Petrogenetic and tectonic implications of major and trace element and radiogenic isotope geochemistry of Pliocene to Holocene rocks from the Tacaná Volcanic Complex and Chiapanecan Volcanic Belt, southern Mexico

Abstract

"New major and trace element, and Sr, Nd and Pb isotope data for samples from the Volcán Tacaná, along with the published data from the Tacaná Volcanic Complex (TVC) and Chiapanecan Volcanic Belt (CVB), were used to better constrain the petrogenesis of the Pliocene to Holocene volcanism in southwestern Mexico. The TVC volcanic rocks sampled in this study were andesite, whereas the literature samples included, besides andesites, one subalkali basalt and a few dacites. The CVB housing the prominent El Chichón volcano, on the other hand, showed more alkalic magmatic products (trachyandesite and basaltic trachyandesite) but also included a few basalts and dacites. The enclaves and lithic fragments sampled from both TVC and CVB showed wide SiO2 compositions similar to the volcanic products. The CVB rocks are more enriched in REE, LILE, and HFSE than the TVC. The combined data of volcanic rocks were evaluated through conventional multi-element diagrams as well as subduction- or crust-sensitive parameters. Although the TVC constitutes the northern end of the Central American Volcanic Arc (CAVA), some chemical differences were documented between them such as the TVC rocks have higher LILE, REE, HFSE, and combined ratio parameters. More importantly, the CVB seems to be significantly different from both TVC and CAVA as well as from other continental arcs such as higher LILE, REE, HFSE, and distinct isotopic signature, which may indicate that the origin of the CVB volcanism represents a direct action of the abundant strike-slip faults and extensional system prevalent in this area. Finally, the relationship of basic and evolved rocks from the CVB, especially on isotope-isotope diagrams, also suggests that the lower crust may have contributed to evolved magmas during the ascent of basic magmas through the crust."