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

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 Pb-Pb Isochron Age of the Kuangshishan Formation in Shennongjia Area on the Northern Margin of the Yangtze Craton and Its Geological Implications

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.