HIGH-MAGNESIUM ANDESITES AND BONINITES FROM THE INITIAL (EARLY) RIPHEIDS OF THE POLAR URALS

Abstract

That pre-Paleozoic volcanic rocks occur widely in the Polar Urals has been known for a long time. High-magnesium andesites and boninites of the Polar Urals resemble in their geological position, as well as their petrography and geochemistry, the Riphean boninites of Northern Mongolia. Their chemical composition is very similar to that of the rocks of marianite-boninite series of the Mariana Trench, the Bonin Islands and New Guinea. The last ones are now thought to be indicators of ensimatic island arcs and indicates the existence of an oceanic crust in the zone of the Sob' uplift in Late Ripean times. Its remnants are the suture zones filled with the relicts of the ophiolite triad of metahypermafics, gabbro and sodic basalt, associated with carbonaceous pelagic shales. The Late Riphean stage closed with andesitic magmatism of the island arc type, which started with the deposition of the boninitic series.