江西宜春武功山地区出露的震旦纪老虎塘组由薄层状的砂岩、粉砂岩和泥岩组成, 岩石普遍经历了强烈的变形和变质作用.由于缺乏古生物化石和年龄值, 其沉积时代和源区存在着争议.本文运用LA-ICP-MS 技术, 对老虎塘组两件变砂岩中的碎屑锆石进行了 U-Pb 和 Hf 同位素测定, 共获得187个U-Pb 年龄值, 主要位于423~537 Ma 和660~1280 Ma 两段.两个样品中最年轻的碎屑锆石年龄为(432.7±1.8) Ma, 结合区域地质资料限定老虎塘组形成时代为志留纪.锆石U-Pb年龄和Hf同位素表明, 年龄为423~537 Ma的碎屑锆石主要来源于华夏板块北缘加里东期的花岗岩, 而年龄为660~1280 Ma碎屑锆石显示物源主要来自钦—杭结合带, 而其它少量的古元古代和太古代物质可能主要来源于华夏板块基底或者再循环的物质.因此, 碎屑锆石年龄显示老虎塘组物源主要来源于华夏板块北緣加里东期岩浆岩和钦—杭结合带.大量的早古生代碎屑锆石数据反映了华夏板块北緣加里东期的造山事件, 这次造山事件为早古生代晚期沉积盆地提供了大量的物质来源.%The Sinian Laohutang Formation, outcropped in the Wugongshan area on the northern margin of the Cathaysia plate, is composed of thin bedded sandstone, siltstone and chert. The sedimentary rocks have undergone strong deformation and metamorphism. There is some controversy on the age of the sedimentary rock due to the lack of paleontological evidence. This study shows that the ages of detrital zircons from the sandstones are predominantly Early Paleozoic, and the youngest detrital zircon grains clearly show that the maximum depositional age of the Laohutang Formation is ca. (432.7±1.8) Ma. The ages of the detrital zircons can be dominantly divided into two groups: 423~537 Ma and 660~1 280 Ma. The zircons in the 423~537 Ma age population show approximately the same εHf(t) values from-20 to +5, suggesting that the source rocks were the igneous rocks formed on the northern margin of the Cathisian block in the Caledonian period. Zircon with ages from 660 Ma to 1 280 Ma shows the Hf values ranging from-20 to + 5. The age data are comparable with the ages of zircons in the Neoproterozic granites and volcanic rocks in the Qinhang belt. The small Paleoproterozoic and Archean zircon population implies the probably derivation of the materials from the basement of the Cathaysia plate. A comprehensive analysis shows that there was a collision-orogenic event on the northern margin of the Cathaysia plate in the Caledonian period, and the orogenic belt contributed abundant materials to the sedimentary basin.
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