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1.
W. Cui  X. Wang 《Island Arc》1995,4(4):347-361
Abstract According to field occurrence and P-T condition, eclogites of southern Henan and northern Hubei Provinces can be divided into two types: medium temperature (MT) and low temperature (LT) eclogites. MT eclogite occurs as layers or lenticular bodies within migmatized gneiss of the Dabie Group. This study is the first to report an occurrence of the assemblages coesite and kyanite + talc in this area. Garnet exhibits a distinct prograde compositional zoning and has mineral inclusions with rotational textures indicating syntectonic growth. Five evolutionary stages are outlined. (1) Pre-eclogite stage, determined by the inclusions of barroisite + zoisite + quartz in the cores of zoned garnets. (2) Eclogite stage, characterized by garnet + omphacite + kyanite ± talc + coesite + rutile, represents the peak metamorphism. The peak conditions are estimated to be T = 600-700°C, P >27 kb. (3) Glaucophane stage, without an appearance of plagioclase, is assigned to a transitional stage. Blades of glaucophane form rims around garnet grains as a result of the reaction talc + jadeite = glaucophane. This marks the beginning of retrograde metamorphism. (4) Symplectite stage, where eclogitic minerals break down, and Amp + Pl symplectite develops around garnet or omphacite; (5) Later retrograde stage is represented by epidote-amphibolite assemblages. Low temperature eclogite appears as blocks in the Qijiaoshan Formation (part of the Susong Group). Four stages can be identified: (1) Pre-eclogite stage, amphibole + epidote + sphene inclusions occur in garnet core; (2) Eclogite stage, consists of garnet + omphacite + rutile + quartz + phengite + glaucophane + zoisite. The peak conditions are T = 490-560°C, P <15 kb; (3) Symplectitic stage, is characterized by the breakdown of eclogitic minerals; (4) Greenschist facies stage, is recorded by a greenschist facies assemblage. The difference between the two types of eclogites suggests contrasting processes. A model is proposed whereby partial melting of continental crust and the emplacement of tonalite occurs during the exhumation of ultrahigh-pressure eclogite terrain.  相似文献   

2.
Wei  Lin  Masaki  Enami 《Island Arc》2006,15(4):483-502
Abstract Jadeite‐bearing eclogites and associated blueschists locally crop out in a greenschist facies area at Kuldkourla, near the Akeyazhi River in the western Chinese Tianshan region, northwestern China. Garnet in these metamorphic rocks shows prograde zoning with increasing Mg and decreasing Mn from the crystal center towards the rim, and is divided into Ca‐poor/Fe‐rich core and Ca‐rich/Fe‐poor mantle parts. The garnet cores include the assemblages of (i) jadeite/omphacite (Xjd = 0.34–0.96) + barroisite/taramite; and (ii) omphacite + barroisite/pargasite, with paragonite, epidote, rutile and quartz as major phases with rare albite. The garnet mantles rarely contain inclusions of omphacite, glaucophane, epidote, rutile and quartz. Major matrix phases of the pre‐exhumation stage are omphacite, glaucophane, paragonite, rutile and quartz. These mineral parageneses give pressure (P)‐temperature (T) conditions of 0.9 GPa/390°C?1.4 GPa/560°C for the stage of the garnet core formation, 1.8 GPa/520°C for the stage of the garnet mantle formation, and 2.2 GPa/495°C‐2.4 GPa/535°C for the peak eclogite facies assemblage in the matrix. The estimated P‐T conditions and continuous changes of mineral parageneses imply a counterclockwise P‐T path which is a combination of (i) an early prograde stage of high‐pressure/low‐temperature (HP/LT) blueschist facies and/or LP/LT eclogite facies; (ii) a later prograde stage involving compression with minimal heating; and (iii) a climax‐of‐subduction stage characterized by a slight decrease of temperature with increasing pressure. The negative dP/dT of the latest subduction stage is possibly a record of the following events after a continuous subduction and ridge approach: (i) material migration within the upper part of the subducting slab, which has an inverse thermal gradient caused by ductile flow and/or slab break during subduction; and/or (ii) temporary cooling of the wedge mantle–slab interface by continuous subduction of a relatively cold slab following subduction of a hotter ridge.  相似文献   

3.
Low temperature eclogite facies metamorphism in Western Tianshan, Xinjiang   总被引：3，自引：0，他引：3  
According to the field occurrences and petrological study, the low temperature eclogite facies metamorphic rocks in Western Tianshan of Xinjiang can be divided into five types: (i) massive glaucophane-epidote eclogites and glaucophane-paragonite eclogites; (ii) schistose or gneissic mica eclogites; (iii) banded calcite eclogites; (iv) pillow glaucophane eclogites; (v) garnet-omphacite quartzites. Their eclogite facies metamorphism has undergone four stages of evolution: (i) pre-peak lawsonite-blueschist facies stage,T = 350–4000°C,P = 0.7–0.9 GPa; (ii) peak eclogite facies stage,T = 530 ± 20°C,P = 1.6–1.9 GPa; (iii) retrograde epidote-blueschist facies stage, T=500–530°C,P = 0.9–1.2 GPa and (iv) retrograde blueschist-greenschist facies stage,T= 450–550°C,P= 0.7–0.8 GPa. The metamorphic PT path of Western Tianshan eclogites is characterized by clockwise ITD resulting from the subduction of Tarim plate northward to Yili-Central Tianshan plate followed by fast uplift to the surface. But there were at least two stages of blueschist facies retrograde metamorphism overprinted during their uplift.  相似文献   

4.
Abstract The amphibolites occur sporadically as thin layers and blocks throughout the Sulu Terrane, eastern China. All analyzed amphibolite from outcrop and drill cores from prepilot drill hole CCSD‐PP1 and CCSD‐PP2, Chinese Continental Scientific Drilling Project in the Sulu Terrane, are retrograded eclogites overprinted by amphibolite‐facies retrograde metamorphism, with characteristic mineral assemblages of amphibole + plagioclase + epidote ± quartz ± biotite ± ilmenite ± titanite. However, coesite and coesite‐bearing ultrahigh‐pressure (UHP) mineral assemblages are identified by Raman spectroscopy and electron microprobe analysis as inclusions in zircons separated from these amphibolites. In general, coesite and other UHP mineral inclusions are preserved in the cores and mantles of zircons, whereas quartz inclusions occur in the rims of the same zircons. The UHP mineral assemblages consist mainly of coesite + garnet + omphacite + rutile, coesite + garnet + omphacite, coesite + garnet + omphacite + phengite + rutile + apatite, coesite + omphacite + rutile and coesite + magnesite. Compositions of analyzed mineral inclusions are very similar to those of matrix minerals from Sulu eclogites. These UHP mineral inclusion assemblages yield temperatures of 631–780°C and pressures of ≥2.8 × 103 MPa, representing the P–T conditions of peak metamorphism of these rocks, which are consistent with those (T = 642–726°C; P ≥ 2.8 × 103 MPa) deduced from adjacent eclogites. These data indicate that the amphibolites are the retrogressive products of UHP eclogites.  相似文献   

5.
In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are garnet+kyanite+chloritoid+phengite+quartz+rutile. Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± ky+ Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry, P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22? (prograde stage); P=2.3–3.1GPa, T=615–700°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred. In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is “in situ” rather than “tectonic emplacement”.  相似文献   

6.
The present paper reports, for the first time, the occurrence of an omphacite‐bearing mafic schist from the Asemi‐gawa region of the Sanbagawa belt (southwest Japan). The mafic schist occurs as thin layers within pelitic schist of the albite–biotite zone. Omphacite in the mafic schist only occurs as inclusions in garnet, and albite is the major Na phase in the matrix, suggesting that the mafic schist represents highly retrogressed eclogite. Garnet grains in the sample show prograde‐type compositional zoning with no textural or compositional break, and contain mineral inclusions of omphacite, quartz, glaucophane, barroisite/hornblende, epidote and titanite. In addition to the petrographic observations, Raman spectroscopy and focused ion beam system–transmission electron microscope analyses were used for identification of omphacite in the sample. The omphacite in the sample shows a strong Raman peak at 678 cm?1, and concomitant Raman peaks are all consistent with those of the reference omphacite Raman spectrum. The selected area electron diffraction pattern of the omphacite is compatible with the common P2/n omphacite structure. Quartz inclusions in the mafic schist preserve high residual pressure values of Δω1 > 8.5 cm?1, corresponding to the eclogite facies conditions. The combination of Raman geothermobarometries and garnet–clinopyroxene geothermometry gives peak pressure–temperature (P–T) conditions of 1.7–2.0 GPa and 440–540 °C for the mafic schist. The peak P–T values are comparable to those of the schistose eclogitic rocks in other Sanbagawa eclogite units of Shikoku. These findings along with previous age constraints suggest that most of the Sanbagawa schistose eclogites and associated metasedimentary rocks share similar simple P–T histories along the Late Cretaceous subduction zone.  相似文献   

7.
Elastic properties of eclogite rocks from the Bohemian massif   总被引：1，自引：0，他引：1  
Summary Compressional velocity anistropy has been studied in detail at atmospheric pressure for 78 specimens of 23 types of eclogite rocks from the Bohemian massif. For nine of these rock types, compressional and shear velocities were measured as a function of pressure to750 MPa at room temperature. The velocity anisotropy for both compressional and shear waves is less than4% at high pressure. The velocities increase with increasing garnet content and decrease with increasing symplectitization. The Moldanubian eclogites have significantly higher velocities, on the average, than the eclogites from the Kruné hory crystalline complex, although the densities of both groups are comparable.  相似文献   

8.
Abstract Eclogites occur in three districts of the northern and southern parts of Tien-Shan. Three eclogites collected from the Aktyuz, Makbal and Atbashy districts were analyzed; the P-T paths of three eclogites were estimated by analyzing compositional growth zoning and retrograde reaction of garnet and omphacite. Aktyuz and Makbal eclogites have not preserved the prograde path. An Aktyuz eclogite that underwent a quartz eclogite facies metamorphism (about T = 600°C, P = 12 kbar) has recorded three stages of retrograde metamorphism. Four stages of retrograde metamorphism were recognized in a Makbal eclogite; the garnet-omphacite geothermometer gave about T = 560°C at 20 kbar as the highest metamorphic condition. Garnet from a garnetchloritoid-talc schist of the Makbal district includes quartz pseudomorphs after coesite; some units evidently underwent a low-temperature part of coesite eclogite fades metamorphism. Prograde and retrograde paths were recognized in an Atbashy eclogite; five stages of metamorphic reaction were observed in the Atbashy sample. The prograde path from stage I to stage III has been recorded in garnet and omphacite in which quartz pseudomorphs after coesite are included. The peak metamorphism of stage III took place at about 660°C at 25 kbar. The stages IV and V are retrograde. UHP eclogite facies metamorphism took place twice in Kyrghyzstan. The Aktyuz and Atbashy eclogites gave Rb-Sr mineral-isochron ages of about 750 Ma and 270 Ma, respectively. The K-Ar age of paragonite from the Makbal eclogite is about 480 Ma.  相似文献   

9.
The experimental studies done at high temperature and high pressure find that increased temperature can lead to dramatic velocity and strength reductions of most of rocks at high confining pressure[1,2]. What causes this phenomenon? Is it due to dehydrati…  相似文献   

10.
The elastic-anisotropic properties of fifteen samples of garnet granulites from xenoliths in the diatreme on Elovyi Island, in Kandalaksha Bay in the White Sea are investigated. The PT-conditions of the formation of these rocks correspond to a depth of 25–40 km, which is the current depth of the lower crust in the region. According to acoustopolariscopy, the elastic anisotropy of these deep rocks is relatively low. The average seismic P and S velocities corresponding to the in-situ PT-conditions are 6.5–6.7 km/s and 3.7–3.8 km/s, respectively. It is shown that the garnet content in the deep-seated rocks can be estimated from the seismic data. According to the obtained results, the formation of the structural and textural pattern of the lower crustal rocks in the region was poorly affected by the paleotectonic factors.  相似文献   

11.
Shunsuke Endo 《Island Arc》2010,19(2):313-335
Evidence for eclogite‐facies metamorphism is widespread in the Western Iratsu body of the oceanic subduction type Sanbagawa Belt, Southwest Japan. Previous studies in this region focused on typical mafic eclogites and have revealed the presence of an early epidote‐amphibolite facies metamorphism overprinted by a phase of eclogite facies metamorphism. Ca‐rich and titanite‐bearing eclogite, which probably originated from a mixture of basaltic and calc‐siliceous sediments, is also relatively common in the Western Iratsu body, but there has been no detailed petrological study of this lithology. Detailed petrographic observations reveal the presence of a relic early epidote‐amphibolite facies metamorphism preserved in the cores of garnet and titanite in good agreement with studies of mafic eclogite in the area. Thermobarometric calculations for the eclogitic assemblage garnet + omphacite + epidote + quartz + titanite ± rutile ± phengite give peak‐P of 18.5–20.5 kbar at 525–565°C and subsequent peak‐T conditions of about 635°C at 14–16 kbar. This eclogite metamorphism initiated at about 445°C/11–15 kbar, implying a significantly lower thermal gradient than the earlier epidote‐amphibolite facies metamorphism (～650°C/12 kbar). These results define a P–T path with early counter‐clockwise and later clockwise trajectories. The overall P–T path may be related to two distinct phases in the tectono‐thermal evolution in the Sanbagawa subduction zone. The early counter‐clockwise path may record the inception of subduction. The later clockwise path is compatible with previously reported P–T paths from the other eclogitic bodies in the Sanbagawa Belt and supports the tectonic model that these eclogitic bodies were exhumed as a large‐scale coherent unit shortly before ridge subduction.  相似文献   

12.
Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ18O values of eclogites cover a wide range of −5‰ to+9‰, but the δD values of micas fall within a narrow range of −85% to −70‰. Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with reversed fractionations between omphacite and garnet in some eclogite samples. The δ18 O values of −5‰ to −1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water-rock interaction prior to plate subduction. The preservation of oxygen isotope heterogeneity in the eclogites implies a channelized flow of fluids during progressive metamorphism caused by rapid subduction. Retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in the stable isotope compositions. Project supported by the Chinese Ministry of Science and Technology (Grant No. 95-Pre-39), the National Natural Science Foundation of China (Grant Nos. 49794042, 49473173 and 49453003) and the Chinese Academy of Sciences (Grant No. KZ951-A1-401-5)  相似文献   

13.
The decompressional pressure–temperature (P–T) path was estimated for ultrahigh‐pressure (UHP) eclogite from the Sulu region of eastern China by applying geo‐thermobarometers to well‐preserved equilibrium mineral pairs. The sample studied is a kyanite‐bearing eclogite that was collected from the Taohang area of the Sulu region. Garnet is relatively homogeneous in chemical composition, but omphacite has a clear chemical zoning with decreasing jadeite content from core to rim. Assuming that peak‐P equilibrium compositions are preserved in the cores of garnet (Grt) and omphacite (Omp), P–T conditions were calculated to be about 700°C and 3.4 GPa. On the other hand, the jadeite content of omphacite rims varies from 0.35 to 0.46 mol.%. Nevertheless, the variation in Fe/Mg ratios of omphacite rims is very small. Temperatures of 566 ± 54°C were obtained at 1.5 GPa for garnet rim and omphacite rim pairs. These petrological considerations indicate that temperatures should have significantly declined during the early decompression stage of this eclogite. In other areas of the Sulu region, isothermal decompression paths were proposed, and it was concluded that the UHP rocks were exhumed as a large mass tens of kilometers in thickness to avoid thermal effects from the surrounding materials. However, the newly identified decompression path accompanying the significant cooling may indicate that the Taohang outcrop was located at the margin of the Sulu UHP terrane. Thus, the decompressional P–T path is not unique in the Sulu region and varies depending on the location.  相似文献   

14.
Compositional zoning patterns of the major elements and REEs in prograde-zoned garnets whose Mg/(Mg + Fe) atomic ratios increase rimward have been widely used to understand the metamorphic P–T–t trajectories, and the diffusion-limited REE-uptake model is a promising way to interpret their growth rates and the REE diffusion kinetics in the low-temperature eclogite. In order to elucidate their growth kinetics with Skora et al.'s (2006) diffusion-limited REE uptake model for prograde-zoned garnets, we examine the trace-element zoning patterns of two prograde-zoned porphyroblastic garnets (~6 mm in size) in low-temperature eclogites from two different localities. Core-to-rim trace-element profiles in a garnet (prp5–9alm61–67sps1–3grs24–30) of a glaucophane-bearing epidote eclogite of Syros (Cyclades, Greece) are characterized by the presence of Y + HREE peaks in the mantle, which might be attributed to a continuous breakdown of the titanite to form rutile during the garnet growth. In contrast, those in a garnet (prp4–7alm61–68sps3–10grs23–24) extracted from a lawsonite-eclogite of the South Motagua Mélange (SMM) (Guatemala) have prominent central peaks of Y + HREEs. Although the REE profiles of both the garnets can be explained by the diffusion-limited uptake, their Mn profiles suggest that their growth-rate laws are different: i.e., diffusion-controlled (Syros) and interface-controlled (SMM). Prior to the model application, we optimize the number of the parameters as the garnet grows with the interface-controlled processes based on the growth Péclet number. In particular, we propose the ratio of the REE diffusivity in the eclogitic matrix to the garnet growth rate as the new parameter. Visualizing the values of the new parameters allows to readily understand the relationship between the REE profiles and the REE-diffusion/garnet-growth kinetics in low-T eclogite. Our model refinement leads to the simple quantitative characterization of core-to-rim REE profiles in garnet in low-temperature eclogites.  相似文献   

15.
Modern adakite, Archean tonalite-trondhjemite- granodiorite (TTG) and adakitic rocks derived from lower continental crust are high Na and Al felsic rocks and are characterized by strong heavy REE and Y de- pletion and high Sr/Y and La/Yb ratios, which sug…  相似文献   

16.
H. Tabata  S. Maruyama  & Z. Shi 《Island Arc》1998,7(1-2):142-158
The ultrahigh- and high-pressure (UHP–HP) metamorphic belt of the Dabie Mountains, central China, formed by the Triassic continental subduction and collision, is divided into four metamorphic zones; from south to north, the greenschist facies zone, epidote amphibolite to amphibolite facies zone, quartz eclogite zone, and coesite eclogite zone, based on metabasite mineral assemblages. Most of the coesite-bearing eclogites consist mainly of garnet and omphacite with homogeneous compositions and have partially undergone hydration reactions to form clinopyroxene + plagioclase + calcic amphibole symplectites during amphibolite facies overprinting. However, the least altered eclogites sometimes contain garnet and omphacite that preserve compositional zoning patterns which may have originated during their growth at peak temperature conditions of ∼ 750 °C, suggesting a short duration of UHP metamorphic conditions and/or consequent rapid cooling during exhumation. Systematic investigation on peak metamorphic temperatures of coesite eclogite have revealed that, contrary to the general trend of metamorphic grade in the southern Dabie unit, the coesite eclogite zone shows rather flat thermal structure (T = 600 ± 50 °C) with the highest temperature reaching up to 850 °C and no northward increase in metamorphic temperature, which is opposed to the previous interpretations. This feature, along with the preservation of compositional zonation, implies complicated differential movement of each eclogite mass during UHP metamorphism and the return from the deeper subduction zone at mantle depths to the surface.  相似文献   

17.
Lower crustal high grade metamorphic rocks have been successively found at Pamirs nearby the western Himalayan syntaxis, Namjagbarwa and Dinggye nearby the eastern Himalayan syntaxis and the central segment of the Himalayan Orogenic Belt, respec-tively[1―4]. In particular, some researchers deduced that there were probably eclogites at some locations[5]. Moreover, some geochronological data of these lower crustal granulites also have been accumulated. For example, the high-pressure granulit…  相似文献   

18.
Abstract To investigate the regional thermobaric structure of the diamondiferous Kokchetav ultrahigh‐pressure and high‐pressure (UHP–HP) massif and adjacent units, eclogite and other metabasites in the Kulet and Saldat–Kol regions, northern Kazakhstan, were examined. The UHP–HP massif is subdivided into four units, bounded by subhorizontal faults. Unit I is situated at the lowest level of the massif and consists of garnet–amphibolite and acidic gneiss with minor pelitic schist and orthogneiss. Unit II, which structurally overlies Unit I, is composed mainly of pelitic schist and gneiss, and whiteschist locally with abundant eclogite blocks. The primary minerals observed in Kulet and Saldat–Kol eclogites are omphacite, sodic augite, garnet, quartz, rutile and minor barroisite, hornblende, zoisite, clinozoisite and phengite. Rare kyanite occurs as inclusions in garnet. Coesite inclusions occur in garnet porphyroblasts in whiteschist from Kulet, which are closely associated with eclogite masses. Unit III consists of alternating orthogneiss and amphibolite with local eclogite masses. The structurally highest unit, Unit IV, is composed of quartzitic schist with minor pelitic, calcareous, and basic schist intercalations. Mineral assemblages and compositions, and occurrences of polymorphs of SiO2 (quartz or coesite) in metabasites and associated rocks in the Kulet and Saldat–Kol regions indicate that the metamorphic grades correspond to epidote–amphibolite, through high‐pressure amphibolite and quartz–eclogite, to coesite–eclogite facies conditions. Based on estimations by several geothermobarometers, eclogite from Unit II yielded the highest peak pressure and temperature conditions in the UHP–HP massif, with metamorphic pressure and temperature decreasing towards the upper and lower structural units. The observed thermobaric structure is subhorizontal. The UHP–HP massif is overlain by a weakly metamorphosed unit to the north and is underlain by the low‐pressure Daulet Suite to the south; boundaries are subhorizontal faults. There is a distinct pressure gap across these boundaries. These suggest that the highest grade unit, Unit II, has been selectively extruded from the greatest depths within the UHP–HP unit during the exhumation process, and that all of the UHP–HP unit has been tectonically intruded and juxtaposed into the adjacent lower grade units at shallower depths of about 10 km.  相似文献   

19.
A new method of reconstruction of the temperature profile in the lunar mantle from the velocities of seismic P- and S-waves for different models of chemical composition is developed. The procedure of the solution of an inverse problem is realized with the help of the minimization of the Gibbs free energy and the equations of state of a mantle substance, taking into account phase transformations, anharmonicity, and the effects of inelasticity. The geophysical and geochemical constraints on composition and temperature distribution in Moon’s mantle are established. The upper mantle can be composed of olivine pyroxenite, depleted by low-volatile oxides (∼2 wt % of CaO and Al2O3). On the contrary, the lower mantle must be enriched by low-volatile oxides (∼4–6 wt % of CaO and Al2O3). Its composition can be represented by a mineral association of the olivine + clinopyroxene + garnet or olivine + orthopyroxene + clinopyroxene + garnet type, which is close in composition to pyrolite. The temperature distribution at depths 50–1000 km are approximated by the equation: T(°C) = 351 + 1718[1–exp (−0.00082H)]. The constraints inferred make it possible to conclude that the published values of the velocities of P- and S-waves for the lunar mantle, obtained by processing the data of seismic experiments of the Apollo lunar mission are inconsistent with each other at depths below 300 km. Otherwise, the variations in the velocities of P- and S-waves disturb the symmetry between the petrological model (composition), the temperature profile, and the seismic profile.  相似文献   

20.
The carbon isotope compositions of high- and ultrahigh-pressure eclogite and apatite separate from Huangzhen and Shima in SE Dabie Mountains were analyzed by EA-MS online technique. The δ13C values of the eclogites cover a wide range of -30.7‰ - +1.5‰, whereas those of apatites only have a small range of -28.1‰--21.0‰. Some of the eclogites with the high δ13C values suffered retrogressive alteration by CO2-bearing fluids. The low δ13C values of the apatites indicate that the eclogites contain surficial carbon of organic origin. It is concluded that protoliths of the eclogites were exposed to the surface of the Earth, and that the carbon-bearing fluid was depleted in 13C during the eclogite-facies metamorphism.  相似文献   

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