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DIFFUSION MODeLLING IN GARNeT FROM TSO MORARI eCLOGITe AND IMPLICATIONS FOR eXHUMATION MODeLS

地学前缘 2000年第S1期7卷 25-27页

作者： Patrick J.,O’Brien 1,Himanshu K. Sachan 2 (1 Bayerisches Geoinstitut, Universitt Bayreuth, D\|95440 Bayreuth, Germany,e\|mail:Patrick. Obrien@uni\|bayreuth.de 2 wadia institute of himalayan geology, dehra dun\|248001, india,e\|mail:wihg@giasdl01.

The results of recent geothermobarometric and geochronological investigations of scarce eclogites of the NW Himalaya (Tso Morari (Ladakh), india and Kaghan Valley, Pakistan) have caused a major rethink of tectonometamorphic models for india\|Asia collision. Numerous petrologic studies have been undertaken on the age and origin of metamorphism in the Higher himalayan Crystallines (HHC) and Lesser Himalaya formations (LH) and their relationship to granite magmatism and movements along the Main Central Thrust (MCT) and South Tibetan Detachment Fault (STDF). However, all of these events are essentially Miocene (or younger) in age and can clearly be distinguished from subduction and exhumation processes undergone by the eclogites which are of eocene age (Tonarini et al. 1993; Spencer & Gebauer; 1996; de Sigoyer et al. 1999) and relate to the very early stages of the collision. eclogites of eastern Ladakh are mafic lenses found in granitic gneisses (Ordovician intrusive age: Girard & Bussy 1999) and their surrounding late Pre\|Cambrian to early Cambrian sedimentary units in the Tso Morari dome (see Steck et al. 1998). Detailed petrological and geochronological studies (Guillot et al. 1997; de Sigoyer et al. 1997, 1999) have identified an eclogite facies stage (2000±300)MPa, (580±60)℃ followed by isothermal decompression associated with glaucophane growth at around (1100±200)MPa. Dating of different phases by different methods yielded ages around 55Ma for this stage ((55±17) Ma, U\|Pb, Aln; (55±12) Ma, Lu\|Hf, Grt\|Cpx\|Rt; (55±7) Ma, Sm\|Nd, Grt\|Gln\|Rt). A subsequent amphibolite facies overprint at slightly higher temperature (610±70)℃ was dated at 45～48Ma (metabasite: (47±11) Ma, Sm\|Nd, Grt\|Hbl; metapelite: (45±4) Ma, Rb\|Sr, Mu\|Ap\|WR and (48±2) Ma, Ar\|Ar, Phe). By (30±1) Ma (Ar\|Ar, Bt\|Mu) retrogression into the greenschist facies had occurred (de Sigoyer et al. 1999). These data indicate a two stage history with early exhumation being much faster (>4mm/a) than

关键词： eclogite Tso Morari diffusion modelling garnet temperature\|time\|path

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GeOBAROMeTRIC CONSTRAINTS ON THe DePTH OF eMPLACeMeNT OF GRANITe FROM THe LADAKH BATHOLITH, NORTHWeST HIMALAYA, india

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地学前缘 2000年第S1期7卷 110-111页

作者： T. N. Jowhar(wadia institute of himalayan geology,33 General Mahadeo Singh Road, dehra dun\|248001, india,e\|mail: wihg@***)

The Ladakh batholith is exposed along the 600km long and 20 to 80km wide NW—Se trending Ladakh range north of the Indus\|Tsangpo Suture Zone. It was emplaced into an unmetamorphosed thick pile of mafic and felsic volcanics, ultramafics and sediments of Upper Cretaceous\|eocene age (Dras Volcanics, Khardung Volcanics). The granites from the Ladakh batholith within the Leh\|Khardung La and Sakti—Chang La sections (samples collected between altitude of 3600m and 5440m above mean sea level, Fig.1) have been estimated for pressure and temperature of crystallization employing the hornblende geobarometer of Schmidt (1992) and hornblende\|plagioclase geothermometer of Blundy and Holland (1990), with the results of pressure of (250±60)MPa and temperature of (695±22)℃. Therefore, these granites were solidified at a depth of (8 6±2)km suggesting an unroofing of this thickness in this region. The importance of this geobarometric data in conjunction with age data on the cooling and unroofing history of the Trans\|himalayan Ladakh batholith and geodynamic implications of the india—Asia collision are discussed.

关键词： Himalaya Ladakh batholith geothermobarometry granite

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SUPRA-SUBDUCTION ZONe eNVIRONMeNT AND eCONOMIC POTeNTIAL OF THe NIDAR OPHIOLITe OF INDUS SUTURe ZONe, eASTeRN LADAKH,THe HIMALAYA

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地学前缘 2000年第S1期7卷 434-435页

作者： N.Siva Siddaiah[WT5,5”BX](wadia institute of himalayan geology,33,General Mahadeo Singh Road,dehra dun\|248001,india)

Ophiolites along the indus Suture Zone (ISZ) are important not only for the information they provide about the india\|eurasia collision,but may also contain economic mineral deposits (chrome,noble metals,and Ni\|sulfides).Several ophiolites occur in the ISZ,and the Nidar ophiolite is one that occurs on the eastern *** paper presents the geochemistry of ultramafic rocks from the Nidar ophiolite to understand tectonic environment and economic *** ophiolite consists of pillow lavas,radiolarian cherts,rodingites,peridotites and *** lower part of the ophiolite consists of tectonized harzburgite,hosting dunite enveloped podiform *** transition zone between upper mantle and lower oceanic crust is characterized by serpentinized dunite with disseminations of *** in Nidar have low whole\|rock values of w (TiO\-2)(0 02%～0 03%), w (Al\-2O\-3)(2%～3%), w (CaO)(0.5%), w (Zr)(40×10 -6 ),and w (Y)(30×10 -6 ),and enriched in refractory elements such as w (Cr)((3000～5000)×10 -6 )and w (Ni)((3000～4000)×10 -6 ).Thus,the Nidar peridotites are more depleted in elements partitioned into the liquid,such as Al and Ca and the moderately refractory element *** peridotites have fractionated chondrite\|normalized PGe *** geochemical characteristics suggests their formation by high degrees of partial melting in a supra\|subduction zone environment,where melting was enhanced by addition of *** Cr # of 0.82 in the chromite of the chromitites also suggests a depleted mantle source and a supra\|subduction zone environment for the host *** formed in supra\|subduction zone setting are very conducive for many metallic and non\|metallic mineral deposits.

关键词： supra\|subduction zone ophiolites mineral potenti al Himalaya

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MAPPING OF OPHIOLITeS IN THe INDUS-SUTURe ZONe OF NORTHWeSTeRN HIMALAYA, USING SATeLLITe ReMOTe SeNSING DATA

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地学前缘 2000年第S1期7卷 116-117页

作者： K.V. Ravindran 1,G. Philip 2(1 Regional Remote Sensing Service Centre, Dept of Space, 4 Kalidas Road, dehra dun\|248001, india 2 wadia institute of himalayan geology, 33\|Gen. Mahadeo Singh Road, dehra dun\|248001,india)

Ophiolites, which have been tectonically emplaced along continental margins and island arcs, are significant to the understanding of mountain belt evolution. In the Himalayas, the ophiolitic suite of rocks occur along the Indussuture zone from Hanle in the southeast to Dras\|Kargil sector in the northwest and it represents the remnant of the compressed uplifted wedge of the oceanic crust between the two colliding continental masses, the indian and the Asian plates.. These ophiolites are temporally and spatially correlated with the culminating phase of the himalayan orogeny. The Indus River flows to its north separating the ophiolite from the Trans himalayan litho\|units. Geological mapping in the hostile and inaccessible mountainous terrains of the Himalaya has always posed a great challenge to geologists. Nevertheless, a number of geologists have undertaken such arduous mapping expeditions in the past and prepared fairly good geological maps of these terrains .However there always existed disputes on the accuracy of lithological boundaries and structural details in these maps because many of these boundaries and structural features were completed through extrapolations and/or interpolations as the ruggedness and inaccessibility of a large part of the terrain forbid physical examination of every outcrop. It is in this context the potential of remote sensing, especially of satellite images, is to be appreciated.

关键词： suture zone ophiolite remote sensing satellite image image enhancement digital terrain model

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LATe PLeISTOCeNe—HOLOCeNe RAPID UPLIFT AND eROSION IN TIBeT: CONSTRAINTS FROM COSMOGeNIC eXPOSURe AGe DATA

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地学前缘 2000年第S1期7卷 327-328页

作者： Kewal K.Sharma (wadia institute of himalayan geology Gen. Mahadev Singh Road, dehra dun,india)

Tibet is the largest and highest plateau on the earth (having 82% of the world’s land surface area falling >4km above sea level) attributed to the india and Asian convergence tectonics. Recently, high\|resolution digital topography data (Fielding et al., 1994) confirmed the earlier observations about flat erosional surfaces in the central part of the plateau (Jujin, et al., 1995) and suggested extraordinary flatness at a wide range of scales. Much of the Tibetan plateau across different accreted terranes has shallow slopes between 5°～10° and variation in relief of about 1 km, except in its marginal parts (himalayan ranges; Kunlun mountains) where rough and high topography with intense fluvial dissections (variations in relief up to 7km) is quite frequent. However, in the southern and south\|central part of the plateau along the Pliocene\|Quaternary grabens, slopes generally steepen.

关键词： Tibetan Plateau cosmogenic 10 Be exposure ages Pleistocene Holocene

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OCCURReNCe OF HIGH-PReSSURe RODINGITeS IN THe OPHIOLITeS OF INDUS SUTURe ZONe, eASTeRN LADAKH,THe HIMALAYA:TeCTONIC AND MeTALLOGeNIC SIGNIFICANCe

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地学前缘 2000年第S1期7卷 115-116页

作者： N.Siva Siddaiah[WT5,5”BX](wadia institute of himalayan geology,33,General Mahadeo Singh Road,dehra dun\|248001,india,Fax:91\|135\|625212)

Recently,considerable attention is being paid in studying the high\|pressure (rodingites and eclogites etc)crustal segments for understanding the architecture and evolution of collision *** paper presents the geology,mineralogy and geochemistry of the rodingites,the first reported occurrence in eastern Ladakh,the *** ophiolite is one of the well exposed,nearly a complete ophiolite of the Indus Suture Zone present in the eastern *** studies across the Nidar ophiolite in the Nidar—Kyun Tso section unraveled the occurrence of relatively strongly developed *** are very hard and *** occur as layers and also as boudins within and at the contacts of the *** rodingites are fine to medium *** is the dominant rodingite mineral and occurs as well developed *** places grossular has coronitic ***,clinozosite,rutile and opaques are the other main Ca\|rich minerals present in *** matrix of the rodingite minerals is highly *** rodingite mineral assemblage indicates the development of rodingite in the pressure and temperature range of 18～25 kbar and 700 to 800℃,*** have high abundances (mass fraction) of CaO (10%～12%) and Al\-2O\-3 (12%) contents and generally low in SiO\-2 (46%) and MgO (7%～8%) *** have chondrite\|normalized Rare earth element (Ree) abundances of 25 to 40× on the LRee and 37 to 50× on the MRee and 15 to 24× on the *** the Ree patterns tend to be concave\|upwards,or relatively light\|Ree depleted with almost no eu\|*** geologic occurrence,the mineralogy and geochemical (major,trace and Ree) data of the rodingites indicate that they were initially gabbros/basalt that have undergone Ca\|metasomatism during serpentinization,followed by high\|pressure recrystallization to rodingites.

关键词： high\|pressure rodingites Nidar ophiolite ISZ Himalaya

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CROSS-SeCTIONS OF THe WeSTeRN himalayan FOOTHILLS:PROBLeMS IN ReSTORATION AND IMPLICATIONS FOR CRUSTAL SHORTeNING

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地学前缘 2000年第S1期7卷 35-36页

作者： A.K.Dubey\+1,R.Misra\+2,S.S.Bhakuni\+1(1 wadia institute of himalayan geology,Gen.Mahadeo Singh Road,dehra dun\|248001 2 KDMIPe,Kaulagarh Road,dehra dun\|248001)

A number of geological cross\|sections from the western himalayan foothills are based on field,seismic reflection,and well data of the Oil & Natural Gas Corporation *** cross\|sections have been described by two contradictory *** first interpretation that depicts a prominent basal decollement above the pre\|Tertiary sequence is used for palinspastic reconstruction,using line length balancing,and determination of total shortening in the *** second interpretation reveals a large variation in the thickness of individual stratigraphic horizons and a number of flower *** flower structures never cut the himalayan thrusts but terminate below *** from the thrusts,the faults cut the younger Siwalik molasse (Middle Miocene—Pleistocene)and even reach to the surface as strike slip *** from the presence of strike slip faults,the other constraints for restoration of the section is oblique ramp structure at the Kangra Reentrant (or Punjab Reentrant).The oblique ramp was formed as a normal fault during the tensional regime in the region and later reactivated as thrust fault during the Tertiary himalayan *** features reveal that the assumption of plane strain deformation is not valid for the ***,the amount of extension during pre\|Tertiary rifting and layer parallel shortening during the Tertiary compressional phase is still unknown hence balancing of the sections is problematic.

关键词： Himalaya thrust tectonics section restoration foreland evolution

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PALAeOSHOReLINeS AS INDICATOR OF LATe CeNOZOIC CLIMO-TeCTONIC CHANGeS IN LADAKH TRANS HIMALAYA:AN ILLUSTRATION FROM TSO KAR LAKe

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地学前缘 2000年第S1期7卷 387-389页

作者： R.K. Mazari, G. Philip[WT5,5”BX](wadia institute of himalayan geology 33, Gen. Mahadeo Singh Road dehra dun\|248 001, india)

Compression movements generated by continental collision apart from leading to uplift of the intervening ocean sediments brings about closure of the oceanic body in a phased *** the culminating phase of uplift when ocean sediments assume the form of a gigantic mountain system, a number of depressions or closed basins of various dimensions are developed in the orogenic belt. These depressions are principally developed by the differential folding of rocks coupled with faulting and thrusting associated with the uplift *** mountain drainage gets impounded in these depressions and gives rise to the formation of lakes..During cold climate the depressions are also developed by glacial abrasion wh ich are subsequently filled by snowmelt to form the lakes of various *** is dotted with a number of lakes of both tectonic and glacial origin and signify the crown stage of tectonic development of the World’s tallest and youngest mountain belt.A number of lake basins have developed in the various longitudinal belts of this mountain system. Several lake basins like Tso Morari, Pangong Tso and Tso Kar have developed in close proximity of the Indus Suture zone (ISZ),the tectonic belt which marks the zone of continental collision between india and *** lakes by virtue of their location, size, sediment content, water chemistry and associated geomorphic features are the potential source of information in regard to climo\|tectonic changes witnessed by Himalaya\|Tibet region in late Cenozoic period. The paper attempts at elucidating these changes that have occurred in Ladakh Trans Himalaya citing the illustration of the Tso Kar lake.

关键词： palaeoclimate tectonics palaeoshorelines Ladakh Tibet Him alayan Lakes Pleistocene

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ReCeNT ADVANCeS IN GeOLOGICAL ReSeARCH IN PARTS OF LeSSeR AND TeTHYS HIMALAYA OF india, SOUTH OF TIBeTAN PLATeAU (KUMAON, GARHWAL AND ARUNACHAL PRADeSH)

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地学前缘 2000年第S1期7卷 66-66页

作者： Vinod C. Tewari(wadia institute of himalayan geology, dehra dun, 248001, india)

Recent advances in geological, palaeobiological and stable isotopic research in Kumaon\|Garhwal Lesser and Tethys Himalaya suggest that india was part of a major single super continent Rodinia during Neoproterozoic—Lower Palaeozoic times. The breakup of Rodinia and fragmentation of Gondwana land, existence of large Proto\|Tethys ocean, low latitude glaciation and global warming reflected by carbon isotopes and imprints of Pan African rifting events have been recently recorded in the indian Himalaya, South of Tibetan Plateau (Tewari, 1998). A detailed correlation of these events in other parts of the NW and Ne Himalaya and China further supports that these events are of global *** complete sequence of Lower Palaeozoic is missing in the Lesser Himalaya after regression of sea in the Lower Cambrian, however three major marine transgressions during Permian, Cretaceous and eocene have been recorded over Terminal Proterozoic/Cambrian sequences. The discovery of microstromatolites and microbiota from the Menga (Buxa) dolomite of eastern Himalaya, Arunachal Pradesh (Tewari, 1999) also confirm Terminal Proterozoic age and sedimentation. The Permian marine transgression throughout the Himalaya suggest birth of Neotethys *** marine reef builders, cyanobacteria\|bacteria and stromatolites of early Carboniferous age were thriving in the himalayan Tethys of india. 13 C records from Lesser and Tethys Himalaya reflect global isotopic variations in Neoproterozoic to Palaeozoic oceans of the world.

关键词： Rodinia Lower Palaeozoic transgression microstromatolite microbiota 13 C records

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PLATINUM-GROUP eLeMeNTS MINeRALIZATION IN THe OPHIOLITeS OF INDUS SUTURe ZONe, eASTeRN LADAKH,THe HIMALAYA

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地学前缘 2000年第S1期7卷 428-429页

作者： N.Siva Siddaiah\+1, A.Masuda\+2[WT5,5”BX](1 wadia institute of himalayan geology,33,General Mahadeo Singh Road,dehra dun\|248 001,india 2 Department of Chemistry,The University of electro\|Communications,Chofu,Tokyo 182,Japan)

Platinum\|Group elements (PGe) along with other highly siderophile elements (HSe) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the ***,the transfer of PGe and other HSe from the mantle may occur by tectonic emplacement of mantle material into the crust or by crystallization of the mantle derived magma in the *** formation and emplacement of ophiolites,is therefore,a suitable transfer mechanism in the enrichment of PGe and other metallic mineral *** of this,in recent years,a great deal of attention is being paid in studying the ophiolites in order to better understand the core\|mantle interaction,chemical evolution of the upper mantle and to explore their noble metal *** ophiolites along the Indus Suture Zone (ISZ) in the Himalayas are tectonically related to india\|eurasia *** their detailed geochemical evolution history and economic potentiality (chromite,PGe,gold and Ni\|sulfides) is not evaluated so *** ophiolite of the eastern Ladakh is one of the ophiolitic suites along the *** general geology of the area was presented in several research *** paper presents the geology,mineralogy and geochemistry of the chromitites and reports on the first platinum\|group elements mineralization to have been discovered.

关键词： PGe concentrations Nidar ophiolite Indus Suture Zone Him alayas

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