Eastern North America
The continental margin transect program evolved through a desire to define the specific characteristics of North America’s modern continental margins and to compare the modern margins with Paleozoic examples, now found within the continent. Thus, the features of modern margins can be used to locate and elucidate the structures of ancient analogues. Conversely, the exposed rocks of ancient margins provide an insight into the evolution and deep structures of modern examples. Ocean-continental transitions, rifting mechanisms, development of sedimentary basins, processes of continental breakup, and ancestral controls are all features that warrant comparison between modern and ancient examples.
The Atlantic coast has the best-known passive margin of North America. Inboard of it is the Appalachian Mountain chain, which records a clear history of late Precambrian rifting and the passive development of a Paleozoic continental margin. Transects across both these modern and ancient examples provide information on scale and detail that is useful for comparisons.
The modern continental margin of eastern Canada (Fig. 1a, 1b) has a wider variety of ages and styles than that of its eastern United States counterpart. Segments of the margin southeast of Nova Scotia and east of Labrador are typical of rifted margins, though of different ages. Between them lies the tortuous segments of the northern and eastern Grand Banks where rifting and subsidence occurred over a broad area of the continental shelf. In contrast, the southern boundary of the Grand Banks is a transform segment. Rocks of the Appalachian Paleozoic margin are best preserved and exposed
Figures & Tables
This volume presents syntheses in twelve chapters of the tectonic evolution of continent-ocean transitions of North America (Canada-Mexico-U.S.A.) since the Precambrian. The syntheses are interpretations based on the 19 continent-ocean transects across North American margins published by GSA as part of its Decade of North American Geology (DNAG) series. The transitional region is the part of North America between the craton, little deformed in Phanerozoic time, and the modern ocean basins. The region developed heterogeneously within plate boundary zones that led to sequences of passive, collisional, and active margins that differ place to place. Nine chapters address individual segments of the transitional region, two consider active and passive margin tectonics topically, and one treats the evolution of Phanerozoic transitions of North America as a whole.