GEOL 5903 Seminar: Dylan McKeen
GEOL 5903 Seminar: Dylan McKeen
Title: If “not the Neoacadian”, then what?
Location and Time: Huggins Science Hall, Room 336 (or 324), 4:00 p.m.
Abstract:
Recognition of orogenic events is an important part of interpreting deformational and regional metamorphic episodes in both modern and ancient mountain belts. Deformation and regional metamorphism that do not appear to fall into a previously recognized orogeny necessitate new interpretations and models, and thus the introduction and naming of new orogenies. Choosing a name is largely semantic, but the proposal of an accompanying tectonic model is more fundamental. Recently, controversy has been sparked about the naming of the orogenic event that occurred in the Meguma terrane of southern Nova Scotia prior to its amalgamation with composite Laurentia in the Carboniferous. Some authors prefer that this orogeny be included in an already-named event, either the Acadian or Neoacadian, whereas other authors have suggested a new name, thus requiring a new model. The mid-Devonian orogenic event in the Meguma terrane has historically been considered part of the Acadian orogeny; however, the Middle Devonian timing of deformation and regional metamorphism in Meguma terrane is not consistent with the mainly Late Silurian through Early Devonian timing of the Acadian orogeny. The Neoacadian orogeny, first used to describe Late Devonian through Early Carboniferous metamorphism and plutonism in New England, has recently been expanded to include the orogenic event in the Meguma terrane. However, Meguma terrane is characterized by extension during the Late Devonian through Early Carboniferous. Compressional deformation and metamorphism in the Meguma terrane predated the main phase of Neoacadian orogenesis, which makes this name inappropriate. Including the collision of Meguma with a previously termed orogeny implies shared timing, style, and cause of deformation. These links may be difficult to prove, thus using a new name seems preferable. However, the position of the Meguma terrane during the Middle Devonian is poorly constrained, making any orogenic model uncertain.