Geochemistry, Zircon U-Pb Age and Hf Isotope of the Huilanshan Granitoids in the North Dabie Terrane: Implications for Syn-Collapse Magmatism of Orogen
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Syn-collapse magmatism is a critical issue for evolution of the continental orogen. The Dabie Orogen is a typical orogen which was suffered from a complete collapse. Two kinds of granitoids, namely, the coarse-grained diorite and the fine-grained granite, are recognized at the center of the Luotian extensional dome, providing an opportunity to decipher the syn-collapse magmatism in the Dabie Orogen. The diorites (125±3 Ma) are high K calc-alkaline rocks, with low SiO2 (51.9 wt.%–56.6 wt.%) and high MgO (3.5 wt.%–4.0 wt.%) contents. They are enriched in LREE and LILEs (e.g., Ba, K, Rb) and depleted in HFSEs (e.g., Ta, Nb, and Hf) with low ratio of Sr/Y (30.82–46.89). The granites (118±2 Ma) are shoshonite series rocks, with relatively high SiO2 (68.9 wt.%–72.6 wt.%) and low MgO (0.32 wt.%–0.66 wt.%) contents. They are also enriched in LREE and LILEs with weakly negative Eu anomalies (δEu=0.81–0.85), and are depleted in HFSEs with low Sr contents (338 ppm–477 ppm) and Sr/Y ratios (23.80–33.13). Therefore, the two kinds of granitoids have no geochemical characteristics of adakitic rocks, suggesting that they were generated from a normal or thinned crust level. The diorites have quite negative zircon εHf(t) values (-18.4 to -21.1), suggesting they were from partial melting of the mafic lower continental crust. The granites have relatively higher zircon εHf(t) values (-14.4 to -18.1). The granites also contains a series of old inherited zircon cores, such as two upper intercept ages of 2 628±41 and 1 840±37 Ma, and a concordant age of 807±9 Ma. All these features suggest that the granites were generated from partial melting of the felsic middle-lower continental crust. Thus, the Huilanshan Early Cretaceous granitoids coupled with the Luotian extensional dome revealed the collapsed process of the Dabie Orogen.
Keywordsorogenic collapse magmatism partial melting lower continental crust Dabie Orogen
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This research was supported by the National Natural Science Foundation of China (Nos. 41572039, 41772054, and 41372076) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (No. CUGQYZX1704). Constructive comments from the two anonymous reviewers improved the manuscript significantly. We thank Profs. Jingsui Yang and Changqian Ma for editorial handling. We thank Dr. Keqing Zong from China University of Geosciences (Wuhan) for his help in LA-ICPMS zircon U-Pb dating and Hf isotopic analysis. The final publication is available at Springer via https://doi.org/10.1007/s12583-019-0892-y.
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