JURASSIC ARC VOLCANISM IN WESTERN MEXICO

After several years of arm-waving discussions between Cathy Busby and me on the Jurassic volcano-sedimentary successions of east-central Mexico, she turned it into action. Our paper “The “Nazas Arc” is a continental rift province: Implications for Mesozoic tectonic ..." was published in Geosphere in February 2022. The paper focused on the stratigraphic differences between thick arc-related volcano-sedimentary succession of SW USA, and the mostly sedimentary, scarcely volcanic successions of east-central Mexico. Although the latter have been interpreted by several authors as intra-arc rocks, their lack of large volcanic successions, and the fining upward subaerial to transitional facies are indicative of rift-related basins. Our paper stated that the SW USA arc volcanism fringes southward to the Alisitos-Guerrero Terrane, without further discussion on that. As a tribute to all the great geology that Cathy has done throughout an exemplary scientific carrier, I will discuss field and geochronological evidence for the southern extension of the Jurassic arc of North America along Baja California and the present Pacific Coast of Mexico.

There are few exposures of igneous rocks of Jurassic age in western Mexico, besides outcrops of northern Sonora, which are coeval and stratigraphically similar to those in Arizona. The next exposures to the south are metamorphosed volcano-sedimentary rocks, located in El Fuerte, Sinaloa, and in Cuale, Jalisco (Bissig et al., 2008; Vega-Granillo et al., 2012). Granitoids crop out in El Arco, Baja California (Valencia et al., 2006) and Tumbiscatío, Michoacán (Centeno-Garcia et al., 2011). The last emplaced in subduction-related Arteaga Complex, and are unconformably overlain by Aptian-Albian arc-related volcano-sedimentary rocks. U/Pb ages range between 164 to 151 Ma. Jurassic age volcanism from Vizcaíno Peninsula have a wider age span, from 164 to 145 Ma (Busby, 2004).

Complementary evidence of widespread Jurassic magmatism along Coastal Mexico includes the abundant inherited magmatic and detrital zircons of Jurassic (168 to 150 Ma) age, collected from younger (Cretaceous or younger) batholiths and Cretaceous volcano-sedimentary successions (Centeno-Garcia et al., 2011; Valencia et al., 2013; Pompa-Mera et al., 2013; Peña-Alonso et al., 2015; Schaaf et al., 2020).