UNZIPPING SUPERCONTINENT PANGEA: AEROMAGNETIC DATA AND THE CASE FOR SINISTRAL TRANSTENSIONAL RIFTING PRIOR TO OPENING OF THE ATLANTIC

The amalgamation of Pangea and zippered N-to-S closing of the Theic ocean occurred during the Alleghanian orogeny at the end of the Paleozoic. The Alleghanian orogeny involved rotational-oblique, then head-on collision of Laurentia and Gondwana, producing widespread dextral faulting throughout the orogen. The partially buried Eastern Piedmont fault system (EPFS) in the southeastern Appalachians is one example of transpression-related dextral faulting. Several segments of the EPFS, e.g., Modoc and Augusta faults, are exposed and produce long, narrow, linear aeromagnetic highs. Aeromagnetic data reveal other EPFS-related dextral structures buried beneath the Atlantic and Gulf Coastal Plains, including an easily recognized dextral duplex. Two ~200 Ma diabase Central Atlantic Magmatic Province dike sets (~NW and N-S) cut all of these structures, marking the onset of the rifting process. Paleozoic faults of the EPFS are cut by diabase dikes, but elsewhere sinistral reactivation of suitably oriented Paleozoic faults (e.g., Towaliga) offset some Jurassic dikes implying they are coeval. A large NE-trending sinistral fault (Estill fault) offsets magnetic and gravity highs in the Brunswick (Charleston) terrane (BCt) in SC and GA. The Estill fault is at least 185 km long, with ~100 km displacement, making it potentially the largest sinistral Mesozoic fault in eastern North America. We suggest two hypotheses: (1) Movement along the Estill fault and other sinistral faults represents Early Jurassic transtensional rifting prior to the main phase of Atlantic opening. Alternatively, (2) the Estill fault formed during the last stage of Alleghanian Africa-Laurentia collision as the product of NE sinistral escape of part of the BCt block north of the Florida collision zone. If hypothesis 1 is correct, Jurassic sinistral transtensional faulting marks reversal of Alleghanian rotational transpressional collision, effectively “unzipping” supercontinent Pangea prior to opening of the Atlantic.