中蒙边界亚干变质核杂岩糜棱状钾质花岗岩——早中生代收缩与伸展构造体制的转换标志

Mylonitic potassic granitoids from the Yagan metamorphic core complex on Sino-Mongolian border: a mark of transition from contractile to extensional tectonic regime

中、晚中生代大型推覆和伸展构造的发育是华北地块及北缘构造的一大特色。本文在典型伸展构造亚干变质核杂岩中识别出早期具拉张环境的糜棱状花岗岩,岩石类型为钾质花岗岩及钾玄岩系列,具造山后及板内拉张构造环境特点,锆石U-Pb定年为228±7Ma,这些岩石强烈变形,并发育同侵位岩浆流动和高温固态流动变形。这些特征表明在晚中生代该核杂岩成型之前即早中生代中下地壳层就已经历调整、减薄和伸展变形。它们的组合揭示了一种特有的构造动力学机制和背景。

Occurrences of large-scale: thrusts and extensional tectonics in Middle and Late-Mesozoic are a striking feature of the tectonics in the North China Block. This paper, however, further recognizes Early Mesozoic mylonitic granites with extensional tectonic setting from the Yagan metamorphic core complex (MCC), a typical representative of extensional tectonics. They have features of potassic or. shoshonitic granite types and their tectonic discriminations show extensional setting. The zircon U-Pb dating of the Shuiquangou :mylonitic pluton yields 228 + 7Ma. These granitoids were, strongly deformed by syn-tectonic magmatic flow and high temperature solid flow. All these characteristics;suggest that adjustment, thinning and extensional deformations at the middle low crustal levels might have-started from the early Mesozoic, i.e. much more earlier than the final formation (Mesozoic) of the large-scale extensional tectonics, i.e: the MCC. Integration of all these characteristics displays a peculiar tectonic dynamic mechanism and setting.