Chronology of paleozoic metamorphism and deformation in the Blue Ridge thrust complex, North Carolina and Tennessee

Journal Article · Thu May 01 04:00:00 EDT 1997 · American Journal of Science

DOI:https://doi.org/10.2475/ajs.297.5.488· OSTI ID:563424

Goldberg, S A ^[1]; Dallmeyer, R D ^[2]

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1. New Brunswick Lab., Argonne, IL (United States)
2. Univ. of Georgia, Athens, GA (United States)

The Blue Ridge province in northwestern North Carolina and northeastern Tennessee records a multiphase collisional and accretionary history from the Mesoproterozoic through the Paleozoic. To constrain the tectonothermal evolution in this region, radiometric ages have been determined for 23 regionally metamorphosed amphibolites, granitic gneisses, and pelitic schists and from mylonites along shear zones that bound thrust sheets and within an internal shear zone. The garnet ages from the Pumpkin Patch a thrust sheet (458, 455, and 451 Ma) are similar to those from the structurally overlying Spruce Pine thrust sheet (460, 456, 455, and 450 Ma). Both thrust sheets exhibit similar upper amphibolite-facies conditions. Because of the high closure temperature for garnet, the garnet ages are interpreted to date growth at or near the peak of Taconic metamorphism. Devonian metamorphic ages are recognized in the Spruce Pine thrust sheet, where Sm-Nd and Rb-Sr garnet ages of 386 and 393 Ma and mineral isochron ages of 397 {+-} 14 and 375 {+-} 27 Ma are preserved. Hornblendes record similar {sup 40}Ar/{sup 39}Ar, Sm-Nd, and Rb-Sr ages of 398 to 379 Ma. Devonian {sup 40}Ar/{sup 39}Ar hornblende ages are also recorded in the structurally lower Pumpkin Patch thrust sheet. The Devonian mineral ages are interpreted to date a discrete tectonothermal event, as opposed to uplift and slow cooling from an Ordovician metamorphic event. The Mississippian mylonitization is interpreted to represent thrusting and initial assembly of crystalline sheets associated with the Alleghanian orogeny. The composite thrust stack of the Blue Ridge complex was subsequently thrust northwestward along the Linville Falls fault during middle Alleghanian orogeny (about 300 Ma).

• Sponsoring Organization: USDOE
• OSTI ID: 563424
• Journal Information: American Journal of Science, Journal Name: American Journal of Science Journal Issue: 5 Vol. 297; ISSN AJSCAP; ISSN 0002-9599
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
AGE ESTIMATION
APPALACHIAN MOUNTAINS
DEFORMATION
METAMORPHISM
NORTH CAROLINA
PALEOZOIC ERA
TENNESSEE