AEROMAGNETIC ANOMALIES OF THE APPALACHIANS

We provide an overview of aeromagnetic characteristics of the Appalachians. Whether terrane or domain boundaries are clearly defined by aeromagnetic lineaments depends on differences in rock types, and on whether the boundary is intruded by later plutons or overlain by sedimentary rocks. Sedimentary rocks and plutonic rocks of the Meguma terrane in Nova Scotia form magnetic lows, resulting in clearly defined boundaries with higher anomalies in adjacent terranes. The Caledonia terrane, an Avalonian terrane in New Brunswick, is defined by a strong high. The boundary between peri-Laurentian arcs and Carolinia in the southeastern U.S. is well defined, where the arcs form a magnetic high and parts of Carolinia form a low.

Other terrane and domain boundaries are less well defined by aeromagnetic imagery. The Goochland terrane of Virginia shows a sharp boundary with the magnetic highs of the peri-Laurentian arcs to the northwest, but a diffuse boundary with the slightly lower magnetic rocks of Carolinia to the southeast. Peri-Laurentian arcs of the northern Appalachians form a low, while in the southern Appalachians they have mixed signatures. The boundary between Avalonia and Ganderia in Newfoundland is cut by plutonic rocks, and difficult to trace based on aeromagnetic images. Late Devonian to Permian basins, including the Maritimes basin of southeastern Canada and Narragansett basin of southeastern New England, and Mesozoic basins, including the Hartford basin of southwestern New England, form magnetic lows within and across terranes. They obliterate underlying rocks and structures.

Strong magnetic contrasts also occur within terranes or domains. An example is the magnetite-bearing part of the Nashoba Formation in the Nashoba terrane of eastern Massachusetts, which is part of the trailing edge of Ganderia. Plutonic rocks may form magnetic highs, such as the German Bank Pluton southwest of Nova Scotia, or lows, such as the South Mountain Batholith of Nova Scotia. The New York – Alabama lineament separates a magnetic high to the northwest from a low to the southeast. NE-trending faults, including the Norumbega Fault of eastern New England, form strong lineaments. Two sets of east- and ESE-trending lineaments throughout the Appalachians represent late structures.