SIMILARITIES IN AMPHIBOLITE ASSEMBLAGES OF THE EASTERN AND CENTRAL BLUE RIDGE OF SOUTHWESTERN NORTH CAROLINA

Amphibolites are a ubiquitous minor component of the olistostromal terranes of the Central and Eastern Blue Ridge of North Carolina and Georgia. Identifying likely protoliths for these rocks, through bulk chemical and trace element analysis and their mineralogies and mineral chemistries, provides information about the tectonic settings in which they formed, and places constraints on the origins and histories of the rock packages in which they are enclosed. We are examining a suite of amphibolites from the Ashe Metamorphic Suite (AMS) in the Eastern Blue Ridge province, near the towns of Highlands and Cashiers, NC, for comparison to amphibolite datasets from several locations within the Central Blue Ridge (CBR: Buck Creek/Kimsey Bald, Carroll Knob, Tathams/Savannah Church, Addie/Willets).

Our AMS amphibolites are medium to fine-grained, “salt and pepper” to very amphibole rich, with variable secondary epidote. In outcrop they are lenticular and can exhibit strong folding, but are not migmatitic, unlike many in the CBR. In terms of rare-earth elements (REE’s), AMS samples range from 8-200 x CI in LREE and 10-15 x CI in HREE, with patterns ranging from slightly LREE depleted to enriched [La/Sm]N: 6.8-0.3, [La/Yb]N: 27.5-0.4].

Compared to CBR amphibolites, REE data for AMS samples differ in abundance levels and patterns to those from Buck Creek, Carroll Knob, and Kimsey Bald. These CBR suites show ocean crust affinities, with marine gabbros as likely protoliths. AMS samples are very similar in pattern and abundance to CBR samples from Tathams/Savannah Church and Addie/Willets, and like these occur primarily as small blocks within metasedimentary gneiss/schist country rocks. CBR and Eastern Blue Ridge rocks have been mapped into different terranes due to differences in metamorphic grade and lithology. However, the inclusion of chemically similar amphibolite blocks in olistostromes from both regions may point to commonalities in origin and petrogenetic history.