Post-collisional crustal evolution in the central Lhasa block of southern Tibet: Insights from early and late Cretaceous magmatism

Huanga, Shu-Ya, Hao, Lu-Lu, Wang, Qiang, Kerr, Andrew C. ORCID: https://orcid.org/0000-0001-5569-4730, Hu, Wan-Long, Mo, Qing-Qing, Liu, Mao-Rui, Qi, Yue, Dan, Wei and Zhang, Xiu-Zheng 2025. Post-collisional crustal evolution in the central Lhasa block of southern Tibet: Insights from early and late Cretaceous magmatism. Lithos: Journal of Petrology, Mineralogy and Geochemistry 514-15 , 108213. 10.1016/j.lithos.2025.10821 Item availability restricted.

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Abstract

The identification of post-collisional crustal growth in collisional orogens presents significant challenges due to previous subduction events. This significantly hinders our understanding of post-collisional crustal evolution processes. However, the central Lhasa block in southern Tibet lacks crustal growth during oceanic subduction, and so provides an ideal site to study the post-collisional crustal growth. Here we examine the ∼107 Ma, 83 Ma, and 76 Ma TangraYumco post-collisional granites in the central Lhasa block. The ∼107 Ma granitoids are highly fractionated A-type granites because of their depletion in Ba, Sr, and Eu and low Zr/Hf and Nb/Ta ratios, and the occurrence of adjacent coeval A-type rocks. The ∼76 Ma granites are metaluminous and contain amphibole, consistent with I-type granites. The ∼83 Ma granites show nearly parallel REE (rare earth element) and trace element patterns and similar Sr-Nd-Hf isotopic compositions to those of the ∼76 Ma granites, suggesting a common source. Given their low REE contents and high Rb/Ba and Rb/Sr ratios, we propose that the ∼83 Ma granites are highly fractionated I-type granites. Compared to the >116 Ma granitoids in the central Lhasa block, the ∼107 Ma granites exhibit less enriched Srsingle bondNd and slightly depleted zircon Hf isotope compositions [(87Sr/86Sr)i = 0.70715–0.70751; εNd(t) = −3.0 to −2.6; εHf(t) = −1.3 to 3.8]. This, together with the 113 ± 3 Ma magmatic flare-up in the central-northern Lhasa block, indicates that ∼107 Ma granites were derived from a mixed lower crust (i.e., ancient lower crust with significant juvenile crust input) during the break-off of the Bangong-Nujiang oceanic slab. Thus, significant post-collisional crustal growth occurred at that time. In contrast, the ∼83 Ma and ∼76 Ma granites display more enriched Sr-Nd-Hf isotopic compositions than the ∼107 Ma granites, implying that they may be due to crustal reworking and have originated from both this mixed crust generated at ∼107 Ma and ancient crust. The ∼83 Ma granites are interpreted to have formed during lithospheric delamination, while the ∼76 Ma granites are attributed to the far-field effects of the northward subduction of the Neo-Tethys oceanic lithosphere. Thus, this study has clarified the post-collisional growth and reworking in the central Lhasa block of southern Tibet, and so improves our understanding of crustal evolution in collisional orogenic belts.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0024-4937
Date of First Compliant Deposit:	1 August 2025
Date of Acceptance:	1 August 2025
Last Modified:	24 Sep 2025 09:45
URI:	https://orca.cardiff.ac.uk/id/eprint/180197

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