The Sierra Los Tanques ~1.1 Ga Granite in NW Sonora: Another Example of Mesoproterozoic Plutonism along the Mexican Yavapai Province

It has been proposed that a narrow, NW-SE oriented zone of Yavapai-type rocks is present in NW Sonora (the Mexican Yavapai province). These Paleoproterozoic rocks acted as a zone of crustal weakness that is thought influenced different geological events in NW Mexico, including the spatial alignment of ~1.1 Ga intraplate granites and associated anorthosites (i.e., bimodal plutonism) an the orientation of continental rifting during the final break-up of Rodinia sometime in the Neoproterozoic-Cambrian time.

Sierra Los Tanques is located ~15 km SW of the border town of Sonoyta in NW Sonora. A granite unit from this area was collected just to the NE of a NW-oriented axial zone of a sinistral flower structure proposed to represent outcrops of the hypothetical Mojave-Sonora megashear. These granitic rocks form part of the “Caborca block” that overthrusted (NE directed) a sequence of continental arc volcanic rocks of middle to late Jurassic age of the “North America block”. U-Pb zircon geochronology (LA-MC-ICPMS) of this granite yields a 207Pb/206Pb age at 1100 ± 8 Ma. This crystallization age is in agreement with ages obtained for similar granites in other areas of NW Sonora (e.g., Quitovac, Sierra Prieta, Aibo, Santa Margarita) that have been found to intrude older Paleoproterozoic basement rocks with Yavapai affinities.

If the same geological relationship holds true for the Sierra Los Tanques granite, the “Caborca block” basement in this area may be part of the Mexican Yavapai province and should have a quite different petrogenetic signature from the rather unique Mojave signature predicted by the megashear hypothesis. Further geochemical and isotopic characterization of both, the actual ~1.1 Ga granite and its host rocks will be required to test this idea that may shed some light on one of the most controversial geological features in northern Mexico.