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

Journal Article · Sat Dec 01 00:00:00 EST 1990 · American Journal of Science; (USA)

DOI:https://doi.org/10.2475/ajs.290.10.1169· OSTI ID:5542620

Goldberg, S A ^[1]; Steltenpohl, M G ^[2]

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1. Univ. of North Carolina, Chapel Hill (USA)
2. Auburn Univ., AL (USA)

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} to 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.

• OSTI ID: 5542620
• Journal Information: American Journal of Science; (USA), Vol. 290:10; ISSN 0002-9599
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALABAMA
GEOLOGIC HISTORY
GEORGIA
AGE ESTIMATION
BIOTITE
CARBONIFEROUS PERIOD
FELDSPARS
GARNETS
GEOLOGIC FORMATIONS
GNEISSES
METAMORPHIC ROCKS
METAMORPHISM
MINERALOGY
MUSCOVITE
QUARTZ
RUBIDIUM
SCHISTS
STRONTIUM
TECTONICS
ALKALI METALS
ALKALINE EARTH METALS
CHALCOGENIDES
DEVELOPED COUNTRIES
ELEMENTS
FEDERAL REGION IV
GEOLOGIC AGES
METALS
MICA
MINERALS
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PALEOZOIC ERA
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
USA
580000* - Geosciences