The geological evolution of the Saykhandulaan Inlier, Mongolia : a window into the Palaeozoic growth of the South Gobi mineral belt

This PhD project concerns the Saykhandulaan basement inlier in southern Mongolia, which constitutes a critical window into the Palaeozoic development of the northern margin of the Palaeo-Asian Ocean. Through fieldwork, five litho-tectonic domains are defined; (1) the Northern Slate Belt, comprising Devonian greenschist grade pelites and psammites with deep-marine to coastal siliciclastic protoliths; (2) the Saykhandulaan Valley Lineament Zone (SVLZ), a tectonised zone of faulted and lithogically altered volcanic rocks; (3) the High Strain Belt, consisting of tightly folded and flattened metamorphosed clastic sedimentary rocks; (4) the Molasse Succession, consisting of relatively undeformed coarse conglomerates and sandstones and, (5) the Oyut Volcanic Group, a nearly 5km-thick folded Carboniferous volcanic succession that hosts the mid-Carboniferous Oyut Ulaan mineralised intrusive complex. The structural architecture of the inlier records several ductile and brittle deformations, including folding of all lithologies to differing degrees, folding of cleavage in the Northern Slate Belt, thrusting along the SVLZ and exhumation of the tightly folded High Strain Belt.;Field relations, geochemical signatures and the absolute age of the Oyut Ulaan intrusive complex show that, with the Oyut Ulaan Volcanic Group, it forms a co-magmatic volcano-plutonic complex. Volcanic and intrusive lithologies have subduction zone-related signatures. The Oyut Ulaan Volcanic Group is comprised of four formations with volcanic and thick intercalated siliciclastic and volcaniclastic sediments. Chemostratigraphy of the Oyut Ulaan Volcanic Group illustrates an evolving magma chamber with periodic replenishment by new magma batches. One other intrusion within the Saykhandulaan inlier and six other intrusions within the neighbouring Mandakh inlier were geochemically analysed and U-Pb zircon dated, showing, broadly, that a 180km long belt of monzonitic intrusions were emplaced in the mid-Carboniferous, and post-collisional granites and A-type syenites were emplaced in the Early Permian.