GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 286-10
Presentation Time: 4:05 PM

LARAMIDE-AGE FAULTING & SYNKINEMATIC MINERALIZATION IN UNAWEEP CANYON, CO


BOWERS, Timothy C.1, LIVACCARI, Richard1, FEIL, Michael J.1 and TRUMBO, Adam L.2, (1)Dept of Physical and Environmental Sciences, Colorado Mesa University, 1100 North Ave, Grand Junction, CO 81501, (2)Dept of Physical & Environmental Sciences, Colorado Mesa University, 1100 North Ave, Grand Junction, CO 81501

Unaweep Canyon is an exhumed Laramide-age extensional graben system found on the Uncomphagre Plateau of west-central Colorado. The Uncompahgre Plateau is a 150 km long, Laramide-age, NW-SE striking anticlinal uplift. The NE-SW striking Unaweep Canyon cuts orthogonally across the entire width of the Uncompahgre Plateau. Laramide-age deformation along the Uncompahgre Plateau is controlled by a series of WNW-ESE striking, left-lateral strike-slip faults. These controlling faults bend right into compressive orientations resulting in the classic Colorado Plateau-style reverse faults & monoclines as seen in the Colorado National Monument. Conversely, in Unaweep & subparallel Big Dominguez Canyons, the controlling left-lateral strike-slip faults bend left into extensional grabens that display a lazy ‘S’ pattern in map view. In Unaweep Canyon, deeply-cutting left-lateral strike-slip faults & associated normal faults opened gaps in the Earth’s crust that were filled by hydrothermal fluids that formed mineralized breccias. These breccias are matrix-supported, with no grain-size grading, suggesting that they formed as implosion breccia. Outcropping strike-slip faults, up to 150m wide, cut across Unaweep Canyon & are characterized by spectacular vertical ‘walls’ of mineralized & altered implosion breccia. Elevation differences of the ‘Great Unconformity’ across Unaweep Canyon (<50m) suggest the presence of normal faults within the canyon.

Hydrothermal mineral veins within Unaweep Canyon formed in at least two phases synkinematic with Laramide deformation. Phase 1 includes coarsely crystalline calcite-hematite & Mn-bearing quartz (dark purple amethyst) followed by phase 2 fluorite-quartz (clear, milky to pale purple amethyst). Phase 2 alteration minerals occur as both open space fillings along faults & as partial replacements of phase 1 minerals. Phase 1 & 2 minerals are found along faults as well-preserved veins with massive crystals or pulverized into implosion breccias due to synkinematic deformation. Late- to post-kinematic mineralization includes sulfides (galena, pyrite, auriferous chalcopyrite) & supergene Cu-carbonates (azurite, malachite) & Fe-oxides (limonite, goethite) forming along veins that cut the implosion breccia.