Two Types of High-Grade Metamorphism in West Sangilen (Southeast Tuva)

摘要

The granulite facies metamorphic rocks (garnetbiotite—cordierite gneisses, cordierite—spinel—sillimanite gneisses) in West Sangilen (Southeast Tuva) were first found downstream of the Erzin River [1] and were originally referred to the pre-Riphean basement of the Tuva-Mongolian crystalline massif [1, 2]. Later,their distribution was clarified and the Ordovician age of their formation was justified [3, 4]. Isotope geochronological studies allowed to distinguish two age levels of high-grade metamorphic rocks and the associated migmatite-granites and gabbroids [4—7]. The first type of rocks (480-500 Ma, U-Pb and Ar-Ar age dating) is a part of the Erzin migmatite—granite complex; the second type is represented by contact hornfels, exposed in the eastern framework of the Bashkymugur gabbroid massif (460—470 Ma, U—Pb, RbSr, and Ar-Ar age dating).