Petrogenetic evolution of Uralian-Alaskan-type mafic-ultramafic complexes in the southern and middle Urals, Russia / Петрогенетическая эволюция Уральско-Аляскинского типа мафит-ультрамафитовых комплексов юго-востока и центральной части Урала

Uralian-Alaskan-type mafic to ultramafic complexes form a narrow, 900 km long, N-Strending chain in the northern and central parts of the Ural orogenic belt. Characteristic features like their concentric lithologic zonation, the absence of orthopyroxene in the ultramafic rocks and platinum group element (PGE) mineralization, which is the source for economic PGE placer deposits, discriminate Uralian-Alaskan-type complexes from other mafic-ultramafic intrusions. The genesis, structure and the geotectonic setting of the Uralian-Alaskan-type complexes in the Ural Mountains have been controversially discussed during the last decades. Genetic models include metasomatic, metamorphic and magmatic processes in order to explain the special rock assemblage and structure. Island arc and supra subduction zone environments and a diapiric mantle upwelling related to extensional tectonics along the edge of the east European Craton have been postulated as geological setting. 
The aim of the PhD thesis at hand is to constrain the petrogenetic evolution of three Uralian-Alaskan-type complexes. Based on the detailed analysis of variations in major and trace element concentrations and ratios in rock forming and accessory minerals from mineral grain to regional scale, magma mixing has been found to be the most important petrogenetic process to explain the observed chemical variations. The compositional variation in minerals from the ultramafic rocks can be explained with the successive fractionation of olivine, spinel and clinopyroxene in an open magma chamber system. However, the observed chemical variation in minerals especially clinopyroxene from the mafic rocks requires the presence of a complex magma chamber system fed with multiple pulses of magma from at least two different coeval sources in a subductionrelated environment. One source produces silica saturated Island arc tholeiitic melts. The second source produces silica undersaturated, ultra-calcic, alkaline melts. The presence of exsolved spinel that equilibrated at temperatures close to 600°C in various lithologies in all three studied Uralian-Alaskan-type complexes indicates that this temperature represents the thermal conditions in the intrusion level. After formation and thermal equilibration of the cumulates, a regional tectonic event probably related to the final exhumation of the Uralian-Alaskan-type complexes in the Uralian fold belt terminated a further equilibration.  <...>