Repeated basement reactivation in the northeastern Appalachians

Publisher Website
Google Scholar
Abstract
In the northeastern Appalachians crystalline, basement outcrops within a y‐shaped belt extending southwest from Bonavista Bay, Newfoundland, to Port aux Basques, and thence via the Cape Breton Highland to near Saint John, New Brunswick. Locally a Precambrian platformal sequence lies on the basement. Stratigraphic and isotopic evidence demonstrate that in the Saint John and northern Cape Breton regions, both basement and cover were remobilized about 600 million years ago, the basement probably for the second time. After deposition of a Cambro‐Ordovician cover, these rocks were again mobilized and intruded in mid‐Ordovician and Devonian time. Evidence for basement reactivation in Newfoundland, although fragmentary, is compatible with a similar history. Much of the basement gneiss is presently exposed in uplifted fault blocks.The observations can be explained in plate tectonic terms if the sedimentary accretion prism collapses during plate convergence, and is pushed onto the craton, which is itself thickened due to compressive stress. Because the edge of the cration is heated, due to thickening of both basement and sedimentary cover, the basement rises due to lowering of density by thermal expansion, and ultimately by partial melting. Depending on relative rates of heating, buoyant rise, and erosion, the process can lead either to a characteristic pattern of linear belts of reactivated basement which display positive gravity and magnetic anomalies, or to a chain of elongate gneiss domes exhibiting gravity lows. Application of the model to the northeastern Appalachians suggests that several continental fragments are present, and that basement rocks have been involved in repeated continental collision and breakup.