Deformation mechanisms in the southeastern ramp region of the Pine Mountain block, Tennessee

Sevier–Laramide deformation of the continental interior from calcite twinning analysis, west-central North America

“…Twinning is possible along three glide planes and calcite strain-hardens once twinned; further twinning is possible in a crystal along either of the remaining two ef0112g planes at higher stress levels, provided that stress is oriented >45º from the initial stress orientation (Teufel, 1980). The application of twinned calcite to structural and tectonic problems has been primarily restricted to studies of limestones (e.g., Groshong, 1975;Engelder, 1979a;Spang and Groshong, 1981;Wiltschko et al, 1985;Craddock et al, 1993), calcite veins (e.g., Kilsdonk and Wiltschko, 1988), or, more rarely, marbles (e.g., Craddock et al, 1991). Craddock and Pearson (1994) and Craddock et al (1997) have studied twinning strains in secondary calcite of basalts from DSDP Hole 433C and the Proterozoic Keweenaw rift, respectively.…”

Paleostrain stratigraphic analysis of calcite twins across the Cambrian–Ordovician unconformity in the Tethyan Himalaya, Spiti and Zanskar valley regions, India

“…This is the first study to our knowledge that uses mechanically twinned calcite to investigate strain patterns in the Himalaya. The maximum layer-parallel shortening strain recorded by calcite twins in fold-thrust belts is in most cases parallel to the thrust transport direction (Kilsdonk and Wiltschko, 1988;Craddock et al, 1988;Craddock, 1992, and references therein). The Cenozoic twinning strains in the Carboniferous samples may therefore provide new data on the early thrust transport direction of the Tethyan Himalayan fold-thrust belt during the early stages of the India/Eurasia collision.…”

“…Previous calcite twinning studies from other fold-thrust belts indicate that calcite twinning commonly occurs during the earliest phases of fold-thrust belt deformation, prior to major faulting and folding, and tends to strain harden such that the original layer-parallel shortening strain is preserved during subsequent deformation (Kilsdonk and Wiltschko, 1988;Craddock et al, 1988;Evans and Dunne, 1991;Craddock, 1992;and references therein). LDR and PEV data in our samples show unimodal compression axis maxima that intersect bedding great circle traces and have a similar bearing as the maximum shortening axes (e1; Fig.…”

Revisiting the Hubbert–Rubey pore pressure model for overthrust faulting: Inferences from bedding-parallel detachment surfaces within Middle Devonian gas shale, the Appalachian Basin, USA

“…Elevated pore pressure affects black shale in at least two important ways: pore pressure might exceed least compressive stress to drive natural hydraulic fractures (Engelder and Lacazette, 1990;Lacazette and Engelder, 1992;Secor, 1965) and pore pressure might lower effective normal stress to ease frictional slip on faults (Gretener, 1972(Gretener, , 1981Hubbert and Rubey, 1959). If reduced effective normal stress is common during maturation of black shale, then these shales should preferentially host detachment planes under regional thrust sheets such as the Pine Mountain thrust block (Harris et al, 1970;Kilsdonk and Wiltschko, 1988;Mitra, 1988;Rich, 1934;Wentworth, 1921). This leads to the hypothesis that detachment faulting in black shale is a manifestation of the reduction in effective normal stress during the buildup of maturation-related pore pressure within the shale (Swarbrick et al, 2002) and not exclusively a manifestation of an inherent frictional weakness or plasticity of the shale (Kennedy and Logan, 1998;Wojtal and Mitra, 1986).…”