我国华北及东北地区前寒武纪岩石K-Ar等时年龄

K-Ar ISOCHRON AGES OF PRECAMBRIAN ROCKS IN NORTHERN AND NORTHEASTERN CHINA

The available data on K-Ar isochron ages of Precambrian rocks in Northern and Northeastern China have been disecssed in the present paper. The author has come into the conclusion that the metamorphic rocks in Wutaishan area have undergone, at least, more than one metamorphic events. The Huto Group, which was subjected to the main one of the metamorphisms, is 1740 m.y. in age. Another one took place 1330 m.y. ago. Wutai Group may be probably 2000 m.y.in age, showing a metamorphic event would oceur at that time. The metamorphic ages of the Liaoho Group in the Liaotung Peninsula and Taishan Group are 1840 m.y. and 2460 m.y. respectively. Relatively acceptable explanations have been obtained for some lower apparent ages by K-Ar isochron treatment. The lower apparent ages of the samples as shown by the negative intereeption of K-Ar isochron can be attributed to Ar loss and Kalternation (for example, biotitization of hornblend or microclinization of feldspar)of minerals, both of which, distinctive with each other, operate in combination.

The available data on K-Ar isochron ages of Precambrian rocks in Northernand Northeastern China have been discussed in the present paper. The author has come into the conclusion that the metamorphic rocks in Wu-taishan area have undergone, at least, more than one metamorphic events. The HutoGroup, which was subjected to the main one of the metamorphisms, is 1740 m.y. inage. Another one took place 1330 m.y. ago. Wutai Group may be probably 2000 m.y.in age, showing a metamorphic event would occur at that time. The metamorphicages of the Liaoho Group in the Liaotung Peninsula and Taishan Group are 1840m.y. and 2460 m.y. respectively. Relatively acceptable explanations have been obtained for some lower apparentages by K-Ar isochron treatment. The lower apparent ages of the samples as shownby the negative interception of K-Ar isochron can be attributed to Ar loss and K-alternation (for example, biotitization of hornblend or microclinization of feldspar)of minerals, both of which, distinctive with each other, operate in combination.