The Maronia Magmatic Corridor is a NE-trending belt of Oligocene plutons that intrudes the Kechros Dome of the northern Rhodope Core Complex in northeastern Greece.The post-collisional magmatism transitions from early high-K calc-alkaline magmatism in the NE to a younger, shoshonitic phase in the SW. We use a full suite of whole-rock geochemical analyses, including rare earth elements, to show a shared metasomatized mantle source of the magmatism. Evidence of plagioclase saturation from the onset of crystallization and amphibole-pyroxene-controlled fractionation in the high-K calc-alkaline magmatism suggest a drier (<4.75 wt% H2O) parental magma than is typical of subduction-related magmatism. Continued H2O depletion of the metasomatized source mantle resulted in the transition to a shoshonitic trend where deep crustal fractionation of an H2O-poor (< ~2 wt% H2O) magma in the absence of major olivine resulted in incompatible enrichment over a small range of SiO2. High-precision U-Pb zircon geochronology is presented here for the first time to provide chronological markers for the transition in the magmatic evolution of the Kechros dome. A 2.2 Myr break in magmatism separates the intrusion of the shoshonitic Maronia pluton at 29.8 Ma from the emplacement of the rest of the high-K calc-alkaline Maronia Magmatic Corridor between 32.9–32.0 Ma. The Maronia pluton is the hottest, driest, and youngest episode of post-collisional magmatism in the Kechros dome; we suggest that the emplacement of Maronia marks the cessation of magmatism in the northern Rhodope Core Complex as asthenospheric mantle upwelling migrated southward.