Geochemical and isotopic profile of Pico de Orizaba (Citlaltépetl) volcano, Mexico: Insights for magma generation processes

Pico de Orizaba or Citlaltépetl volcano is the easternmost and highest stratovolcano of the subduction-related Mexican Volcanic Belt (MVB) located > 400 km NNE of the Middle America Trench. This active volcano comprises four evolutionary stages, ranging in age from 0.65 Ma to the Holocene, and is surrounded by Quaternary monogenetic scoria cones and maar volcanoes. Magmatic products of the stratocone range from basaltic andesites to rhyolites and the cinder cones erupted basalts and basaltic andesites. All rock compositions form a continuous calc–alkaline suite. Petrogenetic processes involved in magma generation and evolution include fractional crystallization and mid-crustal assimilation. Trace element patterns with elevated Ba/Nb, positive Pb spikes, and Th enrichments indicate contributions from subducted sediment. Low Ba/Th ratios suggest melting of hydrous sediment without significant loss of fluid-mobile elements prior to melting. Sr–Nd isotopic ratios of Pico de Orizaba and cinder cones are nearly chondritic and are located on a mixing curve between Pacific MORB and Paleozoic crust of SE Mexico. However, vertical Nd distributions in an 87Sr/86Sr vs. εNd diagram cannot be explained by crustal assimilation and indicate contributions of a sedimentary component with unradiogenic Nd. In contrast to other eastern MVB volcanic centres, Pico de Orizaba magmas are derived almost exclusively from a depleted mantle source. ed to other MVB stratocones, Pico de Orizaba shows the least radiogenic Nd isotope ratios at nearly identical 87Sr/86Sr. Steep trends in a 206Pb/204Pb vs. 207Pb/204Pb diagram favour the involvement of young, 207Pb-enriched oceanic sediments in magma generation processes of Pico de Orizaba volcano. The Pb isotope data do not support any assimilation of lower crustal Grenvillian basement.