Stage Subdivision And Tectonic Implications Of Intrusive Rocks In Huancaigou Area,East Tianshan

The Hami Huancaigou area is located in the south slope of harlik mountains,one branch of the East Tianshan Mountain.Tectonically it is a key part of the Central Asian accretive orogenic belt.There are a lot of Paleozoic magmatic rocks developed after many stages of tectonomagmatic events.In this paper,the intrusive rocks in the vicinity of huancaigou area were selected for petrology,geochronology,zircon Hf isotope and geochemistry studies to explore the tectonic background of their formation.The lithology of intrusive rocks in different ages in huancaigou area mainly includes:gabbro diabase,quartz diorite,diorite,granodiorite and monzonite.The zircon LA-ICP MS U-Pb dating of the rock samples showed that the ages were 449.8±3.6Ma,441.6±4.2Ma,329.2±1.7Ma,312.0±4.3Ma and 301.1±3Ma.Combining the previous dating results,the magmatic events are further divided into study areas.The magmatic events are mainly divided into two stages:the late Ordovician-early Silurian and Carboniferous magmatic events.The Hf isotope characteristics show that the source magma is partly melted from the depleted mantle mixed with the crust or the young crust material newly added from the depleted mantle.In terms of rock geochemistry,the late Ordovician-early Silurian quartz diorite have high SiO₂ content and low K₂O content,which is a low-potassium?plaque?series,while the gabbro diabase has low SiO₂ content,K₂O content is high,it is calcium alkaline series,the aluminum saturation index of both A/CNK<1,belonging to metaluminous.In carboniferous magmatic rocks,the content of SiO₂ in diorite is low and the content of K₂O is high,belong to calcium-alkaline series,with an aluminum saturation index of A/CNK<1,belonging to metaluminous;Both monzogranite and granodiorite exhibit high SiO₂ content and high K₂O content,belong to the high-k calc-alkaline series,with A/CNK ratios are 0.97¹.08,belonging to quasi-aluminum to weakly over-aluminum.In The petrogenetic discriminative indicators reveals the formation environment diagram,except for monzonite granite as the intraplate environment?WPG?,all other rocks fall into the island arc environment?VAG?.Based on the analysis of regional geological data,duringthe Early Paleozoic?late Ordovician to Early Silurian?,Harlik orogenic belt is the island arc tectonic environment related to oceanic crust subduction;the Late Carboniferous was the extensional background of post-orogenic?post-collision?,which also verified that the ancient Asian Ocean was closed at the end of the Late Carboniferous and began to enter the intraplate tectonic environment.