Geochemical and petrographic characterization of pyroclastic deposits of Los Humeros Volcanic Complex used as aggregates in the plasters from Teotihuacan (Mexico)

Abstract

This work presents the results of the petrographic and geochemical characterization of pyroclastic deposits outcropping in an area located to the northeast and southeast of Los Humeros Volcanic Complex, in the eastern part of the Trans-Mexican Volcanic Belt (TMVB). The results were compared with the analyses of aggregates in the plasters of Xalla in Teotihuacan (Mexico) in order to determine the provenance of the raw materials (in particular glass shards) used as aggregates. The characterization of the deposits and the raw materials used in the plasters was conducted by OM, SEM/EDS and LA-ICP-MS. Petrographic and geochemical studies have highlighted the geochemical similarity among glass shards used as aggregates in the plasters of Teotihuacan (Teopancazco and Xalla) and the pyroclastic deposits outcropping around Altotonga, a town located in the northeast of Los Humeros Caldera. This similarity shows the importance of the use of a volcanic cinder, rich in glass shards, in plasters from different areas of the Teotihuacan city.The paper also examines the characteristics of plasters – in some cases painted – from Xalla, thus confirming the re-plastering and re-painting phenomena and the use of hematite, identified by Raman Spectroscopy.