"The Process of Melt Differentiation in Arc Volcanic Rocks: Insights from OIB-type Arc Magmas in the Central Mexican Volcanic Belt" by Straub et al., A Critical Comment

Abstract

The recent paper by Straub et al. (2012) provides a detailedgeochemical study of the compound Texcal lava flow andthe eruptive products of Chichinautzinvolcano, twomono-genetic volcanoes located in close proximity to each otherin the central part of the Sierra Chichinautzin VolcanicField (SCVF) south of Mexico City. The authors chosethese mafic [ocean island basalt (OIB)-type] volcanoesthat belong to the Mexican Volcanic Belt because theyerupted lavas displaying a range of compositions and inaddition are believed to have retained some of their initialgeochemical sub-arc mantle and subducted slab signatures.The latter allowed these authors to make inferences re-garding magma generation processes in a subduction-related tectonic setting.I would like to comment here on one specific point onwhich I hold a significantly different opinion, and whichis important to address because of its diverse ramifications(including volcanic hazard assessment in a densely popu-lated area). This concerns the exact location and morph-ology of the vent(s) and the timing and eruptive style ofthe eruption that produced the Texcal lava flows. In theirfig. 1, Straubet al. (2012) present a geological sketch map,which they call a‘refined’ version of a previous map pub-lished by Siebe et al. (2004a, 2004b). At first sight, the‘refined’map seems almost identical to the map publishedby Siebe et al. (2004a, 2004b). However, a closer look (seeFig. 1a) reveals that the source vent for the compoundTexcal lava flow has been changed.The Guespalapa align-ment of scoria cones, which formed between 4700 and2800 years