GEOCHEMISTRY OF PRECAMBRIAN CHARNOCKITIC ROCKS OF THE CENTRAL LOVINGSTON MASSIF, GRENVILLIAN BLUE RIDGE TERRANE, VIRGINIA

Middle Proterozoic rocks, representing 1150-1000 Ma Grenvillian metamorphic and igneous events, of the Lovingston massif are comprised of quartz monzonite/mangerite plutonic suites, such as the Archer Mountain Suite (AMS) that intruded the older Stage Road Layered Gneiss (SRLG) and Hills Mountain Granulite Gneiss (HMGG), which contains relict shallower (opx) granulite-facies mineral assemblages. The subsequent culminating metamorphic event is associated with late stage emplacement of the diapir of Roseland anorthosite (andesine antiperthite) and associated deeper (opx + gar) granulite-facies Border Gneiss along with intrusion of the Roses Mill ferrodiorite (RMF) and nelsonites (ilmenite and apatite). Common chemical signatures and trends of the AMS and related rocks are similar to those of charnockitic rocks of the Pedlar massif with uniform LREE-enriched patterns with variable Eu anomalies, which reflect derivation from mixed protolithic rocks such as the SRLG. REE patterns of the AMS have significantly less variation than charnockitic rocks of the Pedlar massif and are slightly enriched in Th. Divergent REE patterns in the AMS, and related rocks, are attributed to crystallization of quartz/feldspar or HREE-compatible mafic and accessory phases leading to complementary chemical signatures in mafic and felsic layers. REE patterns are not affected by either intrusion of granites during Iapetan rifting or Paleozoic metamorphism.