Facial Composition, Geochemical Features and Geodynamic Settings of Formation of the Late Emsian Island Arc Complexes: the Main Urals Fault Zone, Southern Urals

The facial and geochemical peculiarities of the Late Emsian island arc complexes of the Main Urals Fault Zone (Southern Urals) are considered. The results of geodynamic reconstructions are given. It was shown that the rock composition of the complexes formed in three geodynamic settings: 1) on the island arc slope of the deep-water trench, 2) within the frontal island arc, and 3) in the junction zone of the northern edge of the frontal island arc and back-arc basin. The facies of the island arc slope include serpentinite-clastic edaphogenic breccias containing Co-Cu-massive sulfide mineralization and polymictic olistostrome. Volcanogenic strata and intrusive formations represent the frontal arc. Low-Ti magmatites belonging mainly to the tholeiitic and boninitic series and having a metallogenic specialization for massive sulfide mineralization dominate in the southern areas of the suture zone. Moderate-Ti magmatites of the tholeiitic composition, productive on Au-Cu-porphyry mineralization, are distributed in the northern regions. A gold-bearing volcano-intrusive association has formed in the junction zone of the northern edge of the frontal island arc and back-arc basin, where moderate-Ti rocks of tholeiitic and transitional from tholeiitic to calc-alkaline composition dominate. It is assumed that the differences in the geochemical characteristics and metallogenic specialization of the Late Emsian magmatites are associated with the changes in the geodynamic conditions of magma formation and ore genesis along and across the strike of the island arc system.