The geochronologic and geochemical constraints on the Early Cretaceous subduction magmatism in the central Lhasa subterrane, Tibet

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 (206Pb/204Pb = 18.6287–19.5578, 207Pb/204Pb = 15.7161–15.7720, and 208Pb/204Pb = 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; 206Pb/204Pb = 18.7119–18.8575, 207Pb/204Pb = 15.7159–15.7203, and 208Pb/204Pb = 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.

Petrogenesis and metallogenic implications of Cretaceous magmatism in Central Lhasa, Tibetan Plateau: A case study from the Lunggar Fe skarn deposit and perspective review

“…Furthermore, the widespread ~113 Ma mafic rocks show within‐plate basalt geochemistry, A 2 ‐type silicic character, and coeval bimodal nature, collectively indicating extensional setting (Y. Chen et al, ). The ~113 Ma Coqen volcanic rocks have also been confirmed as the product of slab break‐off (Y. Huang et al, ). Low (La/Yb) N and Sr/Y ratios of ~115–110 Ma magmatism also suggest a thinned crust within extensional setting (Figure e–f).…”

“…However, the weakly depleted ε Hf (t) values of −1.7 to + 1.6 from the granodiorite are mostly greater than those of the Central Lhasa ancient crustal melts (up to −22; Zhu et al, ). In addition, major mafic magmatic events have been recorded during the emplacement of the ~113 Ma granodiorite (Y. Chen et al, ; S. S. Chen, Shi, et al, ; Y. Huang et al, ). Therefore, the Lunggar I‐type granodiorite is considered to be a product of binary mixing through partial melting of the Precambrian Central Lhasa crust and juvenile mantle.…”

“…The results from our study suggest significant crustally derived components in the formation of the Lunggar granodiorite and granite porphyry. Meanwhile, the ~115–110 Ma mafic magmatism in Central Lhasa has been linked to slab break‐off of the Bangong–Nujiang Ocean by several workers (Y. Chen et al, ; Y. Huang et al, ; L. Y. Wang, Zheng, Yang, et al, ). The high temperatures of 630–680 o C and log f O 2 of −14 to −16 in Nixiong deposit (as reported by Y. S. Yu, Yang, Gao, et al, ) can be interpreted by partial melting of juvenile crustal components (X. H. Li et al, ).…”

The structural deformation characteristics and the control of gold mineralization of the upper Triassic flysch (Langjiexue Group) in Tibetan Plateau

“…Some advocates of orogenic gold deposits do not seem to advocate that the Alps Himalayan collision orogenic belt can form large gold deposits, because they believe that their vertical fracture systems are small in scale, shallow in depth, and poor in connectivity of tectonic networks (Barley & Groves, ; Hou et al, ; Huang, Zhao, Zhu, & Gao, ). In fact, this is not the case in the Himalayan orogenic belt.…”

Central China Orogen along the Silk Road (Part I): Tectono‐thermal evolution and its links

“…Determining the provenance of Triassic sedimentary rocks in the Songpan‐Ganzi Basin utilizing heavy minerals and U–Pb geochronology formed the focus in the paper by Tang, Zhang, and Tong (). Geochronology and geochemistry of volcanic rocks in the Central Lhasa region was undertaken by Huang et al (). Finally, U–Pb dating of gneisses from Central Himalaya formed the focus of the study by Wang, Zhang, Li, and Somerville ().…”