Strontium Isotope Composition of Amphibolite of the Cartersville–Villa Rica District, Georgia
Present-day 87 Sr/ 86 Sr ratios for a suite of 19 amphibolite samples from the Cartersville–Villa Rica district of Georgia range from 0.7044 to 0.7077, averaging 0.7063 ± 0.0009 (1 S.D.). Assuming an age of 600 m.y. for these rocks, the initial 87 Sr/ 86 Sr ratios range from 0.7033 to 0.7068, and average 0.7054 + 0.0010. These relatively low values suggest the rocks are of volcanic origin and contain strontium that may have originated predominantly in the upper mantle. Amygdular and pillow structures clearly substantiate a volcanic source and the chemical and mineralogic composition indicate that these amphibolites are meta-basalts. The amphibolite, part of the Ashland group, probably is correlative with the Ashe Formation of North Carolina and the Mount Rogers volcanic series.