Genesis And Tectonic Significance Of Alkaline Basalt In Mayile Area,West Junggar

The ocean island-seamount fragments is an important part of the ancient oceanic crust in the preservation of the ophiolitic mélange in the orogenic belt.Studying the geological significance represented by it plays a vital part in reestablishing the tectonic evolution process represented by the orogenic belt.West Junggar region is located in the southwestern margin of the Central Asian orogenic belt,where there are many ophiolitic mélange belts of different ages.As the remnants of the ancient oceanic crust after subduction and accretion,it has been considered as an important symbol of ancient plate convergence.In this paper,a set of pillow basalts closely associated with siliceous rocks was found on the north side of the Ma yile Mountains in West Junggar,carry on the petrology,petrography geochemistry and other studies.Collect adjacent regions of alkaline basalt age and geochemical data,the characteristics of the age,location and source area to do comparison.The pillow basalts belong to alkaline basalt series in Mayile area,with high Ti(3.28%?3.89%),low Mg(3.49%?6.79%),high?REE(enrichment of LREE,loss of HREE((La/Yb)_N=5.5?7),no obvious negative anomaly of?Eu,relative enrichment of Rb,Th,U,loss of Ba,K,Sr,no obvious negative anomaly of Nb,Ta,Ti.All the pillow basalts show the geochemical characteristics of OIB.According to the trace element ratio,the source area of the basalt is derived from an enriched mantle source area,showing that samples should be 5%?15%spinel and garnet lherzolite products of partial melting.Based on the previous published data,it is believed that alkaline pillow basalt is formed in the oceanic plate environment.In recent years,basalts with OIB characteristics of different geological ages have been found in ophiolitic mélange belt in West Junggar area.These basalt samples enrichment of LREE,HREE loss,weak?Eu or no?Eu anomaly,and not shown Nb,Ta,Ti negative anomaly.They are formed in the seamount or oceanic plateau environment.Combined with the age,geochemical characteristics and spatial distribution of ophiolitic mélange,it is considered that the West Junggar area developed not only intra-ocean subduction,but also mantle plume activity in the Late Paleozoic.The mantle plumes of different ages formed a series of seamounts/oceanic plateaus.With the subduction of the oceanic crust,alkaline basalt was scraped and preserved in the accretionary prism.The study of alkaline basalts will provide a new idea for the study of continental crust accretion and orogenesis in the West Junggar and Central Asia orogenic belt.