Ignacio San José, Cristina deCastiñeiras García, PedroMárquez González, ÁlvaroOyarzun Muñoz, RobertoLillo Ramos, F. JavierLópez Ruiz-Labranderas, Iván2023-06-202023-06-2020030020-68140020-6814/03/700/1020-9https://hdl.handle.net/20.500.14352/57116The rocks of the 1982 eruption of El Chichón volcano (Chiapas, Mexico) display a series of geochemical and mineralogical features that make them a special case within the NW-trending Chiapas volcanic belt. The rocks are transitional between normal arc and adakitic-like trends. They are anhydrite-rich, and were derived from a water-rich, highly oxidized sulfur-rich magma, thus very much resembling adakitic magmas (e.g., the 1991 Pinatubo eruption). We propose that these rocks were generated within a complex plate tectonic scenario involving a torn Cocos plate (Tehuantepec fracture zone) and the ascent of hot asthenospheric mantle. The latter is supported by an outstanding negative S-wave anomaly widely extending beneath the zone, from 70 to 200 km in depth. The adakitic- like trend would be derived from the direct melting of subducting Cocos plate, whereas the transitional rocks would have resulted from the mixing of two poles, one reflecting a mantle source, and the other, the already mentioned adakitic melts. The basaltic source would also account for the high sulfur content and 34S values of the El Chichón system (about +5.8), as result of a contribution of SO2 in fluids released from an underlying mafic magma.engjournal articlehttp://www.tandf.co.uk/journals/titles/00206814.aspopen access552.3El Chichón volcanoMagmatismeGeochemicalMexicoPetrología