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| 1 | Thrusting of the North Lhasa Block in the Tibetan Plateau显示文摘A huge thrust system, the North Lhasa Thrust (NLT), was discovered in the northern Lhasa block of the Amdo-Bam Co profile. The NLT consists of the Dongqiao-Lunpola thrust (DLT), the west Namco thrust (WNT) and the south Damxung thrust (SDT) and ductile shear zones, ophiolite slices and folds extending in a WNW direction. Major thrust faults of the NLT seem to merge into a single deep-seated detachment of the upper-crust and totally displaced southward as far as 100-120 km. Chronological analyses with 39Ar-40Ar of plagioclase and hornblende, Rb-Sr isochron of minerals and fission-tracks of apatite from mylonite within the WNT yield ages of 174-173 Ma, 109 Ma and 44 Ma,showing 3 periods of thrusting in the north Lhasa block caused by subduction of the Tethys oceanic plate and the IndiaEurasia continental collision respectively. | WuZhenhan HuDaogong YePeisheng ZhaoXun LiuQisheng | 2004 | Acta Geologica Sinica(English Edition)2004，78，1： | 16 |
| 2 | SHRIMP U-Pb zircon dating on Nyainqentanglha granite in central Lhasa block显示文摘The Nyainqentanglha granite, a batholith with an area of 1500 km^2 in the central Lhasa block, comprises mainly medium-fine-grained biotite monzonitic granite and medium-coarse-grained biotite monzonitic granite. Their contact relationship suggests that the medlum-fine-grained biotite monzonitic granite was crystallized earlier than the medium-coarse-grained monzonitic granite. A SHRIMP U-Pb dating on zircons from representative samples of the batholith shows that the crystallization age of the medium-fine-grained biotite monzonitic granite is 18.3 Ma and that of the medium-coarse-grained monzonitic granite is 11.01 Ma. The emplacement and crystallization of the Nyainqentanglha granite, the youngest granite batholith ever known inside the Lhasa block, have a close relationship with the collisional orogeny, crustal thickening, plateau uplifting,E-W crustal extension and have a dynamic genetic relationship with the crustal partial melting. | LIUQisheng WUZhenhan HUDaogong YEPeisheng JIANGWan WANGYanbin ZHANGHancheng | 2004 | Chinese Science Bulletin2004，49，1： | 9 |
| 3 | P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications显示文摘Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (Mi) is preserved only in the granulites and represented by plagioclase+homblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of gamet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of horublende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of homblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of gamet+clinopyroxene+plagioclase+homblende were estimated at 769-905°C and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800°C and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708°C and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively. | HUDaogong WUZhenhan JIANGWan YEPeisheng | 2004 | Acta Geologica Sinica(English Edition)2004，78，1： | 8 |
| 4 | Quaternary Geology and Faulting in the Damxung-Yangbajain Basin显示文摘The detailed geological mapping, conducted in the Damxung-Yangbajain basin, shows that there are many types of deposits formed since the Pliocene. The oldest sediments are formed during the Pliocene. The most prominent sediments are three sets of moraines and fluvioglacial deposits. The ESR, U-series and OSL dates indicate they are formed about 700-500 ka B.P., 250-125 ka B.P. and 75-12 ka B.P. respectively and indicate that there are three glacial periods since the mid-Pleistocene in the Nyainqentanglha Range. Along the southeast side of the Nyainqentanglha Range, the main southeast dipping fault zone which bounds the Damxung-Yangbajain Graben on its western edge was mapped. The fault zone consists of three secondary fault zones and their initiation ages that the fault zones became active gradually decrease southeastward. Prominent faulting occurred in about 700-500 ka B.P., 350-220 ka B.P., ~140ka B.P. and 70-50 ka B.P. since the mid-Pleistocene. The height of fault scarps which offset the sediments formed since the mid-Pleistocene suggest that the vertical slip rates change between 0.4 -2 mm/a and the cumulative average vertical movement at rates of 1.1±0.3 mm/a during the Quaternary period and the Holocene vertical throw rate is 1.4+0.6 mm/a along the fault zones on the western side of the Damxung-Yangbajain Graben. | WUZhonghai ZHAOXitao WUZhenhan JIANGWan HUDaogong ZHOUChunjing | 2004 | Acta Geologica Sinica(English Edition)2004，78，1： | 6 |
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