Thrusts, back-thrusts, and detachment of Rocky Mountain foreland arches

Abstract

The basement geometry of the central Rocky Mountains provides a critical test for Laramide tectonic models. On a large scale, Laramide structural highs are better described as anastomosing, connected arches than as individual "uplifts." Thrust and reverse faults on the margins of Laramide arches dip both under and away from the ranges. Structural modeling shows that faults dipping toward the basins are commonly backthrusts off master thrusts which underlie and bring up the arches. These master thrusts alternate between emergent thrusts with major basement overhangs and blind thrusts below imbricate back thrusts.The northwest-trending average orientations of Laramide faults, folds, and arches suggest northeast-southwest-directed slip over the entire province. The continuity of Laramide arches suggests direct linkages between underlying northeast-and southwestdirected master thrusts. Basement rotations and geophysical evidence for a continuous crust-mantle interface in Wyoming indicate that these master faults are listric, and merge in a subhorizontal detachment in the lower crust. Southwest-directed faults like the Wind River thrust are probably backthrusts off the northeast-directed detachment. West-and north-trending sections of basement arches probably form by oblique slip on lateral ramps connecting the northwest-trending arch culminations.The minimal penetrative strain and the variety of fault styles at the surface in the Laramide foreland indicate that horizontal compression on a mid-crustal stress guide drives Laramide crustal shortening and detachment. Unlike shortening in the coeval Cordilleran thrust belt, Laramide shortening parallels the plate convergence vector and may reflect increased interaction between the North American and Farallon plates during low-angle oblique subduction. PREVIOUS TECTONIC HYPOTHESESTectonic hypotheses for the Laramide orogeny of the central Rocky Mountains were delayed by the lack of an immediately proximal plate margin and the popularity of erroneous vertical uplift models during the 1970s. Dickinson and Snyder (1978) noticed the coincidence of the eastern migration of arc volcanism and the initiation of Laramide deformation in the western United Beartooth Mts.

Structural style of the Malargüe fold-and-thrust belt at the Diamante River area (34°30′–34°50′S) and its linkage with the Cordillera Frontal, Andes of central Argentina

“…The measured 23 km 2 of excess area and 3 km of shortening produced by these structures allow to calculate the depth to the regional detachment, which is located approximately 10 km below the sea level. scribed elsewhere that anticlines related to backthrust systems involving basement rocks are characterized by long, gently-dipping backlimbs and shorter, steeply-dipping forelimbs (Erslev, 1993;Dimieri and Nullo, 1993;Turienzo and Dimieri, 2005a,b,c;Neely and Erslev, 2009) as is the case of the Arroyo Tordillo anticlines (Fig. 4b) and the Lomas Bayas anticline (Fig.…”

Nature and distribution of diagenetic phases and petrophysical properties of carbonates: The Mississippian Madison Formation (Bighorn Basin, Wyoming, USA)

“…Previous studies have already provided a well-documented sedimentary and structural framework (Sandberg and Klapper, 1967;Sando, 1976Sando, , 1982Poole and Sandberg, 1977;Gutschick and Sandberg, 1983;Hennier and Spang, 1983;Elrick and Read, 1991;Erslev, 1993;Reid et al, 1993;Sonnenfeld, 1996;Smith et al, 2004;Westphal et al, 2004;Bellahsen et al, 2006;Barbier et al, 2012b). Similarly, the diagenetic framework has been the topic of several researches.…”

“…1B): Wind River Canyon, Sheep Mountain, Shell Canyon, Shoshone Canyon and Clark's Fork Canyon (from the most proximal to the most distal palaeogeographic position respectively). All the present structures were formed during the Laramide Orogeny from Late Cretaceous to Eocene times (Brown, 1993;Erslev, 1993;Stanton and Erslev, 2004).…”

History and causes of post-Laramide relief in the Rocky Mountain orogenic plateau

“…40 Ma; Dickinson et al, 1988;Erslev, 1993), the Rocky Mountains and Colorado Plateau were characterized by narrow basement-cored ranges and monoclines separated by broad structuralsedimentary basins. Overall the difference in elevation between the ridge tops and the valley floors reached proportions similar to modern,…”