中文摘要：

位于大别山造山带北淮阳火山岩带中段的金刚台火山岩的形成时代一直存在争议。新的地质观察表明,其不整合于早白垩世商城岩体之上,不应当归属为侏罗纪。对金刚台火山岩3个样品进行了SHRIMP锆石U-Pb定年,其中喷出相的黑云母粗面岩（B09）年龄为（128.4±3.6）Ma,次火山相的闪长玢岩（B21）年龄为（129.1±2.2）Ma,靠近火山岩层底部的粗安岩（B26）年龄为（129±2）Ma。样品B09的测年数据误差较大,B21和B26则非常一致,表明金刚台火山岩形成于129Ma,火山喷发持续时间较短。金刚台火山岩是大别造山带早白垩世巨量岩浆爆发事件的产物。结合前人的研究成果,区域火山地质特征和商城岩体剥露机制的综合分析表明：（1）金刚台火山岩形成之前,区域发生了强烈的挤压隆升;（2）金刚台火山岩是造山带岩石圈拆沉作用的产物;（3）火山岩形成后区域进入长时间的岩石圈伸展阶段,因而129Ma是大别山地区构造转换的分界时间。

英文摘要：

The age of the Jingangtai volcanic rocks,which spread over the central part of North Huaiyang volcanic rock belt,has been in controversy for a long time. New observations indicate that Jingangtai volcanic rocks unconformably overlie the early Cretaceous Shangcheng Pluton,hence they must have not formed in the Jurassic. A SHRIMP U-Pb dating on individual zircons from three representative samples of Jingangtai volcanic rocks shows that the age of extrusive biotite trachyte （B09） is （128.4±3.6） Ma,the age of subvolcanic diorite porphyrite （B21） is （129.1±2.2） Ma and the age of trachyandesite （B26） representing the lower part of volcanic rock series is （129±2） Ma. The dating error for sample B09 is relatively large,however,the age of sample B21 is consistent with B26,which suggests that Jingangtai volcanic rocks formed at 129 Ma,and the duration of volcanic eruption was short. Jingangtai volcanic rocks are the products of large-scale magmatism in Dabie Orogen in the Early Cretaceous. Combined with the foregoing research works,the regional geological features and the denudation mechanism of Shangcheng Pluton show：that （1） before the forming of Jingangtai volcanic rocks,the region had undergone intensively compressional uplift; that （2） Jingangtai volcanic rocks are the products of lithosphere delamination; that （3） after the forming of Jingangtai volcanic rocks,the regional lithosphere had been extended for a long time,thus 129 Ma is the boundary of tectonic transition for Dabie Orogen.