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
Abstract 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-Devonian. Tonalitic-granitic magmatism and up to granulite-facies metamorphism culminated in Early Devonian, possibly tied to lithospheric detachment below the subducting northwestern plate and consequent asthenosphere upwelling. Newly discovered Neo-Acadian Late Devonian to Early Mississippian tonalitic-granitic magmatism, up to granulite-facies metamorphism, and severe deformation in central Massachusetts took place in a plate context poorly understood. Late Pennsylvanian effects include magmatism, metamorphism, and deformation near south New England gneiss domes and the Sebago batholith, and development of the right-lateral Norumbega fault system. Permian Alleghanian effects include penetrative deformation, granitic intrusions and up to sillimanite-grade metamorphism of Pennsylvanian beds in southeastern New England. These last two episodes relate to the arrival of Africa.
The Gander Conference, an International Conference on Stratigraphy and Structure Bearing on the Origin of the North Atlantic Ocean, was held in Gander, Newfoundland, August 1967. The conference gave geologists familiar with the areas bordering the North Atlantic Ocean with an opportunity to present their knowledge and ideas to colleagues dealing with similar rocks and structures. This publication contains most of the papers that were presented at that conference and a few others that were prepared for the sessions.
Uzuakpunwa and Brownlow (1978) have presented an interpretation of a pre-Taconic angular unconformity in western Massachusetts that disagrees significantly with our published conclusions that we derived from abundant detailed mapping in same area. Their statements and interpretations appear to disregard data that we published, and we cannot agree with their arguments for a preTaconic unconformit y. Uzuakpunwa and Brownlow include in their paper a regional map of western Massachusetts at a scale of 1:500 000 (their Fig. 1) and a more detailed map of parts of Blandford and Woronoco quadrangles at a scale of 1:48 000 (their Fig. 2). Nowhere do they indicate how much mapping they have done, in which areas, nor at what scale. Our mapping was done at a scale of 1:24 000 for all area of their Fig. 1 that pertains to their discussion and was available as quadrangle maps (Hatch and Hartshorn 1968; Chidester et al. 1967; Osberg et al. 1971; Hatch 1969; Hatch et al. 1970; Hatch and Stanley 1976) or as maps in other papers (Stanley 1967,1975; Hatch and Stanley 1973). Uzuakpunwa and Brownlow's maps differ in some important details from ours. They indicate (their Fig. 1) that occurs at a unique stratigraphic horizon and is nearly continuous across Massachusetts from Connecticut to Vermont. Our mapping shows that Chester is a lens which can be traced for only 10 km along strike, and that no amphibolitelgreenstone extends continuously across breadth of state. The amphibolites/greenstones that Uzuakpunwa and Brownlow included in their Chester Amphibolite vary in composition and bedding characteristics, and have very different stratigraphic positions with respect to other mapped lithologic members of Rowe Schist. Uzuakpunwa and Brownlow stated (pp. 1941, 1945) that Chester Amphibolite forms a basal unit to Moretown Formation. Our mapping shows that rocks above and below type Chester body are lithically identical and that distinctively thin bedded, more granulose rocks characteristic of Moretown Formation are not present below a horizon 200-300 m stratigraphically above Chester. Where Chester thins to a feather edge, schists that are no longer separated by it are indistinguishable. Uzuakpunwa and Brownlow asserted (p. 1943) that the Rowe Schist is generally exposed west of western Massachusetts ultramafic belt and infer that this relationship has stratigraphic importance. Our published maps show that ultramafic bodies are found at all stratigraphic positions between base of Rowe Schist and lower part of Moretown Formation (see maps and reports listed above). The stratigraphically lowest body of ultramafic rock within lower Paleozoic section is 200 m above Hoosac-Rowe contact in Rowe quadrangle (Chidester et al. 1967). Uzuakpunwa and Brownlow have ignored stratigraphic redefinitions proposed by Hatch et al. (1966), and have instead adopted a stratigraphy similar to that of Emerson (1898) without any discussion or documentation of their reasons for so doing. Although Emerson (1898) originally mapped Chester Amphibolite as a single horizon across Massachusetts, on his final (Emerson 1917) presentation of this geology, he showed Chester as being discontinuous, but showed separate formations above and below Chester (horizon). We
Includes 14 chapters on the Appalachian orogen, 15 of the Ouachita orogen, and a chapter on the connection between them beneath the eastern Gulf Coastal Plain. The Appalachian chapters synthesize the geologic development of the orogen by tectonostratigraphic intervals (pre-orogenic, Taconic, Acadian, Alleghanian, and post-Alleghanian), and also treat Paleozoic paleontologic control, regional geophysics, thermal history of the crystalline terranes, parts of the orogen buried beneath the Atlantic and eastern Gulf coastal plains, regional geomorphology, mineral and energy resources; an integration chapter also is included. The Ouachita chapters cover physical stratigraphy and biostratigraphy of the Paleozoic rocks, structural geology, a synthesis of the subsurface geology beneath the western Gulf Coastal Plain, a review of the mineral and energy resources, regional geophysics, and a tectonic synthesis. Twelve excellent plates provide four-color geologic maps, structural cross sections, tectonic syntheses, and geophysical maps; a black-and-white synthesis of Appalachian mineral deposits, and a reflection seismic cross section.
Summary In New England highly deformed Silurian and lower Devonian beds are overlain unconformably by middle Devonian sediments. Early structures include westward-verging recumbent folds and thrusts, while younger features include local development of back-folding and upright folds with a NE trend. In the central and southern Appalachians the recognition of Acadian structures is not clearly documented, except for the Talladega Belt. Middle and upper Devonian molasse occurs to the W of the central Appalachians.
