AN EBSD-BASED APPROACH TO CALCULATING PALEOSTRESSES USING CALCITE TWINS: AN EXAMPLE FROM THE ARBUCKLE MOUNTAINS, OK

We present paleostress analyses based on the orientation of twinned calcite crystals in limestone samples from the Arbuckle Mountains of Oklahoma to better understand the broader tectonic processes taking place during the formation of the Ancestral Rocky Mountains (ARM). The ARM was an enigmatic series of late Paleozoic block uplifts and adjacent basins in North America. Proposed drivers for the formation of the ARM include compressive stresses via the Ouachita-Marathon system, flat-slab subduction from the southwest, progressive east-west closing on the Ouachita margin, and transpression along the southwestern margin.

Our objective is to use paleostress analysis to provide new constraints that can help distinguish between the myriad of pre-existing ARM models. We developed an electron backscatter diffraction (EBSD) approach to quantify calcite twin orientation. We developed an approach in which we performed large reconnaissance scans at a coarse step size of 8 microns to identify candidate twinned grains. We then created narrow transects using a fine, 0.5-micron step size sufficiently small to resolve narrow twin domains. We used the MTEX toolbox in MatLab to extract the orientation of twin planes and prepare a data file for analysis via TwinCalc (Rez, 2020).