Geochemical features of volcanites of the northern part of the Tagil structure as a reflection of the evolution of the paleozone of subduction

Abstract

Research subject. Volcanogenic formations of the northern part of the Tagil megazone.Material and methods. Volcanites of the Tagil paleo-island arc system and its frames were studied, including basalts and andesibasalts of the following formations: Khomas’inskaya O1-2, Shemurskaya O3-S1, Pavdinskaya S1, Imennovskaya S1-2, Turinskaya S2-D1, Perevozskaya D1, Krasnotur’inskaya D1, Limkinskaya D2-3, as well as dolerites of the Ivdel complex D3. Silicate (XFA) analyses and determination of rare elements by ICP-MS method were performed. The obtained data was analyzed using discrimination and spider diagrams, as well as indicator geochemical parameters.Results. The geochemical parameters reflecting the degree of depletion of the host rocks of magmatic chambers, as well as the influence of fluids released during the dehydration of rocks of subducted slabs, quite definitely demonstrate an increase in the role of subducted material in the composition of island-arc magmas. This allows the onset of the subduction process, sharp changes in the conditions of its functioning and the time of its completion to be determined.Conclusions. The obtained geochemical data confirms the existing concepts about the onset of the subduction process at the end of the Middle – beginning of the Upper Ordovician, restructuring (jumping?) of the subduction zone in the Lower Devonian and completion in the Upper Devonian.