The magma ejected at Payún Matrú originates during partial melting of enriched mantle; the resulting melts then undergo crystal fractionation, assimilation of crustal material and magma mixing in magma chambers. The magmas eventually reach the surface through deep faults. The edifice of Payún Matrú acts as an obstacle to magmas ascending to the surface; this is why only evolved magmas are erupted in the caldera area of Payún Matrú while basic magmas reached the surface mainly outside of the main edifice.