Collections > Electronic Theses and Dissertations > Alleghanian Plutonism in the Eastern Blue Ridge Province of the Southern Appalachians: Origin and Tectonic Setting

The Alleghanian orogeny was caused by the closing of the Theic ocean basin and subsequent collision of Gondwana with Laurentia. The orientation of the subducted Theic oceanic lithosphere is unknown but may be recorded in Carboniferous magmatism recently discovered in the southern Appalachians. The four Alleghanian plutons located in the eastern Blue Ridge are the oldest of the Alleghanian plutons and predate the estimated collision ca. 330 Ma. These plutons have εNd values in between published values from the Grenville basement and the depleted mantle evolution line (~7.5 at 335 Ma), indicating that they derived from melting of juvenile and crustal sources. Mantle model and xenocrystic zircon ages from the EBR plutons are coeval with Grenville orogenesis suggesting that the crustal component was Grenville basement. Based on the zircon dates combined with the geochemical data, the EBR plutons were likely emplaced when the Theic oceanic lithosphere was subducting beneath Laurentia.