Yarlung Zangbo River Combined With The Eastern Section The Ophiolitic M¨¦lange Features And To Explore The Formation Of The Environment With The Times

The Brahmaputra Suture Zone (BSZ) with its Ophiolite melange, composed of a series of arc-back basin, closed orogenic zone and their relics, resulted from Tethys subduction Southern. The Ophiolite melange, outeropsis western Rikazerenbu, is a typical combination of minor ophiolite melange, and was considered the best and perfectest in construction because of no strong sectonicsm. Eastern section of BSZ Lang county to Linzhi including its location, boundary , materal composition , structural style , construction in the section , and characters is unclear because of strong tectonicsm which came through compression , collision , striokeslips , rapidly structural and uplift.Based on the 1/250000 regional geological survey, we worked on Linzhi county from 2001-2004 and so on, and using recent dateun from 1/200000 regional geological survey and research-ing on the area (Lang county-Linzhi county), the paper focus on the different of phisolope and relative parameters between Gangdisi Arc basement and Himalaya basement, and suggest a important geological boundary located on Brahmaputra between Gangdisi arc and Brahmaputra, set on Zedang-Jiacha-Langlagaze Feature. It is considered that the northern of the boundary is Gangdisi Epicontin-ental Volcanic Arc, to southward, the Arc, southward, links with Himalaya block, in Naidong-Jindong-Molo ductile fracture.According to the petrologcal, petrochemstrical and geochemistrical research, it is suggested that Yeba Fm, Bima Fm and Danshiting Fm of Jurossic-Neogene confirme to prc-volcanic rocks, the early cretaceous I-type granites relate with plate subduction, and the late cretaceous S-type granites related with plate collision, composed of epicontinental volcanic-magmatic are coordinated with BSZ. By Eup, the temperature range is 400-500℃, the pressure is 4-8kb in muscovite of Lang county ophiolite melange. The melange is of low greensclist, and containsmany aetinolite, clworitoid and 2M1 muscovite (b=9.030A), therefore displays high-pressure phrase, and makes up of double metamorphic zone with Gangdisi epicontinenta volcanic-magmatic arc.More perfect ophiolite structure were discovered, such as ultrabasic rock, pillow laua, basalt with vitreous matrix and siliceous rock, in yumen of Lang county.Based on the detail research in the ophiolite melange of Luobusa and Lang county, the following hypotheses wasproviede for:1. There are Utile in terbeds of basaltic andesite, represented in continental margin (epicontinental) orogenic zone, in the basic lava, and thickness of mafic rock, display oceanic crust in the ophiolite is more smaller than that, in modern oceanic crust.2. AH of chrome spinel, in transformed peridotite, is magnesio chromohercynite which is intrusived at the ocean marginal orogenic zone (Maipas.el al, 1975 ) .3. The flysch, with some basalts, is difference from modern ocean, but similar to arc-ophiolite sequence , represents relics of ocean crust in early ocean basin .4. There are some orthorhombic pyroxene, monocline pyroxene and plagioclase phenocryst erupted at benthic enviroment more than olivine in the pillow.Furthermore, depends on the characters of petrochemistrical and geochemistrical representation, the melange, formed at arc-back extensive ocean-basin, is belonge to small ocean-basin more than lost ocean crust.Therefore, BSZ is a relic of arc-back extensive ocean-basin, a sub-suture-zone, but not a relic of new Tethys ocean crust.The melange contains some chert flysch, with Radiolaria (middle to late Triassic), and marble, with Conodonts (early to late Permian), it suggests that the ocean-basin should from in late Triassic or more early, phechronological range is from late Triassic-early Jurassic to middle Jurassic the periodtite , transformed , maybe began at Triassic , and ended at cretaceous , is a lectonic-petrologic stratum . The melange or BSZ is of crust.