The Rock Features And Tectonic Significance Of Hyperplasia Of Depositional Environment Analysis In Central Tibet Qiangtang, Southern Qiangtang

The study area is located in central Qiangtang area south of Mayer Kangri and Snow River region. Tectonic position is exposed in the middle of Long Mu Cuo-Shuang Hu suture zone, The main lithology is Early Paleozoic Ejiumai formation complex(E1-2), The Carboniferous –Permian Gangtangcuo formation complex((CP2)g), Carboniferous–Permian Xueshuihe formation complex((C- P2)x), The Middle-late Triassic Mayer Kangri formation complex(T2-3m). In this paper, we take test analysis for four lithological profile of the sedimentary terrain in accretion melange belt, and using petrological, mineralogical and geochemical methods to analyze the basalt and sandstone. The results show that:Mayer Kangri formation complex and Gangtangcuo formation complex source rock sedimentary environment is submarine fan deposits, Xueshuihe Rock formation complex is semi-deep-deep sea sediments, Paleozoic rock group Ejiumai formation complex is shallow marine depositional environment.Xueshuihe basalt has High levels of Ti O2、P2O5 and REE, the LREE and HREE are strong contrast. Collection of large ion lithophile element Ba、Rb and high field strength elements Zr、Th、Hf, geochemical characteristics and the distribution pattern of trace and rare earth elements are both similar to the standard oceanic island basalt(OIB). Geochemical discrimination diagram show it is the oceanic plate of island environment, the process of magma intrusion had a crustal material contamination, but the extent of dye mixture is not deep.Mayer Kangri sandstone REE is high, the REE partition figure is similar to the oceanic island arc graywacke that Bhatia put forward. The LREE is obvious enrichment, Eu negative anomaly is not obvious, Ce is not abnormal, is not similar to the oceanic island arc graywacke that Bhatia put forward, and continental island arc epicontinental graywacke. In the tectonic setting discrimination, Provenance showed relatively complex, more belong to the oceanic island arc, And tend to continental island arc tectonic environment. Through the analysis of the heavy mineral of the Gangtangcuo rock group and Mayer Kangri rock grou sandstone, Its source is likely to be an unstable orogenic belt and even the volcanic arc. From the perspective of a large arc volcanic rocks, Is more likely to be related to the sediments that distant ocean bring to.Analysis of several major rock In the hyperplasia of mixed rock band, and Combining previous research data, we can draw the conclusion that the evolution characteristics In southern qiangtang hyperplasia mixtite belt : At the beginning of the early Permian, The ancient tethys ocean began to dive, Xueshuihe oceanic island basalt is geological body that the ancient tethys ocean subduction to reduce residual; The late carboniferous to the early Permian period, Heap long jing hui rock Permian ophiolite represents the ancient tethys ocean initial open product; Middle-late Triassic period, the ancient tethys ocean subduction cut has begun to occur, With the formation of metamorphic and island arc volcanic rocks, Subduction is complete to the late Triassic period, the ancient tethys ocean closed. The south and north Qiangtang collide with each other, under the action of a strong collision and formed a typical orogenic belt hyperplasia complex.