气候变化领域集成服务门户(CCPortal): The absence of high-pressure metamorphism in the inverted Barrovian metamorphic sequences of the Arun area; eastern Nepal and its tectonic implication

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DOI	10.1007/s00531-019-01816-5
	The absence of high-pressure metamorphism in the inverted Barrovian metamorphic sequences of the Arun area; eastern Nepal and its tectonic implication
	Imayama T.; Uehara S.; Sakai H.; Yagi K.; Ikawa C.; Yi K.
发表日期	2020
ISSN	14373254
起始页码	465
结束页码	488
卷号	109 期号:2
英文摘要	The metamorphic pressure–temperature (P–T) conditions across the Main central thrust (MCT) in the Arun area have been investigated. The MCT marks the tectono-metamorphic boundary between the overlying high-grade High Himalaya crystalline sequences (HHCS) and the underlying low-grade Lesser Himalaya sequences (LHS). The metamorphic rocks regionally preserve an inverted Barrovian sequence (i.e., intermediate P/T type metamorphism) devoid of previously reported high-pressure metamorphism. The metamorphic grade increases upwards from 670–740 °C and 6.9–9.4 kbar in the MCT zone and lower HHCS to 760–835 °C and 10.0–11.1 kbar in the middle HHCS. Orthoamphibole gneisses in the middle HHCS yield prograde Barrovian-type metamorphism, such as staurolite inclusions in garnets, showing an intermediate P/T gradient. The differences in the tectonic setting and metamorphic evolution imply that the metamorphic units in the Arun area do not correspond to the other high-pressure units in eastern Himalaya. Zircon and monazite U–Pb ages from kyanite gneiss of the lower HHCS reveal the MCT activity, associated with fluid-present anatexis, at ca. 20–14 Ma. Furthermore, similar K–Ar white mica ages (ca. 13–7 Ma) in the hanging wall and footwall of the MCT could represent the timing of later deformation events in shear zones or cooling, possibly associated with exhumation accompanied by activities on younger, structurally lower thrust faults such as the lower MCT. The similar P–T conditions near the MCT in this area could result from recrystallization during syn-metamorphic thrusting, whereas the middle HHCS away from the MCT preserve the original Barrovian metamorphic sequences related to crustal thickening. This and previous studies imply that different P–T profiles near the MCT according to each transect observed in Nepal could be apparent and the cumulative result of polyphase metamorphism. © 2020, Geologische Vereinigung e.V. (GV).
英文关键词	Eastern Nepal; Geochronology; High-pressure metamorphism; Inverted metamorphism; Main central thrust
语种	英语
scopus关键词	amphibole; crustal thickening; deformation mechanism; geochronology; gneiss; P-T conditions; thrust; ultrahigh pressure metamorphism; Nepal
来源期刊	International Journal of Earth Sciences
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/147719
作者单位	Research Institute of Natural Sciences, Okayama University of Science, Okayama, 700-0005, Japan; Emeritus Professor of Kyoto University, Kyoto, Japan; Hiruzen Institute for Geology and Chronology, Okayama, 703-8252, Japan; Geochronology Team, Korea Basic Science Institute, Chungbuk, 363-883, South Korea
推荐引用方式 GB/T 7714	Imayama T.,Uehara S.,Sakai H.,et al. The absence of high-pressure metamorphism in the inverted Barrovian metamorphic sequences of the Arun area; eastern Nepal and its tectonic implication[J],2020,109(2).
APA	Imayama T.,Uehara S.,Sakai H.,Yagi K.,Ikawa C.,&Yi K..(2020).The absence of high-pressure metamorphism in the inverted Barrovian metamorphic sequences of the Arun area; eastern Nepal and its tectonic implication.International Journal of Earth Sciences,109(2).
MLA	Imayama T.,et al."The absence of high-pressure metamorphism in the inverted Barrovian metamorphic sequences of the Arun area; eastern Nepal and its tectonic implication".International Journal of Earth Sciences 109.2(2020).