扬子克拉通北缘神农架地区矿石山组Pb-Pb等时线年龄及其地质意义
The Pb-Pb Isochron Age of the Kuangshishan Formation in Shennongjia Area on the Northern Margin of the Yangtze Craton and Its Geological Implications

扬子克拉通北缘神农架地区出露了大量中元古代碳酸盐岩地层，但已有的同位素年代学资料有限，故对神农架群矿石山组白云岩开展了全岩Pb-Pb等时线测年.研究结果表明，矿石山组白云岩206Pb/204Pb变化范围相对较大，为18.753～23.106，而207Pb/204Pb和208Pb/204Pb则变化范围相对较小，分别为15.606～16.046和37.793～38.599.八件白云岩样品206Pb/204Pb和207Pb/204Pb之间呈良好的线性关系，构成Pb-Pb等时线年龄为1632±75Ma(MSWD=8.7)，代表了矿石山组地层主体沉积时代，与已有的年代学结果可对应，表明Pb-Pb同位素体系可对古老的碳酸盐岩地层进行较为精确地定年.结合前人对于神农架群的年代学资料，确定神农架群的沉积时限应为1600～1100Ma的中元古代.
The Shennongjia Group,located on the northern margin of the Yangtze Craton,shows a series of well-preserved succession of the Mesoproterozoic carbonate strata.However,geochronological data collected from this area are limited.In this study,we report a Pb-Pb isochron age for the Kuangshishan Formation of the Shennongjia Group.The 206Pb/204Pb ratios of the dolostone of the Kuangshishan Formation show wide variations from 18.753 to 23.106.On the contrary,the 207Pb/204Pb ratios and the 208Pb/204Pb ratios have a limited range from 15.606 to 16.046 and 37.793 to 38.599,respectively.8 dolostone samples data show an obvious linear relationship between 206Pb/204Pb and 207Pb/204Pb,yielding a Pb-Pb isochron age of 1632±75Ma (MSWD=8.7) which represent the depositional age for the Kuangshishan Formation.This age accords well with previous published data,indicating that a precise stratigraphic age of the ancient carbonate strata can be obtained through Pb-Pb dating technique.Combined with previous researches,we suggest that the age span of the Shennongjia Group is 1600 to 1100Ma of Mesoproterozoic