The timing of peak high-grade metamorphism in central-eastern New England

Authors

  • J. Dykstra Eusden Jr. Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755 U.SA.; Present address: Department of Geology, Bates College, Lewiston, Maine, 04240 U.S.A.
  • Barbara Barrerio Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755 U.SA.

DOI:

https://doi.org/10.4138/1654

Abstract

Monazite and sphene, separated from sillimanite-grade schists, gneisses and two-mica granites in the Central Maine Terrane and Merrimack Trough, have been dated using the U-Pb system. The ages constrain the timing of peak high-grade metamorphism and plutonism in northern New England. In the Central Maine Terrane metamorphic ages are Acadian (early Devonian); in the Merrimack Trough, across the Campbell Hill-Nonesuch River-Norumbega fault zone, the age of metamorphism is Alleghenian(?) (Permian). The granite ages outline a distinct pulse of Devonian magmatism, characteristic of the Central Maine Terrane. The high-grade terrane of this part of the Appalachian Orogen is composite. It is made up of crustal blocks that experienced discrete pulses of high-grade metamorphism beginning perhaps as long ago as the pre-Middle Ordovician and extending into the Permian. Ages of peak metamorphism support the hypothesis that the Central Maine and Merrimack teiranes had different tectono-metamorphic histories and are coincidentally juxtaposed at the same metamorphic grade. The Campbell Hill-Nonesuch River-Norumbega fault zone has had an active and complex history, beginning approximately 360 Ma and lasting at least to 250 Ma. This boundary is a likely candidate for the western Alleghenian (Variscan) Front in New England. The final juxtaposition of the Central Maine and Merrimack terranes may have occurred during the Mesozoic along extensional, terrane-bounding faults, possibly the reactivated Acadian compressional and/or Alleghenian transpressional structures. RÉSUMÉ L'application de la systènatique U-Pb a permis la datation de la monazite et du sphène extraits de schistes métamorphisés au grade de la sillimanite, de gneiss et de granites à deux micas provenant de la Lanière de Central Maine et de la Fosse de Merrimack. Les èges ainsi obtenus imposent des contraintes précises sur l’époque du paroxysme métamorphique et du plutonisme en Nouvelle-Angleterre septentrionale. Dans la Lanière de Central Maine, le métamorphisme est d'âge acadien (éodévonien). Dans la Fosse de Merrimack, d'un côté à l’autre de la zone de failles de Campbell Hill-Nonesuch River-Norumbega, le métamorphisme date de l’Alléghanien(?) (Permien). Les âges des granites mettent en évidence un épisode distinct de magmaiisme dévonien qui caractérise la Lanière de Central Maine. Dans cette portion de l'Orogène appalachien, la lanière présentant un haut degré de métamoiphisme est composite. Elle comprend des blocs crustaux ayant subi des épisodes distincts de métamorphisme de haut degré qui débutent possiblement à l’Ordovicien moyen pour s'étaler jusqu'au Permien. Les âges du paroxysme métamorphique confortent l’hypothèse voulanique les lanières de Central Maine et de Merrimack aienl eudes histoires techono-métamorphiques différentes et que leur juxtaposition à un même grade métamorphique ne soit que coincidence. L'hisloire de la zone de failles de Campbell Hill-Nonesuch River-Norumbega est active, complexe et s'échelonne d'environ 360 Ma jusqu'à au moins 250 Ma. Cette frontière formé un candidal plausible pour le Front alléhanien (varisque) occidental en Nouvelle-angleterre. La juxtaposition finale des lanières de Central Maine et de Merrimack s'effectua peut-être au Mésozoique le long de failles en extension bordant les lanières, possiblement par réactivation des accidents compressifs acadiens et/ou des structures transpressives alléghaniennes. [Traduit par le journal]

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Published

1988-12-01

How to Cite

Eusden Jr., J. D., & Barrerio, B. (1988). The timing of peak high-grade metamorphism in central-eastern New England. Atlantic Geoscience, 24(3). https://doi.org/10.4138/1654

Issue

Vol. 24 No. 3 (1988)

Section

Articles

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