APPLICATION OF LIDAR TO RESOLVING REGIONAL TECTONIC AND GLACIAL FABRICS IN GLACIATED TERRANE: AN EXAMPLE FROM AN ARCHEAN GRANITE-GREENSTONE BELT IN NE MINNESOTA

In this study, we examine an Archean granite-greenstone terrane in NE Minnesota to illustrate the application of high-resolution LiDAR altimetry to mapping regional tectonic fabrics in glaciated, forested areas. More specifically, we describe how to distinguish between tectonic and glacial fabrics and the effect of glaciation on the overall topographic expression of the tectonic fabric. A 1-m posted LiDAR derived bare-earth DEM (digital elevation model) and shaded relief images constructed from the bare-earth DEM comprise the raw data for this study. Evaluation of the bare-earth DEM and shaded relief images revealed that shaded relied images provide the most potential for lineament mapping. In order to maximize the chance of mapping lineaments at all orientations, we constructed shaded relief images with a sun elevation of 45˚ and varying sun azimuth at 45˚ intervals. Using ESRI ArcScene, we draped shaded relief images over the bare-earth DEM to create a 3D perspective view of the field area and to visualize the topographic surface. Mapping revealed two suites of lineaments. Suite A consists of relatively short (1-2 km), discrete lineaments with a unimodal orientation distribution and a mean trend of 045. We recognize multiple lineated deposits of sediment across the study area. Sediment deposits contain suite A lineaments only. Suite B consists of lineaments ranging in length from 1-30 km. Suite B lineaments are more continuous than suite A and have a quasi-bimodal orientation distribution. Suite B lineaments have a mean trend of 065 across the study area with local areas trending 090. In areas where suite A parallels suite B only one pervasive lineament set is visible. Where suite A and suite B are at high angles to one another, suite A lineaments are shorter and pervasive while suite B lineaments longer and spaced. We interpret suite A as a geomorphological fabric related to glaciation and suite B as the regional tectonic fabric. Field measurements of foliation trajectory are largely consistent with suite B lineaments across the study area. Although not all suite B lineaments correlate to mapped structures, our analysis demonstrates that high-resolution LiDAR altimetry may be used to map regional tectonic fabrics in glaciated terrane.