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.