海南省抱板群研究的新进展

NEW ADVANCED IN THE STUDY OF THE BAOBAN GROUP IN HAINAN PROVINCE

根据对抱板群的最新研究，自下而上建立两个岩石地层单位，即戈枕村组、峨文岭组。戈枕村组由片麻岩类变粒岩组成，厚度大于２３８１ｍ，具混合岩化。该组测得锆石一致曲线上交点年龄（１８２４±７７）Ｍａ，混合岩脉体ＲｂＳｒ等时线年龄（１６３７±３１）Ｍａ，推测形成于１６００～１８００Ｍａ之间，相当于长城纪早期。峨文岭组以各类片岩为主，其次是石英岩和变粒岩，无混合岩化作用。侵入该组的变质花岗岩体，测定３个锆石ＵＰｂ一致曲线年龄分别为（１４５６±６６）、１４４１、（１３６４±２５．６７）Ｍａ；另一件锆石蒸发法２０７Ｐｂ／２０６Ｐｂ峰值年龄为（１４０７±２０）Ｍａ。以上数据表明其形成年龄为１６００～１４００Ｍａ。

According to the latest research, the Baohan Group may be divided in ascending order into the Gezhencun Formation and Ewenling Formation. Their basic features are as follows: (1) The Gezhencun Formation consists principally of gneiss with granulitite, >2 381 m thick, strongly migmatized. This formation has been determined to have a zircon concordant upper intercept age of 1 824±77 Ma, and the migmatite veins have a Rb Sr isochron age of 1 637±31 Ma.It is inferred that this formation orginated between 1 600 and 1 800 Ma B.P., largely corresponding to the early part of the Changchengian period. (2)the Ewenling Formation is chiefly composed of various types of schist with subordinate quartzite and granulitite, no migmatitization being seen. Zircons from a metamorphosed granite body intruded into the formation yielded three U Pb concordant ages: 1 456, 1 441 and 1 364 Ma. Another zircon gave an evaporation 207 Pb / 206 Pb peak age of 1 407 Ma. From these isotopic ages it may be judged that its age ranges from 1600 to 1 400 Ma, corresponding to the late part of the Changchengian Period.