Reconstructing northern Alaska : crustal-scale evolution of the central Brooks Range

Graduation date: 2001Kinematic tectonic models constrained by Airy isostatic equilibrium demonstrate the crustal-scale evolution of the Brooks Range during ocean basin closure, arc-continent collision, and exhumation of the orogen. The Bouguer gravity anomaly low that develops across the orogen is related by wavelength to the amount of shortening during collision, and by amplitude to the combined effects of erosional unroofing and isostatic rebound. Three collision models test a range of pre-collision crustal geometries and investigate a variety of evolution histories. The preferred solution comprises the best aspect of all three models and involves obduction of an oceanic arc onto a passive continental margin with sedimentary cover 250 km wide. Two distinct periods of convergence and unroofing are identified, separated by strike-slip faulting that influences the hinterland. This model involves -200 km of shortening by crustal overlap and up to 17.5 km of erosional unroofing and isostatic rebound; it results in a symmetric, 40 mGal Bouguer gravity low that is consistent with the observed anomaly across the Brooks Range. The Brooks Range can thus be described as a relatively hard collision that is deeply exhumed compared to other orogens. East of the modeled profile a reversal in asymmetry of the Bouguer gravity low across the Northeastern Brooks Range can be attributed to continuing Tertiary contraction. In the central Brooks Range, thickskinned thrusting that formed the Doonerak antiform characterized this period of convergence