中文摘要：

大别造山带东侧、扬子板块上安徽怀宁县的洪镇变质核杂岩,以往认为是早白垩世NE—SW拉张形成的科迪勒拉型变质核杂岩,其核部的董岭杂岩长期被认为是变质基底。然而,该核杂岩所指示的拉张方向与中国东部一系列早白垩世伸展构造指示的NW—SE拉张相矛盾,从而需要对这一重要伸展构造进行再研究和认识。本次11个样的锆石定年表明,董岭杂岩内变形—变质岩体的侵位时代为829~812 Ma,而变火山岩的原岩时代为761~754 Ma,后者属于扬子板块上的新元古代南华纪盖层。锆石生长边揭示了董岭杂岩内一期127 Ma的热事件,应为旁侧同期洪镇岩体侵位的热影响结果,并影响了董岭杂岩内韧性剪切带白云母~（40）Ar/~（39）Ar年龄值。该区董岭杂岩两侧在早白垩世发育了两组北东走向、倾向相背的正断层,南侧与西侧分别上叠同期的怀宁和潜山断陷盆地。断层擦痕应力场反演结果表明,这些早白垩世伸展构造是在NW—SE拉张中发育的,而不是前人认为的NE—SW拉张。综合分析表明,该区在早白垩世两组倾向相背正断层活动与洪镇岩体侵位、隆升的共同控制下发育为伸展穹窿构造,并非科迪勒拉型变质核杂岩。

英文摘要：

The Hongzhen metamorphic core complex in the Yangtze Plate east of the Dabie orogenic belt was considered as the Early Cretaceous metamorphic core complex of the Cordillera-type caused by the NE—SW extension,and the Dongling Complex has long been treated as the metamorphosed basement. However,the extension direction indicated by the core complex is in contradiction with the NW—SE extension shown by many Early Cretaceous extensional structures in eastern China,suggesting necessity for further studies and understanding for this important,extensional structure. Zircon dating of 11 samples gives emplacement ages of 829 ~ 812 Ma for the deformed,metamorphosed plutons in the Dongling Complex and protolith ages of 761 ~ 754 Ma for the metasediments and meta-volcanic rocks in the complex. These demonstrate that meta-volcanic rocks belong to the cover of Neoproterozoic Nanhua period. The zircon growth rims show a thermal event of 127 Ma in the complex that is related to synchronous intrusion of the nearby Hongzhen pluton and affects muscovite~（40）Ar /~（39）Ar ages from the ductile shear zone in the complex. Two groups of NE-striking normal faults with opposite dips were developed on both sides of the exposed Dongling Complex in the Early Cretaceous. The synchronous Huaining and Qianshan rifted basins appeared in the south and west of the region respectively. Fault-slip data indicate that the Early Cretaceous extensional structures were produced by NW—SE extension,rather than the NE—SW extension as proposed previously. It is suggested therefore that an extensional dome,rather than the Cordillera-type metamorphic core complex,formed under the common action of normal faulting along the two groups of faults with opposite dips and exhumation induced by the Hongzhen intrusion during the Early Cretaceous.