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Boletín de la Sociedad Geológica Mexicana Volumen 65, núm. 1, 2013, p. 169-188 http://dx.doi.org/10.18268/BSGM2013v65n1a13 |
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Active sinking at the bottom of the Rincón de Parangueo Maar (Guanajuato, México) and its probable relation with subsidence faults at Salamanca and Celaya
José Jorge Aranda-Gómez1,*, Gilles Levresse1, Jesús Pacheco Martínez2, José Alfredo Ramos-Leal3, Gerardo Carrasco-Núñez1, Elizabeth Chacón-Baca4, Gildardo González-Naranjo1, Gabriel Chávez-Cabello4, Marina Vega-González1, Gabriel Origel5, Cristina Noyola-Medrano3
1 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro. México.
2 Centro del Diseño y la Construcción, Universidad Autónoma de Aguascalientes, Av. Universidad 940, Aguascalientes, Ags., México.
3 División de Geociencias Aplicadas, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, SLP, México.
4 Facultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León, Carretera a Cerro Prieto Km. 8, Linares, Nuevo León, México.
5 AGROASEMEX S.A.
* This email address is being protected from spambots. You need JavaScript enabled to view it.
Abstract
Rincon de Parangueo is a Quaternary maar that had a perennial lake until the 1980s. The lake was gradually desiccated as a consequence of drawdown in the Salamanca-Valle de Santiago regional aquifer and now functions as a playa-lake. In contrast with the features observed in other crater-lakes in the region (La Alberca, Cíntora, and San Nicolás), which also dried up at the same time, the bottom of the Rincón crater displays clear evidence of active deformation associated with mass movement of lake sediments towards the depocenter inside the crater. The most conspicuous topographic feature is a 10 – 12 m high scarp parallel to the former lake coast. The scarp is produced by an annular shaped normal fault system, down towards the depocenter. Evidence of active mass movement is observed along the topographic scarp. Rotational slides associated with rollover anticlines and local grabens produced by antithetic faults are common on the eastern and northern parts of the scarp. Planar slides with open folds at their base occur at western part of the lake basin.
Evaporites (trona, thermonatrite, eitelite, halite, and silvite) are abundant in the playa-lake sediments. Their presence makes us believe that a mass removal process is acting as a consequence of salt dissolution and infiltration of the brine towards the aquifer. This process, probably in conjunction with lake sediment compaction and/or diatreme subsidence, may explain the significantly higher fault displacement rate observed inside the crater ( ≈ 50 cm/year ) in comparison with active faults elsewhere in the Salamanca-Valle de Santiago aquifer ( ≈ 6 cm/year ).
Keywords: drawdown, maar, evaporite, stromatolite, landslide.
