Oxygen isotopic compositions of the late orogenic granites in the Southern Piedmont of the Appalachian Mountains, U.S.A., and their relationship to subcrustal structures and lithologies

Details Oxygen isotopic compositions of the late orogenic granites in the Southern Piedmont of the Appalachian Mountains, U.S.A., and their relationship to subcrustal structures and lithologies Oxygen isotopic compositions of the late orogenic granites in the Southern Piedmont of the Appalachian Mountains, U.S.A., and their relationship to subcrustal structures and lithologies

Jul 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981e%26psl..54..186w&link_type=abstract

Earth and Planetary Science Letters, Volume 54, Issue 2, p. 186-199.

Computer Science

16

Scientific paper

Data were acquired from 143 whole rock samples from 20 late orogenic, post-metamorphic, Hercynian-age granitic plutons from the Piedmont of the southern Appalachians, principally in Georgia and South Carolina. These plutons exhibit a regional gradient in oxygen isotopic compositions in which the granites confined to the Inner Piedmont to the northwest are 18O-enriched (11.4 to 7.9) whereas those toward the southeast within the Charlotte-Slate and portions of the Kiokee belts have distinctly lower 18O/16O compositions (8.2 to 5.5); one body that lies along the southeastern edge of the Piedmont in South Carolina, however, appears to be anomalously 18O-enriched (8.9). Most plutons display 18O/16O variations of <1‰ although two vary by as much as 3-4‰. The regional oxygen isotopic pattern among plutons appears to correlate directly with: (1) regional Bouguer gravity patterns, in which the 18O-enriched plutons occupy areas characterized by negative anomalies, whereas low-18O bodies are invariably restricted to regions of positive anomalies; (2) 87Sr/86Sr data, where granites with δ18O values <8‰ have low initial strontium ratios of ~0.703 to 0.705, while 18O-enriched plutons (>9‰) have ratios >0.710; (3) contrasting chemical and accessory mineral compositions, in which many 18O-depleted granites have a number of I-type characteristics, whereas several of the most 18O-enriched plutons exhibit a number of S-type features. It can be inferred from these data that the 18O-enriched granites were formed from continental crustal protoliths that underlie much of the Inner Piedmont and portions of the Kiokee belt, whereas the low-18O plutons were derived from more mafic sources beneath the Charlotte-Slate and portions of the Kiokee belt. The overall correspondence between the regional 18O/16O patterns exhibited by the granites and gravity data implies that these grantes may be essentially rooted to their protoliths, in turn suggesting that the large-scale translational movement recently proposed for the Southern Piedmont may have occurred prior to intrusion of these granites ~320 m.y. ago.

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