皖南屯溪地区石岭组流纹岩LA-ICP-MS锆石U-Pb年龄及其时代的重新厘定

皖南屯溪地区位于江南新元古代造山带东段,发育少量中生代燕山期石岭组流纹岩、凝灰岩等火山岩。因一直缺乏精确的测年数据,以往研究者根据屯溪地区1∶5万区域地质调查获得的石岭组火山岩全岩K-Ar年龄值115~139 Ma,将其形成时代定为晚侏罗世—早白垩世。由于2004年前后国际地质年代表将侏罗纪与白垩纪界线由135 Ma提前到145 Ma,石岭组火山岩的形成时代便由原来的晚侏罗世—早白垩世更改为早白垩世。在屯溪东面尤溪村石岭组流纹岩中首次获得精确的LAICP-MS锆石U-Pb年龄154.7±2.5Ma,早于145Ma,表明屯溪地区石岭组火山岩形成于晚侏罗世而不是早白垩世。这一发现对构建皖南乃至中国东南部晚中生代构造演化模型具有参考意义。

LA-ICP-MS zircon age of volcanic rock of Shiling Formation in Tunxi area, south Anhui, and redetermination of its epoch

The Tunxi area in south Anhui Province is located in the eastern segment of the Jiangnan Neoproterozoic Orogen and possesses some volcanic rocks of Shiling Formation like rhyolite and tuff. Based on the K-Ar age 115~139Ma by 1:50000 regional geological survey, previous studies believed that these volcanic rocks of Shiling Formation from Tunxi area were formed during Late Jurassic to Early Cretaceous. Owing to the change of the Jurassic-Cretaceous boundary from 135Ma to 145Ma(revised by International Commission on Stratigraphy), the Shiling Formation has thus changed its formation epoch from Late Jurassic-Early Cretaceous to Early Cretaceous. The authors obtained LA-ICP-MS zircon U-Pb weighted average age of 154.7±2.5Ma for the rhyolite from Youxi Village, east Tunxi(D047), south Anhui Province, implying that the volcanic rocks of Shiling Formation was formed in Late Jurassic(older than 145Ma), rather then in Eearly Cretaceous. This precise datum is valuable for a better understanding of tectonomagmatic evolution of south Anhui and even southeast China.