Abstract

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Title:: Clinopyroxene Geobarometer Applied to Mafic Microgranular Enclaves in Granite Originated from Crust-mantle Mixed Source

Author(s):: SUN Lan-lan; YANG Jia-xi; ZHOU Zheng-yan; ZOU Li-fei; MA Ai-ai; GUAN Hao; School of Earth Science and Resources, Chang’an University, Xi’an 710054, Shaanxi, China

Keywords:: granite; crust-mantle mixed source; mafic microgranular enclave; experimental petrology; clinopyroxene; geobarometer; formation depth

Abstract:: The origin of granite from crust-mantle mixed source and the genesis information of mafic microgranular enclaves (MMEs) in this kind of granite are important objects for geological studies. However, there is no geobarometer for the MMEs which have mafic mineral assemblage. According to the research materials of experimental petrology for simulating the process of crust-mantle magma mixing by Patino Douce, it is discovered that the contents of Na and Al in clinopyroxene from the MMEs are closely correlated to pressure. It yields linear relationship between pressure and the content of Na₂O, the content of Al₂O₃, the mole fraction of jadeite, the mole fraction of Tschermak pyroxene molecule and the mole fraction of jadeite and Tschermak pyroxene molecule. There is also linear relationship between pressure and the content of Al₂O₃ in orthopyroxene. Then, the efficient geobarometer applied to the MMEs in granite originated from crust-mantle mixed source is educed. This geobarometer provides a research mean for understanding the formation depth of the granitic magma originated from crust-mantle mixed source. The geobarometer to the MMEs is applied to Chehe granitic pluton in Tianshui area of West Qinling. The significance of this geobarometer is understanding granite originated from crust-mantle mixed source and other deep geological problems.