西伯利亚克拉通南缘奥里洪地块麻粒相变质作用及构造意义

A series of accretion-collision events occurred along the southern margin of the Siberian Craton in Early Paleozoic. The OIkhon terrane records the history of the accretion and collision between the Barguzin microcontinent and southern Siberian Craton. Mineral composition analyses and P-T calculations of two typical high-grade metamorphic rocks, the garnet pyroxenite and. garnet-biotite gneiss in the OIkhon area indicate that both of them, experienced granulite facies metamorphism with peak conditions of 770 ∼800̈C, ∼l.OGPa. The retrograde metamorphism also experienced relatively high temperature, but significantly deceased pressure (700 ∼ 730̈C, 0. 65GPa and 710 ̈ 766̈C, 0.50GPa), showing approximately an isothermal decompression clockwise P-T-t path. In-situ LAICPMS U-Pb dating results of metamorphic zircons from, the garnet-biotite gneiss indicate that peak metamorphism probably took place at 479 ±2Ma, and pre-peak metamorphism may occurred before 500Ma. The post-peak retrograde metamorphism. possibly happened after 475∼460Ma associated with post-orogenic magmatism. Therefore, the accretion-collision events might have lasted for at least 35Ma. Based on the difference in the time of metamorphism and magmatio activities among Mongolian-Tuva terrane, Jiamusi-Erguna terrane and OIkhon terrane, it is suggested that the accretion-collision events along the southern margin of the Siberian Craton occurred, in different periods, and the collision orogeny between the Barguzin microcontinent and the Siberian Craton is slightly later than other terranes.