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Journal Article

Magma Mixing Generated Triassic I-Type Granites in South China

Haijin Xu, Changqian Ma, Junhong Zhao and Junfeng Zhang
The Journal of Geology
Vol. 122, No. 3 (May 2014), pp. 329-351
DOI: 10.1086/675667
Stable URL: http://www.jstor.org/stable/10.1086/675667
Page Count: 23

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Topics: Granite, Enclaves, Magma, Plutons, Plumes, Subduction, Ratios, Plate tectonics, Magmatism, Isotopes
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Magma Mixing Generated Triassic I-Type Granites in South China
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Abstract

AbstractA Triassic granodioritic pluton with mafic microgranular enclaves (MMEs) in central South China provides an important insight into crust-mantle interaction. Here we present a comprehensive study of fieldwork, geochronology, geochemistry, and Sr-Nd-Hf isotopes for the Taojiang granodioritic host and the MMEs in central South China. The host granodiorites (218 ± 3 Ma) are high-K calc-alkaline I-type granites (SiO2: 66.17–69.47 wt%; ANCK < 1.0) that show light rare earth element (REE) enrichment and flat heavy REE patterns with weakly negative Eu anomalies. They exhibit strongly negative Ba, Sr, Nb, P, and Ti anomalies and positive Rb and Pb anomalies and have high initial 87Sr/86Sr ratios (0.712783 to 0.714799), negative εNd(t) values (−8.3 to −7.8), and negative zircon εHf(t) values (−6.4 to −3.1). The coeval MMEs (225 ± 3 Ma) have compositions ranging from mafic to intermediate (SiO2: 49.2–60.8 wt%) with high MgO (2.8–6.3 wt%), FeOT (6.7–15.2 wt%), CaO (4.3–7.1 wt%), TiO2 (0.8–2.0 wt%), Ni (18.2–61.4 ppm), and Cr (17.2–125.4 ppm) contents. They are enriched in light REE, Rb, Pb, and Th and depleted in Ba, Nb, Ta, Sr, Eu, and Ti. The MMEs have lower whole-rock initial 87Sr/86Sr ratios (0.708052–0.713413) and higher whole-rock εNd(t) (−6.3 to −4.3) and zircon εHf(t) (−4.6 to −0.6) values than those of the granodioritic host. Our results suggest that the Taojiang granodioritic host and the MMEs were likely produced by mixing of mantle- and crust-derived magmas. Combined with previous paleomagnetic and magnetostratigraphic results, we propose that the Triassic magmatism in central South China might be related to underplating of mantle-derived magma induced by mantle plume or asthenosphere upwelling.

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