Timing of Brittle Deformation in the Cañon City Embayment, CO: Laser Ablation U-Pb Dating of Carbonate Fractures

Abstract

Currently, little is known about the exact timings of brittle deformation present in the Rocky Mountain Front Range. U-Pb carbonate dating via laser ablation is an emerging field that greatly broadens the potential to date deformation features, especially fault-hosted carbonate deposits. We have tested the feasibility of dating carbonate veins on samples from three different locations in the Cañon City embayment of the Rocky Mountain Front Range.

The results indicate that it is possible to date the carbonate veins crosscutting the Jurassic Morrison Fm. with low uncertainty, 110.4 ± 1.4 Ma, using this approach, which puts this in the timeframe of continuing sedimentation in the basin, prior to uplift of the Rocky Mountains. Fault-hosted carbonate veins in the Ordovician Harding Fm. yield scattered data interpreted as reflecting repeated precipitation of carbonate with the oldest event at ~100 Ma and the youngest between ~12 Ma and ~6 Ma. Ages range from early Cretaceous to Neogene and likely reflect the results of multiple fluid flow events associated with uplift in the area. Fluid events probably coincide with the different stages of uplift, which created the total current elevation (~2-3km) of the Colorado Plateau and Rocky Mountains. Major regional events include the flat slab subduction during the Laramide Orogeny and lithospheric delamination. However, the evidence of deformation occurring prior to the Laramide Orogeny poses new questions about the region. U-Pb carbonate dating using laser ablation - inductively coupled mass spectrometry (LA-ICP-MS) is highly applicable to the Front Range and future work will use this method to create a detailed deformation history of the area.