Mantle metasomatism by subducted Indian continental crust: Evidence from post-collisional basaltic ultrapotassic rocks in southern Tibetan plateau

Zhang, Miao-Yan, Hao, Lu-Lu, Qi, Yue, Wang, Qiang, Kerr, Andrew C. ORCID: https://orcid.org/0000-0001-5569-4730, Ma, Lin, Huang, Cheng-Cheng, Wei, Gang-Jian, Li, Jie, Ma, Jin-Long, Li, Qi-Wei, Wang, Zi-Long, Huang, Tong-Yu and Yang, Yu-Chen 2025. Mantle metasomatism by subducted Indian continental crust: Evidence from post-collisional basaltic ultrapotassic rocks in southern Tibetan plateau. Lithos: Journal of Petrology, Mineralogy and Geochemistry 498-9 , 107966. 10.1016/j.lithos.2025.107966 Item availability restricted.

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Abstract

At continental collisional zones, the continental crust is known to subduct, penetrating the deep lithospheric mantle and undergoing partial melting. However, the extent to which these melts can effectively alter, or metasomatize, the overlying mantle remains a contentious issue. This debate is especially pronounced in the Cenozoic Himalayan-southern Tibet collisional orogen. The complexity arises from the fact that previous research has predominantly concentrated on the post-collisional intermediate ultrapotassic rocks. However, these rocks could have originated either from the subducted Indian continental crust through a process of mantle assimilation or from mélange rocks, thereby primarily reflecting crustal recycling rather than mantle metasomatism by subducted continental crust. In this study, we shift our focus to the less-well-studied post-collisional basaltic ultrapotassic rocks (BUPRs) from the Sailipu region in the Lhasa block of southern Tibet. Our aim is to evaluate the characteristics of the orogenic mantle and the dynamics of crust-mantle interactions. In this study we report major and trace elements and Sr-Nd-Pb-Mo-B isotopes for these Miocene post-collisional BUPRs. The rocks are typically characterized by alkaline affinity, arc-like trace element distribution patterns, and enriched Sr-Nd-Pb isotopes, which point to their derivation from an enriched mantle source. Moreover, the Mosingle bondB isotope ratios of these BUPRs - δ98/95Mo ranging from −0.85 ‰ to −0.27 ‰ and δ11B from −20.2 ‰ to −14.4 ‰ - are notably lower than those found in Mid-Ocean Ridge Basalts (MORBs) and arc lavas. Instead, they are similar to the isotopic compositions of basalts associated with continental subduction, as well as intermediate ultrapotassic rocks from western Anatolia and the Lhasa block, and the gneisses and schists of the Himalayas. These similarities strongly suggest the input of subducted Indian continental crust to the mantle source for these rocks. In conclusion, our study supports the metasomatism of the mantle beneath southern Tibet by subducted Indian continental crust. These results show that continental subduction zones, much like their oceanic counterparts, are key regions for mantle metasomatism, and thus expands our understanding of the geological processes at work in these dynamic areas.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0024-4937
Date of First Compliant Deposit:	14 February 2025
Date of Acceptance:	21 January 2025
Last Modified:	18 Feb 2025 12:45
URI:	https://orca.cardiff.ac.uk/id/eprint/176188

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