SEARCHING FOR THE ALLOCHTHON/PARAUTOCHTHON BOUNDARY: USING LANDSAT FOR STRATIGRAPHIC AND STRUCTURAL MAPPING, EASTERN BROOKS RANGE, ALASKA

BAILEY, Rebecca D., Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, AK 99775-5780, [email protected] and PRAKASH, A., Geology and Geophysics, University Alaska Fairbanks, P.O. Box 755780, Fairbanks, AK 99775-5780

Arctic Alaska's Brooks Range is composed of seven allochthons stacked on parautochthonous rocks of the North Slope; the boundary between allochthonous and parautochthonous rocks remains imprecisely and incompletely mapped in this rugged and remote region. The purpose of this study is to delineate the continuous stretch of this important boundary between the Endicott Mountains allochthon (EMA) and the North Slope parautochthon (NSP) starting at the Brooks Range mountain front directly east of the Dalton highway and working eastward along the boundary between the northern and northeastern Brooks Range to directly west of the Chandalar River. A secondary objective of this study is to demonstrate the usefulness of Landsat data for lithologic mapping in this remote area of Alaska.

Three Landsat-7 Enhanced Thematic Mapper+ images from August 2000 were mosaiced and analyzed for spectral changes that could represent the allochthon/parautochthon boundary. In this area, the most commonly exposed rocks of both the EMA and the NSP are the Lisburne Group carbonates. This study is based on the assumption that the significant tectonic shortening that must have occurred at the EMA/NSP boundary resulted in juxtaposition of differing facies of the Lisburne Group, and that the resulting subtle changes in composition should cause an observable change in the spectral signature of processed Landsat images.

A distinct, continuous, and mappable north to south change in spectral signature of the Lisburne Group was observed at a regional scale in three images: bands 7-5-4 decorrelation stretch; clay minerals index; and fifth principal component. This change in spectral signature does not correlate with known topographic or structural changes in this area, such as the mountain front, the change from upright to overturned thrust faults, or the change from overturned thrust faults to detachment folds. It does correlate well with the few known locations of the EMA/NSP boundary and is interpreted to reflect a change in lithology that also represents the difference between allochthonous Lisburne Group and parautochthonous Lisburne Group.