Resumen

RODRIGUEZ-RIOS, Rodolfo; TRISTAN-GONZALEZ, Margarito  y  AGUILLON-ROBLES, Alfredo. Structure and geochemistry of a group of dacitic domes in the northwestern San Luis Potosí Volcanic Field, Mexico. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.1, pp.109-122. ISSN 1405-3322.

The San Luis Potosi volcanic field (CVSLP), located in the southeastern part of the Sierra Madre Occidental (SMOc), includes a felsic volcanic dome complex in its northwestern portion. Standing out in this group is the Pinos volcanic complex (CVP), which is located in the eastern portion of the state of Zacatecas, about 60 km northwest of the city of San Luis Potosi, and north of the town of Pinos, Zacatecas. The CVP is formed by three domes; the Pinos dome (DDP) is the largest one and includes the Barbechos trachyte , which forms a circular volcanic structure with an average radius of 6 km, an approximate surface of 100 km², and an altitude of 2950 masl. The CVP history began with a pyroclastic episode that preceded the emission of the Barbechos trachyte (Tqb), which is formed by two flow units and constitutes the main volume of the complex. The Santana dacite (Tds), which covers the Barbechos trachyte, was followed by a thin pyroclastic flow. The Santana dacite was extruded in the northern part of the CVP in the form of a dome (Santana Dome, DDS). Lastly, and cutting the previous flows, the Carbonera rhyolite was emplaced as a small dome (Carbonera Dome, DC). The Barbechos volcanic unit, derived from trachydacitic magmatism, has a slightly alkaline and peraluminous character whereas the Santana dacite and Carbonera rhyolite display calc-alkaline affinity with a slight Eu negative anomaly; both units have characteristics that are similar to the topaz rhyolite of sierra San Miguelito, which has been proposed as a result of the fusion of the San Luis Potosi Precambrian crust. In the structural context, the CVP domes are mainly affected by a NE-SW strike fault system, which coincides with the alignment pattern of the trachydacitic/rhyolitic emission centers in the area. This NE-SW normal fault pattern differs from the NW-SE pattern observed in the felsic rock outcrops of sierra San Miguelito, located immediately southeast of the CVP, where the rocks are similar in age. According to the structural analysis performed, two directions of extension are observed in the northern and northwestern parts of the CVSLP: one is NE-SW in sierra San Miguelito, and the other is NW-SE in the CVP area, which are orthogonal between them. The alignment of the CVP felsic domes and the attitude of their lava flows suggest that they erupted along a NE-SW oriented vent system. The CVP lavas formed polygenetic domes in the early Oligocene with several associated effusive and pyroclastic phases, which is different from the topaz rhyolites of the sierra de San Miguelito domes, which are monogenetic with predominantly effusive activity.

Palabras llave : Domes; San Luis Potosí volcanic field; Pinos volcanic complex; structure and geochemistry of Pinos domes.

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