A spectacular exposure of the Tjeras fault, with evidence for Quaternary motion
John C. Abbott and Laurel B. Goodwin
The regionally extensive Tijeras–Cañoncito fault system comprises several northeast-striking, subvertical faults, including the Tijeras fault. Slickensides on minor fault surfaces within the fault zone exhibit a wide range in orientation and record a complex history of strike-slip, and dip-slip motion on the fault system. The oldest documented movement is Laramide ( Late Cretaceous–early Tertiary) in age, though the fault system may he older. A recently discovered steamcut provides the best exposure of the Tijeras fault. It reveals a strongly but heterogeneously deformed zone more than 160 m wide, within which Precambrian, Pennsylvanian, Permian and Oligocene (?) rocks are faulted. Quaternary(?) surficial deposits are locally faulted. The streamcut includes a population of minor faults that are interpreted as right-lateral synthetic Riedel shears, which is consistent with Laramide- age deformation. Neogene deformation is indicated by extreme brecciation of an Oligocene(?) porphyritic intrusive rock and by fault slid slickensides that suggest left-lateral strike-slip motion which is consistent with the development of the Rio Grande rift in the Neogene. Quaternary (?) activity in recorded the streamcut fault that juxtaposes Quaternary(?) surficial deposits, against an Oligocene (?) porphyritic intrusive rock: this fault does not offset an overlying Holocene(?) imbricated gravel deposit. The length of the Tijeras–Cañoncito fault system, the width of the fault tone, and the intense deformation within the Tijeras fault zone, all suggest substantial post -Pennsylvanian displacement on the fault system. Slickenside striae indicate that movement within the fault system was dominantly strike-slip.
- Abbott, John C.; Goodwin, Laurel B., 1995, A spectacular exposure of the Tjeras fault, with evidence for Quaternary motion, in: Geology of the Santa Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 117-125.