The source of the Parinacota magmas is ultimately the mantle wedge above the slab of the Nazca Plate. Fluids released from the slab flux the wedge and trigger the formation of melts, with the assistance of asthenospheric material that is hotter and gets transported into the wedge. These ascending magmas then interact with the crust, resulting in extensive changes to their composition. The area in the crust where such interaction takes place is known as MASH or Melting Assimilation Storage Homogenization, and it is there that the base magmas are formed which then enter into shallow magmatic systems. Further, the relative thickness of the crust and narrowness of the mantle wedge mean that garnet is stable within the wedge, causing the magmas to be influenced by garnet-linked petrogenic processes. Shallower crustal components such as the locally extensive Lauca-Perez ignimbrite may have been assimilated by Parinacota as well. These crustal components contributed about 12% of the primitive magmas as erupted by the Ajata cones, while the mantle wedge contributed 83%. Fluids from the slab and sediments subducted in the Peru-Chile Trench added the remaining 3 and 2%.