19 Unraveling Appalachian Orogenic Events Using Geological and Geophysical Methods

Monday, 18 March 2024
8:00 AM - 12:00 PM
Merrimack Room

NOT THE NEOACADIAN OROGENY

Paper number: 19-2
Program: Theme Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

The term Neo-Acadian was coined by the late Peter Robinson in 1998 for Late Devonian to early Mississippian shortening in southern New England. The earlier Acadian orogeny is bracketed between emplacement of the late Silurian (422 Ma) Pocomoonshine pluton in Maine and the end of westward migration of the Acadian foreland basin around 385 Ma; it has been associated with sinistral transpression and the accretion of West Avalonia to composite Laurentia. As originally defined, the Neo-Acadian orogeny continued from ~370 to 350 Ma. The term has continued to be used in New England with its original meaning, but Robinson subsequently deprecated it, favouring instead the Indigenous-derived name Quaboagian.

The term, now spelled Neoacadian, was further confused from 2005 onward by an association with the accretion of the Meguma terrane outboard of Avalonia, even though published dates for Meguma terrane deformation fall either before or after the Neo-Acadian/Quaboagian as defined by Robinson. Folding of the Meguma terrane occurred at ~400 Ma during the Acadian interval, but possibly in a different tectonic environment from the main Acadian orogen. The Late Devonian and early Mississippian in Nova Scotia was a time of oblique extension, when the lowest unit of the Maritimes Basin was deposited in a basin-and-range setting, unconformably on Meguma terrane rocks, including subduction-related(?) plutons with ages mainly 379-372 Ma. Although the transtensional basins were probably connected with Quaboagian transpression in New England via dextral strike-slip, the tectonic environment in Atlantic Canada at this time was clearly anorogenic. Subsequent basin inversion took place after 330 Ma in a transpressional regime associated with dextral motion on the east-west Minas fault zone.

The (mis-)use of "Neo-Acadian orogeny" for accretion of the Meguma Terrane has led to misconceptions both about the timing of its accretion and about the Late Devonian tectonic regime in Atlantic Canada, and we recommend that this term be abandoned in favour of Quaboagian, restricted to 370–350 Ma convergence in New England (synchronous with extension, not orogeny, in Atlantic Canada). Earlier deformation in the Meguma terrane, falling within the Acadian time-window but potentially unrelated to the rest of the Acadian orogen, may require a new name.

Geological Society of America Abstracts with Programs. Vol. 56, No. 1

doi: 10.1130/abs/2024NE-397329

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