USING ELECTRON BACKSCATTER DIFFRACTION TO PERFORM CALCITE TWIN PALEOSTRESS ANALYSIS: METHODOLOGY AND APPLICATION TO THE ARBUCKLE MOUNTAINS

The Ancestral Rocky Mountains (ARM) system consists of a series of major Pennsylvanian-Permian uplifts and related basins in Oklahoma, Colorado, New Mexico, and Utah. A wide variety of tectonic models for this system have been proposed, including compressive stresses associated with the Ouachita-Marathon system, flat-slab subduction from the southwest, a progressive east-to-west closing along the Ouachita margin, or transpression focused along the southwestern margin of Laurentia. These models each suggest predictions about the paleostress field at the time of ARM deformation. Here, we focus on a suite of carbonate samples from the Arbuckle Mountains in Oklahoma, the easternmost margin of the Amarillo-Wichita Uplift. Calcite from the Arbuckle limestones is commonly twinned, making the rocks suitable for paleostress analysis. We describe a methodology to identify and quantify calcite twin orientations using electron backscatter diffraction (EBSD). A series of narrow EBSD transects with a small step size are capable of resolving even thin twin domains. The orientations of the twinned crystals are plotted and inverted to estimate paleostress directions. We will discuss the implications of our results for models of Ancestral Rocky Mountain tectonics.