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Petrological, Geochemical, Geochronological Characteristics and Their Tectonic Significance of Triassic Volcanic Rocks in Southern Lancangjiang Zone

Author: WangShuo
Tutor: DongGuoChen
School: Chinese Geology University (Beijing)
Course: Mineralogy,petrology, Mineral Deposit Geology
Keywords: The Lancang South zone Triassic volcanic rocks Arc volcanic rocks Ar-Ar plateau age
CLC: P588.14
Type: Master's thesis
Year: 2011
Downloads: 109
Quote: 1
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Abstract


The South the Lancang with volcanic rocks is an important part of the Sanjiang Paleo-Tethys tectonic development process, clarify its formation age, geochemical characteristics reveal the the South Lancang with the complexity of the Paleo-Tethys tectonic evolution and its dynamics mechanism is essential. This article by Triassic volcanic rocks in the south zone of the Lancang study of volcanic rocks, geochemistry and Ar-Ar isotopic characteristics. In the the South the Lancang with northern Yunxian vicinity, in the Late Triassic volcanic rocks outcropping complete, bottom-up can be divided into the Triassic the busy Huai group (T2m), Upper Triassic Dingxi group (T3x) and three on Permian Mans exchange River group (T3mh). The busy Huai group mainly acidic volcanic rocks, the folder for a set of rhyolite pyroclastic rocks combination; development of small Dingxi group for the the mafic lava folder pyroclastic rocks; Mans exchange River Formation rhyolitic pyroclastic rocks the bimodal basalt coexist volcanic rocks. Yunxian the Triassic volcanic rock samples SiO2 content is concentrated in two regions of the 46.05% -54.50% 67.85% -77.34% of the basic and acidic, the lack of intermediate volcanic rocks, Al2O3 content, focused on the 11.60% -18.26%, with an average value of 14.79%. Low TiO2 content of 0.17% - 2.23%, and an average of 0.87%. K2O/Na2O to 0.05-1.39. Total rare earths 80.20ppm-302.11ppm, (La / Yb) N for 5.23-22.00, average 11.46. The chondrite-normalized REE patterns diagram showed the rightist mode, light rare earth medium enrichment, HREE loss. Has a negative Eu anomaly, δEu between 0.43-1.08 between average 0.71. Rock general enrichment of Pb and large ion lithophile elements Rb, where Pb is strongly enriched. Sr and high field strength elements Nb, Ta relative losses. The geochemical characteristics and tectonic discrimination diagrams indicate South Lancang with Triassic volcanic rocks has dual properties arc volcanic continental intraplate volcanic rocks, suggesting the formation environment for the transitional continental margin orogenic belt environment. Ar-Ar age of the the South Lancang band near the southern Jinghong quartz andesite samples collected test the resulting plateau age of 236.7 ± 2.2? Ma for the Middle Triassic. Volcanic Rocks test results, speculated that the Lancangjiang ocean the main collisional Early Triassic, early Middle Triassic and Late Triassic stress relaxation stage after the collision with the ocean basin continued subduction stage, to the late Triassic final the end of the subduction, Lancangjiang ocean off.

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CLC: > Astronomy,Earth Sciences > Geology > Petrology > Classification of rocks > Magmatic rocks ( igneous ) > Extrusive (volcanic )
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