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Slate belt rocks of southern Chatham and northern Moore Counties, North Carolina, constitute an overlapping series of metamorphosed volcanic and volcaniclastic strata reflecting three distinct sites of volcanic activity separated in time, space, and composition. At the base of the section, felsic volcanic and epiclastic rocks had a northeastern source. Subsequently, deposition was dominated by a center of relatively mafic (50 to 57 wt% SiO2) volcanism to the northwest. Accretionary lapilli and sedimentary structures indicate subaerial to shallow subaqueous conditions in the north; southward decrease in grain size and changes in structures suggest deposition on the deeper-water slopes of the volcanic edifice. A still younger site of felsic (68 to 75 wt% SiO2) volcanism abruptly developed on the southern flank of the waning mafic eruptive complex; local depositional paleoslope reversed, as felsic flows and tuffs interfingered northward with banded mudstones.

The bimodal igneous rock geochemistry is consistent with the stratigraphic model. Low K/Na (K2O/Na2O < 0.2) may reflect alteration and metamorphism; some (more stable) minor and trace elements suggest calc-alkalic affinities.

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