Structural inheritance in Carolinia, external to the excised Rheic Suture: Savannah River Site, South Carolina, USA.

Abstract

Phanerozoic reactivations of basement fault zones are documented in 5000m of basement core recovered from beneath the updip Atlantic Coastal Plain underlying the U.S. Department of Energy Savannah River Site. These basement fault zones are adjacent to the excised Rheic Ocean suture. C. 619 and 624 Ma metaintrusive rocks contain a mylonitic fabric and intrude foliated mafic metavolcanic rocks. At c. 305 Ma, granulite facies orthogneisses were thrust over amphibolite facies metaigneous rocks in the transpressive Tinker Creek nappe. The overturned limb of the nappe localizes the Dunbarton Triassic basin border fault. The border fault acted as a conduit for fluids in the Mesozoic and Cenozoic. C. 220±5 Ma, a potassium and silica metasomatic event affected SRS basement. A propylitic event flushed reducing fluids through rocks as young as Santonian. The remains of a Triassic subbasin were identified in the northwest part of the site. A Cretaceous and younger vein paragenesis overprints the previous events. More than thirty pseudotachylytes are found in SRS basement and are preferentially localized on metasomatized Alleghanian chloritic fractures. Pseudotachylyte post-dates mineralized fractures. The Pen Branch fault offsets the basement-Cretaceous unconformity and is present in c. 242 m of core between PBF-7-419 m and PBF-7-660.8 m. The Pen Branch Fault cross-cuts mineralized fractures and must postdate strike-normal zeolites.