The formation age of Kaqiong Rock Group in the northern margin of Gangdese, the Qinghai-Tibet plateau

The Kaqiong Rock Group is consisted of intermediate to high grade metamorphic rocks in the northern margin of Gangdese,the formation age of which was not well constrained.Recently,high resolution LA-ICP-MS in situ dating yielded an upper intercept age of(1082±18) Ma from banded plagioclase amphibolite(orthometamorhpites) of Kaqiong Rock Group in northern Tongka area,Baxoi County,Tibet,and this age limits the formation age of the protolith to late Mesoproterozoic(that is,Late Jixian).The gneissic monzogranite of Kaqiong Rock Group yields an upper intercept age of(549±18) Ma,which belongs to tectonothermal event caused by magma events in Pan-African.Combined with the field geology and petrographics,we believe that these rocks were the materials formed from the meta-volcanic and sedimentary rocks of Kaqiong Rock Group during partial melting,and the magma emplaced nearly autochthonous.After Pan-African Event,Kaqiong Rock Group underwent a strong tectonic deformation at(416±23) Ma,the significance of which is worth to further discussion.