High Pressure Granulites from Eastern Himalayan Syntaxis: P-T Pseudosection and Zircon Dating     

LIU Fenglin  ZHANG Lifei 《《地质学报》英文版》2013,87(Z1):492-493

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华北克拉通孔兹岩带中段大青山-乌拉山变质杂岩立甲子基性麻粒岩年代学及地球化学研究   总被引：12，自引：9，他引：3  

刘平华  刘福来  蔡佳  刘建辉  施建荣  王舫 《岩石学报》2013,29(2):462-484

大青山-乌拉山变质杂岩立甲子基性麻粒岩主要由角闪二辉麻粒岩、含榴角闪二辉麻粒岩和黑云角闪二辉麻粒岩所组成,并以变形岩墙和不规则透镜体形式赋存于富铝片麻岩和花岗质片麻岩之中.立甲子基性麻粒岩中变质锆石含有单斜辉石(Cpx)+角闪石(Amp)+斜长石(Pl)+磷灰石(Ap)的包体矿物,与寄主岩石——基性麻粒岩矿物组合及其化学成分十分一致,相应的207 pb/206 Pb表面年龄变化于1933±39Ma ～ 1834±40Ma,加权平均年龄为1892±7Ma(MSWD =0.50,n=46),应代表立甲子基性麻粒岩原岩经历中低压麻粒岩相的变质时代.在变质过程中,以大离子亲石元素(K、Na、Sr、Rb)为代表的活动元素发生了显著的改变;而高场强元素(Nb、Zr、Ti)和稀土元素基本无变化,保持稳定.立甲子基性麻粒岩原岩属于拉斑玄武质岩石系列,其SiO2集中变化于45.58％ ～51.40％,Mg#值集中介于41 ～54之间;在球粒陨石标准化稀土配分图中,立甲子基性麻粒岩具有平坦型的稀土配分曲线特征((La/Yb)cN=1.30～1.51),Eu异常不明显(Eu/Eu*=0.93～1.04).与显生宙岛孤拉斑玄武岩类似,立甲子基性麻粒岩所有样品皆具有Nb、Zr、Ti负异常特征.综合分析认为,立甲子基性麻粒岩原岩形成于2450～1930Ma,并于～1900Ma经历中低压麻粒岩相变质作用的改造,其主量元素和微量元素组成具有岛弧拉斑玄武质岩石的地球化学特征,其原岩可能是板块汇聚动力学背景下,岛弧构造环境中形成的辉长岩或辉绿岩.  相似文献   

Mineralogical Characterization of Graphite Deposits from Thodupuzha-Kanjirappally Belt, Madurai Granulite Block, Southern India   总被引：1，自引：0，他引：1  

K.R. Baiju  M. Satish-Kumar  H. Kagi  C.G. Nambiar  M. Ravisankar 《Gondwana Research》2005,8(2):223-230

Graphite from deposits occurring in the high-grade metamorphic rocks and their larteritized equivalents of the Thodupuzha-Kanjirappally Belt in Madurai Granulite Block, southern India is structurally fully ordered (crystallite size, Lc₍₀₀₂₎ ranging from 469 to 749 Å), possess high degree of graphitization (DG value ranging from 105 to 267 Å) and reflect crystallization at high temperature (700±100°C). Raman spectra of graphite display profiles corresponding to high crystallinity and high structural ordering. The high temperature crystallinity characteristics of graphite were not obliterated during retrogression of granulites to amphibolite facies gneisses. Preliminary carbon stable isotope results show a spread in isotope values from —11.8 to —26.8 %, which suggest more than one sources for carbon. The lighter carbon isotope values are suggestive of biogenic origin, whereas the heavier ones are probably fluid precipitated graphite.  相似文献   

Geochemistry and isotope (Sr, Nd, O) study of Al–Mg granulites from the In Ouzzal Archaean block (Hoggar, Algeria)     

J. BERNARD-GRIFFITHS  S. FOURCADE  J.-R. KIENAST  J.-J. PEUCAT  F. MARTINEAU  A. RAHMANI 《Journal of Metamorphic Geology》1996,14(6):709-724

The In Ouzzal Al–Mg granulites are found within sedimentary units deposited after 2.7 Ga, the whole association being metamorphosed under extreme temperature conditions (c. 1000 °C) at 2 Ga. The Al–Mg granulites are interlayered with other metasediments, including metapelites, quartzites and magnetite-bearing quartzites, forsterite-spinel marbles, and a few meta-igneous rocks (mainly pyroxenites). They do not occur at a specific position in the sedimentary suite, and they do not reflect any particular structural control. The major and trace element compositions of Al–Mg granulites (especially the high Cr, Ni, Co contents) show that their peculiar ‘refractory’ chemistry is more compatible with premetamorphic sedimentary characteristics rather than with metasomatic, metamorphic or partial melting processes. Sedimentary admixtures of a common mature detrital component coming from the weathering of the local acidic igneous crustal protoliths (normal pelitic component) with an extremely immature component derived from reworking of basic/ultrabasic lithologies (Al–Mg–Cr–Co–Ni–rich chloritic component) is consistent with the geochemistry of such rocks. As in other instances, the quartz-garnet oxygen isotopic thermometer here records an apparent temperature close to the peak metamorphism (c. 1000 °C). Although the persistence of pre-existing δ¹⁸O variations on a small scale during the metamorphism does not support a major pervasive fluid flow during metamorphism, it does not rule out the presence of syn- to post-metamorphic CO₂. The low δ¹⁸O (c.+ 5 to + 6‰) of the most typical Al–Mg granulites indicate that the ‘chloritic component’ in these rocks was derived from hydrothermally altered mafic/ultramafic protoliths rather than dominantly from palaeosols. It is suggested that the presence of such Al–Mg–Cr–Co–Ni–rich sediments is indirect evidence for the presence of greenstone belts in the local crust of the In Ouzzal at 2.6–2.7 Ga.  相似文献   

Metamorphism and Isotopic Evolution of Granulites of Southern India: Reference to Neoproterozoic Crustal Evolution     

A. Mohan  M. Jayananda 《Gondwana Research》1999,2(2):251

Granulites are important component of high-grade metamorphic rocks reflecting intense conditions observed for crustal rocks in terms of temperature, and pressure. This review paper demonstrates how these high-grade granulites are critical to understanding the evolution of the lower continental crust with special reference to southern India. Geothermobarometric traverse across different granulite blocks in southern India shows wide ranging P-T conditions of metamorphism (700–1000 ° C, and 5–10 kbar). The sapphirine-, orthopyroxene-sillimanite, and spinel -bearing quartz-deficient granulites recognised from parts of southern granulite terrain (Ganguvarpatti, Kiranur, and Palani hill ranges etc.) show oriented sillimanite aggregates pseudomorph after course twinned kyanite, staurolite + kyanite assemblages, and corroded blebs of gedrite within orthopyroxene, suggesting a prograde stage of a clockwise P-T evolution. Evidence of ITD history comes from the textures in which an early Mg-rich garnet (X_Mg 52–60) with orthopyroxene (up to 10% Al₂O₃) involving sillimanite breakdown forming variety of symplectites having combinations of orthopyroxene, sapphirine, cordierite, and spinel. These spectacular reaction textures, and mineralogic sensors from the high-grade rocks establish a prograde clockwise P-T-t path with notable decompressive history (ITD) in the southern granulite terrain. The inferred P-T-t paths have been further integrated with the recent geochronological, and isotopic data to constrain the timing, and duration of metamorphism, emplacement of the magmatic protolith for characterising the evolution of the granulites, and their bearing on the geodynamic implications. Based on the emerging evidence for Neoproterozoic tectonothermal imprints in the southern granulite terrain, history of the assembly of dispersed fragments is also addressed within the East Gondwana framework.  相似文献   

New constraints on the P–T path of HT/UHT metapelites from the Highland Complex of Sri Lanka     

P.L. Dharmapriya  Sanjeewa P.K. Malaviarachchi  L.M. Kriegsman  Andrea Galli  K. Sajeev  Chengli Zhang 《地学前缘(英文版)》2017,8(6):1405-1430

We report here rare evidence for the early prograde P-Tevolution of garnet-sillimanite-graphite gneiss(khondalite)from the central Highland Complex,Sri Lanka.Four types of garnet porphyroblasts(Grt_1,Grt_2,Grt_3 and Grt_4)are observed in the rock with specific types of inclusion features.Only Grt_3 shows evidence for non-coaxial strain.Combining the information shows a sequence of main inclusion phases,from old to young:oriented quartz inclusions at core,staurolite and prismatic sillimanite at mantle,kyanite and kyanite pseudomorph,and biotite at rim in Grt_1;fibrolitic sillimanite pseudomorphing kyanite±corundum,kyanite,and spinel+sillimanite after garnet+corundum in Grt_2;biotite,sillimanite,quartz±spinel in Grt_3;and ilmenite,rulite,quartz and sillimanite in Grt_4.The pre-melting,original rock composition was calculated through stepwise re-integration of melt into the residual,XRF based composition,allowing the early prograde metamorphic evolution to be deduced from petrographical observations and pseudosections.The earliest recognizable stage occurred in the sillimanite field at around 575℃ at 4.5 kbar.Subsequent collision associated with Gondwana amalgamation led to crustal thickening along a P-T trajectory with an average dP/dT of ~30 bar/℃ in the kyanite field,up to ~660℃ at 6.5 kbar,before crossing the wet-solidus at around 675 ℃ at 7.5 kbar.The highest pressure occurred at P 10 kbar and T around 780℃ before prograde decompression associated with further heating.At 825℃ and 10.5 kbar,the rock re-entered into the sillimanite field.The temperature peaked at 900℃ at ca.9-9.5 kbar.Subsequent near-isobaric cooling led to the growth of Grt_4 and rutile at T ~880℃.Local pyrophyllite rims around sillimanite suggest a late stage of rehydration at T400℃,which probably occurred after uplift to upper crustal levels.U-Pb dating of zircons by LAICPMS of the khondalite yielded two concordant ~(206)Pb/~(238)U age groups with mean values of 542±2 Ma(MSWD=0.24,Th/U=0.01-0.03)and 514±3 Ma(MSWD=0.50,Th/U=0.01-0.05)interpreted as peak metamorphism of the khondalite and subsequent melt crystallization during cooling.  相似文献   

山东半岛基性高压麻粒岩的成因矿物学及变质演化   总被引：27，自引：22，他引：5  

刘平华  刘福来  王舫  刘建辉 《岩石学报》2010,26(7):2039-2056

在山东半岛的平度-莱西-莱阳-烟台一带,广泛出露基性高压麻粒岩,它们呈大小不等的透镜体或不规则脉状体产于TTG片麻岩中,且与超镁铁质岩石密切"伴生"。根据岩相学、矿物相转变、变质反应以及温压条件的系统研究结果,确定山东半岛基性高压麻粒岩经历了四个阶段的变质演化。早期进变质阶段(M1)的标志性矿物组合以石榴石及其内部的细粒单斜辉石+斜长石±石英为特征,记录的温压条件为T=740～770℃、P=0.9～1.0GPa;峰期高压麻粒岩相变质阶段(M2)的矿物组合以基质中石榴石(富Ca核部)+单斜辉石(富Al核部)+斜长石(富Na核部)±石英为特征,记录的温压条件为T=850～880℃、P=1.45～1.65GPa;峰后近等温减压(中压)麻粒岩相退变质阶段(M3),以发生一系列典型减压反应和斜方辉石的大量出现为标志,典型的矿物组合为斜方辉石+单斜辉石+斜长石+磁铁矿±角闪石,记录的温压条件为T=780～830℃、P=0.65～0.85GPa;晚期角闪岩相退变质阶段(M4)以石榴石发生降温反应、形成角闪石+斜长石+磁铁矿±石英等退变矿物组合为特征,记录的温压条件为T=590～650℃、P=0.62～0.82GPa。高压基性麻粒岩的变质演化的P-T轨迹具有顺时针型式,先后经历了近等温减压过程(ITD)和近等压降温过程(IBC)变质演化过程,指示研究区基性高压麻粒岩是古老陆块之间在俯冲-碰撞造山过程中加厚下地壳折返地表的产物。该项成果对于重新认识华北克拉通在早前寒武纪古老陆块的碰撞-拼贴及其演化的动力学过程具有重要科学意义。  相似文献   

Metapelites of the Kanskiy Granulite Complex (Eastern Siberia): Kinked P-T Paths and Geodynamic Model     

GERYA  TARAS V.; MARESCH  WALTER V. 《Journal of Petrology》2004,45(7):1393-1412

The Southern Yenisey Range (Eastern Siberia) consists of thegranulite-facies Kanskiy complex bordered by the lower-gradeYeniseyskiy and Yukseevskiy complexes. Samples of metapeliteof the Kanskiy complex typically show characteristic garnet-formingreaction textures and near-isobaric cooling P–T paths.An important new result of this study concerns the differencein shape of the P–T paths from different parts of theKanskiy granulite complex: metapelites collected 8 km from theboundary with the Yeniseyskiy complex followed a linear pathwith dP/dT 0·006 kbar/°C; metapelites collected3 km from this boundary reveal a kinked P–T path withan interval of burial cooling (dP/dT –0·006 kbar/°C).The difference in the shape of the P–T paths is supportedby the chemical zoning of garnet studied in the second groupof samples. A mechanism of buoyant exhumation of granulite issuggested by comparison with the results of numerical modelling,which indicate that such a diversity of P–T paths mayresult from a transient disturbance of the thermal structureby rapid differential movement of material from different crustallevels. To arrive at a correct tectonic interpretation, thewhole assemblage of interrelated P–T paths of metamorphicrocks collected from different localities within the same complexmust be studied. KEY WORDS: crustal diapirism; exhumation; granulites; numerical modelling; P–T path  相似文献   

华北新太古代和中生代大陆下地壳中的水:以汉诺坝地区为例     

杨晓志  夏群科  樊祺诚  Etienne Deloule  郝艳涛 《地球化学》2007,36(2):113-119

应用显微傅里叶变换红外光谱技术,对华北克拉通北缘汉诺坝地区的太古宙地体麻粒岩和新生代玄武岩中捕虏体麻粒岩(中生代底侵成因)的主要组成矿物(单斜辉石、斜方辉石、斜长石和石榴子石)进行了详细分析.结果表明,无论是地体麻粒岩还是捕虏体麻粒岩,岩石中的主要组成矿物均含有结构水,主要以OH形式存在.同种产状麻粒岩的矿物水含量(H2O%)均存在较大的变化,而且都远远超出实验误差,表明下地壳内水的分布可能是不均一的.两种产状麻粒岩的矿物结构水含量有着显著的不同,地体麻粒岩中矿物的水含量是捕虏体麻粒岩的2倍以上.太古宙-古元古代形成的安徽女山新生代玄武岩中的捕虏体麻粒岩具有与汉诺坝太古宙地体麻粒岩相似的水含量范围,但明显高于汉诺坝中生代形成的捕虏体麻粒岩.由此看来,早期(太古宙-古元古代)下地壳的水含量要比中生代形成的下地壳高得多,这可能指示不同时代下地壳在形成机制和性质上的不同.  相似文献   

Mineral chemistry,P-T-t paths and exhumation processes of mafic granulites in Dinggye,Southern Tibet   总被引：4，自引：0，他引：4  

LIU Shuwen  ZHANG Jinjiang  SHU Guiming & LI Qiugen The Key Laboratory of Orogenic Belts  Crustal Evolution  Ministry of Education  School of Earth  Space Sciences  Peking Uni-versity  Beijing  China 《中国科学D辑(英文版)》2005,48(11):1870-1881

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