南秦岭元古宙西乡群大陆溢流玄武岩的确定及其地质意义

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中元古代西乡群火山岩是南秦岭元古宙最老的火山岩系,以其大面积分布、具浅海-陆相火山岩组合、属大陆拉斑玄武岩系列,具大陆板内火山岩岩石地球化学特征及与大的基性侵入体共生等特点,可确认其属大陆溢流玄武岩系。西乡群火山岩具有较高的值及低-中等的(~(87)Sr/~(87)Sr)_i值,可判定其源区为与洋岛玄武岩相似的软流圈地幔柱源,在岩石圈较大程度的拉张作用下,上隆的地幔柱减压熔融,产生岩浆。扬子克拉通北缘南秦岭广泛发育中-晚元古代大陆裂谷火山岩系,显示在中-晚元古代该区有大规模大陆张性拉伸作用,晚元古代晚期至早古生代,这种张性拉伸作用发展为陆壳碎裂直至形成洋盆。西乡群大陆溢流玄武岩与扬子克拉通北缘的破裂有密切关系。 The Paleoproterozoic Xixiang Group volcanic rocks are the oldest volcanic rocks in the southern Qinling Proterozoic. They are distributed in large areas with shallow sea-continental volcanic assemblages and belong to continental tholei basalt series. They are characterized by geochemical characteristics of volcanic rocks in the continental shelf, And large basic intrusions and other characteristics of symbiosis, to confirm its continental overflow basalts. The Xixiang Group volcanic rocks have high value and low-moderate (~ (87) Sr / ~ (87) Sr) _i value, and can be identified as asthenospheric mantle plume similar to that of oceanic basalts A larger extent of the lithosphere tension effect, the upper mantle plume vacuum melting, resulting in magma. The mid-late Neoproterozoic continental rift volcanic rocks were widely developed in the southern Qinling of the northern margin of the Yangtze craton, showing large-scale tensile tension in the mainland during the middle-late Proterozoic. Late Palaeozoic to early Paleozoic, The development of sexual stretching to crust the continental crust until the formation of oceanic basin. The overflow of basalts in the Xixiang Group and the northern margin of the Yangtze Craton are closely related.
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