U-Pb ages of zircon from metamorphic rocks of the Gaoligongshan Group in western Yunnan and its tectonic significance
滇西高黎贡山群变质岩的锆石年龄及其构造意义

The Gaoligongshan Group,which has long been interpreted as Precambrian basement of the Tengchong-Lianghe block in western Yunnan,but the forming ages of their protolith and subsequent deformed and metamorphic ages has been an issue of little consensue.Petrograpic and geochemical analyses indicates that biotite monzonite gneiss,biotite amphibolic-plagioclase gneiss and feldspar fels which consisting of the Gaoligongshan Group metamorphosed rocks are orthometamorphites.U-Pb SHRIMP and LA-ICPMS zircons dating of these metamorphosed rocks were carried out firstly and yields ages 497.8 ± 7.2Ma ～ 500 ± 14Ma,83.5 ± 0.9Ma as the timing of their emplacement and 459 ± 5Ma,55.2 ± 1.1Ma as that of metamorphism,respectively.Based on these results,together with the regional comparison and detrital zircons ages obtained from adjacent metamorphic rocks,it is concluded that the sedimentary body of the Gaoligongshan Group had been formed during the Neoproterozoic and then intruded by Cambrian granites formed during the circum-Gondwana orogeny.The Gaoligongshan Group initially experienced an Andean-type orogenesis through the subduction of the Neo-Tethys oceanic lithosphere during Late Mesozoic and then the India-Eurasia continental collision in the Cenozoic and the strike-slip shearing during the extrusion of the Indochina Block.The Indochina Block has resembles with the Lhasa Block in terms of Paleozoic to Mesozoic magmatism and detrital zircon ages.