Rocky Mountain Section - 72nd Annual Meeting - 2020

Paper No. 19-1
Presentation Time: 1:30 PM


VOORHEES, Jake, Geology, Brigham Young University, University Hill, Provo, UT 84602 and HARRIS, Ron, Geological Sciences, Brigham Young University, S-389 ESC, Provo, UT 84602

Asymmetric, isoclinal folds within the metamorphic rocks were measured and found to have axes with a consistent orientation throughout the entire metamorphic complex. This folding has a recursive nature and occurs on wavelengths from thin section scale to outcrop scale and likely beyond. The vergence of the folds gives evidence for top-to-the-south shear at ~191° S, with c-surfaces parallel to the shear zone boundaries dipping ~36° S. This shear zone is interpreted as being associated with island arcs of the Yavapai Province accreting to the margin of the North American Craton.

Resting on and adjacent to the metamorphic rocks are allochthonous Paleozoic limestone blocks and attenuated strata debated to be either the result of landsliding or pieces of hanging wall on a low-angle fault. We document previously unnoticed hanging wall slivers of a low-angle normal fault with underlying cataclastic damage zones tens of meters thick, and an anastomosing zone of greenschist facies alteration hundreds of meters thick. Springs follow the trace of this basin bounding fault and meter thick joints filled with calcite and an orientation consistent with the extension penetrate deep into the metamorphic rocks. Polished, hematized fault surfaces were found dipping ~18° to the SW with dip-parallel slickenlines. Mississippian Redwall Limestone blocks previously interpreted as landslides are mapped as overriding a Tertiary basin fill conglomerate, but the contact between the conglomerate and the Limestone is depositional in nature, with no deformation along the supposed slip surface. This suggests that the conglomerate is an erosional facies of the Redwall Limestone which has been documented in several locations within the Grand Canyon. Additionally, previously unrecognized submarine landsliding on the continental shelf is noted, which is responsible for attenuation wrongly attributed to low-angle faulting or surficial gravity sliding. This submarine sliding formed soft-sediment recumbent folds hundreds of meters across within formations ranging from Mississippian to Permian in age.