A tectonic linkage between the Rodelide orogen (Sierra Leone) and the St. Lucie metamorphic complex in the Florida subsurface

Journal Article · Wed Mar 01 04:00:00 EST 1989 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629293· OSTI ID:6982719

Dallmeyer, R D ^[1]

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1. Univ. of Georgia, Athens (USA)

Hornblende concentrates prepared from cuttings from two deep test wells penetrating the complex display internally concordant {sup 40}Ar/{sup 39}Ar incremental-release spectra defining plateau ages of 510.8 {plus minus} 1.1 Ma and 513.1 {plus minus} 1.8 Ma, which are interpreted to date post-metamorphic cooling through temperatures required for intracrystalline argon retention. The Kasila Group constitutes the western segment of the Rokelide orogen in Sierra Leone. Four hornblende concentrations prepared for amphibolite within the Kasila Group yield {sup 40}Ar/{sup 39}Ar plateau ages of 505.0 {plus minus} 5.2, 508.2 {plus minus} 2.1, 510.5 {plus minus} 2.6, and 546.1 {plus minus} 6.8 Ma. They are interpreted to date post-metamorphic cooling through appropriate argon closure temperature following a ca. 550-560 Ma, Pan-African II phase of tectonothermal activity. A biotite concentrate from paragneiss within the Kasila Group displays an internally concordant {sup 40}/Ar{sup 39}Ar release spectrum defining a plateau age of 524.7 {plus minus} 1.3 Ma, which likely reflects slight contamination with extraneous (excess) argon. Muscovite from the Marampa Group yields a {sup 40}Ar/{sup 39}Ar plateau age of 561.1 {plus minus} 2.3 Ma, which is interpreted to date cooling through appropriate argon closure temperatures. Although these temperatures are generally considered to be lower than those for hornblenede, the muscovite records an older cooling age, suggesting that the Marampa Group experienced slightly earlier post-metamorphic uplift and cooling relative to the Kasila Group. Lithologic comparison combined with similarities in post-metamorphic thermal evolution suggest that the St. Lucie Metamorphic Complex originated within the Rockelide orogen. This and other lithotectonic elements of the Suwannee terrane appear to represent a fragment of Gondwana which accreted to Laurentia during late Paleozoic amalgamation of Pangea.

• OSTI ID: 6982719
• Journal Information: Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 97:2; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
AMPHIBOLE
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
COOLING
CORRELATIONS
DRILL CORES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXPLORATORY WELLS
FEDERAL REGION IV
FLORIDA
GEOLOGIC DEPOSITS
GEOLOGIC STRATA
GEOLOGIC STRUCTURES
GEOLOGY
HORNBLENDE
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MICA
MINERALS
MUSCOVITE
NORTH AMERICA
NUCLEI
RADIOISOTOPES
RESERVOIR TEMPERATURE
SILICATE MINERALS
STABLE ISOTOPES
STRATIGRAPHY
TECTONICS
USA
WELLS
YEARS LIVING RADIOISOTOPES