Search

The Zona Canteras-Puerto Peñasco area, previously known as Seven Hills, is located ~20 km ENE of the town of Puerto Peñasco in NW Sonora, Mexico. Crystalline basement in this area is key to defining Proterozoic provinces of SW Laurentia and has important implications for Phanerozoic tectonics and formation of the active continental margin of North America. New U-Pb zircon ages (LA-MC-ICPMS) of two banded gneisses in this area yield 207Pb/206Pb ages at 1764 ± 3 Ma and 1725 ± 3 Ma. Zircons from both samples are well-behaved in the U-Pb systematics and present age and compositional homogeneity, suggesting that these rocks are Paleoproterozoic orthogneisses. These crystallization ages combined with whole rock major- and trace-element geochemistry and Sm-Nd in whole rock and Lu-Hf isotopic determinations on zircons by laser ablation suggest that the banded gneisses have affinities with rocks of the Yavapai province as defined in the Quitovac area ~45 km to the east and in the region of Gunnison-Salida, Colorado, USA. Both samples plot in the volcanic arc environment of granite formation (Y vs Nb discrimination diagram) and have epsilon Hf (initial) values between +1.85 and +5.05 with corresponding single-stage Hf model ages (TDM) at 1.98-2.07 Ga and two-stage Hf model ages (TDMC) at 2.07-2.50 Ga. Sm-Nd whole rock isotopic analyses from three Paleoproterozoic gneisses have epsilon Nd (initial) values between +1.86 and -0.57 with corresponding Nd model ages (TDM) at 1.91-2.02 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 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 these Mojave province rocks exist in NW Sonora they must be located to the west of the Zona Canteras-Puerto Peñasco area. [ABSTRACT FROM AUTHOR]