New Mexico Geological Society Annual Spring Meeting — Abstracts

Understanding the interplay between magmatic and associated tectonic events and lithospheric response is critically important in our understanding of landscape evolution. This is particularly true in regions with multiple imprints of contrasting tectonic forces. For example, the timing of the rise of the Guadalupe Mountains located in the southeastern Rio Grande and southern Laramide tectonic provinces is likely multi-modal. One model suggests one kilometer of the Guadalupe block uplift was relatively recent (over the last 14 – 12 My) during the Rio Grande rifting (Polyak et al., 1998). Another model suggests that the area arose primarily during the Laramide Orogeny (DuChene and Cunningham, 2006). A third model suggests there were three instances of mountain building (the two previously mentioned and an earlier one when the area first emerged from the Permian sea), and a combination of the three led to the present two kilometer-plus height of the Guadalupe Mountains (Palmer and Palmer, 2000). In this study, I report the ages of 15 cave spar samples (large euhedral calcite crystals lining geode-like caves) collected from various locations in the Guadalupe Mountains. The ages are based on U-Pb geochronology and show multi-modal ranges: 28 – 30 Ma, 33 – 35 Ma and 50 – 55 Ma. There are several outliers as well. The first two modes correlate well with known magmatic pulses in the region and are likely related to the beginning of the basin and range province.  The third mode has not been temporally linked to any known magmatic activity; however it dates to the end of the Laramide. Further work will be required to unambiguously link the cave spar with these geologic episodes and this continuing work will make a significant contribution to the knowledge of the landscape evolution of the Guadalupe Mountains region. More importantly, it will test the feasibility of using cave spar formed deep in the phreatic zone to constrain the timing of uplift and subsidence histories of landscape by establishing links between tectonic events and landscape evolution.