This thesis aims to characterize the melting sources, magmatic evolution and physical magma storage conditions of magmas from several large volcanic complexes located in the Loicas Trough. The Loicas Trough is an extensional structure situated east of the Andean main arc intercepting folded belt sequences of the southern Andean mountain range. The volcanism in the trough is unique as it occurs east of the main volcanism axis and is situated 130-160 km above the subducting Nazca plate slab. Furthermore, it is placed distinctly west of the basaltic back arc and intraplate volcanism occurring on the Pampas plains of Argentina. This thesis focuses on three volcanic complexes, Domuyo, Tromen-Wayle and PalaoPolco, located in the southern part of the Loicas Trough. Specifically, Domuyo is a topic of great interest in light of recent unrest and its large geothermal energy potential. I present petrographic reviews of lava samples, bulk rock major and trace element concentration analysis, radiogenic isotope compositions (Pb, Nd, Sr and Hf), in situ electron microprobe analysis of phenocrysts including plagioclase zonation profiles, in situ Sr-isotope compositions of plagioclase phenocrysts, and several iterations of thermodynamic models including fractional crystallization, partial melting of crust, assimilation, and magma replenishment. In this thesis, three manuscripts are presented which focus on different areas of interest and geochemical tools to thoroughly understand the volcanism occurring here. The first manuscript explores thermodynamic modelling of the magmatic evolution and identification of assimilation and partial crustal melting through major and trace elements. The second manuscript characterizes the isotopic variation of the Loicas Trough lavas through bulk rock and in situ isotope analyses, with emphasis on resolving open system processes like assimilation and recharge events. The third manuscript characterises the physical conditions (pressure, temperature, oxidation and hydration) of the Loicas Trough magma plumbing system through multiple geothermobarometry equations based on multiple mineral phases. Together, these three manuscripts form a comprehensive picture of the magmatism in the Loicas Trough: Melting of a mantle source intermediary between the main arc and a back arc source, where magmas reside at several levels in the middle to upper crust with multiple potential replenishment episodes. Here, the magmas induce partial melting of the crust and are significantly modified by assimilation which changes both their isotope, major and trace element trajectories with differentiation.