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Nazim Imamverdiyev, Baku State University (Azerbaijan)
Mina Gasanguliyeva, Azerbaijan National Academy of Sciences, Institute of Geology (Azerbaijan)
Anar Veliyev, Azerbaijan National Academy of Sciences, Institute of Geology (Azerbaijan)
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The Late Cenozoic volcanic products of the Lesser Caucasus divided into two groups: (1) Late Miocene-Early Pliocene high-K calc-alkaline rocks; (2) Late Pliocene-Early Quaternary calc-alkaline and alkaline rocks. On the basis of the analysis of geophysical, petrology geochemical materials the authors supposes, that time and spatial change chemical magmas in a combination to a history uplift and age connections of volcanic products in the Caucasian Collision zone, may be linked to slab-steepening and breakoff beneath a subduction complex in the southeast of region.
Slab-steepening was possibly associated with asthenospheric flow that resulted in gradual change in geochemical character of the volcanic erupted. The Lesser Caucasian lithospheres currently are deprived of its mantle component under the vast region. For this reason in the basest rocks, the maximum amount of magnesium oxide is up to 7%, respective, the magnesium number does not meet the present mantle value as well. These facts demonstrate that a huge part of the mantle lithosphere was separated from the underlying crust in the past. Such separation of more dense mantle is responsible both for the regional uplifting of the region and for the arising of the late Cenozoic volcanism.
The liberated volumes formed by the removal of the mantle lithosphere, were filled with hot abundant asthenospheric material. This resulted in the formation of regional dome structure and magma and volcanism linked with adiabatic decompression melting. The uplifting of asthenosphere determined the arising of basaltic melts, their segregation in the base of the crust and penetration into higher levels. Morphologically this was expressed in the uplifting of the territory, in the formation of the extension structures and accumulation of the volcanic thickness. Evolution of magmatism linked with the delamination is determined by thickness, composition and thermal state of the crust. Besides, existence of thick warmed crust are the most favorable terms for the wide-range melting of granitic batholiths. At account of the additional heating and inflow of volatile components there were formed large volcanoes of calc-alkaline composition of Neogenic age. And in certain places, there appeared peripheral centers. There cooling resulted in the formation of hypabyssal intrusions.
Later on, in the upper Pliocene-Quaternary age there was formed a bimodal volcanism. Thus, time-spatial conjugation of the crystal and mantle magmatism determined the intrusion of mantle melts in terms of extension into the lower crust. This resulted in its melting and the formation of acid vulcanite's. At the same time, in this situation, change of the contraction by the extension promoted arising of rift depressions, arch-formation and manifestation of alkaline volcanism.
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