Tectonic blocks, magmatic arcs, and oceanic terrains: A preliminary interpretation based on gravity, outcrop, and subsurface data, northeast-central Mexico


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 León. This gravity gradient diverges in western Nuevo León 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 León, 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 León, possible Laramide-age intrusions along the Cretaceous thrust front in Tamaulipas and Nuevo León, 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. Three northeast-trending, 2.5-dimensional (2.5-D) gravity models constrained by geologic, well, and sparse regional seismic data indicate that the boundary between the Late Permian-Early Triassic and Late Triassic-Middle Jurassic volcanic arcs may lie in eastern Coahuila, south-central Nuevo León, and southwestern Tamaulipas. Subtle gravity minima along the center of each profile represent Permian granite, Triassic-Cretaceous arc rocks, or Triassic-Cretaceous oceanic rocks that extend to depths of 10-12 km. High-amplitude gravity maxima in eastern Mexico represent intermediate Permian intrusive rocks or high-grade Paleozoic metamorphic rocks that extend to 10-12 km. Short-wavelength, northwest-trending gravity anomalies may represent Laramide-age or younger intrusive bodies.

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AAPG Memoir