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Gondwanan/peri-Gondwanan origin for the Uchee terrane, Alabama and Georgia: Carolina zone or Suwannee terrane(?) and its suture with Grenvillian basement of the Pine Mountain window

¹ Department of Geology and Geography, Auburn University, Auburn, Alabama 36849, USA
² Department of Geology, University of Florida, Gainesville, Florida 32611, USA
³ Department of Chemistry and Geology, Columbus State University, Columbus, Georgia 31907, USA
⁴ U.S. Geological Survey, Menlo Park, California 94025, USA

View larger version (45K): [in this window] [in a new window]   Figure 1. (A) Tectonic map of the southern Appalachians with section line A–A' (modified from: Hatcher, 2004; Morton et al., 1984, 1989; Hibbard et al., 2002, 2006; Steltenpohl, 2005a). Red square is area of detailed geologic map in Figure 2. (B) Cross section A–A' (modified from: Thomas and coworkers as presented in Hatcher et al., 1990; Steltenpohl 2005a).

View larger version (40K): [in this window] [in a new window]   Figure 2. (A) Geologic map of the Uchee and adjacent terranes depicting sample localities for our U-Pb zircon studies (modified after: McRae, 1992; McRae and Steltenpohl, 1993; Steltenpohl and Kunk, 1993; Hanley et al., 1997; T.B. Hanley, unpublished information). (B) Cross section A–A' (modified from: Thomas and coworkers as presented in Hatcher et al., 1990; Steltenpohl 2005a).

View larger version (124K): [in this window] [in a new window]   Figure 3. Collage of some lithologies and fabric relations from the Uchee terrane. (A) Layered orthogneisses and paragneisses of the Phenix City Gneiss. (B) Outcrop photo of Phenix City Gneiss containing two sets of planar fabrics. S0/S1 is the composite compositional layering (bedding?; S0) and coplanar upper amphibolite-facies schistosity (S1), and S2 is an amphibolite-facies schistosity axial planar to ptygmatic F2 folds. (C) Migmatized North Columbus metamorphic complex gneiss, from which sample A-13 was collected. Note blocks of gneiss containing S0/S1 gneissosity at a high angle to S2 within encapsulating leucosome. (D) Moffits Mill Schist at the type locality at Moffits Mill, Little Uchee Creek. Sample UB-1-03 was collected from this outcrop. (E) Close-up view of slabbed and polished Motts Gneiss sample with characteristic L2 mineral stretching lineation. Dime (1.8 cm diameter) for scale. (F) Two sets of foliations developed in a folded and sheared Moffits Mill Schist sample (from McRae, 1992). S0/S1 is the composite compositional layering (bedding?; S0) and coplanar upper amphibolite-facies schistosity (S1). Middle amphibolite-facies foliation (S2) is axial planar to small-scale open folds and parallels the sheared margin of a granitoidal injection along right-hand edge of the sample. Scale is marked in squares with one-centimeter sides.

View larger version (26K): [in this window] [in a new window]   Figure 4. Collage of U-Pb isotopic results; all error envelopes are 2 sigma. (A) Tera-Wasserburg plot of U-Pb data obtained from individual zircons from Phenix City Gneiss sample TH-04 using the SHRIMP-RG. (B) Combination histogram/relative probability plot of U-Pb ages of individual zircons from the Moffits Mill Schist sample UB-1-03 using the SHRIMP-RG. (C) Tera-Wasserburg plot of U-Pb data from individual zircons extracted from the leucocratic phase of a migmatitic part of Moffits Mill Schist sample A-13 using the SHRIMP-RG. (D) Tera-Wasserburg concordia plot of U-Pb TIMS data from four rutile grains extracted from Hollis Quartzite sample H-1. (E) Histogram plotting U-Pb ages determined for all Paleozoic zircons, mostly rims, from Uchee terrane samples reported herein.

View larger version (23K): [in this window] [in a new window]   Figure 5. Summary diagram comparing Temperature-time (T-t) paths for the Pine Mountain, Uchee, and Suwannee terranes in Alabama and westernmost Georgia. 40Ar/39Ar mineral cooling dates are summarized from Steltenpohl and Kunk (1993) and Steltenpohl et al. (1992) and combined with U-Pb zircon and rutile dates from this report. Analytical age errors and dates between the multiple samples lie within the size of the symbols plotted.