DISCRIMINATION OF THE MILTON BELT AND THE CAROLINA TERRANE IN THE SOUTHERN APPALACHIANS - A ND ISOTOPIC APPROACH

The hypothesis that the Milton belt is a high-grade infrastructural eq uivalent of the immediately adjacent suprastructure of the Carolina te rrane, the Carolina slate belt, was tested by comparing the Nd isotopi c compositions of the two belts. Milton belt samples have epsilon(Nd) (600 Ma) values ranging from approximately -6.5 to +1, and depleted-ma ntle model (T-DM) ages ranging from 930 to 1690 Ma. Samples of the Car olina slate belt, collected from near the ductile shear zone that sepa rates the Milton and Carolina slate belts, have epsilon(Nd) (600 Ma) v alues from +1 to +6, and T-DM ages from 745 to 1040 Ma. The Milton bel t is therefore composed of isotopically more evolved crust than the no rthwestern portion of the Carolina slate belt. These results are not c ompatible with the simple infrastructure-suprastructure relationship e nvisioned for the Milton belt and the Carolina terrane. A more likely interpretation is that the belts are distinct crustal blocks that had unrelated histories prior to their assembly.