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.