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 tectonometam...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 the later evolution (1～2mm/a).展开更多
Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qin...Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qinghai—Tibet plateau. Eclogites occur as pods in the garnet\|muscovite gneiss of the Dakendaban Group (or called Shaliuhe Group in Dulan) of Upper Proterozoic age. In general, the pods of eclogite vary in size; most of them are less than 20m×10m, some large ones up to about 100m×50m. The eclogite\|hosted gneiss is pale\|gray in color, consisting mainly plagioclase and quartz, and minor muscovite (5%～10% in vol.) and garnet (1%～2%). Some of the country rocks of eclogite are mica\|quartz\|(feldspar) schist, quartzite, and ultramafic rocks, the latter also occur in blocks.Over 50 pods were found in a belt of 10km×3km in the Da Qaidam region (No.1 location). Only a few pods of eclogite were found in the Xitieshan region in 1999 field expedition (No.2 location). Eclogite in Dulan occurs in the Proterozoic strata of Shaliuhe Group (same as the Dakendaban Group but with a different name). The eclogites in the Dulan region (No.3 location) expose about 10km wide in SN and an unknown length in EW, and can be subdivided into two belts, the North Eclogite Belt of Dulan (NEBD) and the South Eclogite Belt of Dulan (SEBD).展开更多
The well preserved eclogitic rocks of the Tso Morari dome in eastern Ladakh, northwest Himalaya, provide information relevant to the exhumation of high pressure/low temperature rocks, and the early stage of the Himala...The well preserved eclogitic rocks of the Tso Morari dome in eastern Ladakh, northwest Himalaya, provide information relevant to the exhumation of high pressure/low temperature rocks, and the early stage of the Himalayan orogeny. The Tso Morari unit outcrops south of the Indus suture zone (Fig.1). The eclogitic dome is underlined on its eastern part by the Zildat normal fault where serpentinite lenses and partially hydrated peridotites are abundant. The close association of the high pressure rocks and serpentinites suggests a possible role of serpentinites in the exhumation of ultrahigh\|pressure rocks. To evaluate this possibility, geochemical analyses were carried out on the serpentinites closely associated with the Tso Morari eclogites.展开更多
文摘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 the later evolution (1～2mm/a).
文摘Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qinghai—Tibet plateau. Eclogites occur as pods in the garnet\|muscovite gneiss of the Dakendaban Group (or called Shaliuhe Group in Dulan) of Upper Proterozoic age. In general, the pods of eclogite vary in size; most of them are less than 20m×10m, some large ones up to about 100m×50m. The eclogite\|hosted gneiss is pale\|gray in color, consisting mainly plagioclase and quartz, and minor muscovite (5%～10% in vol.) and garnet (1%～2%). Some of the country rocks of eclogite are mica\|quartz\|(feldspar) schist, quartzite, and ultramafic rocks, the latter also occur in blocks.Over 50 pods were found in a belt of 10km×3km in the Da Qaidam region (No.1 location). Only a few pods of eclogite were found in the Xitieshan region in 1999 field expedition (No.2 location). Eclogite in Dulan occurs in the Proterozoic strata of Shaliuhe Group (same as the Dakendaban Group but with a different name). The eclogites in the Dulan region (No.3 location) expose about 10km wide in SN and an unknown length in EW, and can be subdivided into two belts, the North Eclogite Belt of Dulan (NEBD) and the South Eclogite Belt of Dulan (SEBD).
文摘The well preserved eclogitic rocks of the Tso Morari dome in eastern Ladakh, northwest Himalaya, provide information relevant to the exhumation of high pressure/low temperature rocks, and the early stage of the Himalayan orogeny. The Tso Morari unit outcrops south of the Indus suture zone (Fig.1). The eclogitic dome is underlined on its eastern part by the Zildat normal fault where serpentinite lenses and partially hydrated peridotites are abundant. The close association of the high pressure rocks and serpentinites suggests a possible role of serpentinites in the exhumation of ultrahigh\|pressure rocks. To evaluate this possibility, geochemical analyses were carried out on the serpentinites closely associated with the Tso Morari eclogites.
