Restraining bends, transpressional deformation and basement controls on development
Published:January 01, 2007
Restraining bend mountain ranges are fundamental orogenic elements in the Altai, Gobi Altai and eastern Tien Shan. In this paper, 12 separate restraining bends are reviewed to identify common structural and topographic characteristics. The 12 restraining bends occur in one of three different tectonic settings: (1) strike-slip fault termination zones; (2) at a major strike-slip fault bend where the individual strike-slip fault can be traced continuously from one end of the range to the other; and (3) where two separate strike-slip fault segments converge and overlap. Fault maps of the 12 separate bends reveal that they are all flower or half-flower structures in cross-section, but there is considerable architectural diversity and all have unique individual topographic, structural and dimensional characteristics. Many factors account for the architectural diversity of the restraining bend mountains, especially stepover width, total amounts of strike-slip displacement, reactivation of older structures, tectonic setting, and the angular relation between fault trace and maximum horizontal stress. The stepover sense for regionally important strike-slip faults is controlled by pre-existing basement heterogeneities and is dominantly contractional. Therefore, releasing bends and transtensional basins are largely absent. Throughout the region there is a continuum of mountain range types, from purely contractional ridges to isolated restraining bends along strike-slip-dominated zones. Nucleation, topographic uplift, along- and across-strike growth of the bend, and restraining bend coalescence with adjacent ranges appears to be an important mountain-building process in the Altai, Gobi Altai and eastern Tien Shan; similar processes are likely in other intracontinental transpressional orogens.
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Tectonics of Strike-Slip Restraining and Releasing Bends
Restraining and releasing bends are common, but enigmatic features of strike-slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation. Regional-scale restraining bends are sites of mountain building, transpressional deformation and basement exhumation, whereas releasing bends are sites of topographic subsidence, transtensional deformation, basin sedimentation and possible volcanism and economic mineralization. Because restraining and releasing bends often occur as singular self-contained domains of complex deformation, they are appealing natural laboratories for Earth scientists to study fault processes, earthquake seismology, active faulting and sedimentation, fault and fluid-flow relationships, links between tectonics and topography, tectonic and erosional controls on exhumation, and tectonic geomorphology.
This volume addresses the tectonic complexity and diversity of strike-slip restraining and releasing bends with 18 contributions divided into four thematic sections: (1) a topical review of fault bends and their global distribution; (2) bends, sedimentary basins and earthquake hazards; (3) restraining bends, transpressional deformation and basement controls on development; (4) releasing bends, transtensional deformation and fluid flow.