Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau

Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau The Bayan Har Orogen comprises a major part of the “Qingzang-Dianxi fold region” in western China. It preserves important information of the tectono-thermal evolution covering the time span from the closure of the Paleo-Tethys Ocean up to the formation of the Himalayas. Low temperature metamorphic indicators, such as mineral assemblages, illite “crystallinity” (IC), chlorite “crystallinity” (CC), illite polytype, b-cell dimension of K-white micas, geothermometry of selected minerals were analyzed. The values of Kübler index (KI) of the Triassic flysch in the Bayan Har Orogen range from 0.23–1.63°Δ2θ while Árkai index (ÁI) in a range of 0.21–0.60°Δ2θ. Iso-thermal zones mapped with KI describe a pair of anchizones and an anchiregion within the Bayan Har Orogen: the “Giant Yushu Anchizone” in the southwest (extending >750km long and 100km wide), the “Zaling-Eling-Lakes Anchizone” in the center (about 150km long and 40km wide) and the “Xing-Tong-Zhe Anchiregion” in the northeast (covering an area of roughly 60,000km2). They are separated by diagenetic zones. Peak metamorphic conditions are estimated around 280–330°C and a low to intermediate (N. New Hampshire) pressure type. A slight change with increasing then decreasing pressure was observed from SW to NE. The relationship between anchimetamorphic pattern of Triassic flysch and large-scale folds and faults indicates syn- to post structural metamorphism. Compression at the end of the Triassic, induced by the interaction of the Tarim, North China and Indian blocks caused the closure of the Paleo-Tethys Ocean and led to the folding of the Triassic flysch within the Paleo-Tethys Ocean basin. Anchimetamorphism may have been caused by crustal thickening of >10km due to an accretionary wedge setting and a temperature increase in those rocks due to burial. Such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic-palaeogeograph and the evolutionary history of Tibetan plateau. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Tectonophysics Elsevier

Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau

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Publisher
Elsevier
Copyright
Copyright © 2017 Elsevier B.V.
ISSN
0040-1951
eISSN
1879-3266
D.O.I.
10.1016/j.tecto.2017.12.020
Publisher site
See Article on Publisher Site

Abstract

The Bayan Har Orogen comprises a major part of the “Qingzang-Dianxi fold region” in western China. It preserves important information of the tectono-thermal evolution covering the time span from the closure of the Paleo-Tethys Ocean up to the formation of the Himalayas. Low temperature metamorphic indicators, such as mineral assemblages, illite “crystallinity” (IC), chlorite “crystallinity” (CC), illite polytype, b-cell dimension of K-white micas, geothermometry of selected minerals were analyzed. The values of Kübler index (KI) of the Triassic flysch in the Bayan Har Orogen range from 0.23–1.63°Δ2θ while Árkai index (ÁI) in a range of 0.21–0.60°Δ2θ. Iso-thermal zones mapped with KI describe a pair of anchizones and an anchiregion within the Bayan Har Orogen: the “Giant Yushu Anchizone” in the southwest (extending >750km long and 100km wide), the “Zaling-Eling-Lakes Anchizone” in the center (about 150km long and 40km wide) and the “Xing-Tong-Zhe Anchiregion” in the northeast (covering an area of roughly 60,000km2). They are separated by diagenetic zones. Peak metamorphic conditions are estimated around 280–330°C and a low to intermediate (N. New Hampshire) pressure type. A slight change with increasing then decreasing pressure was observed from SW to NE. The relationship between anchimetamorphic pattern of Triassic flysch and large-scale folds and faults indicates syn- to post structural metamorphism. Compression at the end of the Triassic, induced by the interaction of the Tarim, North China and Indian blocks caused the closure of the Paleo-Tethys Ocean and led to the folding of the Triassic flysch within the Paleo-Tethys Ocean basin. Anchimetamorphism may have been caused by crustal thickening of >10km due to an accretionary wedge setting and a temperature increase in those rocks due to burial. Such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic-palaeogeograph and the evolutionary history of Tibetan plateau.

Journal

TectonophysicsElsevier

Published: Jan 16, 2018

References

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