Poster Number 91
These crystallization ages combined with whole rock major- and trace-element geochemistry and Lu-Hf isotopic determinations on zircons by laser ablation suggest that the banded gneisses have affinities with rocks of the Yavapai-Mazatzal(?) provinces as defined in the Quitovac area ~45 km to the east. Both samples plot in the volcanic arc environment of granite formation (Y vs Nb discrimination diagram) and have epsilon Hf (initial) values between +1.95 and +4.87 with corresponding Hf model ages (TDM) at 1.95-2.09 Ga. The magmatic protoliths of these gneisses could have been formed mostly from mantle sources with some degree of crustal contribution, which is similar to rocks from the Yavapai-Mazatzal province in SW North America. This petrogenesis contrasts with typical Mojave-province rocks that are characterized by significantly greater crustal contamination (as much as 30-40% in Death Valley). If this Mojave province rocks exists in NW Sonora they must be located to the west of the Zona Canteras-Puerto Peñasco area.