The structure, stratigraphy, tectonostratigraphy, and evolution of the southernmost part of the Appalachian Orogen

Higgins, Michael W.; Atkins, Robert; Crawford, Thomas J.; Crawford, R.F.; Brooks, Rebekah; Cook, Robert B.

doi:10.3133/pp1475

Cited by 46 publications

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“…High-precision, U-Pb and 40 Ar/ 39 Ar thermochronological data also are sorely needed from rocks marking the northeast terminus of the Pine Mountain window to establish timing of formation of major Appalachian fault zones (i.e., Towaliga, Goat Rock, and Modoc zone) and their interaction with the Box Ankle fault zone. In addition to being a suspect for the Carolina zone suture, the Box Ankle fault zone has also been interpreted as an exposed segment of the "Appalachian décollement" Sears et al, 1981a;Nelson et al, 1987;Higgins et al, 1988;Steltenpohl and Kunk, 1993;Steltenpohl and Moore, 1988;Steltenpohl et al, 1992;West et al, 1995) that had passed above an autochthonous/parautochthonous Pine Mountain terrane. McBride et al (2005) recently resynthesized and reinterpreted seismic data to provide evidence for scattered and weak subhorizontal refl ectors beneath the Pine Mountain window, but the controversy remains unresolved.…”

Section: Conclusion and Directions For Future Studiesmentioning

confidence: 97%

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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

Steltenpohl¹,

Mueller²,

Heatherington³

et al. 2008

Geosphere

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The poorly known, suspect, Uchee terrane occupies a critical tectonic position with regard to how and when peri-Gondwanan (Carolina) and Gondwanan (Suwannee) terranes were sutured to Laurentia. It lies sandwiched between Laurentian(?) continental basement exposed in the Pine Mountain window and adjacent buried Gondwanan crust of the Suwannee terrane. The Uchee terrane has been proposed as both a septum of Piedmont rocks that once was continuous across the erosionally breached Pine Mountain window or part of the Carolina zone. To help resolve this issue, we conducted U-Pb (SHRIMP-RG) (sensitive high-resolution ion microprobe-reverse geometry) zircon studies and whole-rock isotopic analyses of principal metasedimentary and metaplutonic units. U-Pb ages for zircons from the Phenix City Gneiss suggest igneous crystallization at ca. 620 Ma, inheritance ca. 1000 to ca. 1700 Ma, and a ca. 300 Ma (Alleghanian) overprint recorded by zircon rims. Zircons from the metasedimentary/metavolcaniclastic Moffi ts Mill Schist yield bimodal dates at ca. 620 and 640 Ma. The 620 to 640 Ma dates make these rocks age-equivalent to the oldest parts of the Carolina slate belt (Virgilina and Savannah River) and strongly suggest a Gondwanan (Pan-African and/or Trans-Brasiliano) origin for the Uchee terrane. Alternatively, the Uchee terrane may be correlative with metamorphic basement of the Suwannee terrane. The ca. 300 Ma overgrowths on zircons are compatible with previously reported 295 to 288 Ma 40 Ar/ 39 Ar hornblende dates on Uchee terrane rocks, which were interpreted to indicate deep tectonic burial of the Uchee terrane contemporaneous with the Alleghanian orogeny recorded in the foreland. Temperaturetime paths for the Uchee terrane are similar to that of the Pine Mountain terrane, indicating a minimum age of ca. 295 Ma for docking. In terms of tectono-metamorphic history of the Uchee terrane, it is important to note that no evidence for intermediate "Appalachian" dates (e.g., Acadian or Taconian) has been reported. This younger history, together with the ages of metaigneous rocks and evidence for pre-Grenville basement, suggests the Uchee terrane is likely of Gondwanan origin and may be related to Carolina zone terranes that accreted during the Alleghanian orogeny.

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Section: Conclusion and Directions For Future Studiesmentioning

confidence: 97%

“…To the east, the Uchee terrane is mostly covered beneath sedimentary rocks of the Gulf and Atlantic Coastal Plains. To the northeast, however, it is in tectonic contact with the Milledgeville terrane, a largely unknown suprastructural block within the Carolina zone (Higgins et al, 1988;Hibbard et al, 2002).…”

Section: Geologic Contextmentioning

confidence: 98%

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

Steltenpohl¹,

Mueller²,

Heatherington³

et al. 2008

Geosphere

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“…Separating the eastern Blue Ridge from the Inner Piedmont is the Brevard fault zone (Jonas, 1932;King, 1955;Hatcher, 1978Hatcher, , 2001Higgins et al, 1988). The Brevard fault zone changes character at Jacksons Gap, Alabama (Fig.…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

confidence: 94%

“…It is framed by the Towaliga fault that separates the window from the Inner Piedmont to the northwest, the Box Ankle fault that closes the east end of the window and is truncated by the Towaliga fault, and the Dean Creek and Bartletts Ferry-Goat Rock faults that separate the Pine Mountain window from the Uchee terrane (peri-Gondwanan; Steltenpohl et al, 2008) to the southeast (Bentley and Neathery, 1970;Sears et al, 1981;Hooper et al, 1997). The Pine Mountain basement-cover units are considered to be an outboard remnant of the ancient, subducted Laurentian margin (Clarke, 1952;Odom et al, 1973;Schamel et al, 1980;Sears et al, 1981;Higgins et al, 1988;Hooper and Hatcher, 1988;Mueller et al, 2005;Steltenpohl et al, 2005bSteltenpohl et al, , 2010a.…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

confidence: 96%

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et al. 2013

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We dedicate this paper to the memory of coauthor Isidore (Izzy) Zietz, who died at age 93 while this paper was in review. After contributing to the early theoretical foundation for analysis of airborne magnetic surveys, Izzy became a leading advocate for aeromagnetic survey acquisition and interpretation throughout the U.S., combining surveys into regional, state, and national maps, and working with regional geologists in interpreting geophysical anomalies. Like many geologists, we have been energized by Izzy's contagious enthusiasm for using magnetic and gravity anomalies to delineate and characterize major tectonic features. Lessons from working with him on data from Alabama and elsewhere over the years will continue to infl uence our appreciation and understanding of aeromagnetic and gravity anomalies for interpreting the Earth's upper crust."Magnetics is never good, and gravity is even worse!" "…all of it can just be dashed." -Isidore Zietz ABSTRACT Aeromagnetic and gravity data sets obtained for Alabama (United States) have been digitally merged and fi ltered to enhance upper-crustal anomalies. Beneath the Appalachian Basin in northwestern Alabama, broad deep-crustal anomalies of the continental interior include the Grenville front and New York-Alabama lineament (dextral fault). Toward the east and south, high-angle discordance between the northeast-trending Appalachians and the east-west-trending wedge of overlapping Mesozoic and Cenozoic Gulf Coastal Plain sediments reveals how bedrock geophysical signatures progressively change with deeper burial. Highfrequency magnetic anomalies in the Appalachian deformed domain (ADD) correspond to amphibolites and mylonites outlining terranes, while broader, lower-amplitude domains include Paleozoic intrusive bodies and Grenville basement gneiss. Fundamental ADD structures (e.g., the Alexander City, Towaliga, and Goat Rock-Bartletts Ferry faults) can be traced southward beneath the Gulf Coastal Plain to the suture with Gondwanan crust of the Suwannee terrane. Within the ADD, there is clear magnetic distinction between Laurentian crust and the strongly linear, high-frequency magnetic highs of peri-Gondwanan (Carolina-Uchee) arc terranes. The contact (Central Piedmont suture) corresponds to surface exposures of the Bartletts Ferry fault. ADD magnetic and gravity signatures are truncated by the eastwest-trending Altamaha magnetic low associated with the Suwannee suture. Arcuate northeast-trending magnetic linears of the Suwannee terrane refl ect internal structure and Mesozoic failed-rift trends. Geophysical data can be used to make inferences on surface and subsurface geology and vice versa, which has applicability anywhere that bedrock is exposed or concealed beneath essentially non-magnetic sedimentary cover.

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“…Numerous researchers (McConnell, 1980;McConnell and Abrams, 1984;German, 1985;Higgins et al, 1988;Gillon, 1989;Spell and Norrell, 1990;McClellan et al, 2007) determined major, trace, and/or rare earth element (REE) compositions of the Pumpkinvine Creek Formation amphibolites and their possible equivalents. These data demonstrate that these units have tholeiitic compositions.…”

Section: Previous Workmentioning

confidence: 99%

Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the southern Appalachians

Holm-Denoma

Das

2010

Geological Society of America Bulletin

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Detailed mapping, U-Pb ages of igneous and detrital zircons, and isotopic and geochemical characterization of a bimodal volcanic sequence from the Appalachian Blue Ridge province provide constraints for the timing and tectonic setting of volcanism along the Early Paleozoic southeastern Laurentian margin. These units, the Pumpkinvine Creek Formation and related rocks, are interpreted as having been deposited along an extended Laurentian margin in a backarc setting during the mid-Ordovician, and tectonically emplaced as late as the late Paleozoic Alleghanian orogeny. Two felsite layers from the Pumpkinvine Creek Formation, a bimodal metavolcanic sequence, have ages of 466 ± 5 Ma and 461 ± 3 Ma. Geochemical analyses of metabasalts indicate compositions derived from a suprasubduction zone, and more specifi cally a backarc. Furthermore, ε Nd(460 Ma) = (+)3.3-(+)7.7 and 87 Sr/ 86 Sr (initial) = 0.7044-0.7069 indicate a juvenile source. The protoliths of the felsic lithofacies were low-potassium rhyodacite, and have ε Nd(460 Ma) = (−)3.2-(+)4.65 and 87 Sr/ 86 Sr (initial) = 0.709-0.722, suggesting incorporation of an evolved crustal component, which we interpret as Laurentian continental lithosphere. Furthermore, detrital zircons derived from within the Pumpkinvine Creek Formation yielded a majority of ages between 1017 and 1190 Ma, indicating that the source is likely a component of the rifted eastern Laurentian margin. A backarc origin for the Pumpkinvine Creek Formation indicates that the geodynamic setting of the southeastern margin of Laurentia included a retreating subduction zone resulting in extensional accretionary tectonism. These results have implications for the evolution of the southeastern Laurentian margin during a time traditionally linked to collision of an exotic Taconic arc with Laurentia. Additionally, we suggest that there are signifi cant along-orogen disparities that may result from fundamental tectonic boundaries.

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The structure, stratigraphy, tectonostratigraphy, and evolution of the southernmost part of the Appalachian Orogen

Cited by 46 publications

References 0 publications

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

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

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Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the southern Appalachians

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