Physical Modeling of Primary and
Progressive Orogenic Curvature
Needle,
Mattathias D., Tindall, Sarah E.,
and Sussman, Aviva, 2010, Physical Modeling of Primary and
Progressive Orogenic Curvature [abs]: Geological Society of
America Northeastern Section (45th Annual) and Southeastern
Section (59th Annual) Joint Meeting (13-16 March 2010).
Displacement paths of curved orogenic
systems are based on field observations of timing relationships
between thrusting and vertical axis rotations. In the present study,
physical analog models permit systematic investigation of the
evolution of primary and progressive curvature, and identification
of characteristic structures associated with these curvature types.
Models were constructed of colored sand layers overlying thin,
rigid, plastic sheets. In primary curve models, layers in the
hanging wall moved over an arc-shaped footwall ramp. For progressive
curve models, differential displacement of parallel plastic strips
caused thrust faulting to nucleate in the center of each model and
propagate laterally, resulting in growth of an arcuate thrust
salient. Models with straight footwall ramps perpendicular to the
shortening direction served as experimental controls. Surface
deformation was tracked throughout each experiment using a colored
sand grid with 2 cm spacing, and models were dissected after
deformation to reveal serial cross sections.
Primary curve deformation produced insignificant surface rotation,
whereas the progressive curve models experienced surface rotation in
the arc corners. Tear structures and wrench faults near the axes of
rotation developed only in the progressive curve models. In both
primary and progressive curve models, thrust fault dips decreased
from the center of the salient to the edges. Thrust faults at the
center of the arc of the primary curve models formed at dip angles
similar to the straight, control model thrust faults.
Conceptual models of curved orogens have predicted vertical axis
rotation associated with progressive curves, and an absence of
rotation associated with primary curves. Our experiments
substantiate this interpretation, and they reveal structures and
characteristics that may be useful to differentiate between
curvature processes in the field.
Physical Modeling of Primary and
Progressive Orogenic Curvature
Displacement paths of curved orogenic
systems are based on field observations of timing relationships
between thrusting and vertical axis rotations. In the present study,
physical analog models permit systematic investigation of the
evolution of primary and progressive curvature, and identification
of characteristic structures associated with these curvature types.