MAJOR IGNIMBRITES AND VOLCANIC CENTERS OF THE COPPER CANYON AREA: A VIEW INTO THE CORE OF MEXICO’S SIERRA MADRE OCCIDENTAL

Mexican national highway 16 between Chihuahua City and Hermosillo, Sonora, has previously served as the locus for a series of mapping projects across the northern part of the Sierra Madre Occidental volcanic field, include those documenting a caldera complex in the heart of the sierra at Tomochic. A secondary paved road now diverges from highway 16 and extends across the central sierra to the tourist destination site of Copper Canyon. The Copper Canyon highway passes 50 km south of the Tomochic volcanic center and opens a large area in the core of the volcanic field to geologic investigation. Reconnaissance mapping of the Copper Canyon area has established the local stratigraphic section and correlated parts of that section with units previous mapped at Tomochic. Two new calderas have been added to those known from Tomochic, and supportive evidence for other calderas has been found. The combined Copper Canyon-Tomochic areas provide the best available view into the geology of the core of the Sierra Madre Occidental volcanic field, expanding that offered by earlier reports, mostly from peripheral regions of the sierra. The emerging picture is one of a dramatically thickened, stratigraphically complex, silicic volcanic section that is related to overlapping caldera complexes, much like that documented for the core of the San Juan volcanic field.