Development of structure of the west part of the Altae-Sayan Orogen (The Mesozoic Stage)

Sues of the western part of the Altai-Sayan folded region (ASFR) development are considered. The Jurassic Period became determining factor for the region's structure development. The youngest plates at the base of tectonic terrains determine age of tectonic activation. The latest occurrence of the Mesozoic tectonic activity in the region is the displacement in the southeast direction of the West Siberian Plate with a fragment of the Tom-Kolyvan folded zone, fixed by the Early Cretaceous Nenya-Chumysh depression origin. Modern structure of the territory of the western part of the Altai-Sayan Folded Region (ASFR) is considered as a collage of terraines formed in the Mesozoic (Triassic, Jurassic, Cretaceous) time. It is confirmed by the presence of a series of tectonic strata in the base of allochthons (Pyzhinsky "graben", the Upper Triassic), the Aigulak ridge (vicinity of the Lake Sorolukel), the Kuraisky ridge (right bank of the Chuya river near the village of Chagan-Uzun), Chikhachev ridge (the upper flow of the Buguzun river), the foot of the Shapshal ridge, Gornaya Shoria (the Lower-Middle Jurassic). Together with the Mesozoic deposits, deposits of the Late, Middle and Lower Carboniferous, the Upper and Middle Devonian are recorded by the series of tectonic plates. The Jurassic period became decisive for regional structure generation. The age of tectonic activation is determined by the age of the youngest plate at the terraines base. The sequence of the Kuznetsk trough structure generation (Fig. 1) due to interaction of the Salair terrane, the Tom-Kolyvan folded zone, the Gornaya Shoria terranes and the Kuznetsk Alatau massif is considered in detail. It is assumed that the Kuznetsk trough is a fragment of a larger structural element - a foothill trough on the border of cratonized framing of the Siberian platform and the Tomsk-Kolyvan mobile belt. Most of this extended Hercynian structure is currently engulfed beneath the Mesozoic terraines of Gorny Altai. Fragments of the trough can be seen in tectonic plates, often together with Jurassic and Carboniferous deposits in the southeastern part of Gorny Altai (Kurai trough), Aigulak ridge (Sugara river), Central Altai (Kuba river), Northern Altai (Lebed river at Baigolsky Krivun and the right bank of the Biya river near the village of Staraya Azhinka). The southeastern displacement of the territory of the West Siberian plate with a fragment of the Kolyvan-Tomsk folded zone, traced by generation of the Early Cretaceous Nenya-Chumysh depression should be considered as the last manifestation of the Mesozoic tecto-genesis in the region. The Mesozoic tectonic activation of the Western part of the ASFR led to generation of revived mountains structure, which has not been changed significantly until now. The region should be considered as the "Altai-Sayan superterrane". Such an interpretation of generation of the western part of the ASFR structure requires serious detailed terraine analysis, delineation and description of the blocks included in the superterraine ensemble. Such an analysis can significantly change understanding of the regional minerageny and improve methodology of its prospecting.

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