SHRIMP zircon dating of meta-sedimentary rock from the Qinling Group in the north of Xixia,North Qinling Orogenic Belt:Constraints on complex histories of source region and timing of deposition and metamorphism

This paper carried out a geochronological research on zircons from a meta-sedimentary rock (biotite plagioclase gneiss) sample in the north of Xixia,a typical distribution area of the Qinling Group in the Qinling Orogen Belt.The zircons show complex core-rim structures in CL images.A total of 56 analyses on forty-seven zircons have ages ranging from 3.0Ga to ~400Ma.Combined with early data,some conclusions can be drawn as follows.(1) The protolith of the meta-sedimentary rock of the Qinling Group was formed after Paleoproterozoic with some probably being Late Mesoproterozoic or even later,the original Qinling Group may be made up of rocks of different ages;(2) the zircon features show that the studied rock underwent metamorphism from upper amphibolite-granulite facies in early stage to amphibolite facies in late stage during the Early Paleozoic;(3) the source region providing detritus for the Qinling sediments shows a long and complex evolution history,there might be Archean basement in Qinling and adjacent areas.