A Tectonic Linkage between the Rodelide Orogen (Sierra Leone) and the St. Lucie Metamorphic Complex in the Florida Subsurface

Abstract

The St. Lucie Metamorphic Complex comprises part of the non-Laurentian, Paleozoic Suwannee terrane beneath the Gulf and Atlantic Coastal Plains of the southeastern United States. Hornblende concentrates prepared from cuttings from two deep test wells penetrating the complex display internally concordant $$^{40}Ar/^{39}Ar$$ incremental-release spectra defining plateau ages of $$510.8 \pm 1.1 Ma$$ and $$513.1 \pm 1.8 Ma$$, 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 concentrates prepared from amphibolite within the Kasila Group yield $$^{40}Ar/^{39}Ar$$Ar plateau ages of $$505.0 \pm 5.2$$, $$508.2 \pm 2.1$$, $$510.5 \pm 2.6$$, and $$546.1 \pm 6.8 Ma$$. They are interpreted to date post-metamorphic cooling through appropriate argon closure temperatures following a ca. 550-560 Ma, Pan-African II phase of tectonothermal activity....