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Research on Early Palaeozoic Tectonic Characters of DHNS, GS

Author: LuoMingFei
Tutor: ZhongKangHui
School: Chengdu University of Technology
Course: Mineralogy,petrology, Mineral Deposit Geology
Keywords: Early Paleozoic Party Nan Shan Volcanic Tectonic environment
CLC: P542
Type: Master's thesis
Year: 2010
Downloads: 48
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Abstract

Party Nan Shan Subei Mongolian Autonomous County in Gansu Province Yanchi Bay Township area. Party Nan Shan region developed a set of early Paleozoic strata. Formation from the old to new forces were I ditch group (O1-2WL), Yanchiwan (O2yc), multi-SUOQU group (O3ds) and Silurian Period Baron Gong Gaer group (Sbl). Early in the ditch Austrian Taoshi Wu Li Qun (O1-2WL) development has three lithologic, were I in the base period of force ditch volcanic group, group I, Sec force ditch acidic volcanic rocks and I force three sections of crystalline limestone trench segment group . Mafic volcanic rocks which is keratophyre lithologic lava breccias, spilite breecia, basaltic lava breccia, almond-shaped basalt, massive basalt, spilite. Both tholeiitic rocks have calc-alkaline basalt series series. Lithologic in acidic volcanic rocks of andesite, Shiying An Shan porphyry, sub Shiying An Shan porphyry. Dominated by calc-alkaline series. Constant element content and mafic rocks similar segments. REE characteristics, low REE, ΣREE39.29 ~ 1205.41μg / g, LREE / HREE = 3.42 ~ 10.51, with weak to moderate positive Eu anomalies, trace elements for the Sr, Rb, Ba, Th of selective enrichment, which is strongly enriched in Th, depleted Nb, Zr, Ti, Y, Yb, with island arc volcanic rocks. In chemical composition and evolution of mafic volcanic rocks relationship. I force ditch volcanic rocks generally reflect the ocean environment and developed on the oceanic crust oceanic island volcanic arc. Yanchiwan Middle Ordovician volcanic rocks, lithology is mainly dark green to muddy siltstone, greywacke feldspar and quartz, feldspar and quartz siltstone and fine sand, feldspar greywacke, quartz sericite phyllite, etc. graded bedding development. Rock composition in mixed groups and higher levels of calcium debris, composition and structure of the low maturity. With sub-sea - sea abyssal facies turbidites and mudstone flysch portfolio construction, reflecting its continental slope formed in the transition to the abyssal plain depositional environment. Late Ordovician Dosso song group containing sandstone and volcanic rock. Dosso song still has a constant element volcanic oceanic tholeiitic basalts. Combined with South Qilian Late Ordovician volcanic geochemistry that many SUOQU volcanic island arc volcanic rocks, indicating that the party Nan Shan exist Late Ordovician subduction. Silurian Baron Gong Gaer group lithology, tapering from the lower part of the sandstone, fine sandstone becomes pebbly, variable sand siltstone, variable calcareous lithic sandstone, lithic sandstone, silty slate, sericite slate, chlorite slate, consisting of abyssal flysch and the upper conglomerate, hard sandstone and other coarse clastic rocks of the sea - continental molasse components. Space with the transition from the north to the south shallow deep dustpan-shaped features, the performance of a typical foreland basin sedimentary characteristics, reflecting the Silurian period the party Henan Mountains ocean basin off into continental collision phase. The area is divided into two granite, the first phase of the Cambrian - Ordovician I-type granites and Adakite major formative period in the 492 ~ 442Ma, responded to the Ordovician period of its existence the party Ocean South Qilian Mountains in Henan northward subduction process. The second period for the IS Devonian granite, forms times for 429 ~ 381Ma, should Qilian plate subduction. Development within the region also have 365Ma mafic dikes, representatives formed in orogenic uplift, stretching phase. According to various periods of rock characteristics of tectonic environment, the establishment of the party Nan Shan Early Paleozoic tectonic evolution mode: ① Tao Shinan Qilian Early Ordovician oceanic subduction by the extensional environment into the environment, in the oceanic crust formed on the basis of the intra-oceanic arc volcanic rocks, and accompanied by the Qilian belt I-type granite intrusion; ② Middle Ordovician tectonic movement once existed a quiet period, making the mountain area in Henan Party formed a deep - bathyal turbidite flysch; ③ late Ordovician Tao Shinan Qilian Ocean again massive dive and party Nan Shan - Lajishan - Fog places mountain line forming trench-arc basin system; ④ Early Silurian Period at the beginning of the South Qilian ocean basin off the party Nan Shan region into collision orogenic process, the final Silurian end fold collision orogeny, has been extended to the Early - Middle Devonian, which then enters the Late Paleozoic intracontinental tectonic new period of development.

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