WIDE-ANGLE REFLECTION MAPPING AND P-WAVE VELOCITY ANALYSIS OF THE SOUTH GEORGIA BASIN AND ROOT OF THE APPALACHIAN MOUNTAINS

The Appalachian Mountains are a product of Alleghanian (Permian) collision and Jurassic/Triassic extension. Once reaching the same height as the Rockies and by some estimates the Andes, the Appalachians have weathered to a present-day maximum height of 6,684 feet. This height is curiously tall for such an old mountain belt, especially when compared to similarly aged mountain belts such as the Ouachita Mountains in Arkansas, a sister mountain belt to the Appalachians with a maximum height of only 2,753 feet. Previous work based on active source wide-angle reflections and passive source receiver function analysis has shown a thickening of the crust under the Appalachians, as the Moho depth increases from 30 to 35 kilometers beneath the coastal plain to a maximum depth of 55 to 60 kilometers beneath the highest elevations of the Blue Ridge Mountains. This suggests the mountains are locally compensated. As we move away from the mountain range we enter the coastal plains of eastern Georgia and South Carolina, characterized by a mixture of unconsolidated carbonate and siliciclastic sediments. Mainly Cretaceous and Cenozoic in age, these sediments are up to 2000 meters thick. The coastal plains overlie a large rift basin, the South Georgia basin, formed by Triassic/Jurassic rifting. Building on previous work, the first half of this study will take a more detailed look at the root system beneath the southern Blue Ridge with a focus on obtaining more accurate, localized estimates of P-wave velocities to gain a better understanding of this “ice cube isostasy” and the root material. The second half of this study will use P-wave velocities to constrain lithologies within the rift basin and underlying basement. Using seismic data from the Southeastern Suture of the Appalachian Margin Experiment (SESAME) array as well as data from stations in the U.S. Transportable Array (TA), this study will focus on using wide-angle reflections generated by distant earthquakes to address the following questions: (1) the mechanisms responsible for the longevity of topography and its supporting root by constraining the velocity, density, and thus the metamorphic grade and fluid content of root material; (2) how much of the original coastal plain basement was modified by injected igneous material during the rifting event.