Geochemistry and geochronology of the Proterozoic magmatic rocks of the Ulkan trough: New data

A model of the formation of the Ulkan trough was specified on the basis of new geochemical and geochronological data. The volcanics of the Ulkan Group exhibit geochemical features typical of the rocks of two modern geodynamic settings: suprasubduction and within-plate ones. The combination of the components derived from the different-depth sources in the magmatic chambers explains the formation of the volcanics with mixed geochemical signatures. The age of the granitoids of three phases of the Ulkan Massif is determined within the range of 1730–1925 Ga. The granites of the first and third phases have positive ɛNd(T) of + 3.5 and + 0.7, respectively. The granites of the first phase of the Ulkan Complex were likely derived from the Paleoproterozoic juvenile crust with an age of 1.84–1.95 Ga. The effusive rocks of the Ulkan Group were presumably formed in a geodynamic setting of a Cordilleran-type transform continental margin. Judging from the model T Nd (DM) age, these geodynamic conditions operated >1.84 Ga ago.