GSA Connects 2021 in Portland, Oregon

Paper No. 96-4
Presentation Time: 9:00 AM-1:00 PM


ZAMANIALAVIJEH, Nina, Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, HEIJ, Gerhard W., School of Geology and Geophysics, The University of Oklahoma, Norman, OK 73019, FERRE, Eric, School of Geosciences, University of Louisiana at Lafayette, 611 McKinley Street, Hamilton Hall, Room 323, Lafayette, LA 70504, MURPHY, Michael, Department of Earth and Atmospheric Sciences, University of Houston, Rm.312, Science & Research Bldg.1, University of Houston-Main Campus, Houston, TX 77204 and BAGLEY, Brian, Department of Earth and Environmental Sciences - X-ray CT Lab, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455

Cataclastic deformation has long been considered to produce unfoliated rocks, i.e., materials devoid of a tectonic fabric. However, the 3 m-thick carbonate ultracataclasite formed by the Heart Mountain Slide, in Wyoming, has a consistent subhorizontal magnetic fabric across its thickness. This ultracataclasite layer developed in the Eocene during one of the largest known continental landslide on Earth (~3,500 km2). A mid-Eocene eruption in the Absaroka volcanic province most likely triggered rupture and subsequent detachment of a ~1 km-thick Paleozoic sedimentary cover. The rapid sliding was enhanced by basal fluidization due by thermo-mechanical decomposition of carbonate rocks and coeval massive production of gaseous CO2. The ultracataclasite layer has a spatially-consistent, strong magnetic fabric, whereas host carbonates preserve their weak sedimentary fabric. The anisotropy of magnetic susceptibility (AMS) arises from synkinematically deformed, pseudo-single domain magnetite grains formed by thermal decomposition of primary iron sulfides. The ultracataclasite does not generally show a visible macroscopic fabric. Yet, the strong AMS in these deformed rocks records the transport direction of the landslide. These results indicate that friction-driven decomposition of carbonates may generate consistent synkinematic fabrics and therefore that some cataclasites/ultracataclasites may indeed bear a foliation.