Stratigraphy and isotope geochronology in the crystalline core of the Appalachians suggest revised interpretations of the extent, nature and timing of Paleozoic orogens in New England. Five major episodes of magmatism, deformation, and high-grade regional metamorphism are recognized: Taconian (455-442 Ma), Acadian (423-385 Ma), Neo-Acadian (366-350 Ma), Late Pennsylvanian (300-290 Ma) and Alleghanian (280-260 Ma). In the Taconian, the passive margin of Laurentia was subducted below a complex magmatic arc lasting from 480 to 442 Ma, founded in part on continental crust of a Medial New England terrane with possible affinities with Amazonia. Questions about Medial New England involve its coherence as a single plate, and the nature of its underlying crust. The Acadian began in Late Silurian as a collision between the amalgamated Laurentia-Medial New England and outer belts of Composite Avalon along a cryptic suture in coastal Maine, and progressed northwestward to the Connecticut Valley basin by mid-...

Paleozoic orogens in New England, USA

Transects produced by the North American Continent-Ocean Transect Program (Speed and others, 1982; U.S. Geodynamics Committee, 1989) describe the complex orogen formed along the Late Proterozoic to Early Cambrian rifted margin of the Laurentian craton, including continental rocks of the Grenville province, which themselves had been earlier formed by a Middle Proterozoic continent-continent collision. Continental accretion was followed by continental separation and the formation of a passive continental margin. This 900-km-long transect crosses the entire Appalachian orogen and the passive continental margin from the craton to Atlantic oceanic crust. It is supported by abundant seismic reflection and refraction data that were gathered specifically for this transect, in part, to resolve questions posed by the earlier transects across the Atlantic passive continental margin. Thus, it is a "second-generation" transect. This transect has been accepted in the Global Geoscience Transects Project (CC-7) of the InterUnion Commission on the Lithosphere, International Council of Scientific Unions (Monger, 1986) as Transect 8. The Quebec-Maine-Gulf of Maine transect provides excellent data that can be used to understand the processes of continental accretion and separation. An uncertain number, possibly ten or more, of tectonostratigraphic terranes of predominantly continental affinity were accreted to the craton, as shown by the transect. In addition, at least two oceanic terranes also were accreted. Although some terranes had been joined together to form composite terranes before being accreted (Boone and Boudette, 1989, describe an example), in general, these terranes were accreted episodically to the southeastern (current geographic direction) part of the craton by thrust and (or) strike-slip faulting at successively younger times during the Paleozoic. The terranes differ principally in the nature of their Late Proterozoic to middle Paleozoic history and stratigraphy (Keppie, 1989) and paleontology (Neuman and others, 1989). Accretion in the part of the orogen shown on this transect took place during multiple collisional or transpressive episodes in the early and middle Paleozoic. . A very thick continental crust was produced during these episodes. Geologic evidence that indicates the formation of this

/pdf/global-geoscience-transect-8-quebec-maine-gulf-of-maine-2gjt80cjlj.pdf

Global geoscience transect 8, Quebec-Maine-Gulf of Maine transect, southeastern Canada, northeastern United States of America

The Hurricane Mountain Formation (HMF) melange and associated ophiolitic and volcanogenic formations of Cambrian and lowermost Ordovician age bound the SE margin of the Precambrian Y (Helikian) Chain Lakes Massif in western Maine. HMF melange matrix, though weakly metamorphosed, contains a wide variety of exotic greenschist to amphibolite facies blocks as components of its polymictic assemblage, but blocks of high-grade cratonal rocks such as those of Chain Lakes or Grenville affinity are lacking. Formations of melange exposed in structural culminations of Cambrian and Ordovician rocks NE of the HMF in Maine and in the Fournier Group in New Brunswick are lithologically similar and probably tectonically correlative with the HMF; taken together, they may delineate a common pre-Middle Ordovician tectonic boundary. The authors infer that the Hurricane Mountain and St. Daniel melange belts define the SE and NW margins of the Boundary Mountains accreted terrane (BMT), which may consist of cratonal basement of Chain Lakes affinity extending from eastern Gaspe (deBroucker and St. Julien, 1985) to north-central New Hampshire. The Laurentian continental margin, underlain by Grenville basement, underplated the NW margin of this terrane, marked by the SDF suture zone, in late Cambrian to early Ordovician time, while terranes marked bymore » Cambrian to Tremadocian (.) lithologies dissimilar to the Boundary Mountains terrane were accreted to its outboard margin penecontemporaneously. The docking of the Boundary Mountains terrane and the initiation of its peripheral melanges are equated to the Penobscottian disturbance.« less

Hurricane Mountain Formation melange: history of Cambro-Ordovician accretion of the Boundary Mountains terrane within the northern Appalachian orthotectonic zone

A geochemical and petrological study of the crystalline basement and associated megablocks of the Eyreville-B drillcore, Chesapeake Bay impact structure, USA

A Guide to Continent Ocean Transect E-1: Adirondacks to Georges Bank

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A Guide to Continent Ocean Transect E-1: Adirondacks to Georges Bank