On the Nature of the Kharamatolou Structure and the Ratio of the Amount of Ultramafic Rocks of the Voykar-Synya Massif to That of the Ray-Iz Massif, Polar Urals

Abstract

There have been petrographic, geochemical, geochronological (Rb-Sr, Ar-Ar) and isotopic (Sm-Nd) studies done on the metamorphic formations of the Kharamatolou structure of the Polar Urals, which were usually assigned to the Precambrian. The temperatures of metamorphism have been shown to range from 450 to 626 °C, and the pressures – from 3.7–9.1 kbar once PT-conditions reached the amphibolite facies. The amphibolites of the Kharamatolou formation are geochemically divided into two groups. According to the distribution spectra of lanthanides and Nd isotope composition, one group has the characteristics similar to depleted N-MORB basalts εNd(0)=+7.0, and another group – those similar to moderately enriched E-MORB basalts εNd(0)=+(4.5–2.4). It has been found that the Kharamatolou structure is probably composed of the Early to Middle Paleozoic continental rise deposit of the Russian Platform, which passed the main stage of folding and metamorphism in the Late Devonian (Rb-Sr, 366±11 Ma). The gabbro-ultrabasic Ray-Iz and Voykar-Synya massifs have been shown to be one during most of their Pre-Triassic history. Now these ultrabasite massifs are separated by the young (Triassic) Kharamatolou uplift which is an erosive-tectonic semi-window where ultrabasic rocks of the Polar-Ural belt are exposed at the base of the thrust fault. The Kharamatolou structure is one of the transverse uplifts of the Urals which probably resulted from the Middle to Late Triassic compression therealong. As a result of the Middle to Late Triassic uplift of the Haramatolou metamorphites, the overlying ultrabasites were washed away by erosion. The mélange serpentinites observed in the center of the Kharamatolou structure are uneroded remnants of the link that once existed between the Ray-Iz and Voikar-Synya massifs. This significantly increases the metallogenic potential of the Voikar-Synya massif, as the Ray-Iz hosts the largest known chromite deposits in Russia.