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 εHf(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
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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.