COMPARATIVE GEOCHEMISTRY AND PETROGRAPHIC ANALYSIS OF LINEATED GNEISS AND META-APLITES FROM UCHEE BELT, GEORGIA

This paper presents a comparison of the petrography and geochemistry of lineated gneiss and associated meta-aplite from the northern (Motts gneiss) and southern limbs (Flat Rock Park (FRP) gneiss) of the Lake Oliver Synform (LOS), Uchee Belt, West Central Georgia. In the field, these rocks appear similar from one side of the LOS to the other. Texturally, rocks on the north side show strain due to involvement with the Goat Rock fault. Modally, both lineated gneiss and meta-aplite are granitic to granodioritic. Though chemically similar, the lineated gneiss from the northern limb of the LOS has higher amounts of Al₂O₃ and CaO than lineated gneiss from the southern limb. The data also shows that River Road, Manchester Expressway (ME) and Midland Trace (MT) samples are less felsic than the other lineated gneiss samples (trace and REE data are pending). Modally the southern aplites are composed of approximately 33% K-feldspar, 33% quartz, 33% plagioclase, 1% mica, and a trace of opaques. The northern aplites are composed of approximately 44% quartz, 35% plagioclase, 21% K-feldspar, and traces of mica and opaques. XRF data from aplites taken from both sides of the LOS show SiO₂ values higher in the north (76%) than in the south (68%). Data for north and south show comparable values for Fe₂O₃ (0.4% to 0.51%), CaO (1.0% to 1.6%), and Al₂O₃ (14.0% to 16.0%). In the south, FRP aplite is Na₂O-rich and K₂O-depleted while the reverse is true of the MT sample. The aplite from ME has an opaque content of approximately 1%. This may be responsible for a high Fe₂O₃ value. Low CaO and Al₂O₃ of ME aplite may be the result of significant alteration of plagioclase. Variations in major element geochemistry among lineated gneiss and meta-aplite samples may be due to original variation in their igneous protoliths or changes caused by involvement with the Goat Rock fault. Also, although outcrop exposures distinctly show that the aplites cross cuts the host lineated gneiss, the REE distributions and patterns of the lineated gneiss and spatially associated aplite indicate that these rocks may not be genetically and/or temporarily related.