Petrogenesis and geochemistry of the host monzogranite and mafic enclaves from the Triassic Wulong pluton in South Qinling,central China |
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| Authors: | Juan Wang Xin Li |
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| Institution: | [1]China University of Petroleum, Shandong, Dongying 257061, China [2]Geological Research Institute of Shengli Oilfield Company Limited, SINOPEC, Shandong, Dongying 257015, China [3]Geophysical Research Institute of Shengli Oilfield Company Limited, SINOPEC, Shandong, Dongying 257022, China |
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| Abstract: | The Wulong pluton was emplaced in the metamorphic complex of the Mesoproterozoic Foping Group, South Qinling. A few mafic
enclaves which are rounded in shape with sharp boundaries with the host granites in the southern part of the pluton. Based
on petrography, geochemistry and chronology data, it is indicated that the Wulong pluton shows some adakitic affinities with
depletion in HREE (Yb=0.33–0.96 μg/g, Y=4.77–11.2 μg/g); enrichment in Sr (643–1115 μg/g) and Ba (775–1386 μg/g), high Sr/Y
ratios (57.3–160) and Y/Yb ratios (11.0–14.3), and slightly negative Eu anomaly (δEu=0.70–0.83). These patterns suggest a
feldspar-poor and garnet±amohibole-rich fractionation mineral assemblage. The mafic enclaves have high concentrations of Mg
(MgO=4.15%–8.13%), Cr (14.8–371 μg/g), and Ni (20.0–224 μg/g), and high Nb/Ta ratios (15.42–21.9). It seems that the underplating
mantle magma was responsible for the generation of the mafic magma. Companied with the results of investigations for the Qinling
Orogenic Belt, it was found that partial melting of the thickened lower crust, which was triggered by the underplated mantle-derived
magmas, had generated the felsic magma. The Wulong pluton provided evidence for a mixing and mingling process of two kinds
of mamma. Its formation probably represents the oceanic slab breakoff during the late orogenic stage in the Qinling area. |
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| Keywords: | mafic microgranular enclave adakite underplation |
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