TRUNCATION AND TRANSLATION OF APPALACHIAN PROMONTORIES?

Accreted arc and microcontinental terranes of the Appalachian Iapetan and peri-Gondwanan realms generally display structural trends concordant with orogen-scale promontories and embayments in native Laurentian rocks. Any redistribution of arcs and microcontinents following their accretion should be reflected in the redispersal of structural trends imprinted by Laurentian promontories on these accreted elements. Post-accretion transcurrent motion in the orogen appears to be recorded by displaced promontories in the southern Appalachians and in Newfoundland.

In the southern Appalachians, the Virginia promontory is defined by a change in structural trends in Laurentian margin and Iapetan rocks, yet peri-Gondwanan rocks outboard of the promontory are undeflected. However, south of the promontory, in the area of the NC-SC state line, peri-Gondwanan rocks display a marked change in structural trends, termed the State Line flexure, that is similar in form and scale, to that of the Virginia promontory. Laurentian and Iapetan rocks inboard of the flexure show no change in structural trends. This geometry suggests that the Virginia promontory was imposed upon the peri-Gondwanan rocks during Late Ordovician-Silurian accretion, but was subsequently subject to approximately 200 km of dextral displacement relative to the Laurentian margin. The dextral strike slip fault system responsible for this geometry may well lie buried beneath Alleghanian hinterland thrust sheets.

The Hermitage flexure affects all accreted elements in the Newfoundland Appalachians and it is truncated against the mid-late Paleozoic dextral Cabot fault system. Structural trends in the region have been interpreted as reflecting the interaction of the Laurentian St. Lawrence promontory with the‘Cabot promontory' in the peri-Gondwanan realm (Lin et al., 1994). Alternatively, the Hermitage flexure may have originated at a previously unrecognized promontory along the Laurentian margin and was subsequently displaced southward during Devonian-Carboniferous motion along the Cabot fault.

Although the timing of the apparent dextral translation of these promontories is loosely constrained at best, they may represent portions of a mid-Paleozoic dextral strike-slip dominated margin along eastern Laurentia.