3D Structural Analysis of the Benton Uplift, Ouachita Orogen, Arkansas
Johnson, Harold Everett
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The date for the formation of the Benton Uplift, Ouachita orogeny, is bracketed by Carboniferous synorogenic sediments deposited to the north and Late Pennsylvanian to Early Permian isotopic dates from the weakly metamorphosed rocks within the uplift. We address the largely unknown structural history between these two constraints by presenting an improved 3-dimensional kinematic model using better constrained retrodeformable sections. These new sections are based on all surface and subsurface data, new zircon fission track dates and thermal maturation data including new ?crystallinity? data to constrain the maximum burial depth. Concordant zircon fission track ages range from 307 ? 18.8 Ma to 333.4 ? 38.9 Ma or from the Late Devonian to Early Permian. Maximum ?crystallinity? of both illite and chlorite indicate these exposed rocks experienced a temperature of ~300?C across the eastern Benton Uplift. This temperature is consistent with reconstructed burial depths using cumulative stratigraphic thickness without having to call on structural thickening. Comparing coarse and fine clay fractions, computed temperature for the fine clay fraction is less by ~100?C than that of the coarse clay fraction. This difference is the same for all formations studied. This uniform difference in temperature may indicate cooling of the orogen as it deformed or more than one thermal event.