Laramide basement-cored uplift and basins in south-central New Mexico
William R. Seager, Greg H. Mack, Michael S. Raimonde, and Ronald G. Ryan
The west–northwest-trending, basement-cored Rio Grande uplift and complementary Love Ranch and Potrillo Basins were the result of late Paleocene and Eocene compressional deformation in south-central New Mexico. The Rio Grande uplift consists of one or more asymmetrical blocks that dip southwest and face northeast. Along the northeastern margin, Precambrian crystalline rocks were raised by movement on southwestdipping reverse and thrust faults exposed in the Bear Peak area of the southern San Andres Mountains, at San Diego Mountain, and in the southern Caballo Mountains. Northeast-vergent folds and subsidiary thrust faults in Paleozoic rocks are associated with the basement faults. The Rio Grande uplift is bordered to the northeast by the Love Ranch Basin, which contains up to 600 m of siliciclastic rocks of the Love Ranch Formation. Basin-margin facies are primarily alluvial-fan conglomerate, locally syntectonically deformed, derived in large part from the Precambrian granitic core of the Rio Grande uplift. Basin-center facies consist of poorly exposed sandstone and shale.
The southwestern flank of the uplift, which is best exposed in the Robledo Mountains, consists of southwestdipping Paleozoic carbonate rocks that locally are repeated by west-trending normal faults. About 30 m of fluvial conglomerate of the Love Ranch Formation were deposited in canyons that dissected the southwestern flank of the uplift. Imbrication paleocurrent data indicate that the canyons flowed southward, and the absence of Precambrian clasts suggests that the canyons were separated from the crystalline core of the uplift by a drainage divide, probably normal-fault escarpments. The southwestern flank of the Rio Grande uplift plunges into the Potrillo Basin that contains 2.1 km of sandstone, shale, and minor conglomerate that were penetrated by the Grimm and others oil-test well. The Potrillo Basin is bounded to the south by Laramide folds and faults in the East Potrillo Mountains.
- Seager, William R.; Mack, Greg H.; Raimonde, Michael S.; Ryan, Ronald G., 1986, Laramide basement-cored uplift and basins in south-central New Mexico, in: Truth or Consequences region, Clemons, R. E.; King, W. E.; Mack, G. H., New Mexico Geological Society, Guidebook, 37th Field Conference, pp. 123-130.