ПАЛЕОПРОТЕРОЗОЙСКИЕ УЛЬТРАМАФИТОВЫЕ ДАЙКИ КУН-МАНЬЁНСКОГО АРЕАЛА (ЮГО-ВОСТОК СИБИРСКОЙ ПЛАТФОРМЫ): СТРУКТУРНОЕ ПОЛОЖЕНИЕ, СОСТАВ И ОБСТАНОВКА ФОРМИРОВАНИЯ

Abstract

Dykes of Paleoproterozoic ultramafic rocks from the Kun-Manie area were studied within the southeastern fringe of the Siberian Platform. At the end of the Paleoproterozoic, the processes of overthrust faulting and folding were widely manifested here, the latest of which were accompanied by the emplacement of mafic-ultramafic dykes and sills that control the location of Cu-Ni-PGE sulfide mineralization. The petrographic structure of ultramafic dykes suggests their emplacement in tectonic settings. The elevated concentrations of LREE relative to HREE, coupled with other data, allow them to be referred to high-Mg ultramafic rocks of the picrite-tholeiite series, the parent magmas of which could be not ultramafic, but picrobasaltic magmas. The level of REE concentrations in ultramafic rocks and the nature of the normalized spectra indicate the involvement of sufficiently enriched sources in the generation of primary melts from which rocks crystallized that radically differed from peridotites of ophiolite associations and typical komatiite melts. In terms of spectral shapes and contents of indicator elements (Nb, Yb and Th), they are close to the «enriched» mantle source of the E-MORB type differing in lower REE concentrations. The Zr/Y – Nb/Y ratio in ultramafic rocks suggests a non-plume source of their primary melts in the upper depleted mantle. Rocks derived from such a melt are characteristically enriched in fluid components (S, Cl, F, As, Te, Se, and H2O), which is evident in the presence of mineral phases rich in hydroxyl, that is, amphiboles and phlogopite of igneous origin. The ore-forming system evolved from Ni-bearing at the early magmatic stage during the formation of disseminated mineralization to Cu-enriched at the postmagmatic stage. The geological data indicate that they formed during the collision between the Paleoproterozoic island arc and the microcontinent. The combination of subduction and intraplate geochemical characteristics in magmatites is characteristic of the transform margin as a result of the oceanic (Verkhnemaya) and continental (Uchur) microplates sliding horizontally past each other.