Geochronology and geochemistry of the Paleogene Magdalena Suite of anatectic granites in northern Sonora, México

New zircon U-Pb geochronology, zircon geochemistry, and whole rock geochemistry are presented from the Magdalena granites in northern Sonora, Mexico that outcrop in the footwall of the Magdalena-Madera metamorphic core complex. Crystallization ages of the Magdalena granites are predominantly Eocene (51 to 38 Ma; n = 21) with two Paleocene ages (60 and 59 Ma). These ages are generally younger than subduction-related magmatism associated with the Cretaceous Eocene Mexican Magmatic Arc (CEMMA) in the northern Mexican Cordillera, including new ages (72 to 61 Ma; n = 8) from this study. The Magdalena granites are also mineralogically, compositionally, and texturally distinct from CEMMA rocks. The granites are moderately peraluminous, two-mica + garnet leucogranite (> 70 wt. % SiO2), relatively depleted in LREE and enriched in HREE, and have major and trace element chemistry consistent with water-absent, muscovite- to biotite-dehydration melting of metasedimentary to metaigneous protoliths. Zircon from the Magdalena granites have high U/Th ratios (median = 11.5) compared to CEMMA zircon (U/Th < 5) and are relatively enriched in HREE compared to CEMMA zircon. The results of this study suggest that the Magdalena granites are anatectic in origin and are part of the North American Cordilleran Anatectic Belt. The Magdalena granites crystallized from evolved melts that underwent early feldspar crystallization and were separated from a feldspar-rich residue, presumably a migmatitic source deeper in the crust. Field and petrographic relationships suggest the Magdalena granites intruded into relatively hot crust, including host rock mushes that exhibit evidence for melt infiltration and disaggregation.