Geology, mineral composition, age and conditions of formation monuntains ophiolite association (South-Western Tuva)

At present time various geological-structural and petrological-geochemical data have been obtained in studying the Caledonian ophiolitic associations widely occurred on the territory of Tuva. The most representative information was obtained from the Agardag, Kaakhem and Western-Tuvinian ophiolitic associations. Rock complexes of ophiolite associations have not been completely preserved anywhere on the territory of Tuva. In most cases, these complexes are cropped out in the form of more or less large blocks, in the structure of which the predominant bodies of ultramafites (serpentinites, serpentinized harzburgites, lher-zolites, verlites, pyroxenites) and subordinate bodies of gabbroids take part. There are fewer blocks that contain a relatively complete "set" of rock complexes, which are usually included in the composition of ophiolitic associations. One example of such blocks described in this article is the Durusugsky section of the Monguntaiga ophiolitic association in the territory of SouthWestern Tuva, which is part of the Central-Asian fold belt. South-Western Tuva is characterized by a complex geological structure and a multi-stage evolution of magmatism including ultramafic and mafic composition. A number of large tectonic blocks composed of metamorphic complexes including sequences of ortho- and paraschists belonging to the Dzhebash and Baratal series (Medium Proterozoic) were identified in this region during medium-scale geological survey work. Relatively small bodies of restitogenic (alpinotypic) ultramafites and units of ultramafic-mafic composition, where titanium-magnetite and later gold-platinoid mineralization occur among these metamorphic formations. At present these ultramafic, mafic bodies remained almost unexplored using modern analytical methods. This paper provides new information on the geology, petrography, geochemistry and isotope age of magmatic rocks distributed within the Durusugsky section of the Monguntaiga ophiolitic association - one of the fragments of an ancient oceanic crust that is cropped out on in the territory of Western Tuva. Complexes of Caledonian ophi-olitic associations structurally confined to the Tsagan-Shibetinsky deep fault zone are well represented to the south, on the territory of Mongolia. It can be assumed that the rock complexes of the Monguntaiga association represent the northern extension of ophiolitic complexes of the Ozyerny megazone of the Caledonides considering the similarity of the composition of magmatic formations widespread in them. The geodynamic reconstructions proposed by some researchers suggested that the Monguntaiga ophiolitic association was formed in the process of accretion as a large tectonic cover, thrust over the side of the Ozyerny zone to structures of rigid framing.

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