Satellite image colored in green and brown tones, showing the area between Cananea and the Sonora River to the east. The El Alacran area is at the lower center of the image. At the center of the image is an area of light blue-gray color that indicates tuff that filled the Ojo de Agua Caldera when it collapsed. The south and east sides of the area has a curved outline (red line) that represents part of the nearly circular outline of the caldera. .
The Mesa Formation extends from Cananea, Mexico, southeast to the Sonora River and is the main host rock of Laramide porphyry copper deposits in the Cananea District and at the Alacran porphyry prospect to the east. The Mesa consists of two members—a lower andesite and an upper dacite. The lowest part of the dacite member is a crystal tuff about 100 m thick. This tuff is the outfall of a caldera centered near the village of Ojo de Agua, dated by 40Ar/39Ar at 65.8 Ma ±0.4. The Ojo de Agua Caldera is about 9 km in diameter and is filled by a light gray biotite dacite tuff with abundant flattened pumice fragments. The volume of the caldera is estimated to be 24 km3.
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URL of this page: http://pubs.usgs.gov/sir/2006/5022/
Maintained by: Michael Diggles
Created: July 21, 2006
Last modified: August 24, 2006 (mfd)