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

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

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

Dallmeyer, R D ^[1]

---

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), Vol. 97:2; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

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