Chronology And Geochemistry Of The Granite In The Dalucao, Dechang, Western Sichuan Province

Neoproterozoic magmatic activities developed on the western margin of the Yangtze plate.Geologists at home and abroad have conducted extensive research on these Neoproterozoic magmatic rocks,and proposed three genetic models of mantle plume,island arc and plate-rift.In this paper,based on the collection of existing research results,a field geological survey was conducted on Neoproterozoic acid intrusive rocks exposed in the continental trough area of Dechang County on the western margin of the Yangtze Plate.Chronology and Hf isotope geochemistry research.Combined with the regional geological background,this paper summarizes the characteristics of Neoproterozoic granite on the western margin of the Yangtze plate,and discusses the rock origin,material source,formation environment,and tectonic significance.In this paper,the zircon U-Pb ages of granite in the continental trough are 770.8±2.0 Ma?DLC1708?and 791.3±1.7 Ma?DLC1712?,and the granite diagenetic age is determined to be Neoproterozoic.The rock belongs to peraluminous high-potassium calcium alkaline granite,with high SiO₂?73.78⁷6.27 wt.%?,High alkali?Na₂O+K₂O=6.17-10.81%?and potassium-rich characteristics;strong differentiation?differentiation index DI The value is 94-98?.The sample is rich in aluminum?Al₂O₃=12.26-13.76%,A/CNK=1.02-1.15?,which is peraluminous granite;the rock belongs to calcium-alkaline rock?Ritman index?=2.03-2.31?.The rock is enriched in Rb,Ba,K and other large ion philophile elements,depleted Nb,Ta,P,Ti and other high field strength elements,and is characterized by a light right rare earth enrichment and a heavy right rare earth gentle right-tilt rare earth element.Continental trough granite belongs to highly differentiated type I granite.The average value of?Hf?t?is a positive value,indicating that its source rock contains new crust material derived from mantle.In this paper,it is believed that the source material is mantle-derived magma intruding into the lower crust to form intermediate-basic igneous rock,which is melted again by magma and mixed with part of the crust-derived material to form granite.In the Neoproterozoic period,the western margin of the Yangtze Plate was in an island arc environment and belonged to the active continental margin.In this paper,the rock origin of Neoproterozoic granites in the western margin of the Yangtze plate supports the"island arc model",that is,the formation of the continental trough granite is related to the subduction under the edge of the convergent plate.Rodinia supercontinent edge.