Styles of Faulting/GSA Abstracts w/Programs

Styles of Faulting in Continental Rift Basins

Abstract--Asymmetric fault-bounded sedimentary basins, or half graben, are widely considered to be the fundamental expression of continental extension. There are three main classes of faults: (1) Faults that have completely cut through the brittle crust, (2) faults that have not not completely cut through the brittle crust, and (3) gravity-driven faults restricted to thick sedimentary successions. Class 1 and 2 faults generally have moderate to high-angle dips and are planar; both hanging-wall subsidence and footwall uplift occur. These faults exhibit a linear scaling relationship between displacement and length over >8 orders of magnitude of fault length, systematic variations in displacement along the fault surface and in the rock volume surrounding the fault (responsible for reverse drag), and a wide variety of fault-related folds. Fault systems are commonly composed of multiple segments that display "soft-linkage" (typically represented by relay zones) early in their development and "hard-linkage" later on. Class 1 faults may exhibit an exponential distribution of fault sizes, whereas Class 2 faults generally exhibit a power-law distribution. Class 1 faults form the border faults of continental rift basins (although these may initiate as Class 2 faults). In many cases, these faults are reactivated structures that may not be orthogonal to the extension direction; this results in oblique deformation. Class 2 faults are commonly intrabasinal faults and typically form normal to the extension direction. Class 3 faults are often strongly listric, detach in a weak sedimentary horizon, and have passive footwall blocks. Domino-style faults are a special type of Class 1 and 2 faults that form when the hanging-wall and footwall deflections of closely spaced parallel faults constructively interfere to give the appearance of rigid fault blocks.

The large-scale geometry of rift basins reflects the displacement geometry and segmentation of border faults. Combined with a fault-growth model, these features can be used to model idealized rift basins and to predict stratal geometries, major facies transitions, and sediment accumulation rates.

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