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Abstract

The Qinling-Tongbai-Hong’an-Dabie Shan area is an about 2000 km long Triassic Indosinian orogenic belt produced by the collision between the Sino-Korean and the Yangtze cratons (Fig. 1). Its eastern extension, the Sulu area, occupies the southeastern side of the Shandong Peninsula, and is considered to be displaced about 500 km by the NE-SW trending left lateral Tan-Lu Fault after the Mesozoic (Fig. 1). Among these areas, most of the UHP rocks were found from Hong’an, Dabie Shan and Sulu areas, suggesting that these areas represent the most extensive UHP metamorphic belt in the world. Their UHP peak is dated around 220-230 Ma (e.g. Ames et al., 1993, 1996; Li et al., 1993; Hacker & Wang, 1995; Hacker et al., 1996; Rowley et al., 1997) and these UHP terrains are considered to be formed chiefly by attempted north-directed subduction of the Yangtze craton or a microcontinent beneath the Sino-Korean craton (e.g. Hacker et al., 1996).

Geological framework

The Qinling-Tongbai-Hong’an-Dabie Shan area is an about 2000 km long Triassic Indosinian orogenic belt produced by the collision between the Sino-Korean and the Yangtze cratons (Fig. 1). Its eastern extension, the Sulu area, occupies the southeastern side of the Shandong Peninsula, and is considered to be displaced about 500 km by the NE-SW trending left lateral Tan-Lu Fault after the Mesozoic (Fig. 1). Among these areas, most of the UHP rocks were found from Hong’an, Dabie Shan and Sulu areas, suggesting that these areas represent the most extensive UHP metamorphic belt in the world. Their UHP peak is dated around 220-230 Ma (e.g. Ames et al., 1993, 1996; Li et al., 1993; Hacker & Wang, 1995; Hacker et al., 1996; Rowley et al., 1997) and these UHP terrains are considered to be formed chiefly by attempted north-directed subduction of the Yangtze craton or a microcontinent beneath the Sino-Korean craton (e.g. Hacker et al., 1996).

Fig. 1.

Tectono-metamorphic sketch map of the Qinling-Dabie Shan-Sulu orogen.

Fig. 1.

Tectono-metamorphic sketch map of the Qinling-Dabie Shan-Sulu orogen.

Many available data concerning petrology, structural geology and geochronology of the Hong’an and Dabie Shan areas have accumulated during this decade, and several geologic subdivisions were proposed in the relevant area. This paper basically follows the subdivision of Hacker et al. (1998) because the locations of UHP/HP rocks are well indicated, except for the geotectonic subdivision of the western part of the Dabie Shan area (e.g. Castelli et al., 1998). Hacker et al. (1998) subdivided the main rock units in the Dabie Shan area from south to north as follows: a fold and thrust belt, Susong Group (blueschist and high-pressure amphibolite), quartz eclogite, coesite eclogite, Northern Orthogneiss unit, Luzhenguang Group and Foziling Group. This subdivision is still supported in the eastern half of the Dabie Shan area but not in the western half by subsequent researchers (e.g. Castelli et al., 1998; Faure et al. 2003). In this paper we follow the geologic subdivision in the western half of the Dabie Shan area by Castelli et al. (1998) (see Fig. 2), where it is provisionally called amphibolite-granulite unit.

Fig. 2.

Tectono-metamorphic map of the Dabie Shan-Hong’an areas, based mainly on Hacker et al. (1998) and Castelli et al (1998). The locations of eclogitic xenoliths in granodiorite follow Faure etal. (2003)

Fig. 2.

Tectono-metamorphic map of the Dabie Shan-Hong’an areas, based mainly on Hacker et al. (1998) and Castelli et al (1998). The locations of eclogitic xenoliths in granodiorite follow Faure etal. (2003)

The northward increase in metamorphic grade is also recognised in the Hong’an area, to the west of the Dabie Shan area bounded by the Shang-Ma Fault. Blueschist facies rocks occur in the southern part, and distinct greenschist, prograde amphibolite and eclogite retrogressed to amphibolite units have been mapped northward (Fig. 2). Quartz eclogite and coesite eclogite units occupy the north-central part. The northern part of the area is occupied by E-W trending fault bounded units, which contain HP rocks. Eide & Liou (2000) reported the similar metamorphic zonal mapping in the Hong’an area and considered that the high-pressure (HP) Hong’an eclogites, often preserving prograde crystallisation histories, can be directly linked in time and space to the blueschist/blueschist-greenschist rocks exposed to the south.

All the units in the Hong’an-Dabie Shan area are intruded by voluminous Cretaceous granitoids, and the northern margin is overlain by Cretaceous and Cenozoic sediments, although Eide & Liou (2000) described that the Hong’an area escaped from the thermal and structural overprint during Early Cretaceous intrusions of voluminous granites and granodiorites. The Cretaceous granitoid intrusion caused the pervasive migmatization in the Northern Orthogneiss unit and the northern half of the amphibolite-granulite unit of the Dabie Shan area. Therefore, Faure et al. (2003) renamed this unit as “Gneiss or mylonitised migmatite zone”.

The geologic framework of the Shandong Peninsula is rather simpler than that of the Hong’an-Dabie Shan area. The Shandong Peninsula can be divided into northwestern and southeastern areas with a boundary along Yantai-Qingdao-Wulian (YQW) Fault (Fig. 3). These areas also have been widely intruded by Cretaceous granitoids, but the nature of the basement rocks to the northwest and southeast of YQW Fault are strikingly different.

Fig. 3.

Tectono-metamorphic map of the Sulu area with locations of coesite eclogite and other ultrabasic and basic rocks with critical mineral assemblages, mainly after Wallis et al. (1997). YQW Fault: Yantai-Qingdao-Wulian Fault.

Fig. 3.

Tectono-metamorphic map of the Sulu area with locations of coesite eclogite and other ultrabasic and basic rocks with critical mineral assemblages, mainly after Wallis et al. (1997). YQW Fault: Yantai-Qingdao-Wulian Fault.

The basement rocks of the northwestern area are characterised by the granulite to amphibolite facies orthogneisses and paraschists characterised by the sillimanite-garnet assemblage, locally overlain by lower-grade to unmetamorphosed rocks of the Upper Proterozoic Sinian system. Metabasic rocks in this area are amphibolite and granulite with or without garnet. The occurrence of eclogite has not been recognised through the extensive study during this decade, although some Chinese geologists had claimed to have found eclogite (e.g. Cheng, 1986). The regional orthogneiss mainly belongs to a tonalitic series (Zhai et al., 2000) and has zircon ages of 2600-2900 Ma (Wang & Yan, 1992), Rb-Sr whole rock ages and chemical U-Th-total Pb ages of 1600-2020 Ma (Enami et al., 1993b; Ishizaka et al., 1994).

The basement rocks of the southeastern area are also predominantly of tonalitic and granitic gneiss with amphibolite facies mineral assemblages, which occupies more than 90 vol% of the area. Metabasic rocks mainly occur as lenses, blocks or layers intercalated with the country gneiss. Most of the metabasic rocks are retrogressed to the amphibolite facies to various degrees, but the eclogitic mineral assemblages are still preserved in the core of less retrogressed rocks. Some eclogites also occur closely associated with peridotite or marble. Eclogites with coesite and/or its pseudomorphs are sporadic but occur throughout the southeastern area (Fig. 3). Garnet peridotite, less abundant than eclogite, also occurs in the southeast area of the YQW fault, although spinel peridotite occurs in the northwest area of the YQW fault. The similar UHP age to the Hong’an-Dabie Shan area is also reported in the area southeast of the YQW fault (218 Ma by Ames et al., 1996; 210-220 Ma by Jahn et al., 1996 and 1998). Most of the protolith ages of the country gneisses (around 700-800 Ma, Ishizaka et al., 1994; Ames et al., 1996; Hirajima & Fanning, 1999 and unpublished data) is strikingly different from those obtained in the area northwest of the YQW Fault, although an Early Proterozoic protolith age (1.7 Ga) was reported for the Weihai eclogite by the Sm-Nd isotopic data (Jahn et al., 1996). These data suggest that the southeastern area of the Shandong Peninsula was derived from the Yangtze craton and suffered UHP metamorphism but the northwestern area belongs to the Sino-Korean craton, characterised by the MP/LP type metamorphism with Archaean and early Proterozoic ages. In this paper, we call the area northwest of the YQW Fault as the Laiyang area and the southeastern area as the Sulu area. The extensive quartz eclogite unit is not recognised in the Sulu area, but the Haiyangsuo area (Fig. 3) is interpreted to be an equivalent to the quartz eclogite unit by Ye et al. (1999). The lower grade schist outcropping around Lianyuguang, located in the southernmost area of the Peninsula, is considered to be an epidote blueschist facies unit (e.g. Faure et al., 2001).

The spatial extent of the UHP terrains and the position of the suture boundary between the Sino-Korean and the Yangtze cratons are still under debate in spite of the accumulation of new data. In the Dabie Shan area, Hacker et al. (1995) have proposed the Xiaotian-Mozitang Fault (Fig. 2), which bounds the Foziling and Luzhenguang Groups to the north and the Northern Orthogneiss unit and the amphibolite-granulite unit to the south. The latter is almost equivalent to the North Dabie Complex of Xu et al. (2001) or the gneiss or mylonitised migmatite zone of Faure et al. (2003) (Fig. 2). Zhang et al. (1996) have placed the suture boundary along the fault between the Northern Orthogneiss unit and the UHP eclogite unit, mainly because the UHP/HP rocks had not been found in the Northern Orthogneiss unit at that time. However, the recent finding of eclogitic xenoliths in Cretaceous granitoid rocks in the amphibolite-granulite unit (localities are shown as × in Fig. 2; Faure et al., 2003) and of eclogites and eclogitic rocks in the ultramafic belt in northern Dabie Mountains by Xu et al. (2001) suggest that the suture boundary should be the northern margin of the amphibolite-granulite unit, i.e., the Xiaotian-Mozitang fault (Xu et al., 2001) or a fault to the north of the Foziling Group (Hacker et al, 1998; Faure et al, 2003).

In the Shandong Peninsula, the suture boundary between the Sino-Korean craton and the Yangtze craton is placed around the Yantai-Qingdao-Wulian (YQW) Fault (e.g. Wallis et al., 1997). Zhai et al. (2000) slightly modified the position of the suture boundary around the northern part of the YQW Fault. They proposed a new tectonic zone, Kunyushan boundary complex, bounded by the Muping Fault (northern part of YQW Fault) to the west and its sub-parallel branch fault (Mishan Fault) to the east. On the other hand, Faure et al. (2001) proposed that the suture boundary is located to the north of the Shandong Peninsula, mainly based on the same deformation style during the exhumation stage throughout the Peninsula, the lack of oceanic basin rocks around the proposed suture (i.e., the YQW fault), and the similarity of exhumation paths of granulites in the both sides of YQW Fault. From the petrological point of view, lack of late Proterozoic orthogneiss with ages of 700-800 Ma and eclogite in the northwestern area of the Shandong Peninsula do not support the idea of Faure et al. (2001).

Reconstruction of pre-HP/UHP stage geology

The HP/UHP units in the Hong’an-Dabie Shan area and the Sulu area mainly consist of felsic gneiss with intercalation of eclogite, garnet pyroxenite, garnet peridotite, marble, jadeite-quartzite, and metapelite. UHP evidence, i.e., coesite, its pseudomorphs, low-Al Opx etc., is found mainly from eclogite and garnet peridotite (e.g. Okay et al., 1989; Wang et al., 1989; Hirajima et al., 1990; Yang et al., 1993). Inclusions of coesite and its pseudomorphs are also found from marble (e.g. Wang & Liou, 1991), felsic gneiss, phengite schist (Wang et al., 1992) jadeite quartzite (Cong et al., 1995; Su et al., 1996; Liou et al., 1997) and felsic whiteschist (Rolfo et al., 2000). However, the felsic gneiss is mainly composed of amphibolite facies mineral assemblages and most of them have no trace of UHP metamorphism. Such an occurrence of the UHP rocks caused an “in situvs. “exotic” argument even in the area in question.

The reconstruction of the pre-UHP geological relationship between the UHP rocks and surrounding rocks is an important job for the geologist to settle this longterm issue. The UHP unit in the Dora-Maira, Brossasco-Isasca Unit, is one of the best examples suggesting the “in situ” origin of UHP rocks from the geological point of view, as the pre-Alpine geology is well reconstructed and various types of the constituent rocks, e.g. metapelite, eclogite, marble, metagranite and whiteschist contain various kind of UHP evidence (e.g. coesite, its pseudomorphs, pure pyrope in the felsic rocks, jadeite-kyanite assemblage after paragonite etc.; Chopin et al., 1991; Compagnoni et al., 1995; Schertl et al., 1991; see also Compagnoni & Rolfo, 2003, on the western Alps in this volume).

The Hong’an-Dabie Shan-Sulu area widely suffered later stage extensive deformations mainly under the amphibolite facies conditions (e.g. Wallis et al., 1997; Faure et al., 2003), which pervasively masked pre-UHP geological relationship between the UHP rocks and the surrounding felsic gneiss. However, the coherency of eclogite-bearing layers is better mapped in the Dabie Shan area than in the Sulu area.

Wang et al. (1990) reported the regional scale coherency of the coesite eclogite-bearing layers derived from the supracrustal metasedimentary sequence, the Chenjiahe Formation, in the coesite eclogite unit of the Dabie Shan area. The Chenjiahe Formation consists of carbonate-bearing biotite or hornblende gneisses with blocks of eclogite, marble, talc schist, amphibolite, pyroxenite and tremolite schist. Although the Chenjiahe Formation itself occurs as a discontinuous belt, Wang et al. (1990) depicted its continuity more than 40 km around Changpu-Wumiao-Shuanghe in the northern part of the coesite eclogite unit and around Shima in the southern part of the unit in Figure 2 of their paper (reconstructed in Fig. 4). Compagnoni et al. (2001) reconfirmed its coherency in the northern part of the coesite eclogite unit and reported a detailed geologic map in the relevant area. They concluded that Changpu-Pailou Unit, characterised by the close association of paragneiss, jadeite quartz granofels, marble, and eclogite, formed a NW-SE trending narrow belt about 1-2 km wide and 40 km long, is derived from a coherent supracrustal metasedimentary sequence which underwent UHP metamorphism. This suggests that the large coherent slices of the continental crust can subduct to the depths deeper than 100 km and be exhumed to the surface maintaining the pre-UHP stage geology. This is one of the concrete evidences of the “in situ” origin of UHP rocks.

Fig. 4.

The equilibrium temperature map in central and southern Dabie Shan. The tectonic boundary follows Carswell et al. (1997) and the distribution of Chenjiahe Formation follows Wang et al. (1990). Po and Pt: Paragonite-bearing eclogite reported by Okay (1993, 1995) and Tabata et al. (1998a), respectively.

Fig. 4.

The equilibrium temperature map in central and southern Dabie Shan. The tectonic boundary follows Carswell et al. (1997) and the distribution of Chenjiahe Formation follows Wang et al. (1990). Po and Pt: Paragonite-bearing eclogite reported by Okay (1993, 1995) and Tabata et al. (1998a), respectively.

In Shuanghe of the Dabie Shan, Cong et al. (1995) succeeded to reconstruct the geology of UHP metamorphic slab over an area of about 1 km2. The UHP metamorphic slab is composed of the compositional layering of the following rock types (Fig. 5):

Fig. 5.

Geological map of the Shuanghe UHP metamorphic slab and its country rocks (after Cong et al., 1995).

Fig. 5.

Geological map of the Shuanghe UHP metamorphic slab and its country rocks (after Cong et al., 1995).

  • 1.

    grey-green massive eclogite,

  • 2.

    dark green foliated and retrograded eclogite,

  • 3.

    epidote two-mica schist,

  • 4.

    garnet-biotite gneiss with minor epidote-mica schist,

  • 5.

    marble with or without eclogite nodules or boudins,

  • 6.

    dark grey jadeite quartzite and

  • 7.

    amphibolite.

They found coesite and its pseudomorphs in garnet in eclogites, which are distributed throughout the whole metamorphic slab and concluded that the metamorphic slab itself suffered UHP metamorphism. However, they stated that the UHP metamorphic slab was tectonically juxtaposed with the country granitic gneiss at high crustal levels later in the tectonometamorphic cycle of Dabie Orogen, because no UHP evidence was found from the surrounding granitic gneiss and the regional structure in the UHP metamorphic slab is discontinuous to that of the granitic gneiss. Liou et al. (1997) found coesite and its pseudomorphs from jadeite and garnet in the jadeite quartzite from the Shuanghe UHP metamorphic slab, and deduced that the country granitic gneiss might have also suffered UHP metamorphism because systematic disposition and variation of metamorphic grade is observed in the Dabie Shan area, i.e., the UHP terrane to the north and the HP terrane to the south, although no UHP evidence was found from the granitic gneiss itself. The Hefei and Turin group is now re-evaluating the geological relationship between the Shuanghe UHP metamorphic slab and the country granitic gneiss. The reader is referred for the new interpretation to their forthcoming paper (R. Compagnoni and F. Rolfo, pers. commun.).

Even though UHP data has been accumulated from many eclogites, the question whether the country granitic gneiss suffered UHP metamorphism along with the enclosed eclogite or not still remains. Tabata et al. (1998b) gave an answer to this question from the extensive study of inclusions in zircon in the country gneiss of the UHP unit of the Dabie Shan. They extracted zircon grains from the orthogneiss that shows amphibolite facies mineral assemblage in the matrix, and confirmed the presence of tiny coesite and jadeite inclusions in zircon using Raman spectroscopy from several localities of the UHP unit of the Dabie Shan area. Therefore they concluded that the whole UHP unit of the Dabie Shan area subducted to the mantle depths. Further extensive studies on mineral inclusions in zircon were carried out both in the Dabie Shan and the Sulu areas (e.g. Ye et al., 2000b; Liu et al., 2001; Liu et al., 2002). They succeeded to confirm the UHP/HP evidence, such as inclusions of coesite and omphacite in zircon, from country granitic and orthogneisses. These data suggest that a large portion of the country gneiss suffered the UHP metamorphism in the relevant area.

Carswell et al. (2000) re-evaluated the P–T conditions at maximum pressure and maximum temperature stages of the country orthogneiss hosting UHP eclogite in the Dabie Shan. The studied orthogneiss mainly consists of garnet with XMn = 0.18–0.45, phengite with Si = 3.20–3.35 p.f.u., zoned epidote with Ps ([Fe3+/(Al + Fe3+)]·100) = 38–97, biotite, titanite, two feldspars and quartz, suggesting a typical assemblage of the amphibolite facies. However, certain orthogneiss samples preserve garnet with XCa up to 0.50, rutile inclusions within titanite or epidote and relict phengite inclusions with Si contents up to 3.49 p.f.u., overlapping with the highest value (3.49–3.62) recorded for phengite in samples of undoubted UHP schist. Further mineral composition features, such as A site deficiencies in the highest-Si phengite, negative correlation of Fe/Mg ratio and Si content of phengite, Na in garnet linked to Y + Yb substitution (e.g. Enami et al., 1995) and AlFTi−1O−1 substitution in titanite (e.g. Enami et al., 1993a), are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated UHP schist and eclogite. The adoption of garnet–phengite and garnet–biotite Fe–Mg exchange thermometry and the 5 rutile + 3 grossular + 2 SiO2 + H2O = 5 titanite + 2 zoisite equilibrium barometry between the inclusion and the matrix phases of the orthogneiss. They also succeeded to show that inclusion phases in some orthogneisses gave UHP conditions at peak pressure stage (their Figs. 16 & 17). Then, Carswell et al. (2000) concluded that the orthogneiss may indeed have followed a common subduction related clockwise P–T path with the UHP paragneisses and eclogites, through conditions of ca. 690–715 °C, 3.6 GPa at Pmax to ca. 710–755 °C, 1.8 GPa at Tmax, to extensive recrystallisation and re-equilibration of these ductile orthogneisses at ca. 400–450 °C and 0.6 GPa. Based on these data, Carswell et al. (2000) emphasised that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these Dabie Shan orthogneisses with undoubted UHP lithologies. In their paper, the authors re-evaluate the equilibrium compositional pairs among omphacite, garnet and phengite at Pmax and Tmax stages, mainly in order to depict the clockwise P–T path attained from the thermal modelling of the continental collision belt (e.g. England & Richardson, 1977).

In the Sulu area, the occurrence of paraschist, jadeite quartzite and marble are limited to a narrow area (e.g. at Donghai by Zhang et al., 1995a; at Rongcheng by Kato et al., 1997; at Yangzhuang by Ishiwatari et al., 1992 and Nagasaki & Enami, 1998; see Fig. 3) and the several tens of kilometres scale coherency of the supracrustal rocks has not been identified yet. However, the geology of the pre-UHP igneous complex was revealed at Yangkou in the central part of the Sulu area by Hirajima et al. (1993) and Wallis et al. (1997). The Yangkou igneous complex, comprising several hundred square meters, is strongly and heterogeneously deformed at the margin but the original gabbroic and granitic textures are still preserved in the core of the complex, where no extensive syn- and post-UHP deformations were present (Fig. 6). Geochemistry (Ishiwatari et al., 1992; Chen et al., 2002) and intrusion relationships between the basic and acidic rocks suggest that the unit represents a cogenetic magmatic suite, originated by the differentiation of a matic parental magma. The parental magma was derived from the melting of an enriched mantle, and was emplaced into crustal levels during continental extension at ca. 700-800 Ma (Chen et al., 2002). The similarity of zircon SHRIMP dating (ca. 742-756 Ma, Hirajima & Fanning, 1999) extracted from the basic rock, now coesite-bearing eclogite, and the acidic rock also supports the single igneous complex origin of this body, which could have formed in the Yangtze craton. The meta-granitoid still preserves the igneous shape of K-feldspar, quartz, plagioclase, clinopyroxene, orthopyroxene and biotite. However, igneous quartz domains are now completely recrytallised to fine-grained polygonal quartz aggregates, plagioclase to the aggregate of zoisite, kyanite and albite, clinopyroxene to diopside-to-salite in the core and omphacite at the margin, and the coronitic garnet developed between biotite and other minerals. These characters are almost identical to the UHP metagranitoid in Dora-Maira massif (cf. Biino & Compagnoni, 1991; Hirajima et al., 1993). With the development of the post-UHP deformations, the UHP metagranitoid was easily transformed to the streaky gneiss that forms the deformed margin of the complex. In the streaky gneiss, the original igneous texture and most of the UHP evidence was completely destroyed. The streaky gneiss is composed of fine-grained quartz, plagioclase, K-feldspar, biotite, epidote and titanite. Rutile surrounded by titanite and a tiny Ca-rich garnet in the matrix of the streaky gneiss are scarce relics of former (U)HP metamorphism, as suggested by Carswell et al. (2000) in the Dabie Shan.

Fig. 6.

Detailed geologic map of the Yangkou UHP metamorphic complex and surrounding Sulu gneiss, mainly following Wallis et al. (1997).

Fig. 6.

Detailed geologic map of the Yangkou UHP metamorphic complex and surrounding Sulu gneiss, mainly following Wallis et al. (1997).

The Yangkou UHP complex is surrounded by the Sulu orthogneiss, which is characterised by monotonous foliation and has a typical amphibolite facies mineral assemblage without distinctive UHP evidence. However, relic coesite was found from the core of the amphibolite layer which is intercalated with the Sulu orthogneiss and is about 50 m apart from the Yangkou UHP complex (Fig. 6). Temperature estimated using garnet-clinopyroxene geothermometer (Powell, 1985) for the eclogite in the Yangkou UHP complex varies from 600 to 900 °C at 3.0 Gpa, with a strong positive correlation to the Xjdcontent of clinopyroxene, which ranges from Xjd = 0.45 to 0.75 (Fig. 14a). The eclogite in the amphibolite layer contains clinopyroxene with Xjd = 0.45-0.55. Comparing the estimated temperatures derived from the eclogite with similar Xjd’s of clinopyroxene in the Yangkou UHP complex, similar temperatures (600-650 °C at 3.0 GPa for Xjd= 0.45-0.55) are obtained from both of them (Hirajima, 1996). More detailed discussion on the P–T estimation in this out crop will be described later. SHRIMP U-Pb zircon ages extracted from the Sulu orthogneiss show 235±16 Ma and 801 ± 45 Ma lower and upper intercept ages, respectively (Hirajima, unpublished data). These data suggest that the Yangkou complex and its neighbouring area probably suffered UHP metamorphism as a whole, and this outcrop represents one of the best examples showing that deformation and accompanied fluid infiltration at low-pressure conditions pervasively erased the precursor UHP evidence without significant heating (e.g. Hirajima, 1998).

Review of the equilibrium temperature of representative UHP rocks at peak stage

The systematic disposition and variation of metamorphic grade (e.g. Liou et al., 1997) and of the equilibrium temperature of eclogite at peak pressure conditions (e.g. Krogh, 1977) are the basic information to determine whether the relevant area suffered the regional eclogite facies metamorphism or not. The northward increase of the metamorphic grade, i.e., from the blueschist unit to the coesite eclogite unit, is established in the Hong’an-Dabie Shan area (Fig. 2), but such kind of metamorphic polarity is not clear in the Sulu area, because most of the Sulu area belongs to the coesite eclogite grade. In the early 1990’s, Wang et al. (1992) reported that the temperature and pressure of the eclogite systematically decrease from about 770 °C of the coesite eclogite in the north to 580 °C of kyanite-quartz eclogite in the south of the southern Dabie Shan terrane, and suggested that the continental crust of the southern Dabie Shan terrane has been subjected to a regional ultrahigh pressure metamorphism as part of a north-dipping subduction zone formed between the Sino-Korean and Yangtze cratons. Enami et al. (1993c) suggested that the equilibrium temperature of the UHP eclogite at the peak gradually decreases from the Sulu area to the Dabie Shan area. If the systematic disposition of the peak eclogite-forming conditions was ascertained, it is a great evidence of the “in situ” model.

Some coesite eclogites in the Dabie Shan–Sulu area are closely associated with garnet peridotites, most of which recorded UHP conditions (e.g. 4.0 to 6.0 GPa or more, e.g. Yang et al., 1993) in their development history. The concordance or the discordance of P–T history between the garnet peridotite and the associated eclogite also gave important information for the development history of root zone tectonics below the continent-continent collision zone and for considering the “in situvs. “exotic” issue. In this section we compile the P–T histories of the garnet peridotite and other UHP rocks and then discuss the equilibrium temperatures and pressures of the eclogite.

P–T history of garnet peridotite and associated UHP minerals

Garnet peridotites mainly occur in two metamorphosed mafic-ultramafic complexes at Maowu and Bixiling in the coesite eclogite unit of the Dabie Shan area (e.g. Medaris, 2000; locations are marked in Fig. 4). Field evidence, mineralogical and geochemical data (Okay, 1994; Zhang & Liou, 1994; Zhang et al., 1994; Zhang et al., 1995b; Cong et al., 1996; Liou & Zhang, 1998; Zhang et al., 2000a; Jahn et al., 2001) suggest that these complexes were emplaced into quartzofeldspathic gneisses prior to Triassic UHP metamorphism and that they originated as low-pressure crystal cumulates.

The Maowu mafic-ultramafic complex is a small body (250 × 100 m2) and exhibits clear magma chamber processes, e.g. characterised by three apparent rhythmic layering (e.g. Jahn et al., 2001). The Maowu complex consists of layers, lenses and pods of garnet orthopyroxenite, garnet clinopyroxenite, harzburgite, eclogite and omphacitite, which are intercalated on a scale of 5 cm to 1.6 m. In contrast to Bixiling, olivine is uncommon at Maowu, and the most abundant ultramafic rock type is orthopyroxenite (Fig. 7a). A zircon U-Pb age from eclogite and mineral Sm-Nd isochrons for a garnet websterite and a garnet clinopyroxenite in Maowu complex constrain the time of UHP metamorphism at 220-230 Ma (e.g. Rowley et al., 1997; Jahn et al., 2001). Pre-UHP mineral history was clearly depicted by Okay (1994) using inclusion phases in garnet. Okay (1994) observed low-pressure assemblages in garnets of a garnet orthopyroxenite as inclusions of chlorite, orthopyroxene, sapphirine, gedrite, hornblende, talc, rutile, phlogopite, corundum and zircon. He interpreted that these minerals were the result of Precambrian granulite facies metamorphism (740 ± 30 °C and 0.2-0.6 GPa) predating the Triassic UHP metamorphism. HP/UHP mineral assemblages are orthopyroxene (0.08 to 0.16 wt% Al2O3) + garnet + chlorite ± clinopyroxene ± Ti-clinohumite (0.8 to 1.3 wt% F) ± magnesite in orthopyroxenite, and olivine + orthopyroxene + garnet ± Ti-clinohumite (0.8 to 1.3 wt% F) ± magnesite ± chlorite in harzburgite. Liou & Zhang (1998) evaluated the UHP conditions of Maowu ultramafics as 650-780°C at 4.0 GPa mainly by Grt-Cpx (Ellis & Green, 1979; Powell, 1985: Krogh, 1988) and Grt-Opx (Harley, 1984a) geothermometers, and 4.5-6.5 GPa by Grt-Opx geobarometer (Brey & Köhler, 1990) (Fig. 8). Subsequent minor amphibolite facies overprint took place at P < 1.5 GPa and 650 °C.

Fig. 7.

Geological sketch map of (a) the Maowu complex (Okay, 1994) and (b) the Bixiling complex (Zhang et al., 1995b).

Fig. 7.

Geological sketch map of (a) the Maowu complex (Okay, 1994) and (b) the Bixiling complex (Zhang et al., 1995b).

Fig. 8.

P–T conditions of ganet peridotite and eclogite in the Maowu and Bixiling complexes in the Dabie Shan area. Data of the Maowu complex are from Okay (1994) and Liou & Zhang (1998), and of the Bixiling complex from Carswell et al. (1997) and Zhang et al. (1995b).

Fig. 8.

P–T conditions of ganet peridotite and eclogite in the Maowu and Bixiling complexes in the Dabie Shan area. Data of the Maowu complex are from Okay (1994) and Liou & Zhang (1998), and of the Bixiling complex from Carswell et al. (1997) and Zhang et al. (1995b).

The Bixiling complex is a 1.5 km2 tectonic block within biotite gneiss and consists mostly of layered eclogite that includes about 20 lenses of ultramafic rocks, measuring from 50 to 300 m in length and from 5 to 50 m in width (Fig. 7b). The ultramafic rocks are garnet lherzolite, garnet wehrlite and garnet websterite, which contain HP/UHP mineral assemblages of olivine + orthopyroxene (0.10 to 0.22 wt% Al2O3) + clinopyroxene + garnet + ilmenite (after Ti-clinohumite), and orthopyroxene + clinopyroxene + garnet + magnesite + Ti-clinohumite (0.05 to 0.2 wt% F). Both eclogites and meta-ultramafic rocks have undergone multistage metamorphism. Zhang et al. (1995b) evaluated the peak P–T conditions of the eclogite as an average of 630 °C (range of 540-725 °C) at 3.0 GPa by the Grt-Cpx geothermometer of Powell (1985) and Krogh (1988), using rim (most cases) and core (a few cases) compositions of adjacent minerals. Meta-ultramafic rocks showed P–T conditions of 700-800 °C and 4.7-6.7 GPa by the two-pyroxene geothermometer (Wood & Banno, 1973), two Fe-Mg exchange thermometers (Opx-Grt of Lee & Ganguly, 1988 and Grt-Cpx of Powell, 1985) and the Grt-Opx geobarometer of Brey & Köhler (1990) using the rim compositions of adjacent minerals (Fig. 8). Carswell et al. (1997) estimated the peak P–T conditions for the Bixiling eclogite as 3.3-3.8 GPa and 830-870 °C (see in detail in the next section). There is a significant disagreement between two research groups on the temperature estimation at peak pressure stage of the eclogite as well as on the peak pressure of the eclogite and the meta-ultramafic rocks. The pressures estimated by the Grt-Opx barometer generally show relatively high values compared with those estimated by other barometers (e.g. garnet-clinopyroxene-phengite barometer; Waters & Martin, 1993) for UHP rocks. This can be due to one or a combination of the following reasons; (i) analytical error because of extremely low Al content of orthopyroxene in UHP rocks, (ii) selection of calibrations on Grt–Opx barometer also cause large variation in estimated pressures (e.g. Hiramatsu et al., 1995), (iii) difficulty in judging the equilibrium compositional pair between garnet and orthopyroxene (e.g. Cuthbert et al., 2000), for example, incomplete Al diffusion during orthopyroxene formation after olivine may preserve low Al composition of orthopyroxene that was not in equilibrium with garnet (e.g. Mørk, 1985).

In the Sulu region, garnet peridotite and pyroxenites are found from seven areas: Weihai, Rongcheng (locality of Chijiadian), Yangkou, Rizhao (locality of Hujialing), Junan, Yangshuang (locality of Zhoubin) and Donghai (localities of Zhimafang, Mengzhong and Jiangshuang) from north to south (Fig. 3; e.g. Yang et al., 1993; Zhang et al., 1994; Hiramatsu & Hirajima, 1995; Hiramatsu et al., 1995; Cong et al., 1996; Yang & Jahn, 2000; Yoshida et al., 2001). The ultramafic bodies generally have small dimensions but locally reach kilometre scale at Hujialing (e.g. Yang, 1991; Hiramatsu & Hirajima, 1995). They have concordant to discordant contacts with surrounding quartzofeldspathic gneisses. The garnet peridotites in the Sulu area also show the multiple P–T equilibria identified from the chemical variations along with changes in microstructure of principal constituent minerals (e.g. the porphyroblasts and the matrix phases) and the inclusion phases in them. The UHP stage mineral assemblage is characterised by the occurrence of garnet and orthopyroxene (0.11 to 0.30 wt% Al2O3) along with olivine + clinopyroxene ± phlogopite. The extremely low Al2O3 content in Opx gave pressures of diamond stability ranging from 4.0 to 7.0 GPa at 700-1000 °C (see the compilation of Medaris, 2000). Low P inclusion minerals in garnet are found from several localities in the Sulu area; e.g. chromite, chlorite, hornblende, Na-gedrite, Na-phlogopite, talc, spinel and pyrite at Zhimafang, Donghai County (Yang & Jahn, 2000), spinel, amphibole and Al-rich clinopyroxene at Hujialing (Yang, 1991; Hiramatsu & Hirajima, 1995). The existence of these low P inclusion minerals suggests many of the garnet peridotites in the Sulu area subducted during the Triassic continental collision stage.

The mineral assemblage associated with garnet and low-Al orthopyroxene in the peridotite and pyroxenite in the UHP region is generally considered to represent a UHP stage chemical equilibrium. Yang & Jahn (2000), recently, proposed two UHP equilibrium conditions for garnet-bearing assemblages for the garnet peridotite at Zhimafang; higher temperature and pressure stage (1000 °C and > 5.1 GPa) defined by the Mg-rich core of porphyroblastic garnet and orthopyroxene, and lower temperature and pressure stage (760 °C and 4.2 GPa) defined by the matrix minerals included in the rims of porphyroblasts (Fig. 9a). The second UHP stage is interpreted as a result of metasomatism of the peridotites by a SiO2-rich melt at UHP conditions. Yang & Jahn (2000) proposed an isothermal decompression path or decompression with a slight temperature decrease path from the 2nd UHP stage to the lower crust (Fig. 9a). Yoshida et al. (2001) also identified two equilibrium stages for garnet-bearing assemblages for the Yangkou garnet peridotite based on the chemical variations along with changes in microstructure of principal constituent minerals: Stage I, a primary garnet lherzolite stage represented by coarse-grained (a few mm size) porphyroclastic aluminous pyroxene + chromian spinel ± garnet, and Stage II, a UHP stage defined by fine-grained matrix phases (0.1-0.3 mm size) of garnet + extremely low-Al orthopyroxene + high-Na clinopyroxene + chromite, and a subsequent Stage III, a medium pressure stage defined by fine-grained mineral aggregates (< 0.1-0.2 mm size) mainly composed of aluminous spinel + high-Al orthopyroxene in the matrix, and Stage IV, an amphibolite to greenschist facies stage defined by poikiloblastic amphibole. Orthopyroxene-clinopyroxene thermometry (Bertrand & Mercier, 1985) and an empirical spinel barometer (O'Neill, 1981) give temperatures of around 820-830 °C and pressures of 2.6 GPa for porphyroclasts of Stage I. Garnet-orthopyroxene (Harley, 1984a,b), garnet-clinopyroxene (Powell, 1985) and empirical spinel (O’Neill, 1981) geothermobarometers give relatively uniform P–T conditions for the matrix garnet-orthopyroxene-clinopyroxene-chromite assemblage of Stage II (~ 730-760 °C and 3.6-4.1 GPa). Aluminous spinel-olivine (Fabriès, 1979) pairs in the aggregates give ca. 650-700 °C at less than 1.5 GPa for Stage III. The P–T conditions of the first garnet stable stage of Yangkou garnet peridotite is quite different from that of Zhimafang complex, but the P–T conditions of the second garnet stable stage is quite similar in both of them. The peak P–T conditions of the Yangkou eclogite, reevaluated by the combination of garnet-clinopyroxene geothermo-meter and garnet-omphacite-kyanite-coesite geobarometer as shown in the next section (cf. Fig. 12), are almost identical to the P–T conditions of Stage II defined from the Yangkou garnet peridotite. Furthermore, both garnet peridotite bodies show a similar decompression path, an isothermal decompression or decompression with a slight temperature decrease. To produce an isothermal decompression path, the ascending UHP body requires either thermal isolation from (or even heating by) the wall rocks. To create such a situation, rapid exhumation and large volumes of ascending hot materials are necessary. Nakamura & Hirajima (2000) estimated that the size of the exhumed mass required to prevent the loss of heat to or addition of heat from the wall rock should be > 10 km on the basis of petrological study of Rongcheng eclogites and with an assumed exhumation rate of 20 mm/year. This result requires that the small Yangkou complex (see Fig. 6) and the Zhimafang peridotite body should have been exhumed together with associated UHP rocks and the surrounding country rock gneiss.

Fig. 9.

P–T paths of representative garnet peridotites in the Sulu area. (a) Zhimafang (Yang & Jahn, 2000), (b) Yangkou (Yoshida et al., 2001).

Fig. 9.

P–T paths of representative garnet peridotites in the Sulu area. (a) Zhimafang (Yang & Jahn, 2000), (b) Yangkou (Yoshida et al., 2001).

Recent transmission electron microscopy works (e.g. Su et al., 2001; Zhang et al., 2002) reveal that a certain diopside and orthoenstatite from garnet pyroxenites in the Dabie Shan-Sulu area contain clinoenstatite lamellae, which is interpreted to have formed either by inversion from orthoenstatite or by the transformation from high pressure C2/c clinoenstatite/clinopyroxene during decompression. The latter interpretation may suggest that the garnet pyroxenites containing clinoenstatite lamellae were once equilibrated under a significantly higher pressure (> 7–8 GPa; e.g. Ulmer & Stalder, 2001) than that evaluated from the conventional geobarometers depending on the Al content in orthopyroxene. Such high pressure demands that the coexisting garnet in the garnet pyroxenites be majoritic in composition (e.g. Akaogi & Akimoto, 1977; Irifune, 1987). Most of the reported compositions of garnet from the garnet-bearing ultramafics, however, have a stoichiometric formula with R3+/R4+ cation ratio around ⅔, although Ye et al. (2000a) reported “subsilicic calculated original garnet composition”, derived from the compositions of the host garnet from an eclogite at Yangkou, and claimed a maximum pressure of Yangkou eclogite to be greater than 7 GPa. However, Yoshida et al. (2001) have not observed similar inclusion-rich porphyroclastic garnet in either eclogite or ultramafic rocks at Yangkou.

After the first report on the finding of diamond from the Dabie Shan metamorphic rocks by Xu et al. (1992), the identification of the peak pressure for the Dabie Shan metamorphic rocks is one of the hot targets for geologists. As compiled in the next section, most of the peak P–T conditions estimated from the mineralogical data in eclogites fall in the graphite stability field (Table 1, 3.0–3.8 GPa in average). To explain the “lower” peak pressure than the diamond stability field, Okay (1993) considered that some assemblages of the hot eclogite terrain suffered re-equilibration during the uplift. On the other hand, the very low Al content of orthopyroxene coexisting with garnet, olivine and clinopyroxene in peridotites gave diamond stability conditions at peak pressure stage as described above (4.0–7.0 GPa). These data and the finding of C2/c clinoenstatite lamellae in host diopside and orthoenstatite by Su et al. (2001) and Zhang et al. (2002) may suggest that some garnet peridotite equilibrated under the diamond stability field once in their P–T history. The intensive search for mineral inclusions in garnet and zircon from both UHP eclogites and country gneisses was attempted by Liou & Zhang (2001) but they failed to find a positive identification of diamond. They, however, explained the lack of the occurrence of diamond in the Dabie Shan–Sulu area due to the lack or low content of C–H–O fluid with appropriate XCO2 and fO2 conditions, as such fluids essentially control the precipitation of microdiamond in gneissic rocks and dolomitic marbles, as suggested by the case studies in Kokchetav and Erzgebirge.

Peak P–T conditions of eclogite

Many garnet peridotites in the Dabie Shan–Sulu area recorded UHP equilibrium conditions during their development history as mentioned above. However, their occurrence is limited at about ten localities in the huge Dabie Shan–Sulu area (Fig. 1), and their outcrop density, lower than that of eclogite, is not convenient to discuss the systematic disposition and variation of metamorphic grade at peak pressure stage. However, the eclogite, less common than the country orthogneiss, is distributed through the Dabie Shan–Sulu area and so the comparison of peak P–T conditions of the eclogites will give fundamental information defining whether the systematic disposition and/or variation of metamorphic grade at peak pressure stage exist in the relevant area or not.

Table 1.

Re-evaluated equilibrium temperatures for the coesite/quartz eclogite in the Dabie Shan area

Carswell et al. (1997)Okay (1993, 1995)Tabata et al. (1998a)
LocalityT(°C, P85)
Xgrs<0.35
T(°C, K88)
Xgrs>0.35
P(kb)*Rock No.T(°C, P85)
Xgrs < 0.35
T(°C, K88)
Xgrs > 0.35
NB:Rock No.T(°C, P85)
Cal-free
T(°C, K88)
Cal-bearing
NB:
Changpu 218690 (at l9kb)PgChangpu west
Changpu 223740Cp407737
409631Pg
303829
Bixiling87033577L720C
83038
Guanjialing87037Wumiao west
308589C
309595
311590C
312764Cal
Wumiao eastWumiao east
229780336629
233-328589
230760c302616Pg
575690301639Pg
290563C
258592
248789
Shuanghe68030Shuanghe 251730
74031Shuanghe 250750c
Dongfeng73030Dongfeng east 585690 (at 19kb)Pg-CpDongfeng east 235569
Shima88036Shima
84534224825C-Cal
80040223651C-Cal
68034221744Cal
average801Shima south 568-Cp172639C-Pg-Cal
Huangzhen60022Huangzhen east
61023272620
Carswell et al. (1997)Okay (1993, 1995)Tabata et al. (1998a)
LocalityT(°C, P85)
Xgrs<0.35
T(°C, K88)
Xgrs>0.35
P(kb)*Rock No.T(°C, P85)
Xgrs < 0.35
T(°C, K88)
Xgrs > 0.35
NB:Rock No.T(°C, P85)
Cal-free
T(°C, K88)
Cal-bearing
NB:
Changpu 218690 (at l9kb)PgChangpu west
Changpu 223740Cp407737
409631Pg
303829
Bixiling87033577L720C
83038
Guanjialing87037Wumiao west
308589C
309595
311590C
312764Cal
Wumiao eastWumiao east
229780336629
233-328589
230760c302616Pg
575690301639Pg
290563C
258592
248789
Shuanghe68030Shuanghe 251730
74031Shuanghe 250750c
Dongfeng73030Dongfeng east 585690 (at 19kb)Pg-CpDongfeng east 235569
Shima88036Shima
84534224825C-Cal
80040223651C-Cal
68034221744Cal
average801Shima south 568-Cp172639C-Pg-Cal
Huangzhen60022Huangzhen east
61023272620

P [kbar]*: estimated by the combination of Grt-Cpx thermometry and Phn-Grt-Cpx barometry of Waters & Martin (1993)

P85: Grt-Cpx geothermometer of Powell (1985), K88: Grt-Cpx geothermometer of Krogh (1988); C: coesite, Cp: quartz pseudomorphs after coesite, Pg: paragonite in the matrix, Cal: carbonate.

The temperature conditions of the eclogites are commonly obtained by several formulations of Grt-Cpx geothermometer and there are systematic discrepancies among the estimated temperatures obtained from different formulations of the Grt-Cpx geothermometer. In the following sections we will add some statement for the Grt-Cpx geothermometer and geobarometers that can be applied to eclogites.

The character of Grt-Cpx geothermometer

Formulations of Ellis & Green (1979), Powell (1985) and Krogh (1988) for the garnet-clinopyroxene geothermometer are favoured and frequently used especially for estimating the equilibrium temperatures of eclogite. However, many formulations have been carried out and proposed for the garnet-clinopyroxene geothermometer (cf. Krogh Ravna & Paquin, 2003 in this volume). The above three formulations are mainly based on the same experimental data (Råheim & Green, 1974; Mori & Green, 1978; Ellis & Green, 1979), and hence these formulations yield more or less similar temperatures. The synthetic experiments used in these formulations are not of the reversal type, and hence reversal experiments for Fe-Mg exchange reaction between garnet and clinopyroxene were carried out by Pattison & Newton (1989). Green & Adam (1991) performed synthetic experiments and tested the reliability of the methods of Ellis & Green (1979) and Pattison & Newton (1989), and they suggested that the method of Pattison & Newton (1989) yielded significantly lower temperatures than the experimental temperatures of Green & Adam (1991). At least in high pressure conditions (3.0 GPa), the Ellis & Green (1979) formulation yielded moderate temperatures compared to the experiments by Green & Adam (1991). Furthermore, Perkins & Vielzeuf (1992) claimed that combination of garnet-olivine (Hackler & Wood, 1989) and olivine-clinopyroxene (Perkins & Vielzeuf, 1992) reversal experiments around 1.0 GPa gave larger KD for the garnet-clinopyroxene pair than Pattison & Newton’s (1989) data. Therefore, Berman et al. (1995) re-evaluated Pattison & Newton’s (1989) reversal experiments considering compositional variations in the run products and proposed a new formulation based on the reversal experiments. However, applications of Berman et al. (1995) to eclogite also yield significantly lower temperatures than experimental temperatures (Nakamura et al., 2001). Thus, formulations of Pattison & Newton (1989) and Berman et al. (1995) are not applicable at least to eclogite.

In the equilibrium experiments using natural fine-grained eclogite as starting materials (Nakamura et al., 2001), formulations of Ellis & Green (1979), Ganguly (1979), Powell (1985), Krogh (1988), Ganguly et al. (1996) and Krogh Ravna (2000) gave temperatures compatible with the experimental temperatures (1100-1200 °C). Ganguly (1979) carried out regression analysis of equilibrium experimental data (Wood, 1976) at high temperatures (1100-1400 °C) and extrapolated it to lower temperatures using thermochemical data, and Ganguly et al. (1996) revised the non-ideal mixing term of garnet. Krogh Ravna (2000) carried out regression analysis of total 311 experimental data and 49 data of natural Mn-rich assemblages and proposed an empirical formulation. These formulations show no significant divergence at high temperatures, but there is significant difference at low temperatures (< 1000 °C). For example, we compare following three formulations, Ganguly (1979), Powell (1985) and Krogh Ravna (2000) in temperature versus KD diagram (Fig. 10). Krogh Ravna (2000) yields slightly lower temperatures than Powell (1985) at low temperature conditions. On the other hand, Ganguly (1979) gives significantly higher temperatures than Powell (1985). To examine the reason why such a difference exists is beyond the scope of this study.

Fig. 10.

Comparison of three formulations (Ganguly, 1979; Powell, 1985; Krogh Ravna, 2000) for garnet-clinopyroxene thermometer. Relationships between temperature and distribution coefficient (KD) are shown at graphic and 3.0 GPa. For Krogh Ravna (2000), Mg number of garnet (Mg#Grt) is fixed as 0.30.

Fig. 10.

Comparison of three formulations (Ganguly, 1979; Powell, 1985; Krogh Ravna, 2000) for garnet-clinopyroxene thermometer. Relationships between temperature and distribution coefficient (KD) are shown at graphic and 3.0 GPa. For Krogh Ravna (2000), Mg number of garnet (Mg#Grt) is fixed as 0.30.

As three formulations of Ellis & Green (1979), Powell (1985) and Krogh (1988) are frequently used especially for estimating the equilibrium temperatures of eclogite, we show the systematic discrepancy in temperatures estimated by these three formulations. The systematic discrepancy is mainly caused by the different expression of the grossular component (XGrs) effect to the thermometry. For example, the application of Powell (1985) systematically gives lower temperature than that of Ellis & Green (1979) by about 20–30 °C (Fig. 11) through the wide range of KD and XGrs. The temperature obtained from Powell (1985), on the other hand, is systematically 5–30 °C higher than that obtained from Krogh (1988) for the eclogite with less calcic garnet (XGrs < 0.4), but Powell’s (1985) formulation gives a significantly higher temperature for the eclogite with calcic garnet (XGrs > 0.4); e.g. Powell (1985) gives 100 °C higher than Krogh (1988) for KD = 10.5 and XGrs = 0.55 (Fig. 11). Carswell et al. (1997) tested whether temperatures obtained from Powell (1985) or from Krogh (1988) are the most consistent with temperatures obtained by the garnet–phengite geothermometer (Green & Hellman, 1982) over the grossular range between 0.26 and 0.53 and concluded that Powell’s (1985) formulation yields significantly overestimated temperatures for samples containing the calcic garnet (XGrs > 0.35). We basically follow their suggestion; i.e., temperatures are estimated using Powell (1985) for the eclogite with XGrs < 0.35 and using Krogh (1988) for the eclogite with XGrs > 0.35.

Fig. 11.

Isotherms based on the alternative formulations of Ellis & Green (1979; EG(79)), Powell (1985; P(85)) and Krogh (1988; K(88)) in XGrs (= Ca/(Ca + Fe + Mg + Mn)) in garnet versus KD (for Fe2+-Mg2+ partitioning between garnet and clinopyroxene) diagram. Inset data from Okay (1993, 1995). For further details see text.

Fig. 11.

Isotherms based on the alternative formulations of Ellis & Green (1979; EG(79)), Powell (1985; P(85)) and Krogh (1988; K(88)) in XGrs (= Ca/(Ca + Fe + Mg + Mn)) in garnet versus KD (for Fe2+-Mg2+ partitioning between garnet and clinopyroxene) diagram. Inset data from Okay (1993, 1995). For further details see text.

The geobarometry of eclogite

The pressure estimation of eclogite-stage equilibrium is rather difficult than the temperature estimation. The garnet–clinopyroxene–phengite barometer (Waters & Martin, 1993, 1996) is one of potential tools for defining pressures of eclogites, as about 40% of eclogites contain phengite in the Sulu area (Nakamura, 2003). We also estimate the peak pressure of the representative kyanite-bearing eclogites using a garnet–clinopyroxene– kyanite–coesite (or quartz) barometer, proposed by Nakamura & Banno (1997). We add some statement for the latter geobarometer.

The garnet–clinopyroxene–kyanite–coesite (or quartz) barometer is based on a reaction: pyrope + grossular + 2 coesite (or quartz) = 2 kyanite + 3 diopside. In this study, thermodynamic data set of Holland & Powell (1998) is used for this barometry. Activity calculations follow Nakamura & Banno (1997). Thermodynamic equilibrium equation for this reaction can be written as follows. 

formula
μi is chemical potential of phase component i and can be written as follows. 
formula
Gi is Gibbs free energy of phase component i, R is the gas constant (0.0083143 kJ/K mol), T is temperature (K), and ai is activity of phase component i. Following Holland & Powell (1998), Gt is calculated as follows: 
formula
where 
formula
In Table 5 of Holland & Powell (1998), terms of S and Smax must be multiplied by 10−3, and b and a° must be multiplied by 10−5. Following Nakamura & Banno (1997), activity of diopside (adi) can be calculated as follows: 
formula
where Xdi = Mg/(Fetotal + Mg + Al) and XCaa = Ca/(Na +Ca). XCaa is dependent on temperature, and the magnitude of XCaa should be independently determined using the following equation: 
formula

To calculate activity of diopside, two-step calculation is necessary in this model. Firstly, the degree of ordering graphic should be determined at each composition (XCa) and temperature with this equation. This equation cannot be rewritten as graphic so we have to look for the value of graphic to satisfy this equation while changing the value of graphic. For this calculation, graphic should be as follows: graphic and graphic In addition, three solutions of graphic are present in this equation when T < Tc (critical temperature at each composition). graphic always satisfies this equation, and so one of the other two solutions should be selected for activity calculation. Thus, we should determine the graphic value at several temperatures before activity calculation. Then, activities of pyrope and grossular components (aprp and agrs) are calculated as follows: 

formula
where Xprp = Mg/(Fe + Mn + Mg + Ca) and Xgrs = Ca/(Fe + Mn + Mg + Ca). Thus, we can draw an equilibrium P–T curve for the reaction pyrope + grossular + 2 coesite (or quartz) = 2 kyanite + 3 diopside. Combination of this P–T curve with the garnet–clinopyroxene thermometer gives P–T conditions at peak stage of the kyanite-bearing eclogite.

Compilation result of the Dabie Shan eclogite

We intended to compile the peak P–T conditions of the eclogite using the combination of the garnet–clinopyroxene geothermometer and the garnet–clinopyroxene–kyanite– coesite (or quartz) barometer. We adopted this combination in the case of the Sulu eclogites as described in the next section. However, the kyanite-bearing eclogite is scarce in the Dabie Shan area and we do not have original petrological data for eclogites in the Dabie Shan. Therefore, we compile and examine the peak P–T conditions in Dabie Shan eclogite from the literatures. The detail is mentioned below.

After the pioneering work of Wang et al. (1990; 1992) in the Dabie Shan, Okay (1993, 1995), Carswell et al. (1997) and Tabata et al. (1998a) carried out the systematic estimation of the peak eclogite-forming conditions combining of geothermometers (Grt–Cpx: Ellis & Green, 1979, EG79; Powell, 1985, P85; Krogh, 1988, K88, Grt–Phn: Green & Hellman, 1982) and geobarometers (e.g. celadonite + pyrope + grossular = muscovite + diopside reaction; Waters & Martin, 1993, zoisite/clinozoisite = grossular + kyanite + quartz/coesite + H2O; Okay, 1995). Our compiled results of their estimated peak equilibrium temperatures are shown in Table 1.

The equilibrium temperatures of Carswell et al. (1997) were calculated at pressures obtained by geobarometry of celadonite + pyrope + grossular = muscovite + diopside reaction (Waters & Martin, 1993). Other equilibrium temperatures in Table 1 were calculated at 3.0 GPa. The difference in pressure between the assumed 3.0 GPa and that obtained by Carswell et al. (1997) cause small differences in estimated temperatures (less than 20 °C), which is of little influence on discussing the thermal structure of the coesite eclogite unit.

Okay (1993, 1995) estimated the peak equilibrium temperatures by the Ellis & Green (1977) formulation at 3.0 GPa. We recalculated them by the Powell (1985) formulation for the eclogite with XGrs < 0.35 and the Krogh (1988) formulation for the eclogite with XGrs > 0.35, using the KD–XGrs relationship shown in Figure 7 of Okay (1993). When Okay (1993, 1995) reported multiple equilibrium temperatures for the same sample number, we report the average value for each sample. Tabata et al. (1998a) estimated the peak equilibrium temperatures for 19 eclogites by Ellis & Green (1979), Powell (1985) and Berman et al. (1995) at 3.0 GPa. According to the description in the text and Figure 11 of Tabata et al. (1998a), carbonate and calcic garnet with XGrs ranging from 0.36 to 0.41 in average seems to be contained in five eclogites and less calcic garnet with XGrs ranging from 0.15 to 0.33 in average to be in the remaining 14 eclogites. Therefore, in our Table 1 we show, following equilibrium temperatures reported by Tabata et al. (1998a), the equilibrium temperatures calculated with the Powell (1985) formulation for the 14 eclogites without carbonate and those calculated with the Krogh (1988) formulation for the 5 eclogites with carbonate.

Ferric/ferrous estimation from microprobe data is one of main factor to scatter the equilibrium temperatures. Generally, ferric/ferrous ratio of clinopyroxene is commonly estimated from one of following three methods: 1) based on four cations and the charge balance concentration, 2) Fe3+ = Na - (Altotal + Cr) and 3) total iron as Fe2+. Carswell et al. (1997) and Okay (1993) adopted the second method and Tabata et al. (1998a) used the first method. As far as we examined, the second method makes the least scattered value among the three methods and the first method generally makes the most scattered result, as all errors of the electron microprobe analysis were propagated to the estimation of the ferric ratio (e.g. Hirajima, 1996; Carswell et al., 1997).

Carswell et al. (1997) took special care in selecting the equilibrium composition pair of garnet and clinopyroxene for the thermometry, i.e., the most calcic garnet and the most jadeite-rich clinopyroxene. This is a reasonable pairing method for estimating the peak P-T conditions of eclogite, if we can regard that the peak pressure stage is coeval with the peak temperature stage in UHP eclogite. Carswell et al. (2000), however, slightly modified their pairing policy following the idea that the peak pressure stage predated the peak temperature stage based on the expected result obtained from thermal modelling under the continent-collision zone (e.g. England & Richardson, 1977), i.e., the jadeite-richest and Si-richest compositions in clinopyroxene and phengite, respectively, and the garnet composition with the maximum aprpa2grs for the peak pressure stage, and highest Fe/Mg ratios of omphacite and phengite and lowest Fe/Mg ratio of garnet for the peak temperature stage. It is almost impossible to identify the relevant phase compositions during the peak pressure and peak temperature stages from the literature, therefore we compile the data following the former idea. The pairing policy of Okay (1993) and Tabata et al. (1998a) is unclear. As Okay (1993) described that garnet and omphacite do not show any clear zoning in some eclogite, his estimated KD may reflect the peak P-T conditions. Based on the calculation method of KD, we regard the data of Carswell et al. (1997) and Okay (1993) as a comparable data set to discuss the peak P-T conditions in the Dabie Shan area.

Okay (1995) reported the occurrence of paragonite in textural equilibrium with garnet, omphacite and kyanite in the matrix of coesite-bearing eclogites and obtained the equilibrium conditions of 1.9 GPa and 710 ± 40 °C for the paragonite-omphacite-garnet association by the combination of Pg87-Jd48-Ky-Qtz isopleth and the Ellis & Green (1979) formulation, and concluded that the matrix minerals in the UHP eclogite have recrystallised during the early decompression stage and that they do not represent the peak UHP assemblages. To test whether his statement is valid or not is beyond the scope of this chapter. As the peak temperature of the paragonite-bearing eclogite (690 °C at 1.9 Gpa, recalculated by the Powell, 1985 formulation) is a bit lower than that of the coesite eclogite from which paragonite was not detected in the matrix (690-780 °C at 3.0 GPa, see column of Okay, 1993, 1995 in Table 1), we tentatively accept his conclusion, i.e., the equilibrium temperature obtained from eclogite with matrix paragonite represents a temperature condition at early decompression stage. Among the compiled data in Table 1, 2 samples of Okay (1993, 1995) and 4 samples of Tabata et al. (1998a) are in this case. Temperatures (620-640 °C at 3.0 GPa) obtained from eclogites with matrix paragonite in Tabata et al. (1998a), however, do not show significant difference from those of 11 eclogites with less calcic garnet (560-830 °C at 3.0 GPa). Among the temperatures of the 11 eclogites, some of them containing coesite, 8 samples are less than 630 °C. Recent synthetic experiments in basalt + H2O system by Schmidt & Poli (1998) indicate that lawsonite, instead of zoisite + kyanite + coesite assemblage, is a stable phase around 600-650 °C at 3.0-4.0 GPa and zoisite/epidote, paragonite and amphibole are stable at 1.5-3.0 GPa around 600-650 °C. The equilibrium temperatures reported by Tabata et al. (1998a) suggest that lawsonite is a stable phase under H2O saturated conditions at UHP stage, but they reported epidote and amphibole as coexisting phases with coesite. These data suggest that the modification of the peak compositions of garnet and clinopyroxene may have taken place during the early exhumation stage and/or the compositions used for the temperature estimation by Tabata et al. (1998a) do not represent equilibrium pairs at the peak stage. In the following discussion on the consideration of the peak P-T conditions of the Dabie eclogite, we regard 12 data of Carswell et al. (1997), 7 of Okay (1993, 1995) and 3 (* in Table 1) of Tabata et al. (1998a) compiled in Table 1 as plausible peak equilibrium temperatures. These data show:

  • 1

    . the quartz eclogites distributed around Huangzhen give 600-620 °C and 2.2-2.3 Gpa;

  • 2.

    the coesite eclogites at Shima give 680-880 °C (800 °C in average) and 3.4-4.0 GPa, at Dongfeng 730 °C and 3.0 GPa, at Shuanghe 680-750 °C (730 °C in average) and 3.0-3.1 GPa, at Wumiao 690-790 °C (755 °C in average) and 3.0 GPa, at Guanjialing 870 °C and 3.7 GPa, at Bixiling 720-870 °C (810 °C in average) and 3.3-3.8 GPa, and at Changpu 740-830 °C (770 °C in average) and 3.0 GPa in the order of the northward direction.

Okay (1993) and Carswell et al. (1997) concluded that the central Dabie eclogites were formed under “hot” and coesite-stable P-T conditions and the southern Dabie eclogites were formed under “cold” and quartz-stable P-T conditions. The coesite eclogite terrane was considered to be structurally overlain by the southern quartz eclogite terrane at a major dipping shear zone along which late orogenic extensional collapse appears to have eliminated at least 20 km of crustal section. Okay (1993) and Carswell et al. (1997) did not support the earlier idea of the regional P-T gradient marked by decreasing peak conditions of both P and T southwestwards by Wang et al. (1990, 1992). Other petrological data, e.g. the lack of coesite in the southern Dabie eclogites and the significant difference in garnet zoning pattern between both eclogite terranes, i.e., distinctive idioblastic, growth-zoned garnets containing abundant small single grains of quartz in the southern Dabie eclogites, and large garnet with homogeneous core and zoned rim in the central Dabie eclogites, support the conclusion of Okay (1993) and Carswell et al. (1997). In the coesite eclogite unit, the peak temperatures obtained around Shuanghe and Wumiao are a bit lower (20-80 °C) than those obtained in the northern (Bixiling and Changpu) and southern (Shima) parts. These data are concordant to the indication by Carswell et al. (1997), a southeastward trend of declining peak temperatures and pressures along the northern transect from Bixiling to the Shuanghe locality (Fig. 4).

The equilibrium temperatures obtained from multiple eclogites collected at one locality often scatter more than 100-200°C, even though there is no clear reason, as pointed out by Carswell et al. (1997) at the Shima locality. The number of the equilibrium temperatures obtained from the quartz eclogite terrane is not sufficient to statistically discuss whether there is a continuous P-T gradient between the quartz eclogite terrane and the coesite eclogite terrane or not. The preliminary pressure estimation by the garnet-clinopyroxene-phengite barometer using the database of Holland & Powell (1998) gave about 3.0 GPa for the phengite-bearing Huangzhen eclogite. Though we do not deny the conclusions of Okay (1993) and Carswell et al. (1997), the acquisition of further petrological data, especially for indicating the peak pressure, is necessary in order to strengthen their idea further.

Results from the Sulu eclogite

In this section, we estimated peak P-T conditions of eclogite from the Sulu area using mainly our own published and unpublished data and partly the literature data. We estimate peak P-T conditions for eclogites collected at the following localities: Qinglongshan and Chizhuang in Donghai County, Taohang in Zhucheng County, Yangkou in Qingdao County, and Chijiadian, Xianguling and Tengjiaji in Rongcheng County. We applied geothermobarometers that were mentioned in the previous section to these eclogites; i.e., the garnet-clinopyroxene thermometer (Powell, 1985 or Krogh, 1988), garnet-clinopyroxene-phengite barometry (Waters & Martin, 1996) and garnet-clinopyroxene-kyanite-coesite (or quartz) barometry. The studied samples have mineral assemblages of garnet + omphacite + kyanite + quartz accompanied by phengite, epidote group mineral or pale green amphibole. Chemical compositions used for P-T estimation are garnet composition richest in grossular component and omphacite composition richest in jadeite component in each sample or each layer in order to avoid effects of chemical modification during decompression and/or cooling stages. Such a manner of selection of chemical compositions was adopted also in Carswell et al. (1997) and Nakamura & Banno (1997). Fe3+ in clinopyroxene was estimated as Fe3+ = Na - Al. It cannot be known whether equilibrium states were achieved and preserved or not, but we assume that garnet and omphacite preserve equilibrium compositions at peak P-T conditions. Evaluation of equilibrium states is one of the problems to be resolved in the future. Chemical compositions of garnet, omphacite and phengite are listed in Table 2, data from Rongcheng County are shown in Nakamura & Hirajima (2000).

Table 2.

Chemical compositions of garnet (Grt), clinopyroxene (Omp) and phengite (Phn) used for P-T estimation of eclogites from Sulu area. D: eclogites from Donghai County, T: Taohang eclogite, Y: Yangkou eclogite.

GrtD-1D-2D-3D-4T-1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO240.1339.4441.1540.1239.8140.3640.2440.4440.0940.5838.7540.06
Al2O321.7821.6223.2522.6422.1222.6422.4522.5122.3522.3521.9422.34
FeO21.5420.3215.3516.9821.2618.3918.9118.9719.5419.3618.8320.51
MnO0.530.600.400.330.580.390.340.380.420.360.380.44
MgO6.786.6610.398.436.466.615.088.467.185.525.115.72
CaO10.8311.5710.8212.0610.8613.2414.7510.0411.5714.0514.1112.88
Total101.59100.21101.36100.56101.09101.63101.77100.80101.15102.2299.12101.95
Si3.0293.0123.0253.0063.0213.0233.0323.0373.0193.0422.9983.016
Al1.9381.9462.0151.9991.9791.9991.9941.9931.9841.9752.0001.983
Fe1.3601.2980.9441.0641.3491.1521.1921.1911.2311.2141.2181.292
Mn0.0340.0390.0250.0210.0370.0250.0220.0240.0270.0230.0250.028
Mg0.7630.7581.1390.9420.7310.7380.5710.9470.8060.6170.5890.642
Ca0.8760.9470.8520.9680.8831.0631.1910.8080.9341.1291.1701.039
Total8.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.000
OmpD-1D-2D-3D-4T1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO256.2156.5255.9656.0656.0157.4756.5356.5456.6257.1756.4556.86
Al2O312.3111.899.6611.7213.6413.1514.6912.0413.1514.7314.2913.72
FeO6.468.062.023.073.724.193.993.723.773.833.684.18
MgO6.285.7910.768.236.586.645.237.586.865.605.415.91
CaO9.588.8315.7712.6010.5410.568.7211.9010.799.369.249.93
Na2O9.259.755.527.378.628.989.888.238.899.819.519.15
Total100.09100.8499.6999.0599.11100.9999.04100.01100.08100.5098.5899.75
Si1.9781.9781.9871.9931.9821.9971.9931.9861.9811.9862.0022.000
Al0.5110.4910.4040.4910.5690.5390.6100.4990.5420.6030.5970.569
Fe0.1900.2360.0600.0910.1100.1220.1180.1090.1100.1110.1090.123
Mg0.3290.3020.5690.4360.3470.3440.2750.3970.3580.2900.2860.310
Ca0.3610.3310.6000.4800.4000.3930.3290.4480.4050.3480.3510.374
Na0.6310.6620.3800.5080.5920.6050.6750.5610.6030.6610.6540.624
Total4.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.000
PheD-2D-4Y-3/2Y-3/4
SiO250.6852.6153.3551.27
TiO20.650.240.630.75
Al2O325.3424.7823.5124.26
FeO2.201.031.591.93
MgO4.334.955.644.21
Na2O0.740.610.490.17
K2O9.7310.7010.9410.80
Total93.6794.9296.1593.39
Si3.4383.5053.5173.504
Ti0.0330.0120.0310.039
Al2.0261.9461.8271.954
Fe0.1250.0570.0880.110
Mg0.4380.4920.5540.429
Na0.0970.0790.0630.023
K0.8420.9090.9200.942
Total7.0007.0007.0007.000
GrtD-1D-2D-3D-4T-1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO240.1339.4441.1540.1239.8140.3640.2440.4440.0940.5838.7540.06
Al2O321.7821.6223.2522.6422.1222.6422.4522.5122.3522.3521.9422.34
FeO21.5420.3215.3516.9821.2618.3918.9118.9719.5419.3618.8320.51
MnO0.530.600.400.330.580.390.340.380.420.360.380.44
MgO6.786.6610.398.436.466.615.088.467.185.525.115.72
CaO10.8311.5710.8212.0610.8613.2414.7510.0411.5714.0514.1112.88
Total101.59100.21101.36100.56101.09101.63101.77100.80101.15102.2299.12101.95
Si3.0293.0123.0253.0063.0213.0233.0323.0373.0193.0422.9983.016
Al1.9381.9462.0151.9991.9791.9991.9941.9931.9841.9752.0001.983
Fe1.3601.2980.9441.0641.3491.1521.1921.1911.2311.2141.2181.292
Mn0.0340.0390.0250.0210.0370.0250.0220.0240.0270.0230.0250.028
Mg0.7630.7581.1390.9420.7310.7380.5710.9470.8060.6170.5890.642
Ca0.8760.9470.8520.9680.8831.0631.1910.8080.9341.1291.1701.039
Total8.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.000
OmpD-1D-2D-3D-4T1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO256.2156.5255.9656.0656.0157.4756.5356.5456.6257.1756.4556.86
Al2O312.3111.899.6611.7213.6413.1514.6912.0413.1514.7314.2913.72
FeO6.468.062.023.073.724.193.993.723.773.833.684.18
MgO6.285.7910.768.236.586.645.237.586.865.605.415.91
CaO9.588.8315.7712.6010.5410.568.7211.9010.799.369.249.93
Na2O9.259.755.527.378.628.989.888.238.899.819.519.15
Total100.09100.8499.6999.0599.11100.9999.04100.01100.08100.5098.5899.75
Si1.9781.9781.9871.9931.9821.9971.9931.9861.9811.9862.0022.000
Al0.5110.4910.4040.4910.5690.5390.6100.4990.5420.6030.5970.569
Fe0.1900.2360.0600.0910.1100.1220.1180.1090.1100.1110.1090.123
Mg0.3290.3020.5690.4360.3470.3440.2750.3970.3580.2900.2860.310
Ca0.3610.3310.6000.4800.4000.3930.3290.4480.4050.3480.3510.374
Na0.6310.6620.3800.5080.5920.6050.6750.5610.6030.6610.6540.624
Total4.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.000
PheD-2D-4Y-3/2Y-3/4
SiO250.6852.6153.3551.27
TiO20.650.240.630.75
Al2O325.3424.7823.5124.26
FeO2.201.031.591.93
MgO4.334.955.644.21
Na2O0.740.610.490.17
K2O9.7310.7010.9410.80
Total93.6794.9296.1593.39
Si3.4383.5053.5173.504
Ti0.0330.0120.0310.039
Al2.0261.9461.8271.954
Fe0.1250.0570.0880.110
Mg0.4380.4920.5540.429
Na0.0970.0790.0630.023
K0.8420.9090.9200.942
Total7.0007.0007.0007.000

Results of calculations are shown in Figure 12. The estimated P–T conditions of eclogites from Donghai County range from 750 °C, 2.85 GPa to 880 °C, 3.6 GPa. The calculated conditions are in the coesite-stable field, consistent with the preservation of coesite in eclogite from Donghai County (e.g. Hirajima et al., 1990; Zhao et al., 1992). However, the estimated P–T conditions for the Taohang eclogite in Zhucheng County are about 790 °C, 2.65 GPa, that is in quartz-stable field, but Yao et al. (2000) estimated 3.1 GPa at 800 °C for eclogite from Taohang using garnet–clinopyroxene–phengite barometer. Coesite itself is not found in the Taohang eclogite, but peak pressure conditions of the Taohang eclogite show probably near the coesite–quartz transition pressures. The estimated P–T conditions for Yangkou eclogites range from 700 to 800 °C, 3.1–4.1 GPa. From this locality, coesite was found in eclogites (e.g. Hirajima, 1996; Wallis et al., 1997), and the calculated pressure is consistent with this observation. However, the estimated pressures are widely scattered and we cannot determine accurate peak P conditions. This is caused by the heterogeneity of mineral compositions and by the uncertainty of thermodynamic properties and data. Recently, thermodynamic properties and data have been modified and sophisticated, but quantitative problems still exist. The estimated P–T conditions of eclogites from Rongcheng County are about 790–880 °C, 2.9–4.0 GPa. In Rongcheng County, coesite was found in a Chijiadian sample among our studied kyanite-bearing eclogites (Nakamura & Hirajima, 2000), and the calculated results support regional UHP metamorphism in this county.

Fig. 12.

Calculated pressure-temperature conditions for eclogites from the Sulu area. Chemical compositional data used for calculations are shown in Table 2 and Nakamura & Hirajima (2000). Fe3+ in clinopyroxene is estimated as Fe3+ = Na - Al. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988). Equilibrium curves for the garnet-clinopyroxene-kyanite-coesite assemblage (this study) are calculated using thermodynamic dataset of Holland & Powell (1998) with activity models of Nakamura & Banno (1997). Pressures are also estimated for eclogites from Donghai and Yangkou by the garnet-clinopyroxene-phengite barometer calibrated by Waters & Martin (1996) (WM96). Quartz-coesite and diamond-graphite transition curves are based on Holland & Powell (1998). Qtz: quartz, Coe: coesite, Dmn: diamond, Gr: graphite.

Fig. 12.

Calculated pressure-temperature conditions for eclogites from the Sulu area. Chemical compositional data used for calculations are shown in Table 2 and Nakamura & Hirajima (2000). Fe3+ in clinopyroxene is estimated as Fe3+ = Na - Al. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988). Equilibrium curves for the garnet-clinopyroxene-kyanite-coesite assemblage (this study) are calculated using thermodynamic dataset of Holland & Powell (1998) with activity models of Nakamura & Banno (1997). Pressures are also estimated for eclogites from Donghai and Yangkou by the garnet-clinopyroxene-phengite barometer calibrated by Waters & Martin (1996) (WM96). Quartz-coesite and diamond-graphite transition curves are based on Holland & Powell (1998). Qtz: quartz, Coe: coesite, Dmn: diamond, Gr: graphite.

In the Sulu area, coesite was found in several localities: Weihai (e.g. Wang et al., 1993), Rongcheng (Chijiadian: Nakamura & Hirajima, 2000), Zekou (Kurahashi et al., 2001), Yangkou (e.g. Wallis et al., 1997), Donghai (Mengzhong: Hirajima et al., 1990; Hetang: Zhao et al., 1992), although many eclogites transformed to granulite in the northeastern and to amphibolite in the central and southwestern parts of the county to various degrees. Most of the calculated P–T conditions fall in the coesite-stable field (Fig. 12), suggesting that most of the eclogite bodies from the Sulu area, except for the rocks around Haiyangsuo (Fig. 3), suffered UHP metamorphism. If eclogite bodies were exhumed as a tectonic block and were trapped into the country gneiss after decompression, some eclogite bodies would have ascended from relatively shallow levels (i.e., quartz-stable depth). The calculated results, however, indicate that they were formed under coesite stability field, suggesting that the “in situ” model is a plausible tectonics in the Sulu area.

Enami et al. (1993a) proposed a southwestward decrease of metamorphic temperatures in the Sulu area, but no such tendency was identified in this study. Comparing Donghai County in the southwestern part with Rongcheng County in the northeastern part, there is no apparent difference in temperature conditions (Fig. 12). However, the estimation of temperatures has a potential difficulty: identification of equilibrium compositions, non-ideality of solid solution and analytical problems (estimation Fe3+ in omphacite). For example, the estimated temperatures for Yangkou eclogites are scattered (700–800 °C), even though they were collected from the same locality. As one of the problems, the non-ideality of the jadeite component was pointed out by Hirajima (1996), who showed that nominal calculated temperatures increase with increasing jadeite component in omphacite with high jadeite component (> 50 mol%), and suggested that the variety of the estimated temperatures for Yangkou eclogites may be due to the non-ideal effect of the jadeite component. Therefore, we investigate the relationship between the estimated temperatures and jadeite component (Al of clinopyroxene) (Figs. 13 & 14). However, our calculated data in the other localities of the Sulu area do not show a clear positive correlation, although Rongcheng eclogites, which were collected at several localities, show a weak positive correlation (Fig. 13). Zhang et al. (2000b) reported the equilibrium P-T conditions for the eclogites collected from the 558 m deep ZK703 drill hole at Mobei, Donghai County, as around 3.2 to 4.0 GPa and 770 to 880 °C using the combination of Powell’s (1985) Grt-Cpx thermometry and Grt-Cpx-Phn geobarometry for the average compositions of Grt and Omp in each sample, and by assuming Fe3+ = Na - Al in Cpx and all Fe as divalent in Grt. They estimated P-T conditions very similar to our P-T estimations in Donghai(Fig. 12). However, their original data (Table 3 in Zhang et al., 2000b) suggest that the estimated temperatures positively correlate with the jadeite component, ranging from 623 to 853 °C at 3.0 GPa for XJd = 0.31 to 0.72 (Fig. 14b). Zhang et al. (2000b) regarded the temperature lower than 700 °C, obtained from two samples with lower XJd (0.31-0.38) omphacite, as a “false value” due to an incorrect estimate of Fe3+ content in omphacite and/or possible retrograde re-equilibration of mineral compositions. We think that it is not reasonable to simply abandon the lower temperature data from their description, and the ZK703 drillhole eclogite may show the second example of positive correlation between wstimated temperature and XJd. The estimated temperatures in eclogites with omphacite with low jadeite component (< 50 mol%) from Donghai and Rongcheng Counties are relatively high comparing with Yangkou eclogites. Although the problem of the effect of the jadeite component still remains, metamorphic temperatures for Yangkou eclogites may be slightly lower than those for eclogites from the other counties (cf. Figs. 12 and 13).

Fig. 13.

Relationship between estimated temperature and jadeite content of clinopyroxene (Al p.f.u.) for eclogites from the Sulu area. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988) at 3.5 GPa. For eclogites from Yangkou, there is a clear positive correlation between estimated temperature and jadeite content, but no clear correlation is observed for eclogites from other areas, except for Rongcheng.

Fig. 13.

Relationship between estimated temperature and jadeite content of clinopyroxene (Al p.f.u.) for eclogites from the Sulu area. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988) at 3.5 GPa. For eclogites from Yangkou, there is a clear positive correlation between estimated temperature and jadeite content, but no clear correlation is observed for eclogites from other areas, except for Rongcheng.

Fig. 14.

Relationship between estimated temperature and jadeite content of clinopyroxene for eclogites at (a) Yangkou (Hirajima, 1996) and (b) ZK703 drillhole at Mobei, Donghai (Zhang et al., 2002b). Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) at 3.0 GPa.

Fig. 14.

Relationship between estimated temperature and jadeite content of clinopyroxene for eclogites at (a) Yangkou (Hirajima, 1996) and (b) ZK703 drillhole at Mobei, Donghai (Zhang et al., 2002b). Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) at 3.0 GPa.

At last, we cannot identify significant difference in metamorphic temperatures between Donghai and Rongcheng County. There is no apparent regional metamorphic gradient that was proposed by Enami et al. (1993a). In the Sulu area, most of eclogite bodies suffered UHP metamorphism that are mostly in the same P-T conditions, although eclogites from Yangkou show slightly lower temperature. At present, more precise analyses of P-T conditions are still difficult, and we have to overcome several problems to obtain accurate temperatures.

Concluding remarks

Wang et al. (1992, 1995) and Enami et al., (1993a) emphasised that the peak metamorphic temperatures of eclogites systematically decrease from east to west through the Dabie Shan-Sulu area and from north to south in the Dabie Shan. Continuous variation of peak metamorphic temperatures for UHP/HP rocks is one of the positive evidences for the “in situ” school. The present compiled data suggest that the coesite eclogites show a relatively uniform peak temperature between 700-850 °C in the Dabie Shan-Sulu area, which does not support the former idea mentioned above. The equilibrium temperatures in the Dabie Shan support the conclusion of Okay (1993) and Carswell et al. (1997), i.e., that there is a distinct gap of the peak P-T conditions between the quartz eclogite terrane and the coesite eclogite terrane. Their conclusion claimed to partly modify the conclusion of Wang et al. (1992, 1995) but does not deny the “in situ” model of the UHP/HP eclogite in the study area. However we emphasise again that the number of the reported P-T estimations for the quartz eclogite terrane is not enough to discuss the tectonic relationship between the two terranes.

Several tenacious field surveys guided by Chinese geologists and their co-workers succeeded to confirm that many UHP eclogites and associated UHP rocks, some of which were certainly derived from crustal materials, were exposed as coherent formations in the coesite eclogite unit of Dabie Shan and Sulu area (e.g. Shima, Changpu, Xinjian, Shuanghe in southern Dabie Shan; Donghai and Yangkou in Sulu). Among them, the areal scale reconstruction of pre-UHP geology was succeeded in Shuanghe (Cong et al., 1995) and Yangkou (Wallis et al., 1997) in several hundred-meter scales, and the several tens of kilometres scale continuity of the Chenjiahe Formation of Wang et al. (1990) in the central Dabie Shan was recently confirmed by Compagnoni et al. (2001) as their Changpu-Pailou unit. These geological contributions support the “in situ” school of the UHP rocks. However, these data cannot explain the existence of the apparent P–T gaps between the UHP rocks and the surrounding amphibolite facies country gneiss. Finding of tiny coesite and other UHP minerals as inclusions in zircons of the country gneisses (Tabata et al., 1998b; Ye et al., 2000b; Liu et al., 2002) encourages the “in situ” school. A further comprehensive study on the Changpu-Pailou unit will give more interesting data on this long-term argument in the near future.

A precisely determined exhumation path of UHP/HP rocks can contribute to define the exhumation mechanism of UHP/HP rocks and/or to reveal the root zone tectonics of the collision belt (e.g. Hacker & Peacock, 1995). Most UHP eclogites and garnet peridotites suffered multiple re-equilibrium reactions, chiefly represented by the amphibolite and/or greenschist facies overprint during the latest stage of the exhumation. Some of them recorded the subsequent overprints during the early decompression stage, as suggested by the development of paragonite in the UHP eclogite matrix under quartz eclogite facies in Dabie Shan (Okay, 1995) or during the late decompression stage represented by granulite facies minerals in the northeastern part of the Sulu area (e.g. Wang et al., 1993; Nakamura & Hirajima, 2000). If we can estimate each re-equilibrium P–T condition precisely, we can propose the precise exhumation path. Although we do not give a detailed assessment to each proposed decompression path in this chapter, two types of exhumation paths (isothermal decompression path, ITD; e.g. Liou et al., 1997; Banno et al., 2000; Castelli et al., 1998; Nakamura & Hirajima, 2000; Compagnoni et al., 2001; Yoshida et al., 2001; or decompression with significant cooling path, DSC; e.g. Schmidt et al., 2001; Wang et al., 2001) were proposed in the Dabie Shan–Sulu area. If the UHP eclogites formed around 750–800 °C exhumed maintaining the isothermal state, they can suffer the granulite facies overprinting around the lower crustal depths. The northeastern part of the Sulu area can fit to this case. In the Dabie Shan area, both ITD and DSC paths were reported. Further efforts to delineate the precise exhumation path and collate it with the geotectonics obtained from geophysical and numerical models in the relevant area are attractive targets for the petrologists.

The apparent pressure gap at the UHP stage obtained from garnet peridotite and eclogite is one of unsolved problems for the “in situ” school. Some garnet peridotite recorded the diamond stability pressure around 4-6 GPa at peak stage, which is significantly higher than the peak pressure for the eclogite. The finding of clinoenstatite lamellae in the host orthoenstatite and diopside (Su et al., 2001; Zhang et al., 2002), and the reconstructed majoritic garnet composition from a Yangkou eclogite (Ye et al., 2000a) may suggest that at least some of the coevally subducted crustal rocks have been subjected to peak metamorphism at P–T conditions much higher than that obtained from the eclogite (∼ 3–4 GPa and 700–850 °C). This is another extensive target remaining for the petrologists.

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Acknowledgements

We express our sincere thanks to D.A. Carswell and R. Compagnoni for giving a chance for writing this review, to all members of the co-operative research on Sulu area between Kyoto University and Academia Sinica originally guided by S. Banno and the late Cong Bolin for their help of carrying out the field and indoor survey. We also acknowledge Keisaku Matsumoto for his computer drawing of some geological maps of the Dabie Shan area and J.G. Liou and B.M. Jahn for their constructive and critical comments for this chapter.

Figures & Tables

Fig. 1.

Tectono-metamorphic sketch map of the Qinling-Dabie Shan-Sulu orogen.

Fig. 1.

Tectono-metamorphic sketch map of the Qinling-Dabie Shan-Sulu orogen.

Fig. 2.

Tectono-metamorphic map of the Dabie Shan-Hong’an areas, based mainly on Hacker et al. (1998) and Castelli et al (1998). The locations of eclogitic xenoliths in granodiorite follow Faure etal. (2003)

Fig. 2.

Tectono-metamorphic map of the Dabie Shan-Hong’an areas, based mainly on Hacker et al. (1998) and Castelli et al (1998). The locations of eclogitic xenoliths in granodiorite follow Faure etal. (2003)

Fig. 3.

Tectono-metamorphic map of the Sulu area with locations of coesite eclogite and other ultrabasic and basic rocks with critical mineral assemblages, mainly after Wallis et al. (1997). YQW Fault: Yantai-Qingdao-Wulian Fault.

Fig. 3.

Tectono-metamorphic map of the Sulu area with locations of coesite eclogite and other ultrabasic and basic rocks with critical mineral assemblages, mainly after Wallis et al. (1997). YQW Fault: Yantai-Qingdao-Wulian Fault.

Fig. 4.

The equilibrium temperature map in central and southern Dabie Shan. The tectonic boundary follows Carswell et al. (1997) and the distribution of Chenjiahe Formation follows Wang et al. (1990). Po and Pt: Paragonite-bearing eclogite reported by Okay (1993, 1995) and Tabata et al. (1998a), respectively.

Fig. 4.

The equilibrium temperature map in central and southern Dabie Shan. The tectonic boundary follows Carswell et al. (1997) and the distribution of Chenjiahe Formation follows Wang et al. (1990). Po and Pt: Paragonite-bearing eclogite reported by Okay (1993, 1995) and Tabata et al. (1998a), respectively.

Fig. 6.

Detailed geologic map of the Yangkou UHP metamorphic complex and surrounding Sulu gneiss, mainly following Wallis et al. (1997).

Fig. 6.

Detailed geologic map of the Yangkou UHP metamorphic complex and surrounding Sulu gneiss, mainly following Wallis et al. (1997).

Fig. 7.

Geological sketch map of (a) the Maowu complex (Okay, 1994) and (b) the Bixiling complex (Zhang et al., 1995b).

Fig. 7.

Geological sketch map of (a) the Maowu complex (Okay, 1994) and (b) the Bixiling complex (Zhang et al., 1995b).

Fig. 8.

P–T conditions of ganet peridotite and eclogite in the Maowu and Bixiling complexes in the Dabie Shan area. Data of the Maowu complex are from Okay (1994) and Liou & Zhang (1998), and of the Bixiling complex from Carswell et al. (1997) and Zhang et al. (1995b).

Fig. 8.

P–T conditions of ganet peridotite and eclogite in the Maowu and Bixiling complexes in the Dabie Shan area. Data of the Maowu complex are from Okay (1994) and Liou & Zhang (1998), and of the Bixiling complex from Carswell et al. (1997) and Zhang et al. (1995b).

Fig. 9.

P–T paths of representative garnet peridotites in the Sulu area. (a) Zhimafang (Yang & Jahn, 2000), (b) Yangkou (Yoshida et al., 2001).

Fig. 9.

P–T paths of representative garnet peridotites in the Sulu area. (a) Zhimafang (Yang & Jahn, 2000), (b) Yangkou (Yoshida et al., 2001).

Fig. 10.

Comparison of three formulations (Ganguly, 1979; Powell, 1985; Krogh Ravna, 2000) for garnet-clinopyroxene thermometer. Relationships between temperature and distribution coefficient (KD) are shown at graphic and 3.0 GPa. For Krogh Ravna (2000), Mg number of garnet (Mg#Grt) is fixed as 0.30.

Fig. 10.

Comparison of three formulations (Ganguly, 1979; Powell, 1985; Krogh Ravna, 2000) for garnet-clinopyroxene thermometer. Relationships between temperature and distribution coefficient (KD) are shown at graphic and 3.0 GPa. For Krogh Ravna (2000), Mg number of garnet (Mg#Grt) is fixed as 0.30.

Fig. 11.

Isotherms based on the alternative formulations of Ellis & Green (1979; EG(79)), Powell (1985; P(85)) and Krogh (1988; K(88)) in XGrs (= Ca/(Ca + Fe + Mg + Mn)) in garnet versus KD (for Fe2+-Mg2+ partitioning between garnet and clinopyroxene) diagram. Inset data from Okay (1993, 1995). For further details see text.

Fig. 11.

Isotherms based on the alternative formulations of Ellis & Green (1979; EG(79)), Powell (1985; P(85)) and Krogh (1988; K(88)) in XGrs (= Ca/(Ca + Fe + Mg + Mn)) in garnet versus KD (for Fe2+-Mg2+ partitioning between garnet and clinopyroxene) diagram. Inset data from Okay (1993, 1995). For further details see text.

Fig. 12.

Calculated pressure-temperature conditions for eclogites from the Sulu area. Chemical compositional data used for calculations are shown in Table 2 and Nakamura & Hirajima (2000). Fe3+ in clinopyroxene is estimated as Fe3+ = Na - Al. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988). Equilibrium curves for the garnet-clinopyroxene-kyanite-coesite assemblage (this study) are calculated using thermodynamic dataset of Holland & Powell (1998) with activity models of Nakamura & Banno (1997). Pressures are also estimated for eclogites from Donghai and Yangkou by the garnet-clinopyroxene-phengite barometer calibrated by Waters & Martin (1996) (WM96). Quartz-coesite and diamond-graphite transition curves are based on Holland & Powell (1998). Qtz: quartz, Coe: coesite, Dmn: diamond, Gr: graphite.

Fig. 12.

Calculated pressure-temperature conditions for eclogites from the Sulu area. Chemical compositional data used for calculations are shown in Table 2 and Nakamura & Hirajima (2000). Fe3+ in clinopyroxene is estimated as Fe3+ = Na - Al. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988). Equilibrium curves for the garnet-clinopyroxene-kyanite-coesite assemblage (this study) are calculated using thermodynamic dataset of Holland & Powell (1998) with activity models of Nakamura & Banno (1997). Pressures are also estimated for eclogites from Donghai and Yangkou by the garnet-clinopyroxene-phengite barometer calibrated by Waters & Martin (1996) (WM96). Quartz-coesite and diamond-graphite transition curves are based on Holland & Powell (1998). Qtz: quartz, Coe: coesite, Dmn: diamond, Gr: graphite.

Fig. 13.

Relationship between estimated temperature and jadeite content of clinopyroxene (Al p.f.u.) for eclogites from the Sulu area. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988) at 3.5 GPa. For eclogites from Yangkou, there is a clear positive correlation between estimated temperature and jadeite content, but no clear correlation is observed for eclogites from other areas, except for Rongcheng.

Fig. 13.

Relationship between estimated temperature and jadeite content of clinopyroxene (Al p.f.u.) for eclogites from the Sulu area. Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) or Krogh (1988) at 3.5 GPa. For eclogites from Yangkou, there is a clear positive correlation between estimated temperature and jadeite content, but no clear correlation is observed for eclogites from other areas, except for Rongcheng.

Fig. 14.

Relationship between estimated temperature and jadeite content of clinopyroxene for eclogites at (a) Yangkou (Hirajima, 1996) and (b) ZK703 drillhole at Mobei, Donghai (Zhang et al., 2002b). Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) at 3.0 GPa.

Fig. 14.

Relationship between estimated temperature and jadeite content of clinopyroxene for eclogites at (a) Yangkou (Hirajima, 1996) and (b) ZK703 drillhole at Mobei, Donghai (Zhang et al., 2002b). Temperatures are estimated by the garnet-clinopyroxene thermometer of Powell (1985) at 3.0 GPa.

Table 1.

Re-evaluated equilibrium temperatures for the coesite/quartz eclogite in the Dabie Shan area

Carswell et al. (1997)Okay (1993, 1995)Tabata et al. (1998a)
LocalityT(°C, P85)
Xgrs<0.35
T(°C, K88)
Xgrs>0.35
P(kb)*Rock No.T(°C, P85)
Xgrs < 0.35
T(°C, K88)
Xgrs > 0.35
NB:Rock No.T(°C, P85)
Cal-free
T(°C, K88)
Cal-bearing
NB:
Changpu 218690 (at l9kb)PgChangpu west
Changpu 223740Cp407737
409631Pg
303829
Bixiling87033577L720C
83038
Guanjialing87037Wumiao west
308589C
309595
311590C
312764Cal
Wumiao eastWumiao east
229780336629
233-328589
230760c302616Pg
575690301639Pg
290563C
258592
248789
Shuanghe68030Shuanghe 251730
74031Shuanghe 250750c
Dongfeng73030Dongfeng east 585690 (at 19kb)Pg-CpDongfeng east 235569
Shima88036Shima
84534224825C-Cal
80040223651C-Cal
68034221744Cal
average801Shima south 568-Cp172639C-Pg-Cal
Huangzhen60022Huangzhen east
61023272620
Carswell et al. (1997)Okay (1993, 1995)Tabata et al. (1998a)
LocalityT(°C, P85)
Xgrs<0.35
T(°C, K88)
Xgrs>0.35
P(kb)*Rock No.T(°C, P85)
Xgrs < 0.35
T(°C, K88)
Xgrs > 0.35
NB:Rock No.T(°C, P85)
Cal-free
T(°C, K88)
Cal-bearing
NB:
Changpu 218690 (at l9kb)PgChangpu west
Changpu 223740Cp407737
409631Pg
303829
Bixiling87033577L720C
83038
Guanjialing87037Wumiao west
308589C
309595
311590C
312764Cal
Wumiao eastWumiao east
229780336629
233-328589
230760c302616Pg
575690301639Pg
290563C
258592
248789
Shuanghe68030Shuanghe 251730
74031Shuanghe 250750c
Dongfeng73030Dongfeng east 585690 (at 19kb)Pg-CpDongfeng east 235569
Shima88036Shima
84534224825C-Cal
80040223651C-Cal
68034221744Cal
average801Shima south 568-Cp172639C-Pg-Cal
Huangzhen60022Huangzhen east
61023272620

P [kbar]*: estimated by the combination of Grt-Cpx thermometry and Phn-Grt-Cpx barometry of Waters & Martin (1993)

P85: Grt-Cpx geothermometer of Powell (1985), K88: Grt-Cpx geothermometer of Krogh (1988); C: coesite, Cp: quartz pseudomorphs after coesite, Pg: paragonite in the matrix, Cal: carbonate.

Table 2.

Chemical compositions of garnet (Grt), clinopyroxene (Omp) and phengite (Phn) used for P-T estimation of eclogites from Sulu area. D: eclogites from Donghai County, T: Taohang eclogite, Y: Yangkou eclogite.

GrtD-1D-2D-3D-4T-1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO240.1339.4441.1540.1239.8140.3640.2440.4440.0940.5838.7540.06
Al2O321.7821.6223.2522.6422.1222.6422.4522.5122.3522.3521.9422.34
FeO21.5420.3215.3516.9821.2618.3918.9118.9719.5419.3618.8320.51
MnO0.530.600.400.330.580.390.340.380.420.360.380.44
MgO6.786.6610.398.436.466.615.088.467.185.525.115.72
CaO10.8311.5710.8212.0610.8613.2414.7510.0411.5714.0514.1112.88
Total101.59100.21101.36100.56101.09101.63101.77100.80101.15102.2299.12101.95
Si3.0293.0123.0253.0063.0213.0233.0323.0373.0193.0422.9983.016
Al1.9381.9462.0151.9991.9791.9991.9941.9931.9841.9752.0001.983
Fe1.3601.2980.9441.0641.3491.1521.1921.1911.2311.2141.2181.292
Mn0.0340.0390.0250.0210.0370.0250.0220.0240.0270.0230.0250.028
Mg0.7630.7581.1390.9420.7310.7380.5710.9470.8060.6170.5890.642
Ca0.8760.9470.8520.9680.8831.0631.1910.8080.9341.1291.1701.039
Total8.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.000
OmpD-1D-2D-3D-4T1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO256.2156.5255.9656.0656.0157.4756.5356.5456.6257.1756.4556.86
Al2O312.3111.899.6611.7213.6413.1514.6912.0413.1514.7314.2913.72
FeO6.468.062.023.073.724.193.993.723.773.833.684.18
MgO6.285.7910.768.236.586.645.237.586.865.605.415.91
CaO9.588.8315.7712.6010.5410.568.7211.9010.799.369.249.93
Na2O9.259.755.527.378.628.989.888.238.899.819.519.15
Total100.09100.8499.6999.0599.11100.9999.04100.01100.08100.5098.5899.75
Si1.9781.9781.9871.9931.9821.9971.9931.9861.9811.9862.0022.000
Al0.5110.4910.4040.4910.5690.5390.6100.4990.5420.6030.5970.569
Fe0.1900.2360.0600.0910.1100.1220.1180.1090.1100.1110.1090.123
Mg0.3290.3020.5690.4360.3470.3440.2750.3970.3580.2900.2860.310
Ca0.3610.3310.6000.4800.4000.3930.3290.4480.4050.3480.3510.374
Na0.6310.6620.3800.5080.5920.6050.6750.5610.6030.6610.6540.624
Total4.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.000
PheD-2D-4Y-3/2Y-3/4
SiO250.6852.6153.3551.27
TiO20.650.240.630.75
Al2O325.3424.7823.5124.26
FeO2.201.031.591.93
MgO4.334.955.644.21
Na2O0.740.610.490.17
K2O9.7310.7010.9410.80
Total93.6794.9296.1593.39
Si3.4383.5053.5173.504
Ti0.0330.0120.0310.039
Al2.0261.9461.8271.954
Fe0.1250.0570.0880.110
Mg0.4380.4920.5540.429
Na0.0970.0790.0630.023
K0.8420.9090.9200.942
Total7.0007.0007.0007.000
GrtD-1D-2D-3D-4T-1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO240.1339.4441.1540.1239.8140.3640.2440.4440.0940.5838.7540.06
Al2O321.7821.6223.2522.6422.1222.6422.4522.5122.3522.3521.9422.34
FeO21.5420.3215.3516.9821.2618.3918.9118.9719.5419.3618.8320.51
MnO0.530.600.400.330.580.390.340.380.420.360.380.44
MgO6.786.6610.398.436.466.615.088.467.185.525.115.72
CaO10.8311.5710.8212.0610.8613.2414.7510.0411.5714.0514.1112.88
Total101.59100.21101.36100.56101.09101.63101.77100.80101.15102.2299.12101.95
Si3.0293.0123.0253.0063.0213.0233.0323.0373.0193.0422.9983.016
Al1.9381.9462.0151.9991.9791.9991.9941.9931.9841.9752.0001.983
Fe1.3601.2980.9441.0641.3491.1521.1921.1911.2311.2141.2181.292
Mn0.0340.0390.0250.0210.0370.0250.0220.0240.0270.0230.0250.028
Mg0.7630.7581.1390.9420.7310.7380.5710.9470.8060.6170.5890.642
Ca0.8760.9470.8520.9680.8831.0631.1910.8080.9341.1291.1701.039
Total8.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.0008.000
OmpD-1D-2D-3D-4T1Y-1Y-2Y-3/2Y-3/3-2Y-3/3Y-3/4Y-3/5
SiO256.2156.5255.9656.0656.0157.4756.5356.5456.6257.1756.4556.86
Al2O312.3111.899.6611.7213.6413.1514.6912.0413.1514.7314.2913.72
FeO6.468.062.023.073.724.193.993.723.773.833.684.18
MgO6.285.7910.768.236.586.645.237.586.865.605.415.91
CaO9.588.8315.7712.6010.5410.568.7211.9010.799.369.249.93
Na2O9.259.755.527.378.628.989.888.238.899.819.519.15
Total100.09100.8499.6999.0599.11100.9999.04100.01100.08100.5098.5899.75
Si1.9781.9781.9871.9931.9821.9971.9931.9861.9811.9862.0022.000
Al0.5110.4910.4040.4910.5690.5390.6100.4990.5420.6030.5970.569
Fe0.1900.2360.0600.0910.1100.1220.1180.1090.1100.1110.1090.123
Mg0.3290.3020.5690.4360.3470.3440.2750.3970.3580.2900.2860.310
Ca0.3610.3310.6000.4800.4000.3930.3290.4480.4050.3480.3510.374
Na0.6310.6620.3800.5080.5920.6050.6750.5610.6030.6610.6540.624
Total4.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.0004.000
PheD-2D-4Y-3/2Y-3/4
SiO250.6852.6153.3551.27
TiO20.650.240.630.75
Al2O325.3424.7823.5124.26
FeO2.201.031.591.93
MgO4.334.955.644.21
Na2O0.740.610.490.17
K2O9.7310.7010.9410.80
Total93.6794.9296.1593.39
Si3.4383.5053.5173.504
Ti0.0330.0120.0310.039
Al2.0261.9461.8271.954
Fe0.1250.0570.0880.110
Mg0.4380.4920.5540.429
Na0.0970.0790.0630.023
K0.8420.9090.9200.942
Total7.0007.0007.0007.000

Contents

GeoRef

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