Devonian Island-Arc Magmatism of the Voikar Zone in the Polar Urals

Abstract

The studied deep-seated plutonic rocks of the Malyi Ural Paleozoic island arc include Sob’ gabbroid, diorite, and plagiogranitoid and Kongor gabbroid, diorite, and monzonitoid, which formed under similar P–T conditions. U–Pb LA-ICP-MS zircon dating established similar concordant age values: 406 ± 2 Ma for hornblende gabbrodiorite of the major intrusive phase in the Sob’ complex and 396 ± 1 and 393 ± 2 Ma for bipyroxene gabbrodiorite of the early and major phases in the Kongor complex. Our age data have made it possible to determine the formation time of the Kongor complex as Late Emsian–Early Eifelian (399–393 Ma). The largest volumes of island-arc igneous rocks belonging to the calc-alkali gabbro–diorite–tonalite–plagiogranite series formed in the Praghian–Early Eifelian (410–393 Ma). The Late Emsian–Early Eifelian (399–393 Ma) was characterized by the development of much smaller bodies consisting of Kongor rocks pertaining to the calc-alkali and high-K calk-alkali range, gradually transitioning into shoshonite–latite. High-K rocks formed upon completion of calc-alkali magmatism, likely due to the gradual decay of Devonian suprasubduction magmatism and partial melting in magma generation or due to the involvement of a second magma source.