(U-Th)/He chronologic constraints on secondary Fe-oxide mineralization in southwestern New Mexico
Class
Article
Department
Geology
Faculty Mentor
Alexis Ault
Presentation Type
Poster Presentation
Abstract
Temporal constraints on fluid flow, mineralization, and brittle deformation are important for understanding a variety of upper-crustal processes. However, limited radioisotopic methods exist to directly date these processes. Hematite commonly co-precipitates with economically valuable mineral phases in hydrothermal ore deposits, such as copper, uranium, gold, and other rare-earth elements, and occurs in fracture systems and faults. Hematite is amenable to (U-Th)/He dating, and we will apply this method to two case studies in the Rio Grande rift, New Mexico. First, a suite of millimeter-thick hematite- and turgite-coated fracture surfaces cross-cut an ~54-60 Ma porphyritic rhyolite near Lordsburg in southwest New Mexico. Preliminary hematite (U-Th)/He (HeHe) dates for two hematite-coated fracture surfaces yield highly reproducible dates at ~1.4 Ma and ~1.3 Ma. These dates are appreciably younger than the ~10-20 Ma regional cooling recorded by conventional low-temperature thermochronology data. This suggests that the HeHe results may record the timing of hematite and turgite mineralization; however, additional site-specific low-temperature thermochronology data are required to confirm this interpretation. A second case study from the Sandia Mountains, central New Mexico, involves polished, striated hematite-coated fault surfaces cross-cutting the ~1.4 Ga Sandia granite. Preliminary apatite (U-Th)/He dates, which record the cooling of rocks from 90-30 °C and exhumation of rocks through the upper 1-3 km of the Earth's crust, are consistent with published results and suggest that the Sandia Mountains were exhumed ~13.6 Ma and are associated with Rio Grande rift extension and erosion. These data will be compared with on-going HeHe analyses to evaluate the significance of the HeHe results as recording the timing of brittle deformation or regional cooling. These case studies will shed light on those datasets and time-temperature conditions required to interpret HeHe results as directly constraining mineral formation or brittle deformation.
Start Date
4-9-2015 3:00 PM
(U-Th)/He chronologic constraints on secondary Fe-oxide mineralization in southwestern New Mexico
Temporal constraints on fluid flow, mineralization, and brittle deformation are important for understanding a variety of upper-crustal processes. However, limited radioisotopic methods exist to directly date these processes. Hematite commonly co-precipitates with economically valuable mineral phases in hydrothermal ore deposits, such as copper, uranium, gold, and other rare-earth elements, and occurs in fracture systems and faults. Hematite is amenable to (U-Th)/He dating, and we will apply this method to two case studies in the Rio Grande rift, New Mexico. First, a suite of millimeter-thick hematite- and turgite-coated fracture surfaces cross-cut an ~54-60 Ma porphyritic rhyolite near Lordsburg in southwest New Mexico. Preliminary hematite (U-Th)/He (HeHe) dates for two hematite-coated fracture surfaces yield highly reproducible dates at ~1.4 Ma and ~1.3 Ma. These dates are appreciably younger than the ~10-20 Ma regional cooling recorded by conventional low-temperature thermochronology data. This suggests that the HeHe results may record the timing of hematite and turgite mineralization; however, additional site-specific low-temperature thermochronology data are required to confirm this interpretation. A second case study from the Sandia Mountains, central New Mexico, involves polished, striated hematite-coated fault surfaces cross-cutting the ~1.4 Ga Sandia granite. Preliminary apatite (U-Th)/He dates, which record the cooling of rocks from 90-30 °C and exhumation of rocks through the upper 1-3 km of the Earth's crust, are consistent with published results and suggest that the Sandia Mountains were exhumed ~13.6 Ma and are associated with Rio Grande rift extension and erosion. These data will be compared with on-going HeHe analyses to evaluate the significance of the HeHe results as recording the timing of brittle deformation or regional cooling. These case studies will shed light on those datasets and time-temperature conditions required to interpret HeHe results as directly constraining mineral formation or brittle deformation.