In this paper,the geochronology,mineralogy and mineral chemistry of Luojiashan gabbro in Yingyangguan area of northeastern Guangxi were studied,to constrain the regional tectonic background.The main mineral compositions of Luojiashan gabbro are clinopyroxene(Cpx)and plagioclase(Pl).The clinopyroxene of Luojiashan gabbro is characterized by high Fe,Al,and low Ca,Na,Ti,and its composition is Wo27-31En36-47Fs21-32,which belongs to augite.Plagioclase is characterized by high Si,Al,Na,and low Ca,K,and its composition is An0-3Ab96-100Or0-2,which belongs to albite.According to the chemical composition of clinopyroxene,the parental magma of the Luojiashan gabbro should belong to tholeiitic series.The crystallization temperature and pressure of clinopyroxene were estimated by the clinopyroxene-melt equilibrium and clinopyroxene isotherm,which yielded crystallization temperature of 1 282-1 292℃,with an average of 1 287℃.The pressures are 1.53-2.37 GPa,with an average of 2.02 GPa,and corresponding to a formation depth of 50.49-78.21 km,with an average of 66.80 km.The Luojiashan gabbro was formed at(768.9±6.8)Ma based on LA-ICP-MS zircon U-Pb dating.The chemical composition of clinopyroxene indicates that Luojiashan gabbro is a typical intraplate tholeiite.Combined with the characteristics of regional tectonic evolution,it is inferred that the Luojiashan gabbro in northeastern Guangxi originated from the extensional rift tectonic background of lithosphere thinning and mantle upwelling.
estimating the temperature and pressureclinopyroxeneintraplate riftingLuojiashan gabbroYingyangguan area of northeastern Guangxipetrologymineralogy
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