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《Acta Petrologica Et Mineralogica》 2005-05
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Geochemical characteristics and origin of garnet migmatitic granites in Daqingshan area, Inner Mongolia

SONG Hai-feng, XU Zhong-yuan and LIU Zheng-hong(College of Earth Sciences, Jilin University, Changchun 130061, China)  
The garnet migmatitic granite (GMG) was formed by partial melting of Ga-Bi gneiss within Ga-Bi gneiss complex of Archaean khondalites in Daqingshan area, Inner Mongolia, in the process of subhorizontal shearing and granulite facies metamorphism. The GMG mainly inherited mineral composition and geochemical features from the Ga-Bi gneiss, while its difference from Ga-Bi gneiss in textures and geochemistry (especially REE) indicates the process of partial melting and evolution. In spite of its small bodies, GMG shows heterogeneity in mineral composition, textures and geochemistry, and can be divided into two types, of which the former has high K_2O and low Na_2O, CaO, showing apparently positive anomalies and Low ∑REE, whereas the latter has low K_2O and high Na_2O, CaO, assuming negative Eu anomalies and high ∑REE. It is suggested that the development of the two types of GMG is related to the gradual separation of partial melts from the solid residue during the partial melting and subsequent flowing. The relative lack in the former and enrichment in the latter of the restite and relic minerals, especially the REE behavior-controlling refractory minerals such as garnet, monazite, apatite and zircon, caused the difference in REE distribution of the two types of GMG. The available data suggest that the GMG was developed in Neoarchaean and is hence quite different from the Paleoproterozoic anatexis-derived garnet-bearing granite in Sanggan area.
【Fund】: 中国地调局区域地质调查项目(200113000021)
【CateGory Index】: P588.121;P59
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