A PROPOSED ARCHITECTURE FOR THE NEOPROTEROZOIC MAGMA-RICH IAPETAN MARGIN AS EXPRESSED IN THE EXHUMED CENTRAL TO SOUTHERN APPALACHIAN BLUE RIDGE AND PIEDMONT (Invited Presentation)

Whether oceanic basins develop as magma-poor or magma-rich may depend on localization and rate of strain of the continental mantle lithosphere, as well as pre-strain mantle temperatures. Triassic graben associated with the formation of central Atlantic basin in eastern North America were intruded by 200 Ma basaltic magmas as rift-related continental extension ebbed. At ca. 185-175 Ma, SDRs were emplaced on the Atlantic continental margin that presently comprise the East Coast Magnetic Anomaly, localizing strain to the nascent ridge, marking lithospheric breakup.

Roughly 360 million years earlier in the late Neoproterozoic, the Iapetan ocean basin formed along Laurentia in largely the same position as the central Atlantic. From the Pennsylvania embayment to the Alabama promontory, ca. 565 Ma Catoctin volcanic rocks and amphibolites presently exposed in the central Appalachian internides are associated with the formation of the Iapetan ocean basin and, like other magma-rich margins, could mark the end of lithospheric extension and the birth of a new plate margin. Alternatively, the presence of ultramafic rocks in structural juxtaposition to crustal rocks and metasediments could instead represent magma-poor lithospheric extension, with the Iapetan basalts pre-dating breakup (analogous to CAMP).

Crustal extension and subsequent magmatism provide a way to classify Neoproterozoic–early Cambrian metasedimentary rocks in the central Appalachians in a rifted margin architecture, most simply with respect to Catoctin and Sams Creek volcanic rocks and their high-grade equivalents to the south. This architecture helps contextualize many long-standing stratigraphic debates, including the significance of the Martic Line and the relationship of the Glenarm Supergroup to the Neoproterozoic–lower Cambrian continental shelf. In addition, it places the much of the late Neoproterozoic/early Cambrian Chilhowee stratigraphy on the continental shelf into the post-rift drift stage.

The Catoctin volcanic rocks are limited northeastward at the New Jersey transform, which offset the rift dextrally at the Pennsylvania embayment of the rifted margin and provided a crustal template for the central Appalachian Iapetan passive margin. By the end of early Cambrian, a carbonate ramp formed along the new Iapetan margin.