Paper No. 6
Presentation Time: 8:00 AM-12:00 PM
GEOCHEMICAL COMPARISON AND STRUCTURAL SIGNIFICANCE OF MOTTS GNEISS AND SIMILAR LINEATED GNEISS FROM THE UCHEE BELT OF GEORGIA AND ALABAMA
The Motts Gneiss (MG), a lineated granitoidal gneiss which locally host meta-aplite, is located on the northwest limb of the Lake Oliver synform (LOS) where it is associated with the Goat Rock fault (GRF) in the northwestern Uchee Belt (UB). Similarities in major, trace and Rare Earth Element (REE) data indicate that the MG is the same unit as lineated gneiss and meta-aplite, like at Flat Rock Park (FRP), on the southeast limb of the LOS. Major elements: Lineated gneiss varies from 62% to 78% SiO2. Meta-aplite varies from 68% to 78% SiO2, and tends to be less Ti-rich, less mafic, more alkalic and less phosphatic than associated lineated gneiss. Trace elements: Both aplites and their hosts are depleted in Nb and enriched in Ta. Aplites tend to be depleted in Th, Nd and Sm and enriched in Sr; most host rocks are enriched in Nd and Sm and depleted in Sr. River Road (RR) MG and the Stroud Cemetery (SC) MG are also depleted relative to Th, Nd and Sm; most aplites are also depleted in Nd and Sm. Unlike other aplites, Manchester Expressway (ME) aplite is enriched in Nd and Sm and depleted in Sr. REE: The ME is enriched in REEs relative to associated lineated gneiss and both have a slight negative Eu anomaly. FRP and Midland Trace (MT) meta-aplite are depleted in REE compared to host. In both of these the host has a distinct negative Eu anomaly while the meta-aplites have a small positive Eu anomaly. RR meta-aplite has a flat REE pattern which crosses the associated lineated gneiss pattern at the Eu value. Both are depleted in REE relative to the other rocks. Chattsworth Road (CR) lineated gneiss is similar to the MT lineated gneiss; the SC has a REE pattern that cuts across patterns defined by the other rocks and contains no Eu anomaly. FRP, CR and MT show negative Eu anomalies while SC, ME and RR, less enriched in REE, show no Eu anomalies. In the aplites, REE are less than 10X chondrite for all except the ME aplite. Only the MT meta-aplite shows a distinct positive Eu anomaly. If the MG and the lineated gneiss on the south limb of the LOS are the same unit then the lineated character of the MG is not restricted to the GRF as currently mapped and should not be used as a marker for the GRF. However, this correlation provides a source for the MG within the UB and suggests that other rocks from the southern limb of the LOS may also be contributing to the GRF.