A TESTABLE HYPOTHESIS FOR THE DISTRIBUTION OF PALEOPROTEROZOIC PROVINCES ALONG THE SW MARGIN OF LAURENTIA: INSIGHTS FROM NW SONORA, MEXICO

The SW margin of Laurentia is one of the key Neoproterozoic to Early Paleozoic rifted margins used in continental reconstructions of the Rodinia supercontinent (e.g. SWEAT, AUSWUS, Siberian-west Laurentian connection). A common premise for all these reconstructions is that the SW margin of Laurentia is an amalgamation of juvenile volcanic arc complexes of Paleoproterozoic (Mojave, Yavapai, and Mazatzal) and Mesoproterozoic (Grenville) crustal terranes juxtaposed along distinct tectonic boundaries.

Detailed isotopic, geochemical, and temporal characterization of representative Proterozoic granitoids in the Quitovac region of NW Sonora, Mexico, has identified two distinct Paleoproterozoic basement blocks that coincide spatially with the previously proposed, age-defined, Caborca and "North America" blocks. Caborca block rocks exhibit geochemical and isotopic affinities to rocks from either the Yavapai province or the Mojave-Yavapai Transition zone, whereas rocks of the "North America" block have signatures similar to those of the Mazatzal province of southern Arizona.

Proterozoic basement rocks of N. Sonora are a critical piece of this puzzle. We present several alternative hypotheses for the distribution of Paleoproterozoic provinces in the SW margin of Laurentia: (1) Caborca basement in N. Sonora is an extension of Mojave-Yavapai Transition zone crust that is juxtaposed against the Mazatzal province. In this scenario, only the Mojave province represents the SW margin of Laurentia; (2) The Caborca block is an extension of Yavapai crust that is juxtaposed against the Mazatzal province. In this scenario the margin would be a triple-junction of Mojave, Transition Zone, and Yavapai crust; and (3) The NW part of the Caborca block is composed only of Yavapai crust and the remainder of the Caborca block is in fact Mazatzal crust. The resulting margin in this last case would contain parts of the Mojave, Transition Zone, Yavapai, and Mazatzal provinces.

These competing scenarios can be tested by undertaking structural, geochemical, and isotopic studies in appropriate parts of the Sonoran Desert that expose portions of Precambrian basement.