Provenance of Mudstones from two Ordovician Foreland Basins in the Appalachians
Mudstones from the Taconic and Blountian foreland basins were analyzed for whole-rock chemical composition and clay mineral composition. These foreland basins formed during the middle and late Ordovician when exotic terranes collided with Laurentia. The purpose was to determine if the mudstones record first-order trends in provenance that are related to tectonic history.
In both basins, the ratio of chlorite to illite and the ratio of the concentration of three "mafic" elements (Ti, Cr, Ni) to Nb (a "felsic" element) increases with time. However, mudstones from the Taconic foreland basin have a higher proportion of Ti, Cr, and Ni than those from the Blountian foreland basin. Results from the Blountian foreland basin showed the greater amount of scatter.
The outboard terranes that collided with Laurentia were the most important sources of siliciclastic sediment because carbonate platforms fringed the continental margin of each basin. Thus, compositional trends in each basin reflect an increase in the proportion of sediment eroded from mafic source rocks within the colliding terrane. In presently accepted tectonic models for the Taconic foreland basin, the colliding terrane is an arc system. The provenance signature in the mudstones suggests the sediment source shifts from a non-magmatic outer arc to the inner volcanic arc during the collision. The comparatively lower concentration of mafic elements in the Blountian foreland basin mudstones may indicate that the colliding terrane was composite or that its angle of convergence was more oblique.