Cretaceous evolution of the Lhasa-Qiangtang Orogen: insights from mafic igneous rocks

ABSTRACT

The compositional changes of successively emplaced mafic magmatites provide insights into the evolution of orogenic belts, particularly the transformation processes and properties of the orogenic lithospheric mantle. Herein, we present new zircon U‒Pb ages and Lu‒Hf isotopes, as well as whole-rock major, trace element, and Sr – Nd isotope compositions from three mafic intrusions in the Asuo area, central Tibet, to clarify the evolution of the Lhasa – Qiangtang Orogenic Belt (LQOB). These mafic intrusions can be classified into calc-alkaline basalts and are enriched in large ion lithophile elements and depleted in high-field strength elements. Significant differences in the whole-rock trace element compositions, Sr – Nd isotope values, and U – Pb ages stratify them into two groups, namely Groups I and II, of which Group I rocks (ca. 105 Ma) show lower⁸⁷Sr/⁸⁸Sr_i = (0.70694–0.70701), [Sm/Yb]_N = (1.51–1.54) and higher ε_Nd (t) = (−0.74 to −0.61) than Group II (ca. 97–95 Ma) (⁸⁷Sr/⁸⁸Sr_i = 0.70759–0.70870; ε_Nd (t) = –4.58 to −3.75; [Sm/Yb]_N = 2.43–2.94). These features indicate that the mantle source exhibits a progressive increase in the proportion of garnet, along with significant addition of subduction-related components into the primary melts. One scenario for producing such trace element patterns and gradually enriched radioactive isotope signatures involves the extensive heating of an oceanic slab beneath the LQOB by upwelling asthenosphere, which leads to the extensive melting of sediments within the slab. Identification of ca. 105–95 Ma Asuo mafic rocks suggests their formation in a post-collisional setting with additional heat input from the deep mantle. These results provide new evidence supporting the occurrence of the Lhasa – Qiangtang collision within the framework of north-south bidirectional subduction.

Graphical Abstract

KEYWORDS:

• Tibet plateau
• mafic rocks
• Lhasa-Qiangtang Orogen
• Early Cretaceous- Late Cretaceous

Acknowledgments

We appreciate Chao-Ming Xie, Jian-Jun Fan, Meng-long Duan, and Bo-Chuan Zhang for their help in the field. Yu-Jie Hao is thanked for the LA-ICP-MS zircon U-Pb dating analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2364207

Additional information

Funding

This work was funded by Special Support from the National key research and development programme [2022YFC3080200], the National Natural Science Foundation of China [Grant No.41602230], the Major Research plan [Grant No. 91955205], the Programme of the China Geological Survey [Grant No.121201010000150014 and No. DD20160026] and the Opening Foundation of the Key Laboratory of Mineral Resource Evaluation in Northeast Asia, Ministry of Natural Resources [Grant No.DBY-ZZ-18-11].