Evolución volcánica del maar Joya de Los Contreras, San Luis Potosí México, a partir de estratigrafía y análisis de facies

Abstract

The Joya de Los Contreras is one of four phreatomagmatic structures in the Santo Domingo Volcanic Field, a Pleistocene intraplate monogenetic field related to extensional faulting and cortical thinning, located north of San Luis Potosí state (Mexico). Previous publications include mainly geochemical and petrological studies on its lavas and abundant lower-crust xenoliths but lack a description of the volcanic evolution in detail. The Joya de Los Contreras is an elliptical crater excavated in upper Cretaceous limestone terrain (El Abra Formation), nearly 1, 160 m in diameter and 210 m deep. It exposes mafic lavas at the base (basanites), a well-preserved tuff ring with good exposures, and also mafic lavas at the top of the sequence. To better know the volcanic processes that originated it, we performed stratigraphic logs, facies analysis, petrography, granulometry, componentry, and geochemistry. Resulting in the following sequence: 1) Pre-maar units, mafic and basanite lavas at the base; 2) Maar forming units, tuffs forming the crater ring; and 3) Post-maar units, mafic lavas at the top of the sequence. One of these lavas was dated at 447 + 11 ka (40Ar/39Ar). Although there is no direct evidence of the existence of a diatreme, we infer the presence of a diatreme based on some geomorphological diagnostic criteria, like the high volume of limestone lithics in the tuff ring (excavation and re-filled - recycling), the aspect ratio of the crater and the crater fill.