32-3 3D Structural Development During Oblique Shortening: Results From Serial Sectioning of an Experimental Clay Model

Session: Latest Research Advances in Structural Geology and Tectonics (Posters)

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Abstract:

Oblique shortening, also known as oblique convergence or transpression, occurs in many tectonic settings, including convergent and transform margins and even rift systems. Deformation associated with oblique shortening can resemble that produced by basin inversion or pure strike-slip deformation, resulting in an ambiguous tectonic interpretation. Thus, it is important to better define the key diagnostic characteristics of oblique shortening. We use a scaled experimental model to examine 3D fault and fold geometries that develop during highly oblique shortening. In our model, a multicolored but mechanically homogeneous clay layer overlies a basal discontinuity. During the experiment, the clay layer moves at a 20˚ angle relative to the discontinuity, producing a highly oblique shear zone with both left-lateral and shortening components. Surface photographs taken during the model and ~100 closely spaced cross sections (~1.5 mm apart) allow detailed 3D analysis of the shear zone. Kinematically, the model evolves through three distinct stages: (1) a distributed strain stage, (2) an early strain partitioning stage, and (3) a late strain partitioning stage. During Stage 1, deformation is broadly distributed across a wide area above the basal discontinuity, and the clay surface undergoes subtle uplift and clockwise rotation. Stage 2 marks the onset of strain partitioning at the surface, where strike-slip faulting and folding accommodate oblique shortening. Stage 3 is characterized by well-developed strain partitioning, with deformation concentrated along a throughgoing oblique-slip fault that accommodates most horizontal displacement. Simultaneously, folding and reverse faulting accommodate the shortening component of deformation adjacent to the main fault zone. The final deformation patterns are highly variable, both laterally and with depth. Numerous faults show cross-sectional geometries that change over short distances, ranging from gentle and listric to steep and planar. Changes in dip direction and separation (normal and reverse) along strike and with depth are common. Fault orientations also change systematically with depth: shallow faults strike parallel or subparallel to the clay movement direction, whereas deeper faults are parallel or subparallel to the basal discontinuity. A broad, commonly fault-bounded anticline also develops within the shear zone, with an axial surface parallel to the underlying discontinuity. Our modeling results can help identify structures associated with oblique shortening and partially explain fault and fold development in the transpressive Dent fault system, NW England.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8401

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