WILLIAMS, JONATHAN D.¹, ROBERT J. LILLIE¹, CATHERINE L. HANKS², and WESLEY K. WALLACE^2
1Oregon State University, Corvallis, OR
²University of Alaska, Fairbanks, AK

Abstract: Reconstructing Northern Alaska: Constraints on Crustal Scale Shortening and Subsequent Isostatic Rebound Based on Gravity Modeling

The Brooks Range is a Mesozoic to Cenozoic mountain belt of collisional origin that changes character and width along its 1000 km length. The Bouguer gravity anomaly of the fold-and-thrust belt and its adjacent foreland basin has been preserved during opening of the Arctic Ocean to the north, thus providing a record of the anatomy of the orogen. The Bouguer gravity anomaly increases in width by 70 km and in amplitude by 30 mGal eastward along the strike of the orogen, suggesting that crustal shortening increases eastward.

Geological and geophysical data available along the Dalton Highway corridor make this a suitable transect for examining the crustal-scale evolution of the central part of the orogen. A kinematic model of ocean basin closure and arc-continent collision incorporates gravity anomalies and topography into a system of crustal shortening, erosional unroofing, and isostatic rebound. A crustal root that extends 14 km below the average Moho depth for the region supports the average 1.3 km topography of the Brooks Range. Based on gravity models of other collisional mountain belts, this crustal configuration is consistent with 150 to 200 km of crustal shortening followed by approximately 10 to 15 km of erosion and isostatic rebound. The Brooks Range thus attained a state of collision more advanced than that of the Ouachita and Carpathian mountains, approaching amounts calculated for the Alps.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas