Lead isotope ratios of galenas from stratabound massive sulfide deposits in upper Precambrian metasediments of the Blue Ridge (BR) geologic province are too radiogenic for their presumed synsedimentary, late Precambrian age. A positive correlation between lead and sulfur isotope ratios in galenas from Ducktown, Tennessee, is interpreted as an original characteristic of the ores, and indicates that the radiogenicity of the lead is not the result of metamorphic processes, but of derivation of lead from U/Pb-enriched elastic sediments. At Ducktown, however, lead and sulfur isotope ratios indicate a component derived from a mafic source, and suggest that rift basin faulting may have controlled mineralization. Lead isotope ratios in Mount Rogers Formation rhyolites and in BR Paleozoic plutons indicate different sources of lead than those contributing to lead in massive sulfide deposits. / Lead isotope ratios of galenas from Piedmont province polymetallic massive sulfide (PMS) deposits define a trend of decreasingly ensialic volcanism from northeast to southwest. A regression through the data has a slope that corresponds to a secondary isochron age of about 3.7 b.y. The line is proposed to represent mixing between variable amounts of upper crustal lead (decreasing to the southwest) with lead from a source depleted in U/Pb and Th/Pb ratios relative to upper crust. The depleted source has, however, experienced either continuous or episodic enrichment of uranium relative to lead. The occurrence of a similar trend in galenas from Kings Mountain belt ores is further evidence for such a source. Sulfur isotope ratios in PMS are consistent with derivation of sulfur from lower Paleozoic seawater sulfate. / Rocks and ores from the southern Appalachians have lead isotope patterns that suggest three distinct isotope provinces. Rocks and vein deposits of the Blue Ridge and Inner Piedmont appear to be dominated by lead derived from Grenville-age crust. Some rocks of the eastern Piedmont are characterized by lower ('207)Pb/('204)Pb and ('208)Pb/('204)Pb ratios than BR and Inner Piedmont rocks. PMS and the Kings Mountain belt have isotope ratios suggesting a mixed source with Grenville-age basement as one end menber and mantle or mantle-derived material as the other. / Source: Dissertation Abstracts International, Volume: 44-09, Section: B, page: 2688. / Thesis (Ph.D.)--The Florida State University, 1983.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75182 |
| Contributors | LEHURAY, ANNE P., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 451 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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