IS LARAMIDE DEFORMATION STILL ACTIVE NEAR THE RIO GRANDE RIFT?

The Nacimiento-Gallina fault system is understood to be a primarily Laramide, down-to-the-west structure with some modern microseismicity. Laramide deformation resulted in uplift of the Nacimiento Mountains, with relative subsidence on the west that accommodated the San Juan basin, which is filled with Cretaceous and Eocene sedimentary rocks. Differences in fold axes on either side of the Nacimiento-Gallina fault system indicates that the majority of slip was contemporaneous with deposition of these Cretaceous and Eocene deposits. Following the compressional Laramide Orogeny, the region switched to extension, as evidenced by the Rio Grande Rift. Here we show InSAR results of ground displacement from the vicinity of the Nacimiento and Gallina fault junction, spanning ~M3 earthquakes. Our analysis shows that, where observable, uplift-subsidence pairs show down-to-the-west displacement. This pattern of displacement is consistent with the Laramide deformation, but not Rio Grande rifting at this location. This makes it challenging to understand the current tectonic driver for modern deformation along the Nacimiento-Gallina fault system.