Triassic granites in the West Qinling Orogen, China: implications for the Early Mesozoic tectonic evolution of the Paleo-Tethys ocean

ABSTRACT

The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative ε_Hf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites.

Graphical abstract

KEYWORDS:

• Petrogenesis
• granites
• Palaeo-Tethys ocean
• West Qinling Orogen (China)

Highlights

• Granites in the Zeku district were emplaced during 251–236 Ma.

• Weakly fractionated, arc-related I-type granites.

• Magma derived from partial melting of Paleoproterozoic to Mesoproterozoic lower crust.

• Long-duration magmatism is relative to the subducting slab.

Acknowledgments

Authors would like to thank two drivers Bai Yongliang and Wang Qiang for their patient help during the fieldwork. Authors are also thankful to two anonymous reviewers whose comments and suggestions have refined this manuscript significantly. Further thanks are owed to the editor who provided detailed and constructive comments and suggestions.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that seemingly could influence the research.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2022.2114106

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was jointly funded by the National Natural Science Foundation of China (Grant Nos. 41872071, 40672049, 42101073), the China Geological Survey Project (Grant Nos. DD20190006, DD20160022-06), the Key Project of Philosophy and Social Science of Hubei Education Department (Grant No.21D106), the Doctoral Foundation of Huanggang Normal University, China (Grant No. 2042019010), the Scientific Research Project of Huanggang Natural Resources and Planning Bureau (Grant No. 20120200460), and the 2022 University-Level Teaching Research Project of Huanggang Normal University—Elementary Education (No. 82) (Research on the collaborative development of geography teachers and teaching resources of middle school in eastern Hubei Province, China, from the perspective of the cooperation between museum and school).