Date of Award
Physical and Applied Science
College of Science
Type of Degree
The Blue Ridge province of the Appalachian Mountains has a complex geologic history characterized by more than one metamorphic and deformational event. Mapping of the Blue Ridge has allowed for the province to be broken into the “sub” provinces western, central, and eastern Blue Ridge. The boundaries for these, however, are not well understood due to the difficulty in determining which orogenies caused each metamorphic event.
Detailed petrographic and microprobe analyses were carried out on 17 and 10 samples respectively. Outcrops from Ducktown and Marble in the western Blue Ridge (WBR), Savannah Church, Sylva, and Little Pine Garnet Mine in the central Blue Ridge (CBR), and Beaucatcher Mountain in the eastern Blue Ridge (EBR) that expose pelitic and psammitic rocks metamorphosed under amphibolite to granulite facies conditions were chosen to be used in these analyses. The Ducktown metapelites contain the assemblage garnet, biotite, staurolite, and plagioclase, whereas Savannah Church metapsammites are characterized by the assemblage garnet, biotite, plagioclase, and hornblende. The Sylva metapsammitic outcrop in the middle of the CBR contains the assemblage garnet, biotite, plagioclase, sillimanite, and hornblende. Beaucatcher Mountain metapsammites contain the same assemblage as Savannah Church.
Samples from the WBR are characterized by almandine rich garnet with considerable amounts of spessartine (Xalm = 0.54 - 0.56, Xgrs = 0.02 - 0.05, Xprp = 0.15 - 0.17, Xspss = 0.20 - 0.22). All samples from the CBR and EBR are characterized by almandine rich garnets (Xalm = 0.50 – 0.75, Xprp = 0.07 – 0.2, Xgrs < 0.1), with the exception of samples from Sylva which have garnets with Xprp = 0.17 – 0.25. All garnets are for the most part unzoned with the exception of garnets from Savannah Church, Sylva, and Beaucatcher Mountain where there is an increase in manganese along the rims. Feldspars from these samples are albite rich plagioclases (Xab = 0.50 - 0.70, Xan = 0.21 - 0.50, Xor = 0.0 - 0.02).
Using the average P-T routine of Thermocalc 3.26 and conventional garnet-biotite and garnet + biotite + aluminosilicate + plagioclase thermobarometry, peak metamorphic conditions for Marble (WBR) were calculated at 530 °C, 6.5 kbars. P-T conditions calculated for Little Pine Garnet Mine are 450 ˚C - 550 ˚C and 4.5 - 5.5 kbars. Conditions for Savannah Church were calculated at 660 ˚C – 700 °C, 8 - 9 kbars with Sylva having conditions at 700 °C- 750 ˚C and 11 - 13 kbars. On the other hand, P-T conditions for Beaucatcher Mountain are estimated at 750 °C - 800 ˚C and 7.0 - 7.7 kbars. These results show that the P-T conditions across the Blue Ridge are only broadly consistent with the isograds mapped for the terrane. The most striking anomaly is the unusually high pressures calculated for the Sylva outcrop, which are inconsistent with the overall trend of decreasing temperatures and pressures from Winding Stair Gap in the south to outcrops in the north established by Carpenter (1970) and Hatcher et al. (2005; 2010).
The purpose of this study is to give a better understanding of the tectonic history of the Blue Ridge. Based on the results of this study, the western Blue Ridge boundary may in fact extend farther east than was believed, to include Little Pine Garnet Mine. The central Blue Ridge exhibits higher pressures and temperatures than the western and eastern Blue Ridge, possibly from being deeply thrusted and brought back to the surface. The eastern Blue Ridge conditions are lower than the results for the central Blue Ridge, which is consistent with the Tugaloo terrane being thrust on top of Laurentia.
Geology -- Appalachian Mountains.
Felix, Breana A., "P-T Conditions of Selected Samples Across the Blue Ridge Province" (2012). Theses, Dissertations and Capstones. 300.