Cordilleran Orogenic Belt of Northern Chihuahua, Mexico
R. Dyer, R. Chavez-Quirarte, R. S. Guthrie
The Cordilleran orogenic belt of northern Chihuahua, Mexico, shows three important differences from the "classic" fold-thrust belts of Canada and Idaho-Wyoming. These differences are manifest in (1) the geometry of Mesozoic (and late Paleozoic) basins, (2) timing of deformation, and (3) structural style of deformation. Mesozoic deposition in northern Chihuahua was initially restricted to the Chihuahua trough, a northwest-trending basin bordered by stable blocks (Diablo platform on the northeast and Aldama platform on the southwest). The Florida-Moyotes platform protrudes into the northern portion of the basin and marks an important boundary for Mesozoic sedimentation and tectonics. Coarse clastics, succeeded by shallow marine clastics and limestones (Late Jurassic-Early C etaceous), unconformably(?) overlie late Paleozoic shelf, slope, and basinal deposits. Marine transgression from the southeast followed the general trend of the late Paleozoic Pedregosa basin, although the depocenter is offset. The developing Mesozoic basin(s) formed a more or less continuous feature from the opening Gulf of Mexico into southeastern Arizona. Basin development must be closely linked with the opening of the Gulf of Mexico and probably reflects extensional or transtensional processes. Locally in northwest Chihuahua, Early Cretaceous highlands are indicated by basal conglomerates of continental origin, succeeded by a shallow marine sequence. No evidence to support a Jurassic "Sevier" stage of compressive deformation has been documented in northern Chihuahua. By Albian time, arine deposits lapped onto the Diablo and Aldama platforms. The region experienced compressive deformation during the latest Cretaceous-middle Eocene, creating the Chihuahua tectonic belt. No coherent synorogenic foreland basin is recognized in Chihuahua, but terrigenous sediments derived from the Chihuahua tectonic belt accumulated in the structurally controlled Tornillo basin to the east.
Asymmetric folding and thrust faulting characterize Laramide deformation. West of the Moyotes platform, fold vergence is toward both the northeast and southwest, whereas major thrusts, locally involving Paleozoic strata, show northeasterly transport of more than 2 km. In northwestern Chihuahua, Precambrian(?) granite boulders in an early Tertiary(?) conglomerate indicate basement involvement in deformation. East-southeast of the Moyotes platform, compressive deformation was complicated by involvement of evaporites. Fold asymmetry and thrust geometry along the international border indicate generally uniform transport, toward the east or northeast of up to 80 km. Posttectonic(?) calc-alkalic volcanism in northern Chihuahua may have started as early as 65 Ma and was extensive by 45 Ma.
AAPG Search and Discovery Article #91034©1988 AAPG Southwest Section, El Paso, Texas, 21-23 February 1988.