Magmatic Consanguinity Of Mafic Dyke Swarm And Basalt In Southern Qiangtang

The mafic dyke swarms are the product of the mafic magma and structure, which has the same composition with the basalt and its production form stabl-e.The basalt are the product of the expulsion of the basic magma.The geneticst udy of basalt has the extremely vital significance to restore the formation of th-e tectonic environment.There are widespread basic and ultrabasic igneous rocks distributing in sou-th Qiangtang. Basic dykes and basalt are distributed near the east-west directio n along south of the Longmu Co—Shuanghu suture zone. The mafic dyke swa-rm and the basalt are close symbiosis, they lies on the northern margin of G-ondwanaland. They had a range of 800km from the border in the west to Shu-anghu area.Some of the scholars had did some research of the mafic dyke sw-arm and the basalt, who pointed out that the mafic dyke and the basalt are th-e product of the breakup of the northern margin of Gondwana.Surrounding roc k of the mafic dyke swarm and the basalt are the active continental margin rif-t type sediments metamorphic rock series, which have a characteristic of ice-s ea mix conglomerate,and the age is the late carboniferous. The basalt are outp-ut in the surrounding rock of the mafic dyke swarm, some of the scholars poi-nted out that the basalt are the product of the breakupof the northern margin of Gondwana. In the study area, the main rock type of the mafic dyke swarm is diabas-e. Research shows that the mafic dyke swarm has experienced Greenschist Fa-cies metamorphis, massive tectonic, become gabbro texture or diabasic texture, embedded chip containing long structure. The main mineral composition are cli-nopyroxene and plagioclase, part of the pyroxene are altered and the plagiocla-se are chloritization.There is a little quartz Granular distribution In the rock. Accessory mineral including magnetite,titanium iron ore,apatite,zircon and s-o on. Secondary minerals including hornblende,albite,epidote,chlorite,leuc oxene and so on.The basalt are output in the Surrounding rock of the mafic dyke swarm, t-he main rock type is basalt and basaltic andesite. In some area, there are doz-ens of layer of the basalt,the thick of the single-layer of basalt may up to several meters, the biggest thick of the layer may up to more than 100 meter s. The mafic dyke swarm and the basalt are close symbiosis and interdependen-t, both of them has experienced Greenschist Facies metamorphis also, Rock fo-r adark grey green, massive tectonic or stomatal tectonic, porphyritic-like textu re.T-he main mineral composition has been changed, But we can still clearly s-ee the original outline fraser of the pyroxene, most of the phenocrysts are c1 ino-pyroxene. hypidiomorphic texture, accounted for 25～30% of the rock. The ma-trix of the rock are Consistsed by albite,epidote,chlorite,leucoxene and so on.Basic dykes and basalt are mostly of kalium alkaline series, few subalkali ne series, with high content in titanium and iron and low content in Mg#, whi-ch indicates that they are residual granitic melts from different magmatic crysta-llization of primary magma. There are no significant differences in the concen trations of the main mineral composition,major elements,REE elements and the trace elements between the mafic dyke swarm and the basalt. The elements concentrations of the mafic dyke swarm and the basalt have the same feature as the within-plate basalt.On that basis, combined with the regional geological data, the authors think that the mafic dyke and the basalt come from a consan guineous magma, and the causes of the mafic dyke and the basalt may both h-ave something with the mantle plume.