桐柏山花岗岩类Pb、O、Sr同位素特征

LEAD,OXYGEN AND STRONTIUM ISOTOPIC CHARACTERISTICS OF GRANITOIDS,TONGBAI MOUNTAIN

本文首次对桐柏山花岗岩类的Ｐｂ、Ｏ、Ｓｒ同位素进行研究。其长石铅同位素组成是２０４Ｐｂ＝１．４００（１．３８９－１．４１１），２０６Ｐｂ／２０４Ｐｂ＝１７．１４８（１６．８４７－１７．４３８），２０７Ｐｂ／２０４Ｐｂ＝１５．４２８（１５．３７８－１５．４８４），２０８Ｐｂ／２０４Ｐｂ＝３７．８８６（３７．５８３－３８．２９６）。与邻区花岗岩类相比，基本相当于胶东地区。全岩矿δ１８Ｏ＝８．４８（７．４９－９．３７）。８７Ｓｒ／８６Ｓｒ（ｉ）＝０．７０９０（０．７０６４－０．７１３８）。这些数据结合岩石矿物特征表明，本区花岗岩类的成因类型属Ⅰ型或同熔型。铅同位素组成揭示本区大地构造可能归属华北地台。

Described in this paper are the Pb, O and Sr isotopic characteristics of granitoids in the Tongbai Mountain region. The results are presented as follows: 204Pb=1.400 ( 1.389-1.411), 206Pb/204Pb= 17.148(16.847-17.438), 207Pb/204Pb= 15.428 ( 15.378-1 5.484) and 208Pb/204Pb= 37.886 (37.583-38.296) for 8 feldspars and one wholerock sample. In comparison with those of granitoids in the vicinity, the authors have come to the conclusion that the geotectonics of this region may be the same as that of the Jiaodong region. δ18O values range from 7.49‰ to 9.37‰ (averaging 8.48‰) and 87Sr/86Sr(i) ratios range from 0.7064 to 0.7138(averaging 0.7090).These isotope data indicate that the granitoids of this region are similar in origin,belonging to I-type granites as proposed by Chappell and White or syntexis-type granites as proposed by Xu Keqin. The Pb isotopic compositions revealed that geotectonically this region may be assigned to the North China platform.