Geochronology and geochemical characteristics of a set of Tertiary rhyolitic domes in the San Luis Potosi Volcanic Field, Mexico [Geocronología y características geoquímicas de un conjunto de domos riolíticos terciarios en el Campo Volcánico de San Luis Potosí, México]
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abstract
The San Luis Potosí volcanic field includes two annular-shaped tectonic structures. Rhyolitic domes with topaz and cassiterite vapor phase mineralization were erupted along the smaller one. The lavas are characterized by high SiO2 (>75 wt. %25), Al2O3 (11-14 wt. %25), Na2O %2b K2O (7.5-9 wt. %25) and low CaO (< 1 wt. %25), MgO and TiO2 (< 0.15 wt. %25). Furthermore the topaz-bearing lava flows have a K2O/Na2O ratio that ranges between 1.22 and 2.48, Sn mineralization, and high F contents. Five of the domes were extruded in a short time period between 32.7 ± 1.0 Ma and 30.4 ± 0.5 Ma, before the emplacement of the Cantera ignimbrite (29.0 ± 1.5 Ma). Another dome (El Tocho) was emplaced just afterwards, but well before the eruption of the Panalillo ignimbrite (26.8 ± 1.3 Ma). The last dome (Rincon Reyna) was emplaced 21.1 ± 0.3 Ma ago. Remnants of the Panalillo ignimbrite are found on top of the fluorine-rich El Gato and Cerro Silva domes, which represent a smaller and different magmatic pulse than the pulse that formed the larger Cerro Grande and Cerro El Potosí domes in the San Luis Potosí volcanic field. They also differ from garnet-bearing (almandine) domes that crop out in other regions of the volcanic field. Between 29 and 27 Ma, the studied domes were erupted through a cone sheet structure, formed by the forceful emplacement of a magma chamber before faulting and tilting of the volcanic field, which was synchronous with the emplacement of the lower member of the Panalillo Ignimbrite. The upper member of the overlying Panalillo Ignimbrite (26.8 ± 1.3 Ma) was emitted after this tilting.
