Strontium isotope evidence for petrogenesis of Mexican andesites

Abstract

THE Mexican volcanic belt (MVB) consists of several inactive and active volcanoes1 (Fig. 1). The active volcanoes include Colima1,2 and Ceboruco3 near the Pacific coast, Popocatepetl and Iztaccihuatl in central Mexico, and San Martin4 close to the Caribbean coast. The MVB rests on continental crust approximately 40 km thick5,6, and is associated with subduction of the Cocos plate below central Mexico3,7. The link between plate subduction and the disposition of the MVB is not simple since the latter makes an angle of about 20° with the Middle America Trench3. This complexity might be related to the structure of the continental crust5, or to a combination of subduction and extensional processes4. The most prominent products of volcanism of the MVB are the large composite volcanoes built up from successive eruptions of intermediate lavas and pyroclastic rocks3,8. The lavas of the active volcanoes shown in Fig. 1 are dominantly calc-alkaline andesite and dacite3,8–10. In contrast, the easternmost active volcano, San Martin, is built from lavas of a picritic basalt–basanitoid–alkali basalt–hawaiite association4,11,12. This volcanic area occurs at a change in direction of the MVB and might therefore be linked with extension or fracturing associated with the destructive margin setting of the MVB (ref. 4). Here we report new Sr isotope data for lavas from Ceboruco, Colima, and San Martin. These data, and published Sr isotope data for Cainozoic volcanics from central Mexico13 constitute evidence for petrogenesis of Mexican volcanic rocks.