Regional metamorphic P-T path suggesting control by thrusting, northern Alabama Piedmont, Appalachians
Analysis of metamorphic textures and mineral chemistry in Wedowee Group metapelites near the Blakes Ferry pluton reveals a regional metamorphic P-T path dominated by pressure fluctuations attributable to thrusting. Country rocks contain the post-S/sub 2/ equilibrium assemblage Mu+Bt+Chl+Gar+Ep+Pc+Qz+/-l 1+/-Ti (M/sub 2/); St inclusions in Gar and graphite inclusions in Bt oblique to S/sub 2/ record the presence of an earlier Bt+St+Gar assemblage (M/sub 1/). Published experimental data, Mu-Bt-Gar-Pc thermobarometry, and aluminosilicate reaction textures found elsewhere in the Wedowee Gp constrain P-T conditions to 610+/-40/sup 0/C, 4+/-1.5kb for M/sub 1/ and 580+/-40/sup 0/C, 9.5+/-1 kb for M/sub 2/. Post-S/sub 2//M/sub 2/ emplacement of the Blakes Ferry pluton caused garnet resorption and growth of radiating Chl clots within 50m of the pluton. Ca- and Fe/Mg-enriched Gar rims and more calcic Pc in the aureole than country rocks indicate a reversal of reaction (2) during contact metamorphism. Thermobarometry suggests conditions of 560+/-40/sup 0/C at 5.5+/-1kb. Shear bands and weak crenulations (S/sub 3/) post-date the contact metamorphism. These data define a P-T path initially characterized by isothermal compression over a range of 5kb which is interpreted to record emplacement of a approx. 15km thick Piedmont Allochthon onto the Wedowee Gp. Subsequently decreasing P reflects tectonic uplift and partial unroofing prior to pluton emplacement. This scenario implies progressive SE to NW nappe stacking during Paleozoic crustal thickening and provides independent verification for large-scale thrust tectonics recently suggested on the basis of structural analysis in the southernmost Appalachians.
- Research Organization:
- Virginia Tech, Blacksburg (USA)
- OSTI ID:
- 6596758
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALABAMA
METAMORPHIC ROCKS
CHEMICAL COMPOSITION
GEOLOGIC HISTORY
MINERALOGY
PETROGENESIS
APPALACHIAN MOUNTAINS
GEOCHEMISTRY
GEOLOGIC FAULTS
INCLUSIONS
METAMORPHISM
PRESSURE EFFECTS
TECTONICS
CHEMISTRY
FEDERAL REGION IV
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MOUNTAINS
NORTH AMERICA
ROCKS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)
580201 - Geophysics- Seismology & Tectonics- (1980-1989)