Direct signs of eruptive fluid-rupture breccias on the Ufa Plateau (East European Platform)

New data on eruptive fluid-rupture breccias of the Ufa Plateau – geomorphological uplift on the eastern (cisural) periphery of the East European Platform (EEP), bordering the Cis-Ural 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, the so-called “foraminated breccia limestones” (FBL), which sometimes contain debris and pebbles from siliceous rocks as well as metamorphic and igneous minerals. There are indications of an association between xenogeneic material and eruptive fluid-rupture breccias, wherein the authors conducted special studies. 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, immersed in finely dispersed material with the same composition. Up to 50% of the matrix volume consists of magnetic and glass spheres and shapeless masses. The microbreccia matrix is very mild and easily breaks down when touched. Moissanite, native metal plates and their alloys (Ni, Fe–Ni, Fe–Cr–Ni, Fe) were noted in samples. The authors explain the presence of microbreccia fragments in the FBL by tectonomagmatic activation of the EEP margin during the Early Kungurian, crustal degassing, accompanied by the formation of eruptive fluid-rupture breccias, the removal of dispersed rock material of the crystalline basement, and the enrichment of weakly consolidated sedimentary rocks. As a result of thermal processes, magnetic and glass spheres were formed in the microbreccia.

fluidolites, xenogenic minerals, magnetic spherules, glass, tectonomagmatic activation, Eastern European Platform