江南造山带西段前寒武纪基性--酸性火成岩及壳幔演化研究

The island arc volcanics and the plume-derived high Mg lavas with arc.signatures are associated in Mesoproterozoic Sibao and Lengjiaxi groups from northern Guangxi and Hunan respectively.It suggested that there was a interactions between the Mesoproterozoic arc and the local plume induced by subduction of ocean.crust along the southern margin of Yangtze plate.The Neoproterozoic.mafic-ultramafic volcanic-intrusive rocks in Danzhou group from northern Guangxi are , geochemically,distinct from the contemporary GDS dyke swarm and Amata suite in Australia.They never show plume-derived magma characters .They should be included in island arc volcanics series and the products of magmatism in subducted zone along convergent plate margin.They ,therefore,could’t be regarded.as a sign of breakup of Rodinia.However,the late Neoproterozoic mafic rocks from Hunan show some signatures of plume-derived magmas.They might be a trace left behind by the breakup of Rodinia.The geochemical features of the Neoproterozoic.SP （strongly peraluminous） granites from northern Guangxi and Hunan indicated that the Jiangnan orogen,like the Lachlan fold belt of stralia,shares some high-temperature collision orogen signatures. The abraded zircon ( 2491Ma )was found in the SP granites.Nd model age of the granites approach to those of Mesoproterozoic basement strata.They might be derived from the partial melting of the Mesoproterozoic epimetamorphic psammitic rocks.The features of zonal distribution of all these Neoproterozoic SP granites in this and other areas along the Jiangnan orogen suggest that their formations were not related to the activities of mantle plume .These Sp granites are post-collisional.The .asthenosphere-derived basic magma during underplating due to the slab breackup after collision provided the thermal source for the formation of granites.

本项目将对江南造山带西段黔贵，雪峰地体中相伴生的前寒武纪基性（超基性）－－酸性火成岩进行深入调查，寻找造山带形成过程中物质再循环的证据，研究古地壳增长与铁，镁质岩浆演化的联系，了解该地区上地幔在中，晚元古代时期所发生的变化，弄清″壳幔作用″对地壳增长和″壳幔演化″的制约，从而加深对华南显生宙″构造－岩浆作用″的认识。