Modeled effects of deep-seated fault
offset and strike on supracrustal geometries in basement-cored
uplifts Modeled effects of deep-seated fault
offset and strike on supracrustal geometries in basement-cored
uplifts Folk, Shane N., Needle, Mattathias D., and Tindall, Sarah E., 2010, Modeled effects of deep-seated fault offset and strike on supracrustal geometries in basement-cored uplifts [abs]: Geological Society of America - Denver Annual Meeting (31 October –3 November 2010).
The Precambrian basement of the
Colorado Plateau contains a network of ancient faults, reactivated
during late Mesozoic to early Cenozoic horizontal compression. The
resulting Laramide basement-cored uplifts show diverse fault/fold
patterns in the Paleozoic and Mesozoic sedimentary cover. In this
study, physical analog models were conducted to investigate how
differences in the strike and displacement of pre-existing basement
faults affect the development of secondary structures in overlying
sediment. Each model contained a 45º-dipping basement fault with a
strike orientation of 90°, 75°, 60° or 45° relative to the
horizontal shortening direction. The rigid basement was constructed
of high-density polyethylene (HDPE) blocks. Overlying sedimentary
cover was modeled using eight individually colored layers of 2φ
sand, each 0.5 cm thick. Each model configuration was deformed at a
rate of 4.0 cm/hr to a total horizontal displacement of 1.0 and 2.0
cm, for a total of eight models. After deformation, models were
sliced in a series of 2 cm spaced cross sections and ~2 mm spaced
horizontal sections (map views) to reveal fault and fold patterns in
the sand layers. Fault strikes in the sedimentary cover generally
paralleled that of the basement fault in all models. Models with 1.0
cm of displacement developed a single fault plane propagating
approximately 1.5 cm into the sedimentary cover; while the overlying
layers deformed in a broad open fold. All models with 2.0 cm of
displacement, excluding the 45º basement block fault, developed
multiple fault planes that propagated to the model surface forming
structural terraces and fault-bounded lenses, suggesting that
basement fault strike affects the formation of these structures.
Fold and fault patterns in the models resemble structures associated
with many Laramide uplifts on the Colorado Plateau and may be useful
in understanding basement fault orientation, amount of displacement,
and progressive fault and fold growth associated with basement-cored
uplifts.