Study On Chronology And Geochemistry Of The Basic Rocks Of Diyanmiao In Inner Mongolia

This article choose Diyanmiao temple gabbro and basalt in Inner Mongolia as the research object,and studied the petrography gabbro and basalt,zircon U-Pb chronology,trace element,main elements and whole rock mineralogical analysis,whole rock,Sr,Nd isotopes study to determine the existence of magmatism,and find out its genesis,closing deadline which restrict the clousure of Paleo-Asian Ocean,magma source area quality and its tectonic background,and then to provide basis of magma evolution of orogenic belts.The U-Pb age of gabbro zircon from Diyanmiao area,Inner Mongolia is 329Ma,MSWD is 0.034,indicating that it was formed in the early carboniferous.Some of the zircons are older than the age of the rocks,and they were formed in the Precambrian period,confirming the existence of a Precambrian metamorphic basement at Diyanmiao temple.The related diagrams of the petrochemical characteristics and rare earth element characteristics of thebasite of Diyanmiao indicate that the gabbro and basalt samples of the early carboniferous of Diyanmiao belong to N-MORB series and were formed in extensional environment.The crystalline minerals of basalt are pyroxene,the crystalline minerals in gabbro samples are feldspar,and the basic rock mother magma of diyanmiao is mantle melting of spinel peridotite,with a depth range of 30km-80km,which is the product of low-degree partial melting.Mineralogical analysis of the samples of Diyanmiao rock-monoclinic pyroxene shows the temperature of crystallization is 1007?1120?,with rich amphibole.It indicates that the magma originated in the mantle source area which is subject to the metasomatism of water-rich fluids and the high oxygen futility.The occurrence of hornblende in large quantities proves that its source area is rich in water.It can be concluded that the source area of the Diyanmiao basic rock material is mantle source material and is subject to MORB which is enriched by metasomatism of water-bearing fluid.The Diyanmiao base rock has a low initial ratio of ⁸⁷Sr/⁸⁶ Sr,but a relatively high value of?_Nd(t)which indicate that its isotopic composition deficit,indicating that the mother magma originated in the isotopic deficit mantle source region.The Sr-Nd isotope composition of the diyanmiao basalt samples fell in the continental basalt region.The high value?_Nd(t)of the samples proved that the mother magma had a high oxygen fugicity,so the mother magma of the diyanmiao basalt samples originated in the mantle source region with high oxygen fugicity.In conclusion,the Diyanmiao basite developed in the extensional area with the ancient Precambrian basement and the young basement of the early Paleozoic orogenic belt,and the mother magma originated from the mantle source area that was subjected to the metasomatism of water-rich fluids and the high oxygen fuggeness.Genesis of the neimon Diyanmiao basite:the melting products of the water-rich mantle source area under the continental extensional background.