145 Precambrian Geology (Posters)

Paleoproterozoic (~1.76–1.73 Ga) Banded Gneisses from the Zona Canteras-Puerto Peñasco Area: A New Occurrence of Yavapai-Mazatzal(?)-Type Rocks in NW Sonora, Mexico

Paper number: 145-10
Program: Technical Sessions
Time: 8:00 AM – 4:45 PM

Authors

Abstract

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. 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 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 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.