金沙江缝合带元古宙残留基底的发现——来自同位素地质年龄的证据

DISCOVERY OF PROTEROZOIC REMNANT BASEMENTS IN THE JINSHAJIANG SUTURE ZONE——EVIDENCE FROM ISOTOPIC AGE

应用颗粒锆石U—Pb法和Rb-Sr全岩等时线法重新研究了金沙江东岸苏洼龙地区原统归于早二叠世额阿钦群中的一套高级变质岩系的原岩时代和变质时代。其中含蓝晶石二云母片岩Rb-Sr等时线年龄为（432±35）Ma;而斜长角闪岩U-Pb锆石的上交点年龄为（1627± 192）Ma,暗示这套变质岩系的原岩时代应大于（1627±192）Ma。（432±35）Ma的Rb-Sr等时线年龄可能代表其变质时代。首次提出金沙江地区应存在早中元古代残留变质基底或微陆块,层位上可与哀劳山杂岩对比,金沙江缝合带和哀牢山缝合带是相关联的同一条缝合带。

High-grade metamorphic rocks which used to be considered as part of the early Permian Eaqing Group are exposed in Suwalong area along the eastern bank of the Jinshajiang river, western Sichuan Province. Their ages of protolith and metamorphism have been dated with single zircon U-Pb and whole-rock Rb-Sr isochron methods. 6 whole-rock samples from the kyanite-bearing two-mica schist give a Rb-Sr isochron age of (432±35) Ma, probably representing the age of a metamorphic event. Zircons from the plagioclase-amphibolite give an upper intercept age of (1627±192)Ma, reflecting the minimum age of its basic volcanic protolith. It is suggested for the first time that there may exist a Palaeo-, Meso-Proterozoic remnant metamorphic basement (micro-block) in the Jinshajiang suture zone, equivalent to the Ailaoshan complex in horizon.