Paper No. 21-5
Presentation Time: 8:00 AM-12:00 PM
1:24K MAPPING AND U/TH GEOCHEMICAL SURVEY OF A SEGMENT OF THE EASTERN BLUE RIDGE BELT IN ALABAMA
The northern Alabama Piedmont is the southwestern-most extension of the Blue Ridge belt in Alabama. Both western and eastern Blue Ridge lithologies are represented by the Talladega Belt and Ashland-Wedowee belts respectively. The structurally lowermost lithotectonic unit in the Ashland-Wedowee is the Higgins Ferry group that is bounded below by the Talladega-Cartersville thrust and is stratigraphically overlain by the Wedowee group. The Higgins Ferry group is an 8 km thick interbedded sequence of graphite garnet schist, metagraywacke, graphitic quartzite (metachert), amphibolite, and calc-silicate gneiss that represents continental slope-rise protolith. The stratigraphically conformable amphibolite units are interpreted as basalt flows or sills perhaps related to a late Proterozoic rifting event. The metamorphic grade of the Higgins Ferry group is typically upper amphibolite facies, however, in the immediate hanging wall of the Talladega-Cartersville thrust geothermobarometry results indicate granulite facies P-T conditions. 1:24K scale mapping and structural analysis in a 4-quadrangle area indicates that the Higgins Ferry lithotectonic block is a monoclinaly dipping metaclastic/metavolcanic sequence conformable to the Appalachian trend in the study area. Map-scale F3 tight asymmetric folds may locally disrupt the trend and repeat stratigraphic units. In addition to mapping, U/Th geochemical sampling has revealed the following map-scale trends: 1) regional background U3O8 concentration of 5-50 ppm range, and 2) point-source U3O8 concentrations in the 350-600 ppm range. The locations of U/Th high concentrations seem to lie along a strataform trend parallel to regional strike, however, the local high concentrations are point sources. The locations of high U3O8 values seem to occur proximal to quartzite (metachert) units, however, more data is needed to verify this speculation.
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