40AR/39AR THERMOCHRONOLOGY, THE TECTONO-THERMAL EVOLUTION OF THE SOUTHERN BROOKS RANGE HINTERLAND, AND TIES WITH EXTERNAL PARTS OF THE OROGEN

VOGL, James J., Department of Geology, Univ of Florida, Gainesville, FL 32611, [email protected], CALVERT, Andrew, U.S. Geol Survey, 345 Middlefield Road, MS-937, Menlo Park, CA 94025, and GANS, Phillip, Dept. of Geological Sciences, Univ of California, Santa Barbara, CA 93106

Gil Mull's detailed studies in the Brooks Range foreland and his reconnaissance work in the hinterland have greatly advanced our understanding of the Brooks Range and have addressed the link between these two regions. Unfortunately, a comprehensive view of foreland-hinterland connections was limited by the radiometric data available during his pioneering work. Over the last 15 years, however, the quality of the 40Ar/39Ar data set has improved dramatically allowing a more detailed view of the tectono-thermal events in the Brooks Range hinterland. In this contribution we summarize and interpret the 40Ar/39Ar data in terms of the tectono-thermal evolution of the southern Brooks Range (hinterland). We also discuss the events of this region in the context of the Brooks Range orogenic system, including the more external parts of the orogen such as the fold-thrust belt and flanking sedimentary basins. Some of the salient tectono-thermal events revealed by the 40Ar/39Ar data include: (1) A poorly understood tectonic and/or metamorphic event between ~130 and 115 Ma that likely produced little or no cooling on the regional scale. (2) An Aptian-Albian metamorphic event that produced amphibolite-facies metamorphism at the deepest levels presently exposed in the Brooks Range. (3) Rapid cooling from >500°C through 300°C between 103 Ma and ~95 Ma that was likely related to extension and erosion. (4) A period of little or no cooling that spanned most of the Late Cretaceous (5) A short-lived rapid cooling event at ~60 Ma. Some of these events fit well with interpretations of more external parts of the orogenic system (i.e, fold-thrust belts and flanking sedimentary basins) to provide a simple picture of Brooks Range evolution. Ties between the hinterland and adjacent areas for other tectono-thermal events, however, remain ambiguous and need to be addressed to create a more comprehensive view of Brooks Range evolution.