Convergent orogens are typically linear with laterally continuous,
orogen-parallel folds and thrusts. Over the years, geoscience research
has revealed evidence for important orthogonal/cross structures as well
as lateral heterogeneity in deformation style, igneous activity,
metamorphic grade, geomorphology, and seismic activity. To assess the
occurrence, causal mechanisms, and implications of these lateral
heterogeneities, a selection of convergent orogens, with different
tectonic settings and history are reviewed. The Appalachians, the North
American Cordillera, the Alps, the Himalayas, the Zagros, the Andes, and
several other belts all exhibit a degree of lateral heterogeneity. Major
factors driving the lateral heterogeneity and/or cross structures
include the pre-existing deformational history of the cratonic blocks
involved, lateral change in lithology of crustal rocks, variations in
crustal/lithospheric rheologic properties, or changes in plate
kinematics. The Appalachian orogenic front mimics the Iapetan rift
margin. Pre-existing basement structures have control on pre- and
syn-orogenic sedimentation, which subsequently impacts how an orogenic
wedge evolves. A thicker sedimentary column generally evolves into a
salient (as opposed to a recess), which is further enhanced by the
presence of weak horizons as seen in the Zagros and the Cordillera.
Lateral variation in sedimentary facies also creates changes in
thrust-ramp geometry. During orogenic contraction, inherited basement
structures can be preferentially reactivated based on their orientation.
Several cross faults in the Himalayas spatially coincide with
orogen-perpendicular, lower plate, basement structures. In a similar
way, oceanic subducting plate physiography can also influence
deformation in the overriding plate. Along-strike variations in
subduction dynamics have been reflected in the Andean deformation.
Orogenic extension in the Alps has been accompanied by a system of
orogen-parallel strike slip faults and extensional cross faults. It is
evident that lateral heterogeneities can form crucial control on the
evolution of orogenic belts and can influence seismic rupture patterns,
resource occurrence, and landslide-related natural hazards.