GEOCHEMISTRY AND GEOCHRONOLOGY OF LEUCOCRATIC ROCKS OF MAGDALENA GRANITES, NORTH-CENTRAL SONORA, MEXICO

Petrographical, geochemical, and geochronological studies of leucocratic rocks located in the Magdalena region, north-central Sonora, Mexico, suggest the presence of a distinctive suite of rocks with geochemical features and temporal constraints. These leucocratic rocks intrude the Jurassic and Cretaceous rocks that constitute the lower plate of the late Oligocene - early Miocene Magdalena core complex. In general, these leucocratic rocks are characterized by muscovite and the presence of garnet, and in general, are petrographically and geochemically classified as granites, and two of them are classified as granodiorites. The rocks are calc-alkaline and are related to continental arc magmatism. These rocks are mainly weakly-peraluminous to peraluminous, and the geochemical features indicate an anatectic nature. U-Pb zircon geochronological data record a magmatic pulse at the end of the Cretaceous (ca. 68-61 Ma), and three younger magmatic pulses constrained at ca. 48-46 Ma, ca. 44-42 Ma and ca. 39-38 Ma. The most significant population of inherited zircons yielded Jurassic ages, although few Proterozoic, Paleozoic, Triassic, and Cretaceous zircon ages were recorded. The geochemical features of the leucocratic rocks of the Magdalena region are in agreement with those of the Cordilleran Anatectic Belt. Finally, this study contributes to a new geochemical and geochronological database of the leucocratic rocks of north-central Sonora, representing the southern end of the Cordilleran Anatectic Belt.