Geochronology in the north segment of the Derbugan fault zone, Great Xing''an Range, NE China
大兴安岭地区德尔布干断裂带北段构造年代学研究

Derbugan fault zone, a NE tending fault zone in the West of the Great Xing'an Range uplift and along the western margin of the Hailar-Labudalin-Genhe basins, is the famous zone which is the NS boundary fault zone of the Derbugan metallogenic belt. In order to understanding the character for the activity and timing of this fault, and its relations to the Hailar-Labudalin-Genhe basins, and polymetal ore deposit along this fault, we show the SHRIMP zircon and mica 40Ar/39Ar dating for the granule-biotite granitic vein, granodioritic gneiss with ductile deformation and mica-quartz schist in this fault zone. SHRIMP zircon U-Pb dating of the granodioritic gneiss yield concordant age of 300.6±9.3Ma, together with its igneous zircon in CL image, indicate that age of 300.6±9.3Ma is the protolith ages for this gneiss. The biotite 40Ar/39Ar dating also from this granodioritic gneiss, which yield the plateau age of 130.9±1.4Ma, together with the biotite 40Ar/39Ar plateau age of 115.6±1.6Ma from the mica-quartz schist, indicate that those ages between the 115~130Ma are the extensional event ages at the Early Cretaceous in the Derbugan fault zone. The granule-biotite granitic vein also analyzed by the SHRIMP method, which yield the concordant age of 130.1±1.4Ma with the igneous zircon in CL image, indicate that age of 130.1±1.4Ma are the protolith age and incursion due to the syn- extensional event during the Yanshanian in this fault zone. Those results from this study, suggest that the Derbugan fault zone is the youngest extensional structure with the ages between 110~130Ma during the Yanshanian in this area. Derbugan fault zone has dominated the framework of the Mesozoic volcanism in the Hailar-Labudalin-Genhe basins, the crust evolutions and ore-forming types in the Great Xing'an Range. Therefore the Derbugan fault zone with the extensional event ages of 115~130Ma are the typical evidence for the intra-continental orogen at Yanshanian during the Mesozoic.