浙江景宁鹤溪群斜长角闪岩变质新生锆石特征、离子探针(SHRIMP)U-Pb年龄及地质意义

METAMORPHIC NEWLY PRODUCED ZIRCONS,SHRIMP ION MICROPROBE U-Pb AGE OF AMPHIBOLITE OF HEXI GROUP, ZHEJIANG AND ITS IMPLICATIONS

景宁鹤溪群斜长角闪岩变质新生锆石特征是粒度均匀（约70μm），晶体结晶和透明度极好，色调一致的淡粉红色，呈金刚光泽．未见裂隙、表面熔蚀、环带和核心构造。离子探针质谱GHRIMPⅡ）的206Pb／238U、207Pb／235U两组年龄在误差范围内基本谐和，206Pb／238U年龄的加权平均值（252±5Ma）为变质新生铁石的结晶年龄。锆石的精确定年（252±5Ma）为丽水—余姚断裂以东地区呈“天窗式”零星出露于中生代火山岩系中的鹤溪群提供了一个变质作用的确切年龄，也为印支运动在丽水—余姚断裂以东地区的存在提供了重要的年代学佐证。

Zircons in amphibolite from the Hexi Group in Jingning, Zhejiang Province are newly produced in origin, which are good in crystal form and transparency, and have uniform grain size and light pink color, but have no fracture, surface dissolution and zoning or core structure. The SHRIMP ion microprobe 206Pb/238U, 207Pb/235U ages of zircons are essentially consistent within the error range. The average 206Pb/=238U age is 252±Ma, representing the age of zircon ctystal-lization. This age implies the accurate metamorphic age of the Hexi Group occurring in the Meso-zoic volcanit rocks as nwindow" scattered to the east of the Lishui-Yuyao fault, and provides lso-topic chronological evidence suggesting that the Indosinian movement was developed east of the Lishui-Yuyao fault.