Broken foreland basins and the influence of subduction dynamics, tectonic inheritance, and mechanical triggers

Broken foreland basins are caused by crustal-scale contractional basement structures that compartmentalize (or break) a contiguous retroarc or collisional foreland basin into smaller disconnected basins. Broken foreland basins differ from their unbroken counterparts in their deformational, depositional, and geodynamic framework. Whereas contiguous (unbroken) foreland basins are generated mainly by regional flexural loading due to shortening of supracrustal cover strata and uppermost basement in organized ramp-flat thrust systems, broken foreland basins are governed principally by isolated topographic loads and structural tilting associated with widely spaced crustal-scale reverse faults that accommodate intraplate basement shortening. These structural contrasts foster either décollement-style fold-thrust belts (orogenic wedges) with large integrated erosional drainage systems (watersheds) spanning diverse sediment source regions (including thin-skinned fold-thrust belts, elevated hinterland zones, accreted terranes, and magmatic arcs) or independent foreland block uplifts with local drainage systems dominated by basement sources. Although the genesis of broken foreland basins has been uniquely attributed to flat slab subduction, these basins are also sensitive to inherited structural, stratigraphic, thermal, and rheological configurations, as well as synorogenic mass redistribution in relationship to climate, erosion, sediment transport efficiency, and sediment accumulation. Despite the many modern and ancient examples, questions persist over the underlying geodynamic processes that promote development of a broken or compartmentalized foreland basin instead of a single regionally unified flexural foreland basin. Additional uncertainties and misconceptions surround the criteria used to define broken foreland basins and their linkages to subduction dynamics (chiefly slab geometry), strain magnitude, and structural reactivation. Here we review the tectonic framework of broken foreland basins—with emphasis on South and North America (Pampean and Laramide provinces)—and propose that their genesis can be ascribed to a combination of: (i) underlying conditions in the form of tectonic inheritance, including precursor structural, stratigraphic, thermal, and rheological heterogeneities and anisotropies; and (ii) mechanical triggers, such as increased stress, enhanced horizontal stress transmission, and/or selective crustal strengthening or weakening.