Timing and characteristics of Paleozoic deformation and metamorphism in the Alabama inner Piedmont

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ID: 308725
1990
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Abstract
The Opelika Complex in the Inner Piedmont of Alabama and Georgia records multiple periods of Paleozoic deformation and metamorphism. Rb-Sr isochron ages and thermobarometric data are reported for pelitic schists and spatially associated metagranite. A whole-rock Rb-Sr isochron age of 369 {plus minus} 5 Ma for Farmville Metagranite is interpreted as the time of syntectonic emplacement and crystallization within Auburn Gneiss and Loachapoka Schist of the Opelika Complex. Metapelitic units from the Auburn Gneiss and Loachapoka Schist exhibit a dominant S{sub 1} foliation which is continuous into Farmville Metagranite. Metamorphic assemblages defining this foliation (garnet + biotite + plagioclase + quartz + muscovite {plus minus} kyanite {plus minus} staurolite) indicate middle- to upper-amphibolite-facies conditions. Garnet-biotite geothermometry yields temperature estimates for final equilibration of 541{degree} to 580{degree}C, and garnet-plagioclase-kyanite-quartz and/or garnet-plagioclase-biotite-muscovite geobarometry indicate pressures of 6.8 to 8.2 kb for the matrix assemblage. This schistosity is retrograded by a S{sub 2} crenulation cleavage exhibiting greenschist-facies assemblages. The S{sub 2} cleavage in the Opelika Complex represents a late-stage (D{sub 2}) deformational event showing similar fabric and kinematic relationships to spatially associated mylonites from the Towaliga fault. Two feldspar thermometry from an extensional shear band in Farmville Metagranite yields temperatures of 302{degree} tomore » 406{degree}C. A Rb-Sr mineral isochron from a strongly foliated sample of Farmville Metagranite yields an age of 296 {plus minus} 4 Ma. This age is interpreted as the time of Sr isotopic reequilibration, apparently in response to a period of uplift or thrusting associated with the Alleghanian orogeny.« less
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Authors Steven A. Goldberg, Mark G. Steltenpohl
Journal american journal of science
Year 1990
DOI
10.2475/ajs.290.10.1169
URL
https://ajs.scholasticahq.com/article/60511.pdf
Keywords Keywords not found

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