The Geochronology, Geochemistry and Petrogenesis of the Weibozhan intermediate-acid granites in the northern margin of the Alxa block.

The northern Alxa block is the key area for studying the closing of the Paleo-Asian Ocean, Owing to the Carboniferous granites have been rarely investigated in the Yagan area, Leading to importartly restriction for the time of the closing of the Paleo⁃Asian Ocean in northern Alxa block. In this paper, we carried out a systematic study of the petrography, geochemistry, zircon U-Pb dating for the Weibozhan intermediate-acid granites, which are located in the north of the Yagan Fault. The Weibozhan intermediate-acid granites have mainly composed of monzogranite and pyroxene diorite. The zircon LA-MC-ICP-MS U-Pb dating results show that the monzogranite and pyroxene diorite are formed during the Late Carboniferous in 320±1.7Ma, 323 ±4 Ma.The Weibozhan intermediate-acid granites are characterized by high K calc-alkaline or calc-alkaline. are relatively enriched in large in lithophile elements, such as Rb , Th, Hf and depletions in high field strength elements, such as Nb, P and Ti. They show right-leaning chondrite-normalized patterns, which means enrichment in LREE and depletions in HREE. Based on the formation age and geochemical characteristics, it is concluded that the the Weibozhan intermediate-acid granites are likely formed in a continental margin arc setting, and products of the subduction of the paleo-Asian ocean during Late Carboniferous. Combined with regional geological background, it is inferred that the closure of the paleo-Asian ocean in the northern margin of the Alxa block should postdate the Early period of Late Carboniferous.