THE EL CRESTÓN GRANITE: A NEW CONFIRMED PALEOPROTEROZOIC LOCALITY IN THE OPODEPE AREA, NORTH-CENTRAL SONORA, MEXICO

The El Crestón Granite in the Opodepe area in north-central Sonora is among the easternmost outcrops of Proterozoic crystalline rocks in Sonora, and presumably is part of the southeast transported Caborca block. A Paleoproterozoic age was suspected for more than two decades based on lithologic correlation with other dated rocks in the region. Our new SHRIMP U/Pb zircon geochronology studies have effectively confirmed a Paleoproterozoic age of 1730.1 ± 9.1 Ma for El Crestón Granite. Sm-Nd isotopic data yielded an initial epsilon neodymium value of +3.1. Major- and trace-element data suggest a high-K calcalkaline composition, and fairly high Y, Rb, Ba, Th, and REE concentrations. We propose that the El Crestón Granite derived from a depleted to nearly-depleted source, possibly of island-arc affinity. Another, undated porphyritic granite characterized by large K-feldspar phenocrysts, which may correlate with other 1.4 Ga intrusions in northern Sonora, was also studied. It plots in the intra-plate region of the Pearce-type granite discrimination diagram, and is more enriched in K2O, Y, Rb, Nb, Th, and REE than the Paleoproterozoic granite it intruded. Geochemical and isotopic similarities with Paleoproterozoic granitoids from the Caborca block in the Quitovac region in northwestern Sonora allow us to speculate that the El Crestón Granite may be part of this block. However, further regional work is needed to more clearly determine the relationship of this granite with other granites in the crustal provinces of southwestern United States. We consider that a future effort in this sense would help to test the hypotheses of major Mesozoic and/or older truncations of the basement in Sonora, as well as determining a coherent distribution of the Proterozoic basement provinces along the southwestern margin of Laurentia in Mexico.