Tectonic Geomorphic Characterization of a
Transcurrent Fault
Zone, Western Brooks Range, Alaska
By
R.R. Casavant (University of Arizona), and S.R. Miller (Pennsylvania State University)
We present a
hypothesis that the western Brooks Range is partitioned by several large,
possibly tectonically active, NW- and NNE-trending transverse fault
zones that
trend obliquely to the range. The study has implications for petroleum
exploration in the adjacent NPRA and mineral exploration to the south. Our
hypothesis of neotectonic activity is not novel, but represents the first foray
of such thinking into the westernmost foothills. In the northwestern DeLong
Mountains north of the Red Dog mine, we surveyed a large, high-angle
transpressional
fault
zone with inferred sinistral offset that intersects and is
parallel to an anomalous long, linear, NNE-trending stretch of the Kukpowruk
River, along with adjacent strath terraces and pediments. The river parallels
several NE-trending thrust faults in the adjacent area and generally exhibits a
graded longitudinal profile with the exception of a west-facing, 1 m-high
channel knickzone that correlates with a prominent NE-trending linear scarp on
an uplifted planation surface on the north side of the river, and with a lesser
scarp on river terraces on the south side. The alignment suggests that the
knickzones and scarps may be the result of active faulting. Down-to-west throw
on these non-structural surfaces matches the sense of offset on nearby thrust
faults. Block tilting within the
fault
zone is inferred from consistent shifts
in channel avulsion toward one margin of the river floodplain. Multiple levels
of strath terrace formation suggest a neotectonic base-level drop. Further
mapping and dating of key surfaces are necessary to clarify this region’s
complex structural history.
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.