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Petrogenesis of Luchuba and Wuchaba granitoids in western Qinling : geochronological and geochemical evidence.

Kong, J.J. and Niu, Y.L. and Duan, M. and Zhang, Y. and Hu, Y. and Li, J.Y. and Chen, S. (2017) 'Petrogenesis of Luchuba and Wuchaba granitoids in western Qinling : geochronological and geochemical evidence.', Mineralogy and petrology., 111 (6). pp. 887-908.

Abstract

The West Qinling Orogenic Belt (WQOB) is a major portion of the Qinling-Dabie-Sulu Orogen and holds essential information for understanding the prolonged evolution of the northeastern branch of the Paleo-Tethys in East Asia. This study focuses on the petrogenesis of granitoids from Luchuba and Wuchaba plutons in the WQOB. We obtained zircon U-Pb ages of 211 ± 1.4 Ma for the Luchuba pluton and 218.7 ± 1.3 Ma for the Wuchaba pluton, which are the same as the proposed timing of continental collision at ∼220 Ma. We thus interpret the granitoids to represent a magmatic response to the collision between the North China Craton (NCC) and the Yangtze Block (YB). The two plutons are metaluminous to weakly peraluminous I-type granitoids. Samples from the two plutons show strong light rare earth element (REEs) enrichment and weak heavy REE depletion, with varying negative Eu anomalies, which is most consistent with significant plagioclase fractionation although the possible effect of plagioclase as residual phase in the magma source region cannot be ruled out. In primitive mantle normalized multi-element variation diagrams, nearly all the samples show negative Nb, Ta, P and Ti anomalies and relative enrichment in Rb, Pb, U and K. These characteristics resemble those of the average continental crust. The Luchuba pluton has lower (87Sr/86Sr)i (0.7051 to 0.7104), higher εNd(t) (−8.11 to −5.73) and εHf(t) (−6.70 to −1.65) than mature continental crust ([87Sr/86Sr]i > 0.72, εNd(t) < −12). The Wuchaba pluton also has lower (87Sr/86Sr)i (0.7069 to 0.7080), higher εNd(t) (−9.86 to −3.34) and εHf(t) (−5.69 to 1.58) than mature continental crust. We conclude that the Luchuba and Wuchaba granitoids in the WQOB are best explained as resulting from fractional crystallization with crustal assimilation of parental magmas derived from melting of Mianlue oceanic crust under amphibolite facies conditions during the initial stage of continental collision between the North China Craton and the Yangtze Block. Mafic magmatic enclaves (MMEs) of Wuchaba pluton are earlier cumulates of the same magmatic system. The Mianlue oceanic crust (MORB-like) contributes to the source of the Luchuba and Wuchaba granitoids, pointing to the significance of melting of oceanic crust for continental crust accretion.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1007/s00710-017-0501-7
Publisher statement:The final publication is available at Springer via https://doi.org/10.1007/s00710-017-0501-7
Date accepted:14 February 2017
Date deposited:15 March 2017
Date of first online publication:08 March 2017
Date first made open access:08 March 2018

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