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Late Paleozoic granitic rocks have been identified in two drill holes south of the proposed Alleghanian suture separating the Suwannee terrane from terranes to the north. These granites are the only known expression of magmatism on the accreted Gondwanan plate during the Alleghanian collision of Laurentia and Gondwana, an event that represents the final episode in the assembly of Pangea. Zircons from samples of granite from drill holes in southwestern Georgia and northern Florida were analyzed by ion probe, yielding igneous crystallization ages of 294 ± 6 and 296 ± 4 Ma (2σ), respectively. Xenocrystic zircons with ages of ca. 1.0–1.2 Ga and ca. 560 Ma were also obtained from one sample. The Proterozoic ages of these grains are consistent with previous proposals of a Gondwanan origin for the Suwannee terrane, particularly those proposals involving the Orinoquian or Sunsas-Rondonian provinces of South America. The major- and trace-element geochemical compositions of the granites are inconsistent with generation in a subduction environment. Instead, the data support models of the Alleghanian event in the Southern Appalachians involving an oblique collision between Laurentia and Gondwana followed by a late-stage, postorogenic episode of magmatism related to a postcollisional, lithospheric collapse event that may have included delamination.

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