Terranes

By the time of the Acadian orogeny, a terrane called Medial New England, derived from Gondwana, had already been added to Laurentia (in Middle Ordovician time). This terrane forms much of what is now New England. Medial New England consists of a number of crystalline basement blocks related to the Taconic orogeny. The boundary between Medial New England and Laurentia is marked today by isolated remnants of small mafic and ultramafic intrusions, and ophiolite, hinting at the former presence of an ocean between the two plates (Tucker). Laurentia and Medial New England also have a very different stratigraphy.

The terrane called Composite Avalon, or Avalonia, was derived from a different Gondwanan terrane, and it was the collision of Composite Avalon with the Medial New England terrane (already sutured to Laurentia) that created the main deformational phase of the Acadian orogeny. The boundary between Medial New England/Laurentia and Avalon has been identified based on differences in stratigraphy and fossil provinciality (Tucker).

 

Figure showing where different parts of Composite Avalon are situated today (Cocks).

 

Carolina was another terrane that collided with Laurentia, forming a later phase of Acadian deformation in the southern Appalachians.

 

*Bold face words are defined in the glossary.

 

Present-day locations of the Avalon and Carolina terranes