The Mesozoic metamorphic–magmatic events in the Medog area, the Eastern Himalayan Syntaxis: constraints from zircon U–Pb geochronology, trace elements and Hf isotope compositions in granitoids

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• 作者：Hanwen Dong ; Zhiqin Xu ; Yuan Li ; Zhao Liu…
• 关键词：Mesozoic ; Zircon ; Medog area ; The Eastern Himalayan Syntaxis
• 刊名：International Journal of Earth Sciences
• 出版年：2015
• 出版时间：January 2015
• 年：2015
• 卷：104
• 期：1
• 页码：61-74
• 全文大小：3,368 KB
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• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Geology
  Geophysics and Geodesy
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1437-3262

文摘

Based on the regional geological mapping, several granitoid intrusions had been discovered in the Eastern Himalayan Syntaxis (EHS). In order to constrain their petrogenesis and discuss their relations with the regional tectonics, we carried out U–Pb dating, trace elements and Hf isotope geochemistry studies on zircons separated from the granitoid rocks, in the area of the EHS. In this contribution, the granitoid rocks are mainly composed of diorites (X20-1-6) and granitic gneissic rocks (X2-15-1). The U–Pb zircon dating of diorites yields a crystallization age of 193.8?±?2.0?Ma. These zircon have ε Hf(t) values ranging from ?.48 to ?.05, indicating an involvement of ancient crustal materials in the generation of these igneous rocks. The zircons from the Medog granitic gneissic rock commonly show zoning structures. The REE patterns and abundances of the inherited cores are different from those of the oscillatory rims. The LA–ICP-MS U–Pb zircon in situ analyses indicate that: (1) the zircon cores give multi-stage magmatic event ages ranging from 516 to 1,826?Ma, of which six ages are converged on 1,330-11?Ma, it is considered that the migmatitic gneiss has been formed in this time, and (2) while the zircon rims yield 206Pb/238U weighted mean ages of 217.4?±?3.0?Ma (MSWD?=?3.2), which was interpreted to represent the ages of the Triassic anatexis. Their ε Hf(t) values range from ?8.98 to ?.36 and ?4.22 to 8.72, respectively. The timing of the anatexis in the Medog area is coeval with the widespread metamorphism in Lhasa terrane.