Thick- and thin-skinned Laramide deformation, Fra Cristobal Range, south-central New Mexico

Abstract

The Fra Cristobal Range in south-central New Mexico exposes different styles of deformation variably affecting Precambrian crystalline rocks and Paleozoic, Mesozoic, and Cenozoic cover strata. Three main structural domains are recognized: I is a thickskinned domain (basement-involved) along the northwest flank of the range; II is a thin-skinned domain along the southwest flank of the range; and III is a combined thickand thin-skinned domain along the east flank of the range. Domains with thick-skinned deformation are characterized by fault-propagation folds cored by basement blocks bounded by reverse or thrust faults. These domains are segmented by transverse faults into two subdomain types: (1) east-vergent, overturned folds cored by a basement block with corners rounded by cataclastic flow; and (2) upright folds overthrust by basement that is imbricated by east-directed thrust faults. Thin-skinned deformation involves only Paleozoic cover strata and is characterized by decollement-style thrust faults, duplexes, and related upright to overturned folds. Assuming a balance of basement shortening along strike, it is likely that a basement uplift formed west of domain II but is now buried in the Rio Grande rift. Domain II structures developed either as thrusting propagated from basement into cover, by out-of-syncline thrusting east of the uplift, or by gravity sliding off the uplift. Domain III is characterized by a large, east-vergent, overturned monocline (probably basement cored at depth); the overturned limb was subsequently overthrust by its western subhorizontal limb (similar to a cross-crestal fold). A two-stage development is suggested: (1) basement-cored fault-propagation folding in domain III, and (2) shortening in domains I and II to the west and late-stage cross-crestal faulting of the domain III fold. Behavior of basement rocks during deformation includes: (1) shortening and uplift of basement by reverse faulting, (2) cataclastic flow of basement on fault-block corners allowing folding of the basement-cover contact, (3) longitudinal segmentation of some domains by transverse faults, and (4) possible control of basement faulting by preexisting weaknesses.

Structural evolution of an en echelon fold system within the Laramide foreland, central Wyoming: From early layer-parallel shortening to fault propagation and fold linkage

“…Relations of flanking fold system formation to basement deformation have also generated multiple models, including (i) detachment and buckle folding of the sedimentary cover related to crowding (Petersen, 1983;Nelson, 1993); (ii) fault-propagation folding associated with basement reverse faults, as in fold-thrust and trishear models (Berg, 1962;Erslev, 1991;Stone, 1993); and (iii) drape folding above subvertical basement faults ( Fig. 2B; Matthews and Work, 1978).…”