Migmatite terranes commonly develop at mid crustal levels as a result of decompression melting. The Loma de las Chacras of the western Sierras Pampeanas, Argentina preserves a lower crustal migmatite terrane that formed as a result of advective heating under increasing pressure conditions. Pelitic migmatites in the footwall of the Villarcan shear zone contain greater than 40% leucosome and preserve the assemblage Bt-Ky-Grt- Qtz-Pl-Kfs±Ms. Thermobarometry indicates that melting occurred under increasing pressure conditions from approximately 700˚C at 9kb to 900˚C and 12kb. Hanging wall schists contain less than 10% melt and preserve the assemblage Ms-Bt-Qtz-Grt-Pl-Ep and amphibolites contain the assemblage Hbl-Grt-Pl-Qtz±Ep. Thermobarometry estimates from both units record conditions of approximately 700˚C and 12kb. U-Pb zircon ages of leucosome in pelitic and mafic migmatites of 461±7 and 456±2 Ma, respectively, are synchronous with mafic/ultramafic intrusive ages of 472±3 and 462±4 Ma. At the lowest structural levels, migmatites exhibit metatextite textures and become progressively foliated towards the Villarcan shear zone. Foliation parallel leucosomes feed discordant dikes and sills. Hanging wall map-scale amphibolite layers arrested the upward migration of partial melt through migmatite and gneissic host rock. Lateral migration of leucocratic sills beneath the amphibolite horizons facilitated localization of deformation into the Villarcan shear zone. A preliminary hornblende Ar/Ar cooling age of 440 Ma indicates that cooling from peak temperatures may have been gradual and not associated with decompression following migmatization. This study emphasizes the role of advective heating in migmatization at lower crustal levels and the importance of inherited lithologic heterogeneity in arresting the upward migration of melt.