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 Colima^1,2 and Ceboruco³ near the Pacific coast, Popocatépetl and Iztaccihuatl in central Mexico, and San Martin⁴ close to the Caribbean coast. The MVB rests on continental crust approximately 40 km thick^5,6, and is associated with subduction of the Cocos plate below central Mexico^3,7. 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 rocks^3,8. The lavas of the active volcanoes shown in Fig. 1 are dominantly calc-alkaline andesite and dacite^3,8–10. In contrast, the easternmost active volcano, San Martin, is built from lavas of a picritic basalt–basanitoid–alkali basalt–hawaiite association^4,11,12. 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.