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Phanerozoic sedimentary and volcanic rocks exposed in the Joyita Hills area (Socorro County, New Mexico) record structures that developed in response to three deformational episodes: ancestral Rocky Mountain, Laramide, and Rio Grande rift. Additional exposures of Proterozoic gneiss in the core of the Joyita Hills reveal three preferred orientations of high-angle to vertical, gneissic to mylonitic foliations. These strike north, northwest, and east-northeast. Proterozoic amphibolite dikes parallel the east-northeast foliations. Comparison of Phanerozoic fault and dike orientations with attitudes of Proterozoic structures indicates that reactivation of basement flaws was a factor common to each Phanerozoic orogenic event.

Reactivation of Proterozoic foliations during ancestral Rocky Mountain tectonism resulted in basins and uplifts of north and northwest trend. Normal, left-oblique slip on north-striking faults and normal slip on northwest-striking faults, when combined with the orientation and spatial distribution of basins and uplifts, indicates that late Paleozoic deformation in central New Mexico was the result of north-trending, divergent, sinistral wrench faulting.

Laramide tectonism reactivated Proterozoic structures in a strike-slip sense. North-striking (synthetic) and east-northeast-striking (antithetic) faults define a north-trending, dextral wrench fault system. Other dextral wrench faults strike northeast, and parallel the Montosa and Del Curto fault zones. Thrust faulting and associated folds were a lesser component of Laramide deformation, and were apparently related to Laramide wrench fault systems.

Extensional reactivation of Proterozoic structures influenced the development of basins and uplifts of the Rio Grande rift. Northwest-striking and east-northeast-striking normal fault and dike systems paralleled Proterozoic foliations and amphibolite dikes. North-striking foliations and ancestral Rocky Mountain faults observed along the East Joyita fault influenced the development of this major, down-to-the-east normal fault (approximately 3 km stratigraphic throw). Moreover, north-striking foliations and ancestral Rocky Mountain structures (the north-trending Lucero basin and adjacent uplift) influenced the location and orientation of the Albuquerque Basin segment of the Rio Grande rift.

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