RECONSTRUCTING THE ACADIAN HINTERLAND FROM UPPER DEVONIAN SEDIMENTS IN THE CENTRAL AND SOUTHERN APPALACHIAN BASIN

In order to better understand the nature of the Devonian Appalachian Acadian hinterland, trace element concentrations and Pb isotope compositions have been determined for shales, sands and silts from four locations in the southern and central portion of the Upper Devonian Appalachian Basin. These shales, and time equivalent more proximal sediments deposited during the latest Frasnian and earliest Famennian stages in the southern and central portion of the basin, record an apparent range in the character of the source components to the basin. While all rock types at each of the four locations exhibit characteristics consistent with a distinctly Grenvillian component, there are a number of deviations which reflect the addition of both older (archean) and juvenile source components as well as evidence of a recycled orogenic source.

Whole rock elemental ratios and Pb isotopic composition suggest four distinct groups of source characteristics; 1) Th/Sc > 1, Zr/Sc > 17, and ²⁰⁷Pb/²⁰⁴Pb < 15.7 reflecting a recycled Grenville-type source, 2) Th/Sc > 1, Zr/Sc > 17, and ²⁰⁷Pb/²⁰⁴Pb > 15.7 reflecting the addition, through sedimentary recycling, of an Archean zircon component, 3) Th/Sc ≤ 1, Zr/Sc ≈ 10, and ²⁰⁷Pb/²⁰⁴Pb < 15.7 reflecting a dominantly Grenville-type source, and 4) Cr/V > 0.6 and Y/Ni < 1.1 possibly suggesting the presence of an ophiolitic component.

These results suggest the Acadian hinterland in the southern and central portion of the Devonian Appalachian Basin was composed of multiple components in addition to those with a Grenvillian character. This represents significant new information about the Acadian orogen. This is especially important because little is known of its nature, especially in the central and southern Appalachians where several diverse tectonic elements were available along the Laurentian margin to source the Acadian foreland basin.