Mechanisms of folding by cataclastic flow, and its role in the evolution of the Canyon Range thrust sheet, Sevier fold-thrust belt, west-central Utah.

摘要

The upper part of any evolving orogenic wedge deforms in the elastico-frictional (EF) regime, mainly by fracturing and frictional sliding along fractures (i.e. cataclastic flow). The folded Canyon Range (CR) thrust sheet, in the internal portion of the Sevier fold-thrust belt (FTB) of west-central Utah, preserves evidence for folding of miogeoclinal sedimentary rocks under EF conditions.; A detailed study of the geometry and progressive deformation patterns in the CR syncline, part of the CR thrust sheet, reveals five distinct and partly overlapping deformation stages that span the entire period of evolution of the FTB. Thus, CR structures record a significant portion of the deformation history in the FTB as a whole. The deformation at any stage is strongly influenced by the geothermal gradient and lateral variations in the geotherm.; The CR syncline tightened at shallow crustal levels, and thick-bedded quartzite within it deformed in the EF regime. Initial folding occurred by bending of beds and flexural slip between beds. Fracture and deformation zone (DZ) networks accommodated later fold tightening by limb rotation and thinning, and the formation of transverse zones across the fold. Mesoscopic and microscopic evidence reveal several generations of networks that can be related to stages of folding. A cooperative relationship exists across fracture networks at different scales, resulting in a continuous deformation that is homogeneous at the outcrop scale.; The initial mesoscopic fracture/DZ network geometry results from growth and linking of micro-cataclasite zones, in turn controlled by primary lithological variations. During progressive folding, additional factors regulate cataclastic flow, such as DZ reactivation or healing. In the CR syncline, initial fracturing resulted in unit-specific network geometries. These interacted with one another as deformation progressed, resulting in feedback mechanisms regulating the later stages of network development. Thus, the nature of cataclastic flow changed dramatically from the initial to the final stages of folding.; The fracture networks dominate the porosity/permeability in the CR and would have controlled the migration of fluids (and hydrocarbons) during folding. These migration/reservoir patterns reveal how fracture networks may redistribute fluids through space and time. The network patterns also help to elucidate the role lithology plays in fluid localization.