Two types of high-grade metamorphism in West Sangilen (Southeast Tuva)

The granulite facies metamorphic rocks (garnet biotitecordierite gneisses, cordieritespinelsilli manite 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 geo chronological studies allowed to distinguish two age levels of high grade metamorphic rocks and the asso ciated migmatite granites and gabbroids [47]. The first type of rocks (480500 Ma, UPb and ArAr age dating) is a part of the Erzin migmatitegranite com plex; the second type is represented by contact horn fels, exposed in the eastern framework of the Bash kymugur gabbroid massif (460470 Ma, UPb, Rb Sr, and ArAr age dating).