Nine basement blocks were sampled from locations spanning from Pennsylvania to Georgia in the eastern United States. These basement blocks are similar in that they have radiometric ages of approximately 1.0 billion years (with one exception), they are all at upper amphibolite to granulite grades, and are compositionally similar. Whole rock lead isotopic studies were performed on these samples in order to distinguish any possible differences in source regions that could be used to discriminate potential terranes within this 2700 km long region of the Appalachians.
The lead isotopic system was used to decipher differences between these basement blocks. Traditional display of the data, in the form of ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagrams did not adequately bring out the similarities or differences in the data. Therefore, another method of displaying the data (e.g. Hart, 1984) was used in which the data from the Blue Ridge of Virginia was used as the reference against which all other data were compared. This method proved successful and trends were recognized.
There are at least three different isotopic reservoirs within the central and southern Appalachians. There is the reservoir represented by the Blue Ridge of Virginia and six of the basement blocks that are isotopically similar (Honeybrook Upland, State Farm Gneiss, Sauratown Mountain, Tallulah Falls, Corbin Gneiss, and Pine Mountain), a second reservoir represented by the Baltimore Gneiss, and the third represented by the 1.8 billion year Carvers Gap Gneiss.
The terrane that is represented by the Blue Ridge of Virginia and the six isotopically similar basement blocks is defined by ²⁰⁶Pb/²⁰⁴Pb ratios of 16.5-17.5, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.4-15.5, and ²⁰⁸Pb/²⁰⁴Pb ratios of 36.0-37.0. The Baltimore Gneiss has ²⁰⁷Pb/²⁰⁴Ph ratios ranging from 15.2-15.6 and ²⁰⁸Pb/²⁰⁴Pb ratios ranging from 33.1- 38.1. These ratios although they show a broader range in values are elevated and suggest that the Baltimore Gneiss is isotopically different from the reference Blue Ridge. Carvers Gap Gneiss has ²⁰⁸Pb/²⁰⁴Pb ratios of 36.3-40.3 and ²⁰⁶Pb/²⁰⁴Pb ratios of 15.9-18.2. These ratios show that Carvers Gap Gneiss is isotopically dissimilar from the reference also. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/43326 |
| Date | 16 June 2009 |
| Creators | Parks, Jane Elizabeth |
| Contributors | Geology |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | vii, 71 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 29551626, LD5655.V855_1993.P378.pdf |
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