中扬子地区江汉盆地古新统沙市组物源——来自碎屑锆石U-Pb年代学及地球化学证据

文章利用LA_ICP_MS分析技术,对江汉盆地西南缘古新统沙市组碎屑岩进行了碎屑锆石的U_Pb年代学研究,获得该区沙市组时期碎屑物源的重要信息。97组协和年龄数据产生了12个年龄峰值,分别为2500 Ma、1870 Ma、995 Ma、850 Ma、708~775 Ma、603~640 Ma、505~553 Ma、408~458 Ma、356 Ma、300 Ma、235 Ma和172 Ma。锆石的年龄峰值主要集中于古元古代、新元古代和早古生代,这些年龄峰值与黄陵隆起和江南造山带中的锆石年龄相同。早中生代年龄峰值也较明显,该年龄通常和大别山的高压和超高压变质岩有关,江南造山带也发育印支期花岗岩。结合该时期岩相古地理特征,认为沙市组主要物源来自黄陵隆起以及扬子板块与大别造山带之间的碰撞带,而南部江南造山带的贡献是次要的。黄陵隆起花岗岩含钾量高,其风化可以给盆地带来丰富的成钾物源。

Provenance of Paleocene Shashi Formation in Jianghan Basin of Middle Yangtze area: Evidence from U-Pb geochronology and geochemistry of detrital zircons

Using the U-Pb LA-ICP-MS analysis technique the authors analyzed geochronological features of detrital zircons from Paleocene clastic rock of Shashi Formation in southwestern Jianghan basin. Significant clastic source information was obtained. The 97 groups of U-Pb age yielded 12 peak ages: 2500 Ma, 1870 Ma, 995 Ma, 850 Ma, 708~775 Ma, 603~640 Ma, 505~553 Ma, 408~458 Ma, 356 Ma, 300 Ma, 235 Ma and 172 Ma. The ages are concentrated in three epochs: Paleoproterozoic, Neoproterozoic and Early Paleozoic. The peak ages are consistent with the zircon ages in Huangling dome and Jiangnan orogen. Predominant Early Paleozoic peak ages are usually related to high- and ultrahigh- pressure metamorphic rocks in Dabie orogen, and Indosinian granites are also developed in Jiangnan orogen. In conjunction with lithofacies paleogeography in this period, the provenance of Shashi formation might have mainly been derived from Huangling dome and the collision belt between Yangtze Block and Dabie Orogen, with the Jiangnan Orogen to the south playing the subordinate role. Granites in Huangling dome are rich in potassium, and granite weathering could provide the basin with abundant source of potassium.