Field
studies
of
curved
orogens have focused on timing relationships between
thrusting and vertical axis rotation to distinguish systems that
initiate in an arc shape (primary curvature) from those that develop
curvature during deformation (progressive curvature). In the current
study, physical analog models of primary and progressive curvature are
examined in cross section to identify characteristics of fault
displacement and orientation that may help distinguish between these
curvature processes in the field.
Construction of analog models involved layering colored sand on top of
thin, rigid, plastic sheets. Three model designs were used: (1)
experimental control models contained straight footwall ramps
perpendicular to the shortening direction; (2) primary curve models
contained an arc-shaped footwall ramp over which hanging wall layers
translated; (3) in progressive curvature models, movable plastic strips
below the hanging wall sand layers allowed for differential
displacement over a straight footwall ramp, with displacement beginning
in the center of the salient and progressing symmetrically out toward
salient corners. Following deformation, models were dissected parallel
to the imposed shortening direction to reveal serial cross sections in
the deformed sand.
Cross sections demonstrated uniform vertical displacement along the
primary arc and control models, and a systematic decrease in vertical
displacement from the progressive arc center to the arc corners. The
number of backthrusts remained constant throughout primary arc and
control cross sections, whereas backthrusts decreased in quantity from
the arc center to arc corners in the progressive curve model. These
spatial variations in progressive curvature of a curved orogen mirror
the temporal development of an individual thrust sheet because the
total horizontal displacement decreases from the center to the corners
of the progressive curve. Horizontal displacement is constant across
the entire length of the primary arc and the control models. These
distinguishing fault characteristics reflect more spatially homogeneous
strain in primary arcs and more heterogeneous strain along the axes of
progressive arcs.
A deeper look
into orogenic curvature: Analog models in cross section 
Field
studies
of
curved
orogens have focused on timing relationships between
thrusting and vertical axis rotation to distinguish systems that
initiate in an arc shape (primary curvature) from those that develop
curvature during deformation (progressive curvature). In the current
study, physical analog models of primary and progressive curvature are
examined in cross section to identify characteristics of fault
displacement and orientation that may help distinguish between these
curvature processes in the field.