Boletín de la Sociedad Geológica Mexicana
Volumen Conmemorativo del Centenario
Grandes Fronteras Tectónicas de México

Vol 57, núm. 1, 2005, p. 1-26

La Megacizalla Mojave-Sonora: la hipótesis, la controversia y el estado actual de conocimiento

Roberto S. Molina-Garza* y Alexander Iriondo

Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230, México
* This email address is being protected from spambots. You need JavaScript enabled to view it.


The Mojave-Sonora megashear model, which implies left-lateral strike slip motion of northern Mexico in Jurassic time, remains as one of the most influential ideas in the geology of Mexico. A comprehensive review of the literature related to this topic does not yet allow to resolve the controversy over the validity of this hypothesis. A clear conclusion is that the original hypothesis was based on a relatively simplistic model of the geology of Sonora, as the basement of the Caborca terrane is not simply a fragment of the Mojave Precambrian basement Province of eastern California. Attempts to use quantitative techniques in testing the model have yielded results contrary to the hypothesis, such as clockwise rotations indicated by paleomagnetic data, and the diversity and complexity of the basement of Caborca indicated by geochemical and geochronological data. Other quantitative methods such as zircon provenance studies in quartzites of the sedimentary cover yield non-conclusive results. The main conclusion of the studies of detrital zircons is that Grenvillean zircons are relative abundant, but their presence cannot be attributed solely to sources in the Grenville Province in a fixist model. Stratigraphic correlations of upper Paleozoic and Mesozoic rocks in Caborca with similar sequences in California and Nevada do not provide convincing arguments of large displacement, but should be evaluated in more detail. Elements that have the potential to test the hypothesis with greater certainty include detailed studies of basement rocks, a refined stratigraphy of the Jurassic volcanic and volcaniclastic arc rocks south of the inferred fault trace, and better understanding of depositional trends in the miogeoclinal sequence. Structural studies are sparse in the region. In particular, is important to gain a better understanding of the effects in time and space of Late Cretaceous-Tertiary contractional deformation. A tectonic evolution model that does not conflict the existing data is the proposal that displacement of a parautochtonous Caborca terrane may have occurred in the Late Paleozoic. Nonetheless, available data and geologic relations in the Caborca region do not require Late Jurassic slip of several hundred kilometers.

Keywords: Mojave-Sonora megashear, Caborca terrane, northwestern Mexico, Proterozoic.