Tilted Fault Blocks and Subthrust Basins? A Morphotectonic Investigation in the Central Foothills and Brooks Range, Alaska

By

R.R. Casavant and E. Gross (University of Arizona)

A new geotectonic model of the basement architecture of Arctic Alaska terrane is proposed. It is based on spatial linkages between a number of geomorphic and subsurface structural lineaments that were independently mapped across a number of east-west striking provinces. It is hypothesized that deep basement rocks of the underlying south-vergent and underthusting North Slope plate are segmented into discrete, mostly northeast-trending megablocks. Fault reactivation along keyboard-like block boundaries results from differential uplift, tilting and minor translation of the blocks. These is inferred from geomorphic and structural-stratigraphic discontinuities in the overlying, allochthonous North Alaska plate.

The block architecture, first observed segmenting the relatively shallow basement rocks of the Barrow arch, appears to be transplate. The southward projection of some northeast-trending block margins across the arch, coincide with segmentation of the Colville basin. One such boundary correlates to a diffuse zone of transverse fault fabrics and structural-stratigraphic discontinuities within the central Brooks Range. The axial trend of the range changes across this zone. Geomorphic indices are used to develop the hypothesis that subthrust faulting and basinal inversion might exist beneath the range, and that Mesozoic-Cenozoic compressional events were controlled, in part, by the presence of long-lived, rift-related basement fault fabrics. Could the inversion of underlying, clastic-rich transtensional basins have propagated faulting/fracturing upward through the thinner allochthonous units of the North Alaskan plate? Could this explain some of the modern drainage patterns seen in the area? Implications of long-lived basement control should be of interest to the mineral and petroleum explorationist, alike.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.