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Address : 1Geological Institute of the Russian Academy of Sciences, Russian Federation; 2Aerogeophysica, Russian Federation
Celebration date : 4 Saturday October 2008
Author name : Mints, Michael1; Philippova, Irina1; Babayants, Pavel2; Blokh, Yury2; Trusov, Alexey2

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  • Article title : Deep crustal structure and evolution of the Neoarchaean Volgo-Uralian granulite-gneiss terrane, east European craton: Evidences of plume related origin of the granulite facies metamorphism
    Article type : Paleontology and Stratigraphy
    Location : International Geological Congress,oslo 2008

    Fulltext :

    Basis for the volume model of deep crustal structure and new ideas on the Neoarchaean evolution of Volgo-Uralian granulite-gneiss terrane (VUGGT) have been derived from published geological, petrological and geochronological data (Bogdanova, 1986; Postnikov, 2002) and recently obtained geophysical data - reflection seismic profile Tatseis (Trofimov, 2006) and 3D density and magnetic models of the upper crust.
    The main tectonic units within VUGGT of c.600 000 km2 are Tokmov, Busuluk, Krasnokamsk and Verkhnekamsk "ovoids" 350-500 km in diameter. A number of oval-lengthened synforms are distributed between main ovoids. VUGGT is built generally by granulite-gneiss assemblages and products of their regressive reworking. Maximal P and T estimates reached 940-950oC and 9.5 kbar. Cross-section along the Tatseis geotraverse demonstrates two types of the crustal structures:
    (1) within Tokmov ovoid and (2) characteristic for the rest of VUGGT.
    Margins of the Tokmov ovoid can be traced from basement surface to crust-mantle discontinuity at c.60 km depth. Its central part is built by mafic granulites associated with ultramafic and metagabbro-anorthosite bodies. Tectonic slices that form ovoid’s limbs surround central Uren’ cylindrical block 75-90 km in diameter and overtrust adjacent tectonic structures. Three-layer structure is typical for the crust beyond Tokmov ovoid. Down to 20 km it is formed by a number of oval synformal structures. The low crust c.35 km thick is built by succession of tectonic slices plunging toward western edge of the profile and penetrating into the mantle. Acoustically transparent area 10-20 km thick replaces boundary between the upper and low crust. It can be traced to the basement surface. Drill-holes that reached basement in this place record large granitoid body.
    Creation of the VUGGT resulted from a succession of the Neoarchaean events that reworked more ancient (~3.1-3.0 Ga) continental crust: ~ 2.74-2.71 Ga - heating and underplating of mantle melts reasoned by emplacement of the large plume that generated a number of local plumes; 2.74-2.71 Ga - granulite-facies metamorphism of ancient and juvenile rocks, subsidence of the thickened heavy crust and creation of rapidly submerging depressions filling in by contaminated juvenile volcanics and sediments, high-grade metamorphism of volcano-sedimentary deposits; creation of the Tokmov rotation structure reasoned probably by local spiral plume; 2.71-2.70 Ga - partial melting and origin of granitic magmas in the middle crust< creation of detachment divided upper (metamorphosed filling of depressions including) and low crust; 2.62-2.59 Ga - second pulse of granulite-facies metamorphism and granite origin; ~2.6 Ga - general compression, pressing out of synforms inherited previous sedimentary basins resulted in over- and underthrusting of their marginal zones; formation of inclined pockets of low-crustal slices and their merging down to the mantle due to general crustal shortening.

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