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Early Mesozoic Talbotton diabase dikes in west-central Georgia: Compositionally homogeneous high-Fe quartz tholeiites

By
Katherine A. Milla
Katherine A. Milla
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Paul C. Ragland
Paul C. Ragland
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Published:
January 01, 1992

The early Mesozoic Talbotton diabase dike set in west-central Georgia consists of four en-echelon, multiply intruded segments with an overall N17°W strike. Compared to other known dikes in Georgia and Alabama, dikes in the Talbotton set are unusually wide, and have pronounced magnetic anomalies due to their relatively high Fe-Ti oxide content. Both chemical and modal compositions of the Talbotton rocks are remarkably homogeneous along strike as well as in cross section. Total variation for a given element or mineral commonly does not exceed analytical error. No compositional differences were observed within the dikes for large-ion-lithophile (LIL) elements across three pre-Mesozoic lithotectonic belts.

The Talbotton dikes appear to be similar to dikes of the north-south swarm in the Carolinas and Virginia. Dikes of the Talbotton set and the north-south swarm are comparable with respect to their high-Fe quartz-tholeiite (HFQ) compositions, orientations, and individual dike widths and lengths. The Talbotton magma, however, does not fall upon the fractionation trend of this swarm and cannot be associated by mineral control as evidenced by observed phenocryst assemblages.

Major- and trace-element relationships between diabases in the Talbotton dikes and other diabases in Georgia and Alabama cannot be reasonably explained by crystal fractionation or partial melting. A distinct Eu anomaly in the Talbotton dikes, however, indicates fractionation of plagioclase. Mafic index values suggest that ferromagnesian minerals, most probably clinopyroxene, were also part of the fractionation assemblage. The Talbotton dikes were apparently derived from a parental magma not represented at the current level of erosion in the Georgia-Alabama Piedmont.

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GSA Special Papers

Eastern North American Mesozoic Magmatism

John H. Puffer
John H. Puffer
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Paul C. Ragland
Paul C. Ragland
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Geological Society of America
Volume
268
ISBN print:
9780813722689
Publication date:
January 01, 1992

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