滇西高黎贡山群变质岩的锆石年龄及其构造意义

被认为是腾冲-梁河地块前寒武纪结晶基底的滇西高黎贡山群变质岩系,其原岩及变质时代长期争论不休。岩相学和地球化学表明,组成高黎贡山群的黑云二长片麻岩、黑云角闪斜长片麻岩和变粒岩的原岩均为岩浆岩。首次对这些变质岩进行原位锆石U-Pb定年,分别获得497.8±7.2Ma～500±14Ma、83.5±0.9Ma的岩浆结晶年龄和459±5Ma、55.2±1.1Ma的变质年龄。结合相邻区碎屑锆石年龄及其区域对比分析,认为腾冲-梁河地块高黎贡山群中以石英片岩、石英岩为主体的原始沉积岩系可能形成于新元古代,应与拉萨地块有密切的亲缘关系。在早古生代环冈瓦纳大陆周缘造山过程中被寒武纪花岗岩侵入并发生变质作用;在新特提斯俯冲过程中,经历了晚中生代的安第斯型造弧作用;在印度与欧亚大陆碰撞过程中,又经历了新生代的岩浆作用、变质作用以及走滑剪切形成糜棱岩化作用。

U-Pb ages of zircon from metamorphic rocks of the Gaoligongshan Group in western Yunnan and its tectonic significance

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.