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Identifying Tethys oceanic fingerprint in post-collisional potassium-rich lavas in Tibet using thallium isotopes

Wei, Feixiang; Prytulak, Julie; Baker, Evelyn B.; Xu, Jiandong; Zhao, Bo

Identifying Tethys oceanic fingerprint in post-collisional potassium-rich lavas in Tibet using thallium isotopes Thumbnail


Authors

Feixiang Wei

Evelyn B. Baker

Jiandong Xu

Bo Zhao



Abstract

Following the Indian-Asian continental collision, the Tibetan Plateau experienced continuous magmatism from south to north, most of which is characterized by high potassium (K) content and negative niobium‑tantalum‑titanium (Nb-Ta-Ti) anomalies. We performed the first exploration using thallium (Tl) isotopes as potential tracers of the source of post-collisional K-rich magmatism. A case study on Tl isotope systematics of K-rich lavas in Ashikule volcanic basin (AVB) in northwestern Tibet is provided, which represents the youngest volcanism in Tibet. Thallium abundances of the AVB lavas are significantly enriched compared to other magmatic settings, with concentrations from 148 to 8259 ng/g. Thallium isotope ratios (reported as ε205Tl) extend to some of the heaviest yet measured in igneous materials, with a range of ε205Tl between −2.7 and + 6.4 ε-units. We evaluate if secondary processes can account for the range in Tl isotope ratios, systematically examining the influences of alteration, degassing, fractional crystallization, and assimilation. Only two samples appear to be influenced by secondary processes, interpreted as kinetic fractionation during degassing, and one sample may be contaminated by sulfides with coupled elevated Tl and Pb contents. The remainder of the Tl isotope ratio range (−2.0 to +5.1 ε-units) we interpret to reflect the source region(s) from which the magmas are derived. The AVB lavas have restricted strontium and neodymium isotopes, suggestive of a homogeneous source, and therefore an apparent decoupling of radiogenic and stable isotope systems is apparent in these lavas. The variation in Tl isotope ratios is interpreted to reflect the contribution of oceanic sediments, which may be associated with ancient Paleo- and Neo-Tethys subductions.

Citation

Wei, F., Prytulak, J., Baker, E. B., Xu, J., & Zhao, B. (2022). Identifying Tethys oceanic fingerprint in post-collisional potassium-rich lavas in Tibet using thallium isotopes. Chemical Geology, 607, Article 121013. https://doi.org/10.1016/j.chemgeo.2022.121013

Journal Article Type Article
Acceptance Date Jul 6, 2022
Online Publication Date Jul 9, 2022
Publication Date Sep 30, 2022
Deposit Date Jul 29, 2022
Publicly Available Date Jul 9, 2023
Journal Chemical Geology
Print ISSN 0009-2541
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 607
Article Number 121013
DOI https://doi.org/10.1016/j.chemgeo.2022.121013
Public URL https://durham-repository.worktribe.com/output/1196446

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