Field-Based Observations of La Paz and Las Ventanas Diapirs, La Popa Basin, Northeast Mexico

Frank Graf and Cody Holbrook
Geological Sciences, New Mexico State University, Las Cruces, NM

Cerro La Paz and Cerro Las Ventanas are Lower Cretaceous carbonate outcrops with 200-300m topographic relief that are located at the juncture between two regional structural provinces in northeast Mexico (southern margin of La Popa salt basin and the northern margin of the Sierra Madre Oriental fold belt). Cerro La Paz and Cerro Las Ventanas border active gypsum mines quarrying the Jurassic Minas Viejas Formation. In La Popa basin, Lower Cretaceous carbonate strata were deformed by both regional tectonic shortening during the Hildalgoan orogeny and by local, syndepositional halokinesis of diapiric Jurassic Minas Viejas Formation. In contrast, Lower Cretaceous carbonate strata within the Sierra Madre Oriental are only deformed by Hildalgoan folds detached on Jurassic Minas Viejas evaporites. There have been no documented cases of salt diapirism within the Sierra Madre Oriental. Previous work has placed Cerro La Paz and Cerro Las Ventanas in the Sierra Madre Oriental structural province. New field-based data indicates that the areas lie within the structural province of La Popa basin and show evidence of syn-diapiric deposition and should be placed in La Popa salt basin structural province. Evidence for diapirism includes:(1) beds near the diapir are partitioned into stratigraphic units that are bounded by local angular unconformities, (2) local mass wasting debrite overlying the unconformities due to failure and erosion of diapirically steepened strata (3) stratal onlapping and thinning towards the diapir, (4) metaigneous clasts within surrounding strata derived from diapiric extrusion, (5) presence of radial faulting extending away from the diapir, (6) rotated strata to near-vertical, vertical, and overturned orientations adjacent to the diapir, and (7) extensive fractures and veins associated with radial faulting and/or diapirically rotated strata.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas