黄陵变质地区的同位素地质年代及地壳演化

研究表明,黄陵变质地区崆岭群是神农架群之下的古老结晶基底,其中、下部为典型的孔兹岩系。作者首次在崆岭群孔兹岩系地层中取得可信度较高的锆石UPb一致线年龄2332Ma。同时利用K-Ar稀释法和Rb-Sr全岩等时线法获得的年龄值分别为1891和2010Ma.。这些数据证实,崆岭群属下元古界。由此认为,黄陵变质地区及扬子地台结晶基底的形成时代绝不是中晚元古,而是早元古初期。

ISOTOPIC GEOCHRONOLOGY AND CRUSTAL EVOLUTION OF HUANGLING METAMORPHIC TERRAIN

Traditionally the basement of Yangtze platform was regarded as middle to lat proterozoic.As a combined approach several isotopic dating (U-Pb, Rb-Sr and K-Ar) Were, conducted on metamorphic rocks from Kongling khondalite series in western Hubei province.The isotopic ages of 2332 Ma. (U-Pb), 2010Ma. (Rb-Sr) and 1891 Ma. (K-Ar) indicate that the Kongling Group belongs to lower proterozoic. Combined with field observations,especially of the contrast between Kongling Group and Sttennongjia Group of adjacent area, it seems that the whole area had suffered a high temperature low pressure regional dynamo-thermal flow metamorphism in early proterozoic and, then,a regional low temperature dynamic metamorphism in late proterozoic.In recent years sevaral isotope ages older than 1700-1800 Ma. and other information were reported from West Sichuan, East Yunnan, Zhejiang and other province, all facts imply that the oldest crystalline basement of Yangtze platform is lower proterozoic and not middle-late proterozoic as usually proclaimed.