胶东地区粉子山群及蓬莱群地层铅同位素组成探讨

DISCUSSION ON LEAD ISOTOPE COMPOSITIONS OF THE FNZISHAN AND PENGLAI GROUPS IN THE JIAODONG REGION

由胶东地区粉子山群中大理岩及蓬莱群岩石的全岩Ｐｂ同位素组成，得到两条全岩Ｐｂ—Ｐｂ等时线，代表年龄分别是２６２５．０３Ｍａ和１１６５．８５Ｍａ。作者认为以上两个数据很可能代表粉子山群及蓬莱群的沉积年龄。由此，结合Ｐｂ在沉积作用过程中的地球化学性质，指出碳酸盐岩及粘土质岩石在其沉积成岩过程中，其Ｐｂ同位素经过一定的均一化，在某些情况下，均一化程度相当高。利用全岩Ｐｂ—Ｐｂ等时线法可以测出其成岩年龄。这对于那些目前尚无其他方法求得精确年龄的地层而言，不失为一种可取的方法。

Determination of the whole rock lead isotopic compositions of the Fenzishan and thePenglai groups gives two pb pb Pb pb isochron curves indicating the age of 2625.03 Ma and1165. 8 5MB,respectively. It is suggested that these data represent probably the ages when theFenzishan and the Penglai groupe were deposited. In the Light of the geochemical characterics oflead in sedimetation process the author infers that during sedimentation and diagenetic processes ofthe carbonate and clay rocks its pb isotopes have been homogenised to certain extent,and,insome case,to guite high extent.There fore,the whole rock pb pb isochron method can be usedto determined the age of diagenesis of some sedimentary rocks and has wide applications.