Polyorogenic /sup 40/Ar//sup 39/Ar mineral age record in the Seve and Koeli Nappes of the Gaeddede area, northwestern Jaemtland, central Scandinavian Caledonides

Journal Article · Tue Mar 01 04:00:00 EST 1988 · J. Geol.; (United States)

OSTI ID:5340670

Dallmeyer, R D; Gee, D G

Eugeoclinal terranes represented in the Koeli Nappes were thrust > 500 km onto the Baltoscandian platform during the early to middle Paleozoic. Underlying thrust sheets of the Seve Nappe complex are suspected to have been derived from the outer margin of continent Baltica. Contrasting tectonothermal histories are recorded in Seve and Koeli Nappes. Eclogite-bearing Seve rocks underwent an initial amphibolite-grade regional metamorphism. Subsequent ductile imbrication of high- and intermediate-pressure structural units occurred prior to c. 460-470 Ma. A later thermal overprint everywhere rejuvenated Seve biotite and muscovite argon systems at c. 430 +/- 5 Ma. /sup 40/Ar//sup 39/Ar plateau ages of hornblende suggest attainment of peak metamorphic conditions in the Lower and Middle Koeli Nappes at ca. 430 +/- 5 Ma. Plateau dates of muscovite and biotite in both Seve and Koeli units range down to 417 Ma. Comparison with /sup 40/Ar//sup 39/Ar mineral ages reported elsewhere in the central Scandinavian Caledonides suggests a polyorogenic evolution consisting of: (1) variable high-pressure metamorphism of distal Baltoscandian miogeoclinal sequences during their entrainment in an accretionary wedge that developed in the Late Cambrian-Early Ordovician over a westdipping subduction zone; related arc volcanic activity occurred in more outboard, western terranes; (2) ductile imbrication of high- and intermediate-pressure sequences within the accretionary wedge (diachronous cooling and/or chronologically distinct tectonic episodes are indicated through the Early and Middle Ordovician); (3) ultimate accretion of a variety of eugeoclinal terranes along the Baltic continental margin; and (4) imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the Baltoscandian platform in the Silurian and Devonian.

• Research Organization: Univ. of Georgia, Athens (USA)
• OSTI ID: 5340670
• Journal Information: J. Geol.; (United States), Journal Name: J. Geol.; (United States) Vol. 96:2; ISSN JGEOA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
AGE ESTIMATION
AMPHIBOLE
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOTITE
CONTINENTAL MARGIN
EUROPE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
HORNBLENDE
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
METAMORPHISM
MICA
MINERALS
MUSCOVITE
NUCLEI
PRESSURE DEPENDENCE
RADIOISOTOPES
SCANDINAVIA
SILICATE MINERALS
STABLE ISOTOPES
SWEDEN
TECTONICS
VOLCANISM
WESTERN EUROPE
YEARS LIVING RADIOISOTOPES