Document Type
Thesis
Abstract
The Fish Lake basin, in the High Plateaus of central Utah is located in the structural transition zone between the Basin & Range and Colorado Plateau provinces. Fish Lake (~2700 m) occupies a northeast-southwest trending topographic depression, bounded by the Fish Lake Hightop Plateau and the Mytoge Mountains. Fish Lake drains northeast into the Fremont River. Previous workers interpret the basin to be a structural graben and suggest neotectonic faulting effected a recent drainage reversal at the southwestern end of Fish Lake. We mapped 150 km’ in the southern Fish Lake Plateau to better understand the structural geometry of the basin. The area is underlain by a 600 m-thick sequence of densely-welded ash-flow tuffs including (from bottom to top): 1) phenocryst-rich andesite, 2) highly vesicular to non-vesicular eutaxitic porphyritic andesite, 3) glass-rich phenocryst-poor andesite, and 4) spherulite-rich porphyritic andesite. The sequence is capped by the Osiris Tuff, a densely-welded porphyritic dacite dated by previous workers at 21 Ma. Tuffs experienced a protracted pre-eruptive history evidenced by magma mixing textures as well as post-eruptive deuteric alteration. Fish Lake basin is graben that has been extended by ~6%. Displacement of ~600 m is accomplished by a suite of northeast-southwest striking normal faults and one fault oblique to the dominate set. Faults are steeply dipping with a listric geometry. The modest extension of the Fish Lake basin is inconsistent with low-angle detachment faulting, a common structural feature throughout much of the Basin & Range province. Late Pleistocene moraines cover faults indicating no recent tectonism in the Fish Lake basin. If faulting at Fish Lake occurred at a rate similar to present-day slip on the nearby Wasatch Zone (0.1 mm/yr), Fish Lake could have formed in a minimum of six million years. Faulting in the Fish Lake basin probably initiated ~7-8 Ma ago, contemporaneous with deformation in nearby regions of the High Plateaus. Geomorphic features are inconsistent with a drainage reversal at the southwestern end of Fish Lake. We suggest that Fish Lake was originally an internally drained basin that has been captured by the Fremont River. Paired strath terraces on the Fremont River ~140-150 m above the present river elevation may represent abandonment of the former floodplain due to increased discharge resulting from capture of Fish Lake.
Date Awarded
2003
Department
Geology
Advisor 1
Christopher M. Bailey
Recommended Citation
Webber, Caroline E., "Structural and Fluvial History of the Fish Lake Basin, High Plateaus, Central Utah" (2003). Geology Senior Theses. William & Mary. Paper 123.
https://scholarworks.wm.edu/geologyseniors/123
