Properties Of Lithospheric Mantle In Northern Xingmeng Orogenic Belt

As an important part of the lithosphere,the lithosphere mantle is the link between the shallow crust and the deep asthenosphere mantle.So far,our understanding of the formation and evolution of the continent depends on the understanding of the lithosphere mantle.Orogenic belts,as the most active belts in lithosphere and crust,are the key research areas with the most information storage and records of lithosphere formation and evolution.Lithospheric mantle is a low-density magnesium-rich residue formed with the extraction of crustal melt,which is an important link between asthenosphere and crust,so it is very important to study lithospheric mantle of orogenic belt.Xingmeng orogenic belt is located between Siberian plate,North China plate and Pacific plate,which belongs to the eastern part of Central Asia orogenic belt,generally refers to northeast China and Russia region affected by Paleozoic tectonics,and is a typical area where many tectonic systems are superimposed and reformed.At present,there are still controversies about the basement attribute of each micro-block in Xingmeng orogenic belt,the assembly history of each micro-block,the reconstruction time of ancient oceanic tectonic system and its influence time and space,and the crustal proliferation and reconstruction.In this article,the peridotite captives in Nuomin and Kolo areas in the north of Xingmeng orogenic belt are selected as the research objects,and the properties and evolution process of lithospheric mantle are studied through detailed petrology,geochemistry and oxidation-reduction state of mantle in the study area.The chemical characteristics of major elements of minerals in the study area show that there is a new oceanic mantle in the northern part of Xingmeng orogenic belt,and the remains of ancient mantle are also found.The equilibrium temperature of peridotite inclusions in Nuo Min study area is in the range of 800?1200?,and that in Kolo study area is in the range of796?991?,T _Kolo<T_Nuomin,indicating that the origin depth of peridotite in Nuomin area is deeper than that in Kolo area.The mantle in the study area is stratified,with refractory lherzolite in the deep part and full lherzolite in the shallow part.The trace element characteristics of clinopyroxene in the study area show that the partial melting degree in the north of Xingmeng orogenic belt is similar to the higher partial melting degree experienced by peridotite in Hebi area,which is refractory and deficient,and has undergone metasomatism transformation to a certain extent.The metasomatic medium is silicate flow/melt.By discussing the oxidation-reduction state of mantle in the study area,it is shown that the oxygen fugacity in the north of Xingmeng orogenic belt is obviously higher than that in the south,which is close to the range of oxygen fugacity in the continental lithosphere mantle such as island arc affected by subduction zone.It is different from the relatively low oxygen fugacity in ancient mantle,and the main reason for the increase of oxygen fugacity may be the influence of subduction ocean plate.Under the influence of the northward subduction of the ancient Asian Ocean in Paleozoic and the eastward subduction of the ancient Pacific Ocean in Mesozoic,Fe₂O₃,CO₂ and H₂O in the subduction plate will be released continuously along with the subduction process,and these oxygen-rich substances will enter the upper mantle along with the fluid,and some samples with high melting degree will undergo multiple metasomatism,resulting in the continuous increase of oxygen fugacity value.