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

Abstract

Paleozoic-Mesozoic carbonates that cover cratonic western North America contain a regional layer-parallel shortening (LPS) fabric that is preserved by mechanically twinned calcite. Shortening directions are generally parallel to the Sevier thrust-transport direction (E-W) in carbonates of the Idaho-Wyoming portion of the thrust belt and within carbonates as far as 2000 km into the plate interior. The inferred calcite twinning differential stress magnitudes generally decrease across the thrust belt, and decrease exponentially away from the orogenic front into the craton. Synorogenic calcite cements and veins preserve a distinct twinning deformation history: in the thrust belt, twinning strains commonly record local, out-of-transport piggyback strain events with high differential stresses (<150 MPa), whereas in Laramide uplifts and adjacent basins as far east as the Black Hills, twinned vein calcite preserves a sub-horizontal, N-S-shortening strain, with differential stress magnitudes that decrease to the east. Deformation of the plate interior during the Sevier orogeny was dominated by E-W contraction at the plate margin, which changed into dominantly oblique contraction (¾N-S shortening) along western North America during the younger, basement-involved Laramide event.

Calcite Twins, a Tool for Tectonic Studies in Thrust Belts and Stable Orogenic Forelands

“…Only few samples yield a pre-folding (or possibly a syn-folding) NE-directed compression . This study complements earlier work concerned with the relative timing of calcite twinning strain and fold belt development (e.g., Harris and Van der Pluijm, 1998;Lacombe, 2001), in that it emphasizes that twinning may record not just layer-parallel shortening as often stated or assumed (e.g., Craddock and Van der Pluijm, 1999), but also late fold tightening strain.…”

“…This supports buckling of the cover sequence over the weak Hormuz salt as the dominant regional mechanism of deformation (Mouthereau et al, , 2007a. These differential stress estimates noticeably differ from previously reported stress values in fold belts, which are much higher (e.g., 90-150 MPa in the Idaho-Wyoming belt: Craddock and Van der Pluijm, 1999), and show a strong decay across both the fold belt and the undeformed foreland (e.g., 100 to 20 MPa in the Sevier-Appalachian forelands: Van der Pluijm et al, 1997).…”

“…9b), part of which were transported passively within the thrust sheets as the thrust belt developed. A similar analysis has been carried out by Craddock and van der Pluijm (1999) in the foreland of the Sevier-Laramide belt.…”

“…This assumption is also shared by the technique of Jamison and Spang (1976). Using the latter technique, a constant critical resolved shear stress of 10 MPa is generally adopted (e.g., Craddock et al, 1993;Craddock and van der Pluijm, 1999;Gonzales-Casado and Garcia-Cuevas, 1999). Based on the analysis of experimentally deformed samples, Lacombe and Laurent (1996) and Laurent et al (2000) have not only demonstrated the reliability of the CSIT, but also emphasized that the critical resolved shear stress is sensitive to strain hardening.…”

“…Calcite twins have been considered for a long time as common stress/strain markers, and their analyses have been widely used to constrain the structural and kinematic evolution of orogenic forelands, e.g., Sevier and Appalachian forelands: Craddock and Van der Pluijm (1999); Northern Pyrenean foreland: Tourneret and Laurent (1990), Rocher et al (2000); Southern Pyrenean foreland: Gonzales-Casado and Garcia-Cuevas (1999), Holl and Anastasio (1995); Subalpine chain : Ferrill and Groshong (1993); Taiwan: Lacombe et al (1993Lacombe et al ( , 1996a, Rocher et al (1996), Hung and Kuo (1999); Hudson valley fold-thrust belt: Harris and Van der Pluijm (1998); Zagros: Lacombe et al (2007). These studies have led to regionally significant reconstructions of tectonic stress and strain patterns, and, in few cases, to the quantification of differential stresses associated with folding and thrusting.…”