Geochronology of Early to Middle Paleozoic tectonic development in the Southwest Newfoundland Gander Zone

Journal Article · Wed Jan 01 04:00:00 EST 1986 · J. Geol.; (United States)

DOI:https://doi.org/10.1086/629010· OSTI ID:6827882

Chorlton, L B; Dallmeyer, R D

U-Pb zircon isotopic ages of 452 +/- 51/13 Ma and 458 +/- 29/22 Ma on metavolcanic rocks indicate that Ordovician and possibly older rocks underlie the Gander zone itself. A temporal framework for the three main stages of regional deformation, corresponding to pre-metamorphic recumbent folding (D/sub 1/) and transpression (D/sub 2/ and D/sub 3/), is presented using U-Pb and /sup 40/Ar//sup 39/Ar dates of granitoid and metamorphic rocks. D/sub 1/ is bracketed as late Ordovician or Silurian. Spatial domains of contrasting /sup 40/Ar//sup 39/Ar biotite and hornblende cooling ages reflect the D/sub 2/ and D/sub 3/ episodes, which led to post-metamorphic cooling following uplift of different segments of the amphibolite facies metamorphic terrane. Early Devonian differential uplift on the Cape Ray Fault in the northeast was associated with D/sub 2/ and caused rapid post-metamorphic cooling through Ar retention temperatures to yield nearly concordant biotite and hornblende ages between 374 and 388 Ma. Reverse and oblique-slip faulting during D/sub 3/ produced oblique northwesterly uplift of the still-buried portion of the amphibolite facies terrane against Devonian strata in the southwest part of the Cape Ray Fault zone. Late Devonian to early Carboniferous post-metamorphic cooling in this segment is confirmed by /sup 40/Ar//sup 39/Ar plateau dates of 345-353 Ma for biotite and 361 Ma for hornblende. K-Ar mineral dates are likewise earliest Devonian and younger, in contrast to numerous pre-Devonian K-Ar ages in the Humber and the Dunnage Zones. The Gander zone, already identified as a wide, Acadian ductile shear belt and noted for widely variable metamorphic grade, might represent a mobile zone where coherent relics of the Iapetus or prior stages of Appalachian history were exhumed during Devonian orogeny, many after Silurian or earlier tectonic burial.

• Research Organization: Carleton Univ., Ottawa, Ontario
• OSTI ID: 6827882
• Journal Information: J. Geol.; (United States), Journal Name: J. Geol.; (United States) Vol. 94:1; ISSN JGEOA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
ACTINIDES
AGE ESTIMATION
ALKALI METALS
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CANADA
DEVONIAN PERIOD
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
ISLANDS
ISOTOPE RATIO
ISOTOPES
LEAD
LIGHT NUCLEI
METALS
METAMORPHISM
NEWFOUNDLAND
NORTH AMERICA
NUCLEI
ORDOVICIAN PERIOD
PALEOZOIC ERA
POTASSIUM
RADIOISOTOPES
SILURIAN PERIOD
STABLE ISOTOPES
TECTONICS
URANIUM
YEARS LIVING RADIOISOTOPES