SCANNING, PANNING, AND PROCESSING: DELINEATION OF IGNEOUS DIKE ORIENTATIONS IN THE SOUTHERN PATAGONIAN BATHOLITH, CHILE

The Aysén region of southern Chile encompasses remote and little-studied portions of the Northern Patagonian Ice Field and the Southern Patagonian Batholith. The batholith is dominated by Mesozoic subduction-related granitoids that intruded Paleozoic metamorphic basement rocks. Mafic dikes of uncertain age (late Mesozoic? early Cenozoic?) intruded both basement rocks and granitoids. During a 2018-2019 winter break Study Abroad expedition, we had an opportunity to explore aspects of this geology in the Cachet basin, where increased melting of the Colonia glacier and multiple glacial lake outburst floods have exposed bedrock. In this dynamic landscape mass wasting events are common, and knowledge of discontinuity orientations may be a valuable in predicting where such events are more likely. In a pilot study of the area, we combine satellite imagery, aerial scanned imagery, panning photography, and physical compass measurements to characterize the relationship of orientations of mafic dikes to regional fracture systems.

Despite adverse weather conditions and very limited time constraints, we were able to obtain a wealth of data using image-gathering and image-processing techniques. Aerial imagery was obtained through programmed flights using a compact collapsible UAV. The georeferenced imagery was processed with structure-from-motion software to produce a 2D orthophoto which can be imported into ArcMap or Google Earth, as well as a 3D point cloud and textured mesh for visualization of the landscape and cross-cutting features. The aerial imagery was augmented by detailed ground-level overlapping images taken with a smartphone camera, stitched together to create a high-resolution panorama. Finally, strike and dip measurements of individual dikes were obtained with a Brunton compass. The dikes range in thickness from a few centimeters to >3 meters, and dip moderately steeply to nearly vertical. In the study area, a majority of the larger dikes strike parallel to a major set of discontinuities visible in satellite images, oriented approximately 060°, and a less prominent set oriented approximately due north, forming an apparent conjugate system.