Reserve Graben, Catron County, NM
— April 14, 2021
New Mexico is a great place to study extensional tectonics, or what happens to Earth’s crust as it is stretched and thinned. The Reserve graben, a small rift basin in western Catron County, is part of a longer fault system, including the Plains of San Agustin, at the southeastern margin of the Colorado Plateau. It also sits within the massive Mogollon-Datil volcanic field, where some of the largest explosive eruptions in North America’s history have occurred. The San Francisco River and its tributaries have cut down through the sedimentary rock that filled in the basin, exposing many of the basin’s internal faults. We can measure the orientation of features such as striations on fault surfaces to tell which direction the faults slipped while they were active. Basalt flows are also interlayered with sedimentary basin fill in many places throughout the graben; through radiometric dating on these basalts, we can determine the timing of rifting and sedimentation. New 40Ar/39Ar dating at the New Mexico Bureau of Geology’s geochronology lab shows that the Reserve graben began to form around 16.4 million years ago, and that rifting had ended here by about 1.9 million years ago. We are working to compare the timing and direction of movement on the Reserve graben’s faults to the broader Rio Grande Rift and Basin and Range provinces for a more complete picture of the region’s recent tectonic history.
—Sam Martin, Geology M.Sc. student, NMT E&ES department