DIRECT SIGNS OF ERUPTIVE FLUID-RUPTURE BRECCIAS ON THE UFA PLATEAU (EAST EUROPEAN PLATFORM)

New data on eruptive fluid-rupture breccia from the Ufa Plateau, a geomorphological uplift on the margin of the East European Platform (EEP), which borders the Cis-Uralian foredeep, are presented. The plateau is represented by a 2.5-3 km thickness carbonate platform of D₂-P₁ age overlying a crystalline foundation of AR-PR age. In the apical part of the plateau and at its foot, there are strongly cavernous carbonate rocks (FBL), which sometimes contain debris and pebbles from siliceous rocks as well as metamorphic and igneous minerals. There are signs of a connection with eruptive fluid-rupture breccias, in connection with this, the authors conducted special research. FBL samples weighing 1-5 kg from various parts of the plateau were dissolved in a 10% HCl solution. In the insoluble constituent of several samples, microbreccias were found composed of debris (up to 1-2 mm) of amphiboles, pyroxenes, plagioclase, biotite, titanomagnetite, and serpentine, cemented by finely dispersed material with the same composition. Up to 50% of the volume of cement consists of magnetic and glass spherules. Microbreccia cement is very mild and easily breaks down when touched. Moissanite, native metal plates and their alloys (Ni, Fe-Ni, Fe-Cr-Ni, Fe) are often found in samples. The presence of microbreccia debris in the FBL can be explained by the tectonomagmatic activation of the EEP margin during the Early Kungurian time, the degassing of the Earth's crust accompanied by the formation of eruptive fluid-rupture breccias with the removal of xenogenic material from the crystalline basement rocks and the enrichment of weakly consolidated sedimentary rocks. As a result of thermal processes, magnetic and glass spheres were formed in the microbreccia.