27 Evolution of Cordilleran-type orogenic systems

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
1:30 PM - 5:30 PM
LMH, Isla Carmen

Broken Foreland Basins in the Andes and North American Cordillera

Paper number: 27-3
Program: Technical Sessions
Time: 2:25 PM – 2:45 PM

Authors

Abstract

A broken foreland basin is defined as a region of sediment accommodation that forms in an intraplate continental setting inboard of a retroarc or collisional orogenic belt.  The basin is compartmentalized (partitioned or fragmented) by positive topographic features produced by discrete basement-involved contractional structures.  Accommodation is regulated by flexural loading and fault-block tilting with subordinate dynamic subsidence and sediment infilling (ponding) within internally drained areas.

Discrimination of broken and unbroken (continuous) foreland basin conditions enables time-space reconstructions of deformation patterns responsible for growth of integrated topography in thin-skinned fold-thrust belts and isolated topographic highs in distal foreland regions.  Such reconstructions require delineation of the position and long-term advance (relative to the trench or suture) of (1) the orogenic topographic front (marked by frontal thrust-belt structures) and (2) the foreland deformation front (defined by isolated basement block uplifts).  The dissimilar sedimentary histories of broken versus unbroken foreland basins are manifest in contrasting sediment accumulation histories, time-stratigraphic patterns, depositional environments, sediment routing, and provenance.

Examples from the modern Andes and the Cretaceous-Paleogene Laramide province of North America show a clear spatial correlation between flat slab subduction and zones of distributed intraplate shortening with broken foreland conditions.  However, deformation advance toward the plate interior is sensitive not only to geodynamic configuration but also inherited structural/stratigraphic geometries and mechanical processes related to crustal/lithospheric strengthening and weakening.  Although important, flat slab subduction is neither necessary nor sufficient to uniquely explain all examples of inboard deformation advance within continental plate interiors.

Finally, it is proposed that most broken foreland basins can be ascribed to a combination of: (1) underlying conditions in the form of tectonic inheritance, including precursor structural, stratigraphic, thermal, and rheological heterogeneities and anisotropies; and (2) mechanical triggers, such as increased stress, enhanced horizontal stress transmission, and/or variable crustal strengthening or weakening.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410838

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