Geochemistry And Tectonic Significance Of Mafic-ultramafic Rocks In Taolai Region Of The Inner Mongolia

The study area is Taolai region,located in the northwestern part in Alxa Right Banner of the Inner Mongolia Autonomous Region,and the combination zone between the North China Plate and the Tarim Plate.This paper selects the mafic-ultramafic intrusion in the study area as the research object.Summarize the previous research details and systemic research on petrology,geochemistry,Nd isotope characteristics to preliminary discussion on petrogenesis and tectonic setting:In the petrology characteristics,the intrusion has a tumor-like appearance in the field,the exposed area is about 1.55km~2,The main rock types are Cpx-augite peridotite and medium-fine grained gabbro.The Cpx-augite peridotite serpentinization is in a high degree,with massive structure,granule texture,the main mineral is olivine(70%~80%),and the minor mineral is clinopyroxene(20%~30%);medium and fine gabbro is local existenced chloritization and epidotization,with massive structure,gabbro texture,the main minerals are plagioclase(50%~55%)and clinopyroxene(45%~50%).In the geochemistry characteristics,the mafic-ultramafic rocks are characterized by high magnesium,low potassium and low sodium,and the degree of crystallization is low.These are tholeiitic basalt;the total amount of rare earth elements is low,and the light,heavy rare earth elements showed significant fractionation,Most of the samples are positive Eu anomalies.The distribution pattern and elemental composition are similar to those of normal mid-ocean ridge basalt.The trace elements are relatively enriched in large ion lithophile elements such as Ba,U,Pb,depleted high field strength elements such as Nb,Ce;?Nd(t)=4.3~14.8,all of which are positive and vary greatly,Indicates the magma source may be a depleted mantle and the evolution process is contaminated by crustal contamination.Synthetic analysis of petrology characteristics,geochemistry characteristics and Nd isotope characteristics,compared with previous research results,it is preliminarily concluded that the mafic-ultramafic rocks in the study area belongs to the basaltic magma genesis series,and the magma source may be a depleted mantle.the formation of rocks is controlled by partial melting,and the degree of magma crystallization is relatively low.The magma evolution process is contaminated by a certain degree of crustal contamination.mafic-ultramafic rocks may be formed in the environment of the back-arc basin,which is the magma evolution product of the post-arc secondary expansion caused by the subduction of the Paleo-Asian Ocean plate to the continental plate.