The geochronologic and geochemical constraints on the Early Cretaceous subduction magmatism in the central Lhasa subterrane, Tibet. (30th December 2017)

• Record Type: Journal Article
• Authors: Huang, Yu; Zhao, Zhidan; Zhu, Di‐Cheng; Liu, Yunhua; Liu, Dong; Zhou, Qunjun; Gao, Shasha
• Editors: Yu, S.
• Other Names: Li S. guestEditor.; Suo Y. guestEditor.; Li R. guestEditor.; Yu S. guestEditor.; Yang G. guestEditor.; Somerville I. guestEditor.
• Is Part Of: Geological journal. Volume 52(2017)Supplement 1
• Page Start: 463
• Page End: 475
• Publication Date: 2017-12-30
• Subjects: Early Cretaceous -- Lhasa Terrane -- petrogenesis -- slab break‐off -- Zenong Group; Geology -- Periodicals; 551
• DOI: 10.1002/gj.3112
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : A large volume of Early Cretaceous volcanic rocks are exposed in the central Lhasa subterrane, which are essential for models developed for understanding the evolution of Lhasa Terrane. However, the petrogenesis and geodynamic background of these rocks are still in debate. In this paper, we carried out a detailed study on the volcanic rocks of the Zenong Group, including andesite, dacite, and rhyolite from the Coqen area in the central Lhasa subterrane. Zircons from one dacitic tuff yields an age of 115.3 ± 1.1 Ma. All the rocks are enriched in light rare earth elements (LREEs), Th, U, and Pb and depleted in high field strength elements (HFSEs, e.g. Nb, Ta, P, and Ti). The dacite and rhyolite samples are high‐K calc‐alkaline to shoshonitic and are metaluminous to peraluminous. These felsic samples are characterized by negative ƐNd (t) (−8.9 to −2.1) and ƐHf (t) (−8.1 to −5.6) and have high radiogenic Pb isotopic composition ( 206 Pb/ 204 Pb = 18.6287–19.5578, 207 Pb/ 204 Pb = 15.7161–15.7720, and 208 Pb/ 204 Pb = 39.1440–40.6253). Particularly, a negative correlation between the ƐNd (t) values and SiO2 contents can be observed in these dacites and rhyolites. Meanwhile, the andesites exhibit similar Sr–Nd–Pb isotopic compositions to dacites and rhyolites (ƐNd (t) = −4.3; 206 Pb/ 204 Pb = 18.7119–18.8575, 207 Pb/ 204 Pb = 15.7159–15.7203, and 208 Pb/ 204 Pb = 39.2944–39.6036). Our new data indicate that different geochemical reservoirs are involved in generating the ca. 115 Ma magmatism in the central Lhasa subterrane. It is likely that dacites and rhyolites are derived from the magma mixing between the ancient basement‐derived melts and mantle‐derived melts with varying degrees of partial melting. The andesites might originate from partial melting of an ancient lithospheric mantle that have been metasomatized by fluids and/or melts derived from the Tethyan oceanic slab. Our results, together with recent studies, suggest that the Zenong Group volcanic rocks in the Coqen area may represent the magmatic responses to the break‐off of the southward subduction of the Bangong–Nujiang Tethyan oceanic slab.