Geochronology,Geochemistry And Tectonic Significance Of The Early Cretaceous Granites In The Biliutai Area Of Southern Da Hinggan Moutains

A large number of Late Mesozoic granites have been developed in the southern Da Hinggan Moutains,which is closely related to mineralization and is an important nonferrous metal mineralization base.Based on the previous studies,he Early Cretaceous Granitic Intrusion Complex in the Biliutai area of Chifeng,Chifeng,Inner Mongolia as a research object,and conducted geochronology,petro-geochemistry,and zircon Hf isotopic investigations.Combined with previous research results,the magmatic evolution and its metallogenic significance have been discussed.The granitoid rocks in the Biliutai area are classified into three types of lithology: medium-fine phlogopite-bearing positivity,medium-coarse-bearing biotite bougalite,and rhyolite porphyry.The zircon U-Pb ages are 142± 1Ma,133±1Ma and 131±1Ma,all of them are Early Cretaceous intrusive rocks.but they have a tendency to become younger towards the center of the edge and the embedment depth gradually becomes shallower.In the study area,the samples all showed the characteristics of high-potassium,calcium-alkaline,and weak peraluminous I-type granites.The content of rare earth elements was high,and the fractionation of light and heavy rare earths was obvious,showing strong negative Eu anomalies.Enrichment of large ion lithophile elements Rb,K,etc.,loss of high field strength elements such as Nb,Ta,and Ti,suggesting that the diagenetic process experienced a certain degree of separation and crystallization;in addition,Ba has a strong loss,high Sr,low Y characteristics,It also indicates that there may be a wide range of magmatic sources in this area;a lower Nb/La ratio indicates the involvement of crust-derived materials during diagenesis.The three types of rocks all show the characteristics of high-potential calc-alkaline and weakly peraluminous I-type granites.The content of rare earth elements is relatively high,and the fractionation of light and heavy rare earths is obvious,showing strong negative Eu anomalies.Enrichment of large ion lithophile elements Rb,K,etc.,loss of high field strength elements such as Nb,Ta,and Ti,suggesting that the diagenetic process experienced a certain degree of separation and crystallization;in addition,Ba has a strong loss,high Sr,low Y characteristics,It also indicates that there may be a wide range of magmatic sources in this area;a lower Nb/La ratio indicates the involvement of crust-derived materials during diagenesis.The zircon ?Hf(t)values of the medium and fine-grained biotite-positive feldspathic granite,the medium-coarse biotite-bearing syenite,and the rhyolite porphyry are-9.0 to +0.9?-3.8 to +2.8 and-3.3 to-5.7,respectively.The corresponding two-stage Hf model ages(TDM2)were 1763–1137 Ma,1395–1007 Ma,and 1397–826 Ma,respectively.The characteristics of the Hf isotopes indicate that these three magmas have similar source regions,and that the source regions are older and contain a small amount of ancient material.The Biliutai area is similar to other parts in the southern part of the Da Hinggan Moutains.The Early Cretaceous magmatism was intense and formed a strong extensional extension environment.Combined with regional magmatic evolution and previous studies,it was mainly related to the Mongolia-Okhotsk orogenic belt.The stretching and collapse are related,and the latter may be superimposed by the post-arc extension caused by the palaeo-Pacific subduction.