Origin of the volcanic rocks in Dianzhong Formation, central Lhasa Terrane, Tibet: implication for the genesis of syn-collisional magmatism and Neo-Tethyan slab roll-back

ABSTRACT

The origin and formation of the continental collision-related magmas remain elusive. The volcanic rocks erupted during India-Asia continental collision offer an ideal opportunity to explore their genesis and geodynamic process. Here, we report new zircon U-Pb dating results and Hf isotope, whole-rock element and Sr-Nd isotope data of volcanic rocks in Linzhou Basin, central Lhasa Terrane, southern Tibet. These volcanic rocks are mainly comprised of andesites and belong to Dianzhong Formation. The timing of their formation is ca. 63–66 Ma, coeval with the India-Asia continental initial collision in the central part of southern Tibet. All these rocks show an arc-like geochemical affinity and they have more depleted Sr-Nd-Hf isotopic compositions (⁸⁷Sr/⁸⁶Sr_i = 0.705006–0.705963, ε_Nd(t) = −1.78 to 3.52, zircon ε_Hf(t) = 1.2–7.0) than the Cretaceous pre-collisional andesites and Eocene ancient lithospheric mantle-derived melts beneath the central Lhasa Terrane. The correlation between Mg# and CaO, TiO₂, Al₂O₃, Sr/Y, ⁸⁷Sr/⁸⁶Sr, ε_Nd(t) suggests that they were likely hybrid production between an isotopically depleted end-member and the enriched lithospheric mantle (ELM). The oceanic crust-derived melts would be the best candidate for the former end-member according to their depleted Sr-Nd isotopic compositions. The andesitic rocks of Dianzhong Formation in the central Lhasa Terrane were most likely stemmed from partial melts of altered Neo-Tethyan crust and then mixed with the ELM-derived melts. Given the Cretaceous-Tertiary upper crustal shortening, back-arc extension, and voluminous volcanism in the Lhasa Terrane, along with abrupt increasing in the magma temperature and the convergence rate between India and Asia during Palaeocene, the occurrence of the Dianzhong Formation volcanic rocks can be well explained by the Neo-Tethyan slab roll-back. The mixing between the oceanic crust- and the continental lithospheric mantle-derived melts induced by the oceanic slab roll-back would be a complimentary scenario for the formation of the syn-collisional magmatism in collisional orogeny belts.

GRAPHICAL ABSTRACT

KEYWORDS:

• Andesite
• Dianzhong Formation
• Neo-Tethyan slab
• enriched lithospheric mantle
• Central Lhasa Terrane
• India-Asia collision

Highlights:

1 The newly discovered Dianzhong Formation volcanic rocks formed at 63–66 Ma.

2 Magmatic responses to the slab roll-back of the Neo-Tethyan oceanic lithosphere.

3 Develop a new model for the origin of the andesites in syn-collisional settings.

Acknowledgments

We thank the three anonymous reviewers for their constructive and thoughtful reviews which greatly improved the manuscript and other three anonymous reviewers for their suggestions and comments for the previous version. Editor-in-Chief Dr. Robert J. Stern is thanked for his helpful comments and editorial handling. We thank Jianbin Wu and Xuefeng Chen for their assistance in the field work and whole-rock chemical analyses. This manuscript is benefited from Hongli Li and Pan Hu for polishing the language. Feng Huang thanks Yanan Yang for his help in SIMS zircon U-Pb dating analyses. This research was supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program (Grant No. 2019QZKK0702), the National Key Research and Development Project of China (Grant No. 2020YFA0714800), the 111 Project of the Ministry of Science and Technology, China (Grant No. BP0719021), the National Natural Science Foundation of China (Grant No. 41973027, 41730427, 41803030, and 42121002), and the Fundamental Research Funds for the Central Universities (Grant No. 2652019054).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This research was supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program [2019QZKK0702]; the National Key Research and Development Project of China [2020YFA0714800]; the 111 Project of the Ministry of Science and Technology, China [BP0719021]; the National Natural Science Foundation of China [41973027, 41730427, 41803030, and 42121002]; the Fundamental Research Funds for the Central Universities [2652019054].