THREE CREEK PLUTON: A NEOPROTEROZOIC TRONDHJEMITIC TO TONALITIC INTRUSION IN THE ROANOKE RAPIDS TERRANE, EASTERN PIEDMONT PROVINCE, VIRGINIA

The Roanoke Rapids terrane in eastern Virginia and North Carolina stands as one of the least-studied and therefore poorly understood blocks of peri-Gondwanan crust in the southern Appalachian Piedmont. In Virginia, it consists primarily of low- to medium-grade metavolcanic and metasedimentary rocks of uncertain age, which were intruded by several granitoid plutons. Although some of these plutons may be Alleghanian, the largest (a metagranite near Skippers, VA) has been dated at 615 ± 0.6 Ma (Coler and Samson, 2000, GSA abstract). We report here new results for a second Neoproterozoic pluton that is much smaller (<6 km² in area), but mineralogically distinctive. The body is informally referred to here as the Three Creek pluton, for the stream along which the currently known outcrops occur. Also exposed in the approximate center of the pluton is a large (0.5 x 1 km) block of primarily felsic metavolcanic rock that either represents a roof pendant or xenolith. Rocks of the pluton are typically massive, medium-grained and gray, and locally contain conspicuous secondary epidote. The most abundant mineral is plagioclase, which in most cases has been heavily saussuritized, with lesser amounts of quartz, biotite (highly chloritized), Ca-amphibole, epidote, and opaques (locally with titanite rims). No K-feldspar is present. Whole-rock major element compositions (5 samples) show a small range in SiO₂ (61.6-66.8 wt%) and low K₂O (0.2-1.2 wt%); compositions are metaluminous to slightly peraluminous. Modally and normatively, the rocks range from trondhjemite to tonalite. REE (La_N=41-87) patterns are either relatively flat with negative Eu-anomalies (Eu*=0.44-0.79) or LREE-enriched with no anomalies. Three single grain zircon fractions yield overlapping and concordant results using CA-TIMS methods, with a calculated age of 613.6 ± 0.9 Ma (2σ; including decay constant errors). Some felsic metavolcanic rocks in the Roanoke Rapids terrane have been previously referred to as quartz keratophyre based on petrography (no chemical data have been published). Thus, it is possible that the Three Creek pluton represents a plutonic equivalent of these volcanic rocks, and the trondhjemitic character of this pluton is consistent with the origin of this terrane in an arc setting.