Production of andesite in the western Mexican arc: Constraints from argon chronology, volume analysis, and geochemistry.

40Ar/39Ar geochronology is coupled with quantitative volume determinations (utilizing field mapping, digital elevation models, ortho-airphotos and Geographic Information System software) to constrain magma eruption rates at the Ceboruco-San Pedro and the Volcan Tepetiltic volcanic fields in the western Trans-Mexican arc. Each volcanic field is dominated by an intermediate composition stratovolcano (∼51 and ∼42 km 3, respectively) that was built in tens of kyrs. The smaller volume peripheral lavas (3) are more geochemically diverse than the large volume flows associated with the main edifices. The peripheral flows tend to be crystal-poor (