LAKE MURRAY SPILLWAY – DELVING INTO THE CORE OF THE DREHER SHOALS TERRANE, COLUMBIA, SOUTH CAROLINA

The Lake Murray Spillway is one of the preeminent exposures in the Piedmont of South Carolina and southeastern Appalachians. The Spillway is an emergency overflow channel for Lake Murray and is spectacular for both extent and content. It is on the south side of Lake Murray dam (also known as Dreher Shoals dam) and is located approximately 7 miles west of the Columbia center city just off Route 6. The dam is operated by South Carolina Electric and Gas (SCE&G, a SCANA corporation), and permission must be obtained a few weeks in advance to enter. This exposure is available only for college-level or above organized groups for educational purposes. Several restrictions are imposed by SCE&G. Details concerning restrictions and contact information are provided at the end of this presentation.

The Spillway is an excellent laboratory, which can be used to begin an exploration of the adjacent area. The exposed geology shows structural, petrologic, stratigraphic, mineralogic, and tectonic relations. Much of our understanding of the Spillway and surrounding geology comes from the work of Donald Secor (USC) and his associates. Secor (1986) described 4 deformational events in the surrounding area. Rocks in the Spillway are primarily deformed by the 2^nd (mylonitic deformation) and 4^th events. Evidence for the 1^st and 3^rd deformations, however, is not impossible to recognize. Other relations include: A significant contact between Lake Murray felsic gneiss and garnetiferous pelitic schist exhibits both intrusive and structural origins. The garnetiferous pelitic schist is an excellent example of porphyroblastic relations from multiple deformations and contains amphibolite facies assemblages that include kyanite and staurolite. Numerous pegmatitic and felsic layers are complexly folded. Boudinage structures within amphibolite layers and many other kinematic indicators of movement are present. Tectonically, parts of the exposure also contain structural mélanges. Late Mesozoic mafic dikes are present, and brittle structures offset all younger features.