Multistage, multidirectional Tertiary shortening and compression in north-central New Mexico

The nature of Laramide deformation in the southern Rocky Mountains remains highly debated, Advocates of north-south strike-slip faulting favor transpr ession and northward displacement of the Colorado Plateau, whereas advocate s of east-west shortening by thrust faulting contest evidence for large rig ht-lateral displacements. Minor faults (n = 2552) were measured to determine the Laramide to Holocene structural evolution of north-central New Mexico. Multimodal slickenline a nd ideal sigma (1) orientations, as well as consistent crosscutting relatio nships, indicate multiphase, multidirectional faulting, The oldest set of t hrust and strike-slip faults indicates east-northeast- to east-trending sho rtening and compression. The faults cut rocks as young as the upper Paleoce ne-lo Ner Eocene Diamond Tail Formation. Strike slip faults from a second p hase of northeast- to-north-northeast-trending shortening and compression c ut the Eocene Galisteo Formation but do not cut the 27 Ma Galisteo dike. El sewhere, later north-striking strike-slip faults cut 24 Ma igneous units, i ndicating north-northeast- to north-trending shortening and compression of mid-Tertiary age. Subsequent north-striking normal faults related to Rio Gr ande rifting commonly reactivate the mid-Tertiary strike-slip fault planes. These results show the validity of both strike-slip and thrust hypotheses i n northcentral New Mexico, although neither is adequate in exclusion of the other, Early Laramide east-west thrusting probably formed the north-trendi ng Laramide arches of the region. Later counterclockwise rotation of region al shortening and compression directions may have caused transpression, ope ning some late Laramide axial basins and causing limited northward displace ment of the Colorado Plateau, Subsequent mid-Tertiary strike-slip deformati on may be a missing link between Paleogene Laramide shortening and Neogene Rio Grande rifting.