Introduction

 

The name Acadian came from the French colony of Acadie near the Bay of Fundy. Rocks here are widely known to have been mildly metamorphosed during the Devonian (Tucker, et al.). Most of the evidence we now have of the Acadian orogeny is found in New England and the Maritime Provinces of Canada, but there is also an area in the southern Appalachians where Acadian structures can be found, in the Talladega slate belt of Alabama.

The convergence of Avalonia and other peri-Gondwanan terranes with Laurentia that created the Acadian orogenesis, began in the Middle Silurian and continued into the Early Mississippian (Ferrill and Thomas, 1988). The closure of the southwestern (separating Laurentia and Gondwana) and northeastern (separating Greenland and Baltica) sections of the Iapetus Ocean caused the progressive accretion of terranes, island arcs, and microcontinents onto the Laurentian coast (Van de Pluijm and Others, 1993). Sucessive oblique collisions caused orogenesis to migrate in a southwestward direction. Former terranes from the Iapetus Sea became “compressional indentors” and each subsequent collision produced thickening of the crust, high metamorphism, granite emplacement, and the formation of a clastic wedges (Rast and Skehan, 1993).

This website provides an introduction to the structural styles, metamorphism and plutonism, and stratigraphy of the Acadian orogenesis. You will also find a brief discussion of the time scale of the orogeny, which has been much debated in the literature.

Acadian tectonic sequence in the northern Appalachians

 

*Bold face words are defined in the glossary.