Characteristics And Tectonic Significance Of Carboniferous Intrusive Rocks In Engelwusu,Alashan,Inner Mongolia

The Englewusu ophiolitic melange belt of the Alxa League in Inner Mongolia is at the junction of the Central Asia Orogenic Belt,the North China Plate and the Tarim Plate.The magma activity in the research area is frequent,with long evolutionary time,varied structural backgrounds,and complex rock genetic types.In this paper,the Carboniferous intrusive rocks in Engelwusu,Alashan are selected as the research objects.With the systematic summary of the field geological investigations and the previous research results,the geochemical characteristics of the Carboniferous granites in the research area and the regional tectonic significance are discussed by the use of petrology and geochemistry methods.The Englewusu Carboniferous Intrusion is mainly distributed on the north side of the Englewusu ophiolitic melange belt in the research area.In general,it irregularly spreads in the northeast direction,and it is in fault contact with other geological bodies which make up the ophiolitic melange.Petrological studies have shown that the rock types in the research area are mainly Carboniferous granodiorite and quartz monzodiorite.According to the LA-ICP-MS isotopic dating,the quartz monzodiorite formed in the late Early Carboniferous Epoch(328.2±1.6 Ma)and the granodiorite formed in the early Late Carboniferous Epoch(317.2±0.99 Ma)The geochemical characteristics of the Carboniferous intrusive rocks show that they are both in the Ca-alkaline series,and both are products of the converging plate environment.The analysis of rare-earth elements shows that the magma has received shell source contamination.LILE enrichment and loss of HFSF proved to be arc magmatic rock.The structural discriminant diagram also falls in the arc magmatic environment at the edge of the plate.The study and analysis of the Carboniferous intrusive rocks show that the Engelwusu ophiolite melange began to form in the late Early Carboniferous Epoch.When the ancient Asian oceanic crust subducted South and the Permian continued to subduct,the intrusive rocks formed in the Carboniferous Epoch came from the continents were scraped off and mixed with the formed ophiolite.