29 Piedmont Geology in the Southern Appalachian Orogen: New Insights from Geologic Mapping, Geochemical, and Geochronological Studies (Posters)

Monday, 15 April 2024
1:30 PM - 5:30 PM
Grand Ballroom

NEW WHOLE ROCK MAJOR- AND TRACE-ELEMENT GEOCHEMISTY AND SM-ND ISOTOPIC COMPOSITIONS FROM THE “GREATER RALEIGH TERRANE”: REVISITING THE WARREN TERRANE

Paper number: 29-5
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

In the NC and VA eastern Piedmont, the amphibolite-facies Raleigh terrane (Rt) is bound on its west side by the dextral Nutbush Creek-Lake Gordon faults, and on its east side by the Macon-Hollister faults of the Eastern Piedmont fault system. Traditionally, greater Rt rocks are lumped as one terrane of ca. 633–528 Ma peri-Gondwanan Carolinia. However, the Lake Gordon fault and Pennsylvanian-Permian Rolesville batholith divide the Rt into meta-igneous western (wRt) and primarily metasedimentary eastern (eRt) terranes. Blake et al. (2012) renamed the eRt to the Warren terrane based on the wRt-eRt fault boundary and their lithologic differences. The wRt Raleigh Gneiss contains amphibolite and layered intermediate to felsic orthogneiss of unclear age intruded by the ca. 545 Ma Falls Leucogneiss, a peralkaline leucogranite. In the eRt, 7 schist and gneissic units yield ca. 460–403 U-Pb LA-ICP-MS zircon MDAs with Precambrian ages ca. 2000–800 Ma and unimodal ages ca. 410–403 Ma (Early Devonian) indicating magmatic or single-source sedimentary protoliths.

We present a comparison of 10 wRt and 5 eRt samples using major- and trace-element whole-rock geochemistry and 9 wRt and 8 eRt samples using Sm-Nd whole-rock isotopic compositions. On major- and trace-element diagrams the wRt Raleigh Gneiss plots in subduction fields with most samples plotting in island-arc fields. The wRt Falls Leucogneiss plots as within-plate granite. Eastern Rt samples plot in island-arc, fringing-arc, and continental-arc fields; eRt samples have more evolved trace-element compositions than wRt samples.

Initial εNd values for the wRt are all positive between +1.7 and +7.0, whereas the eRt samples are more negative with initial εNd values between -8.3 and +0.2; one outlier has εNd +3.9. In total, major- and trace-element and Sm-Nd isotopic compositions demonstrate that the wRt and eRt are distinct from one another and indicate that the separating Lake Gordon fault is a major terrane boundary. Sm-Nd compositions of the wRt are consistent with a Carolinia affinity, whereas eRt Sm-Nd compositions are indicative of greater crustal contamination and sedimentary input from cratonic sources. This distinction shows that lumping as the greater Rt is not valid. Renaming the eRt to the Warren terrane based on faults, lithology, and geochemistry is justified.

Geological Society of America Abstracts with Programs. Vol. 56, No. 2

doi: 10.1130/abs/2024SE-398563

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