Kevin Mickus
Department of Geosciences, Southwest Missouri State University, Springfield, Missouri, U.S.A.

ABSTRACT

Complex tectonic plate interactions at the end of the Paleozoic and early Mesozoic, particularly the undefined relationship between circum-Atlantic and circum-Pacific tectonic domains, do not permit a complete understanding of the crustal structure of north-central Mexico. Pre-Oxfordian geologic history, especially the existence of Permian-Early Triassic and Late Triassic-Middle Jurassic volcanic arcs, and general crustal structure of north-central Mexico are approached through gravity modeling and analysis of geologic and well data. Bouguer and isostatic residual gravity-anomaly maps were interpreted to illustrate anomalies caused mostly by Mesozoic and Cenozoic tectonic events, including a large-amplitude, northerly trending gradient marking the edge of Cretaceous thrusting in the Sierra Madre Oriental in Tamaulipas and Nuevo Len. This gravity gradient diverges in western Nuevo Len with one branch trending into southern Coahuila, which also marks the northern limit of Cretaceous thrusting. However, the other branch that trends into northern Nuevo Len, may be caused partially by pre-Cretaceous intrusive and metamorphic rocks or changes in the structural style of the thrust belt north of Monterrey. Lower Bouguer and isostatic residual gravity-anomaly values in central Mexico, as compared with eastern Mexico, indicate a thicker crust formed by the addition of Mesozoic magmatic arcs and sedimentary sequences. Smaller-wavelength isostatic residual gravity-anomalies correspond to Late Permian-Early Triassic plutons or density variations in the Precambrian basement rocks in eastern Tamaulipas and Nuevo Len, possible Laramide-age intrusions along the Cretaceous thrust front in Tamaulipas and Nuevo Len, and Mesozoic sedimentary basins, including the Parras Basin. There is no evidence for large-scale linear anomalies that would correspond to the Late Jurassic Mojave-Sonora megashear transpressive structure across northern Mexico.