Insights into the Acadian orogeny, New England Appalachians: a provenance study of the Carrabassett and Kittery formations, Maine

The Central Maine Basin and Merrimack Trough are Silurian basins that formed adjacent to or were accreted to the Laurentian margin during the Acadian orogeny. The Early Devonian Carrabassett Formation of the Central Maine Basin and the Kittery Formation of the Merrimack Trough have major and trace element compositions indicative of a passive continental margin provenance, not unlike the older formations of the Central Maine Basin that are thought to have been derived from Laurentian sources. However, both the Carrabassett and Kittery formations have paleocurrent indicators of outboard sources. The Carrabassett Formation is one of the youngest formations of the Central Maine Basin and was deposited just prior to the Acadian orogeny. The Carrabassett and Kittery formations have major and trace element concentrations suggestive of passive margin turbidites derived from intermediate to felsic sources, inconsistent with a juvenile Avalonian provenance. The Carrabassett Formation contains detrital zircon grains that match the ages of peri-Gondwanan Ganderia. Unlike the dominance of positive bulk-rock eNd values that are characteristic of Avalonia, Ganderia has negative eNd values that are a better match for the negative eNd values of the Carrabassett and Kittery formations. However, Ganderia accreted to Laurentia during the Salinic orogeny, prior to the deposition of the Carrabassett Formation, and was basement to the sediments of the Central Maine Basin upon which the Carrabassett and other formations were deposited. Wedging of Ganderia by Avalonia during the initial stages of the Acadian orogeny may have uplifted Ganderia, forming highlands outboard of the Central Maine Basin that served as the source of the Carrabassett Formation sediments. RESUME Le bassin central du Maine et la cuvette de Merrimack constituent des bassins siluriens s’etant formes le long de la marge laurentienne ou s’y etant accretes au cours de l’orogenese acadienne. La Formation du Devonien precoce de Carrabassett, dans le bassin central du Maine, et la Formation de Kittery, de la cuvette de Merrimack, presentent des compositions en elements majeurs et traces signalant une provenance d’une marge continentale passive, a l’instar des formations plus âgees du bassin central du Maine qu’on pense originaires de sources laurentiennes. Les formations de Carrabassett et de Kittery comportent toutefois des indicateurs de paleocourants de sources exterieures. La Formation de Carrabassett constitue l’une des formations les plus recentes du bassin central du Maine; elle s’est mise en place juste avant l’orogenese acadienne. Les caracteristiques geochimiques et geochronologique des formations de Carrabassett et de Kittery pourraient par consequent permettre l’identification du terrane de collision. Les formations de Carrabassett et de Kittery possedent des concentrations d’elements majeurs et traces evoquant les turbidites de marge passive en provenance de sources intermediaires a felsiques, ce qui est contradictoire avec une origine avalonienne juvenile. La Formation de Carrabassett comporte des grains detritiques de zircon correspondant aux âges du Ganderia perigondwanien. Contrairement a la predominance de concentrations eNd positives de roche en vrac caracteristiques d’Avalonia, Ganderia presentent des concentrations eNd negatives qui cadrent mieux avec les concentrations eNd negatives des formations de Carrabassett et de Kittery. Ganderia s’est toutefois accrete a Laurentia au cours de l’orogenese salinique, avant le depot de la Formation de Carrabassett, et il a constitue le socle des sediments du bassin central du Maine sur lesquels Carrabassett et d’autres formations se sont deposees. L’enfoncement d’Avalonia sous Ganderia au cours des stades initiaux de l’orogenese acadienne pourrait avoir souleve Ganderia, formant un massif a l’exterieur du bassin central du Maine qui a servi de source aux sediments de la Formation de Carrabassett. [Traduit par la redaction]