TIMING OF BRITTLE DEFORMATION IN THE CAÑON CITY EMBAYMENT, CO: LASER ABLATION U-PB DATING OF CARBONATE FRACTURES

The Rocky Mountain Front Range is one of the most striking geological features of the Midcontinent. The geometry of uplift and relative timing by tilting of strata is well documented. However, there is less information on the exact and absolute timing of associated brittle deformation and its regional distribution. The emerging use of laser ablation U-Pb dating of carbonate minerals has greatly increased the potential for dating these deformation features. Dating carbonate material from the Colorado Front Range could aid in understanding episodes of tectonic activity in the region. Calcite precipitates along fault planes and crack-seal type veins can potentially be dated by U-Pb geochronology via laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS).

This study tests the feasibility of the U-Pb carbonate method to date brittle deformation features in the Colorado Front Range, specifically in the Canon City embayment. Samples were taken from fault surfaces in the Temple Canyon area (Ordovician Harding Fm.), the Marsh Dinosaur Quarry area (Jurassic Morrison Fm.) and in the Harding Fm. along Shelf Road. These samples have been processed into polished sections and will be analyzed by LA-ICP-MS for U-Pb dating after detailed petrographic microscope and cathodoluminescence documentation. If datable carbonate fracture fills can be identified, future work will expand the use of this technique to construct a detailed deformation history for this part of the southern region Rocky Mountains.