HR: 0800h
AN: T41E-1264    [Abstracts]
TI: Rift Geometry and Evolution Associated with the Break-up of Pangea
AU: * Debnam, C
EM: ctdebnam@edisto.cofc.edu
AF: College of Charleston, Dept. of Geology, 66 George St., Charleston, SC 29412 United States
AU: Beutel, E K
EM: beutele@cofc.edu
AF: College of Charleston, Dept. of Geology, 66 George St., Charleston, SC 29412 United States
AB: Diabase dikes related to the rifting of Pangea have been used to elucidate mechanisms by which the super-continent broke-up since the early 1970s. Subsequently, these dikes were related to each other and the massive sills and lava flows that make up the Central Atlantic Magmatic Province (CAMP). Our research focuses on the dikes and mechanisms of continental break-up in the southeastern United States. While, past studies indicate that the majority of Mesozoic diabase dikes within the Carolinas dominantly trend to the northwest, recent work in west-central South Carolina and the Piedmont of North Carolina has revealed numerous previously unmapped dikes with N and NE trends. These dikes have been related to the N and NE trending dikes located in the Northeastern United States via geochemical analyses. Cross-cutting relationships between dikes of different orientation has revealed an apparent pattern whereby the dikes were emplaced in the following order NW, N, and then NE-trending. Recent Ar39/Ar 40 dates suggest that these dikes were all intruded within a 2 million year window, indicating that the least compressive stress field (which would be perpendicular to dike orientation) rotated from NE-SW through E-W to NW-SE within this time period. Based on these observations, which are contrary to previous studies that attribute the northwest trending dikes in the Carolinas to a deep mantle plume, we constructed several finite element models to determine the source of the stress field change. These models were constructed to test the influence of geometry, rifting sequences, and location of force application on the orientation and evolution of stress fields in the Carolinas. Model results suggest that the direction from which rifting progressed has a strong effect on the stress field within the Carolinas and that it is unlikely that rifting began at the Blake Plateau as proposed by the plume hypothesis. Further, it is apparent that the geometry of the rifts themselves has a strong effect on the stress field within the continent, which suggests the need for further mapping of the final rifting events along the southeastern margin of the United States.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8110 Continental tectonics--general (0905)
DE: 8157 Plate motions--past (3040)
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting