Abstract

BOTERO-SANTA, Paola A.; XU, Shunshan; NIETO-SAMANIEGO, Ángel F.  and  ALANIZ-ALVAREZ, Susana A.. Effect of cooling fractures in the formation of normal faults: The example of Santa María del Río, San Luis Potosí, Mexico. Bol. Soc. Geol. Mex [online]. 2020, vol.72, n.1, e011019.  Epub Dec 22, 2020. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2020v72n1a011019.

The reactivation of pre-existing fractures is an important issue in the study of nucleation, union, growth, and evolution of fault systems. Pre-existing zones of weakness, such as cooling fractures, can determine the configuration of important fault systems. In particular, it is important to study the role of cooling fractures in the reactivation of faults for three reasons: first, there are many cooling fractures in volcanic rocks; second, the vertical fractures have a low tendency to slip; and third, there are many strikes and striae in several directions, making it difficult to interpret their mechanical origin. This paper presents an example of a fault system that overprinted on a volcanic field in Santa María del Río, San Luis Potosí, Mexico. We studied the age, geometry, activity, and kinematics of the SLTFS (San Luis-Tepehuanes Fault System) located in Santa Maria del Rio, in central Mexico, as well as the fault mechanisms and interaction with pre-existing structures, like orthogonal and polygonal cooling joints. Three sites were chosen for the measurement of structural data. The results indicate that the major faults have a NW-SE preferential trend and the minor faults show strikes in all azimuths. This faulting caused the tilt of strata. The older units have higher dips (20° to 25°) than the younger ones (~15°). Curved, superimposed slickenlines and striae parallel to the intersection of two fault planes are probably the result of the interaction with pre-existing fractures during reactivation. Based on these results as well as calculations using the ReActiva 2.4 software (Alaniz-Álvarez et al., 2000; Tolson et al., 2001), we propose that faulting began at depth, and propagated through the cooling joints while advancing to the surface in the current SLTFS configuration.

Keywords : Cooling joint; faulting; normal fault; fracture interaction; San Luis Potosí.

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