DETRITAL ZIRCON AGES FOR METAVOLCANICLASTIC SEDIMENTARY ROCKS OF THE SPRING HOPE TERRANE, NORTH CAROLINA EASTERN PIEDMONT

In the NC eastern Piedmont, the Eastern Piedmont fault system includes seven crystal-plastic-brittle faults, which are strands in an orogen-scale dextral freeway that shuffles the Appalachian hinterland from VA to AL. These faults juxtapose greenschist-facies suprastructural and amphibolite-facies infrastructural terranes on the flanks of the Wake-Warren antiform. The antiform and faults result from Alleghanian transpression. On the western fold flank, the easternmost Carolina, Falls Lake, Crabtree, and western Raleigh terranes yield discordant U-Pb zircon TIMS ages interpreted to link them with Neoproterozoic Carolinia. LA-ICP-MS U-Pb zircon analyses from the eastern Raleigh (Warren) terrane in the fold hinge yield Early Devonian ages. On the eastern fold flank, the Triplet terrane is undated. The Roanoke Rapids terrane yields TIMS Pb-Pb zircon ages as young as late Neoproterozoic. The Spring Hope terrane yields TIMS Pb-Pb and U-Pb magmatic zircon ages ca. 628, 544, and 524 Ma.

We report new LA-ICP-MS U-Pb detrital zircon ages from metavolcaniclastic rocks of the northern Spring Hope terrane. Sample EX13-45 contains 44% concordant data (80-105% using 6/8 vs. 7/6; n=55) that include a continuous distribution (n=51) from 559–741 Ma and additional ages ca. 788, 962, 1700, and 1775 Ma. Maximum depositional ages (MDAs) using youngest statistical population (YSP), youngest grain cluster of 3+ grains overlapping at 2s (YGC2s3+) and maximum likelihood algorithm (MLA-Minimum) methods are 644 ± 15, 642 ± 15, and 647 ± 15 Ma (2s total uncertainties), respectively. Sample EX13-291 contains 42% concordant data (n=54) that include a continuous distribution (n=37) from 553–746 Ma and multigrain age modes ca. 1500 and 1825 Ma. MDAs are 651 ± 17, 646 ± 17, and 648 ± 17 Ma. Sample EX15-535 contains a large proportion of high common-Pb discordant data with only 19% passing the discordance filter. Concordant ages (n=23) include three <350 Ma with Th/U ~0.1, a continuous distribution (n=9) from 631–763 Ma, and multigrain age modes ca. 1170, 1700. MDAs are 654 ± 20, 672 ± 16, and 668 ± 26 Ma. Our Spring Hope terrane MDAs are older than previously reported magmatic ages and suggest deposition during or after the late Cryogenian Period (Neoproterozoic). Cryogenian magmatism and ages ca. 1.2–1.7 Ga are consistent with a peri-Gondwanan origin.