大别山西部蓝闪榴辉岩U—Pb测年

应用锆石Ｕ－Ｐｂ法研究了大别山蓝闪榴辉岩的高压低温变质时代和可能的原岩时代。高桥榴辉岩和陈家店榴辉岩给出了基本一致的下交点年龄１１３８Ｍａ和１１２７Ｍａ及相似的上交点年龄２８７２Ｍａ和２６４７Ｍａ。结合岩石学证据和大别山构造演化史分析，将下交点年龄解释为高压低温变质时代，相当于晋宁运动早期，上交点年龄解释训原岩的可能时代，为新太古代，同位素地质年代学研究表明，古大别洋最初形成于新太古代，闭合于早晋

U-Pb Zircon Dating of Glaucophane Eclogites from western Dabie Mountain

Using the single zircon U-Pb technique, the authors have geochronologically investigated two glaucophane eclogites sampled from Gaoqiao and Chenjiadian in western dabie Mountain, which provide the age information ofHP/LT(high pressure/low temperature) metamorphism and their Archean protolith. Seven analyses of zircons from the Gaoqiao eclogite and five analyses of zircons from the Chenjiadian eclogite have yielded the lower intercept ages of 1138± 39 and 1127±234 Ma and the upper intercept ages of 2872±40 and 2674±249Ma. Considering the petrological evidence and tectonic evolution of the Dabie orogenic belt, the ages of 1138 and 1127 Ma are regarded as the time of HP/LTmetamorphism, and the protolith of the eclogite is dated at 2647-2872 Ma. The present work confirms the existence of an Early Jinning HP/LTmetamorphism in the Dabie orogenic belt, which represented the closure of the ancient Dabie ocean. Moreover, the primary opening of the Dabie ocean occurred at Neoarchean. All this suggests that the tectonic evolution during the Jinning period took place under the plate-related mechanism.