Radiometric ages related to the timing of Paleozoic metamorphism and deformation in the Blue Ridge of northwestern North Carolina

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5807688

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

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1. Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Geology
2. Univ. of Georgia, Athens, GA (United States). Dept. of Geology

Thrust sheets within the Blue Ridge (BR) of northwestern NC record different Paleozoic tectonic histories, recognized on the basis of detailed field and petrographic studies. Ar-40/Ar-39, Rb-Sr, Sm-Nd, and U-Pb data are reported on mineral separates, part of an ongoing study to define the ages of Paleozoic metamorphism and deformation within various segments of the Blue Ridge. East of the Gossan Lead fault in vicinity of the Grandfather Mountain window, the BR consists mainly of amphibolite and pelitic schist. These rocks record ordovician Sm-Nd ages, Devonian Rb-Sr ages, and Mississippian Ar-40/Ar-39 ages. A Sm-Nd mineral isochron based on hornblende, plagioclase, and sphene from an amphibolite defines an age of 465 [+-] 35 Ma. Rb-Sr data from an amphibolite of similar metamorphic grade yields Devonian mineral ages ranging from 365--408 Ma. Muscovite separates in associated pelitic schists record Ar-40/Ar-39 plateau ages of 324 [+-] 1 and 329 [+-] 1 Ma. The ages are interpreted to reflect extensive Paleozoic tectonothermal activity in eastern Blue Ridge sequences, commencing with high-grade Ordovician metamorphism, isotopic resetting in the Devonian associated with granitic intrusions, followed by further re-equilibration associated with Alleghanian thrusting. In contrast, thrust sheets from the westernmost BR exhibit low metamorphic grades and record mainly Taconic ages of metamorphism. Preliminary analysis suggests that only the easternmost thrust sheets of northwestern NC experienced thermal resetting during the Devonian.

• OSTI ID: 5807688
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
APPALACHIAN BASIN
DEFORMATION
METAMORPHISM
NORTH CAROLINA
ARGON
GEOLOGIC FAULTS
ISOTOPE DATING
LEAD
MINERALOGY
NEODYMIUM
PALEOZOIC ERA
RUBIDIUM
SAMARIUM
STRONTIUM
TECTONICS
URANIUM
ACTINIDES
AGE ESTIMATION
ALKALI METALS
ALKALINE EARTH METALS
DEVELOPED COUNTRIES
ELEMENTS
FLUIDS
GASES
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
METALS
NONMETALS
NORTH AMERICA
RARE EARTHS
RARE GASES
SEDIMENTARY BASINS
USA
580000* - Geosciences