HR: 17:15h
AN: T14C-06    [Abstracts]
TI: Controls on the architecture of the Sierra Madre Oriental fold-thrust belt
AU: * Murphy, M A
EM: mmurphy@mail.uh.edu
AF: University of Houston, Geosciences Department, Houston, TX 77204, United States
AB: Geologic mapping and structural analysis of east-central Mexico were conducted to assess the architecture and structural evolution of the SMO fold-thrust belt. We present a regional map that synthesizes our results from the hinterland to foreland of the SMO fold-thrust belt over a distance of 180 km. Our results show that several regional east-directed thrust faults step-up structurally via flats and ramps. The deepest rocks exhumed in their hanging walls are Paleozoic metasedimentary rocks and early Mesozoic rift deposits in the cores of hanging wall antiforms. At structurally shallow levels thrust faults sole into a regionally extensive evaporite horizon which forms the basal detachment to fold trains within Late Jurassic through Cretaceous marine strata. Field mapping shows that structurally shallow short-wavelength folds rooted into the evaporite horizon are locally folded by structurally deeper long-wavelength folds that expose Paleozoic metasedimentary rocks and early Mesozoic rift deposits. Stratal geometries of the rift deposits suggest that west-dipping normal faults are reactivated by east-directed thrust faults. Structural restorations indicate that east-west shortening is concentrated where crystalline basement has been exhumed while only modest amounts of shortening has occurred between them where deformation is localized along evaporite floored detachments. Comparisons between our field mapping and a regional DEM show that short wavelength folds display a curved mapview pattern and developed above evaporite. These folds are cross cut by linear trending longer wavelength folds that correlate to reactivated rift-bounding faults. This result implies that the architecture and structural history of the SMO fold-thrust belt is contingent upon events that occurred during the opening of the Gulf of Mexico basin. Results of this study permit an assessment of the spatial distribution of Gulf of Mexico basin-related rifts and evaporite deposits. The distribution we interpret provides a picture of the rift geometry that is best explained by early opening of the Gulf of Mexico as a rift-rift-rift triple junction. One running along the Texas-Louisiana Gulf Coast, another running along the Eastern SMO and a third corresponding to the Chihuahua trough. Cessation of the third rift arm is interpreted to shift the kinematics along the eastern SMO arm from east-west stretching to right-lateral strike-slip faulting which lead to the development of the Tehuantepec transform plate boundary.
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8038 Regional crustal structure
SC: Tectonophysics [T]
MN: 2007 Fall Meeting