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Journal of Geophysical Research 2019 No.7
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Author:
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Xin‐Song Wang1,2 , A. E. Williams‐Jones2 , Xian‐Wu Bi1 , Rui‐Zhong Hu1 , Jia‐Fei Xiao1 , and Ming‐Liang Huang1,3 1 State Key Laboratory of Ore D |
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Abstract:
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The Late Cretaceous is an important geological time interval for the Tibetan Plateau because it
corresponds to the period when the tectonic regime changed from Lhasa‐Qiangtang collision to
Indo‐Asian assembly. However, the nature of and controls on the change in tectonic regime are poorly
constrained. In this paper, we report results of a study of two intrusions in the Changdu area of the Eastern
Tibetan Plateau. Zircon U‐Pb dating shows that both intrusions formed at ca. 77.6–74.3 Ma. The Bangda
intrusion has A‐type granite affinity and a peraluminous character, whereas the Ruduo intrusion is a
metaluminous syenite. Both intrusions have very similar trace element compositions, slightly enriched
zircon εHf(t) values (−9.3 and −1.7), and EM‐2‐like Sr‐Nd‐Pb isotope ratios. These features of the two
intrusions indicate that their magmas were derived from partial melting of an alkali‐rich basaltic lower crust
and a small proportion of mantle melt. The occurrence of alkaline intrusions is consistent with Late
Cretaceous extension in the Eastern Tibetan Plateau. Based on the results of this study and previous data, we
propose an intraplate extensional tectonic model, in which there was NS‐NNW‐directed Late Cretaceous
transtension in the Eastern Tibetan Plateau following the Lhasa‐Qiangtang collision. This extension is
interpreted to have been triggered by the Bangong‐Nujiang slab break‐off at around 110 Ma and driven by
the far‐field subduction of the Neo‐Tethys oceanic crust. |
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