Early Cretaceous arc granitoids from the central Lhasa subterrane: Production of the northward subduction of Yarlung Zangbo Neo‐Tethyan Ocean?

Abstract

There is ongoing debate as to the genesis of the Lhasa Terrane during the Mesozoic (northward subduction of Yanglu‐Zangbo Tethyan Ocean [YZTO] or southward subduction of Bangong–Nujiang Tethyan Ocean [BNTO]). In this paper, we report a dataset of geochronology, geochemistry, and Sr–Nd–Hf isotopes for the Azhale granitoids in order to elucidate the dominant geodynamic processes of the central subterrane. These rocks are dated at 142.2 ± 1.0 and 136.6 ± 0.6 Ma by zircon LA–ICP–MS method, indicating that these rocks were contemporaneous. In situ zircon Hf isotopic analyses yielded εHf(t) values of −4.2 to −0.1. Geochemically, these samples mostly belong to calc‐alkaline series and show strong enrichments in large‐ion lithophile elements (LILE;e.g., Rb, Ba, and Th) and depletions in high‐field‐strength elements (HFSE;e.g., Nb and Ta), indicating the Azhale granitoids are typically I‐type granite. In terms of isotopic composition, these rocks also have low εNd(t) values (−6.51 to −6.80) and high initial 87Sr/86Sr ratios (0.7078 to 0.7084) relative to melts derived from partial melting of ancient mafic lower crust. We considered that these rocks should be interpreted to have resulted from melting, assimilation, storage, and homogenization (MASH process) above subduction zones. In conclusion, combined with the published and our new data, we argued for the petrogenesis of Early Cretaceous arc‐related granitoids were due to the YZTO lithosphere subducted northward beneath the Lhasa Terrane.

Post-collisional magmatism associated with the final closure of the Rushan-Pshart Meso-Tethys Ocean in Pamir, Tajikistan: Inference from Cretaceous igneous rocks of the Pshart accretionary complex

“…However, the samples showed low Sr/Y and relatively high La/Yb, indicating that the melt was forming in the plagioclase stability field, with residues of garnet and plagioclase (Figures 3E,F), similar to those documented in Jurassic (160 Ma) Maofengshan (South China Block) metasedimentary-derived highly fractionated S-type granites that originated in the middle crust (16.5-20 km) (Liu X. et al, 2021). The chondrite-normalized and spidergram patterns showed that our samples were slightly evolved compared to those reported by Li R. H. et al (2019) from the Taxkorgan region. The exception was sample Psh-1 which displayed an identical pattern to those for the Taxkorgan granites (Figures 6A,B).…”

“…This ambiguity is controlled by the entrainment of xenocrystic/or peritectic and accessory minerals and their constituent element concentrations in the melt. In combination with our data, we used the data from 118 Ma granitoids reported by Li R. H. et al (2019) (from the Taxkorgan region (Figure 1)), which plotted in the same fields as our samples (Figure 7D). Garnet containing elements such as Zr, Ce, Ga, Y, and others can be concentrated within refractory minerals such as zircon (Zr, Hf, Y, and Yb) and monazite (Ce and La) (Villaros et al, 2009b).…”

Crustal reworking and growth during India–Asia continental collision: Insights from early Cenozoic granitoids in the central Lhasa Terrane, Tibet

“…Granitoids have been used to investigate the formation and evolution of continental crust, and a large number of granitoids in a specific tectonic domain can provide petrological clues to deep crustal compositions and processes of crustal evolution (e. g., H. Zheng et al, 2018).…”

“…The central Lhasa Terrane contains granitoids of various ages, and these granitoids provide clues regarding the composition of the crust and mantle and the nature of tectonic-magmatic events during India-Asia collision (Cao et al, 2019;Chung et al, 2005;Dai et al, 2020;Sheng et al, 2019;H. Zheng et al, 2018;Zhu et al, 2015).…”

Formation of Late Cretaceoushigh‐Mggranitoid porphyry in central Lhasa, Tibet: Implications for crustal thickening prior to India–Asia collision

“…Several studies were carried out on the southern Lhasa block (i.e., Jurassic to Cretaceous magmatism) which suggest an archetype of Andean‐style margin related to the northward subduction of the Neo‐Tethyan Ocean before the India–Asia collision in the Early Cenozoic (Chu et al, 2006; Chung, Chu, Zhang, et al, 2005; Ding, Kapp, Zhong, et al, 2003; Ji, Wu, Chung, Li, & Liu, 2009; Mo et al, 2007; Mo, Niu, Dong, et al, 2008; Yin & Harrison, 2000; Zhang et al, 2012; Zhou et al, 2018). However, the petrogenesis and tectonic settings of the Cretaceous magmatism in the central‐northern Lhasa block remain equivocal, with diverse models including the northward subduction of the Neo‐Tethyan Ocean lithosphere (Ma & Yue, 2010; Zhang et al, 2012; Zheng, Huang, Cai, et al, 2019), the southward subduction of the Bangong–Nujiang Ocean (Meso‐Tethyan Ocean) lithosphere and subsequent Lhasa–Qiangtang collision (Li et al, 2018; Mo et al, 2005; Pan, Mo, Hou, et al, 2006; Zhu et al, 2013; Zhu, Mo, Niu, et al, 2009a). Recently, delamination of a thickened lithospheric keel (including lithospheric mantle and lowermost crust) has also been proposed to account for the Late Cretaceous magmatism within the Lhasa–Qiangtang collision zone (Cao, Zhang, Santosh, et al, 2019; Chen et al, 2015; Wang, Tang, Wang, et al, 2019; Wang, Zhu, Zhao, et al, 2014; Yi et al, 2018; Yu, Chen, Xu, et al, 2011).…”