Petrogenesis and geochemistry of the host monzogranite and mafic enclaves from the Triassic Wulong pluton in South Qinling, central China  

作　　者：WANG Juan LI Xin 

机构地区：[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

出　　处：《Chinese Journal Of Geochemistry》2009年第4期432-439,共8页中国地球化学学报

基　　金：supported by the National Natural Science Foundation of China (No 40234041)

摘　　要：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.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.

关 键 词：二长花岗岩 地球化学 镁铁质 南秦岭 岩体 飞地 三叠纪 成因 

分 类 号：P588.121[天文地球—岩石学] P618.510.4[天文地球—地质学]