.
,
Zhao
,
Z.D.
et al. 
2011
.
The Lhasa Terrane: record of a microcontinent and its histories of drift and growth
.
Earth and Planetary Science Letters
 ,
301
,
241
255
, https://doi.org/10.1016/j.epsl.2010.11.005
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