The distribution and the interconnection of magmatic bodies beneath volcanic arcs is key to asses volcanic hazard and eruptive processes taking place at convergent margins. We use ambient seismic noise Rayleigh-wave tomography to investigate the three-dimensional shear-wave crustal velocity structure of the Southern Central Andes between latitudes 33°S and 38°S (for the upper 30 km). We investigate the occurrence of magmatic reservoirs in the upper crust and show how their geometry is affected by local tectonics. The first prominent feature to be observed is the shear-wave velocity contrast between the volcanic arc and the faster fore-arc region. We further identify areas of low shear-wave velocity from 3 km to 10 km depth beneath the volcanic arc, striking N-S, that we interpret as zones of fluid-rich crust, possibly characterised by confined regions of partial melts. Our results allow us to derive a model for the crustal structure of the Southern Central Andes. We propose that partial melts, marked by lower shear-wave velocity anomalies, are connected to shallower structural levels and reservoirs by brittle regions where dikes and exsolved fluids may propagate.