Geochronology,Geochemistry And Tectonic Background Of Late Paleozoic Intrusive Rocks In Beishan-Erdaoquan Area,Gansu Province

The study area is in the north of Dunhuang,Gansu Province.In this paper,three types of granodiorite,monzogranite and syenite of Hongliuhe ore body,quartz diorite,monzogranite,granodiorite and syenite of Beishan rock body,granodiorite and syenite of Erdaoquan rock body and syenite of Hongliuhe ore body exposed in the study area are selected as research objects.Through field geological survey,petrography,zircon U-Pb dating and whole rock geochemistry The petrogenesis and tectonic background of the study area are discussed by the analysis of characteristics and the previous research results.In this paper,the following points of understanding are obtained: (1)LA-ICP-MS zircon U-Pb isotope dating shows that the age of granodiorite formation in Hongliuhe orebody is(400.1±2.3 Ma),the age of monzonite formation is(400.8±3.2 Ma),the age of syenite in Beishan intrusion is(425.4±2.3)and the age of granodiorite formation in Erdaoquan intrusion is(383.4±2.3 Ma),which is Early Devonian. (2)The Hongliuhe orebody is generally characterized by high silicon,low aluminium,alkaline,quasi-aluminous to weak peraluminous,and mostly belongs to high potassium calc-alkaline series,while a small amount of granodiorite belongs to potassium basalt series.The chemical composition of Beishan orebody varies greatly.Beishan orebody is rich in iron,magnesium and Ca O,and A/CNK ranges from 1.40 to 2.41.Most of them belong to the high-K calc-alkaline series,while a few quartz diorites and granodiorites belong to the calc-alkaline series.Erdaoquan intrusion is generally characterized by peraluminous A/CNK=1.24?1.71,and is characterized by high silicon,low aluminium and alkaline alkalinity,all of which belong to the high-K calc-alkaline series. (3)The Hongliuhe ore body,Beishan rock body and Erdaoquan rock body have similar cobweb maps of trace elements and REE distribution pattern maps.The rock body is obviously enriched with Rb,Ba,U and high field strength elements such as Zr,Th and Hf,but strongly depleted with K,P,Ti,Nb and Sr.The rock body is enriched with light rare earth elements and depleted heavy rare earth elements,and belongs to the enrichment of light rare earth elements as a whole.The distribution curve is right-leaning on the whole. (4)The types of granite rocks in the study area are relatively complex,and most of them are type A.The Hongliuhe orebody shows FG type,while the Beishan and Erdaoquan rocks fall into OGT type,and the rocks basically fall into the classical island arc rocks.Most of the Hongliuhe and Erdaoquan intrusions fall into the arc,while a few fall into the plate,which is close to the plate.Beishan intrusions fall into the arc environment.Based on the analysis of regional tectono-magmatic data and age,it is concluded that the Tarim plate and Kazakhstan plate did not merge in the Late Silurian,but began to merge in the Early Devonian and turned to the post-collision orogenic stage,i.e.intraplate extension stage.