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A possible schematic lithosphere-scale model for the Ediacaran-Ordovician plate tectonic evolution of the Carolina terrane. Red box in each time frame indicates approximate location of corresponding time frame in Figure 9.
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The Carolina terrane forms the heart of Carolinia, one of the largest accreted peri-Gondwanan crustal tracts within the Appalachian Orogen. The terrane consists of two major lithotectonic elements, the older Neoproterzoic Hyco magmatic arc, ca. 633-612 Ma, and the younger Neoproterozoic-early Paleozoic Albemarle magmatic arc, ca. 555-<528 Ma. Both...
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... with the available data and observations. Clearly, the data are insuf- ficient to formulate a model that is continuous through time and so our model provides 'snapshots' of critical periods in the history of the Carolina terrane and we present these snapshots at both the scale of central North Carolina (Fig. 9) and lithospheric plate scale (Fig. 10). These models also serve other purposes; they highlight the outstanding pro- blems in the region and they provide a target at which other researchers can focus their future ...
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... oldest element in the Carolina terrane is the Hyco arc, a suprasubduction zone arc that was active for approximately 20 m.y. between c. 633-612 Ma (Figs. 9, 10). Isotopically, the arc is juvenile and the magmatic rocks lack inherited zircon; consequently we depict it as forming in the open ocean (Fig. 10). The polarity of subduction was likely from open ocean beneath the Hyco arc, rather than from the sea between the Hyco arc and more easterly Gondwanan elements, because there is no obvious evidence that collision of the Hyco arc with other Gondwanan components caused cessation of the Hyco arc. The apparent cessation of the Hyco arc at ...
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... tectonic setting of the Virgilina sequence is poorly constrained; it may represent renew- ed suprasubduction zone arc activity or it could represent an arc rift. The latter interpre- tation implies that an arc is active, therefore we depict the Virgilina sequence in a magma-tic arc setting in Figure 10. We show subduc- tion from the open ocean side beneath the arc to account for the Virgilina volcanics mainly because of two observations, 1) we need to juxtapose the Hyco-Virgilina arcs with the Charlotte arc by c. 550 Ma and 2) based on the modern distribution of these elements, the Charlotte arc likely lay outboard of the Hyco- Virgilina edifice. ...
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... beneath the Virgilina arc, although subduction could have involved consumption of the seaway at both sides. It is doubtful that subduction occurred beneath the Virgilina arc from the Gondwanan side, as this scenario would result in collision with easterly terranes, a collision for which it appears we lack evidence. The Charlotte arc is shown in Fig. 10 as being constructed on some form of Gondwanan crust. Although isotopic study of the Charlotte terrane to date indicate that it is juvenile with respect to its Nd isotopic sig- nature, the number of samples analyzed to date are very limited ( Fullagar et al., 1997). This bit of evolved crust beneath the Charlotte arc figures into the ...
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... example, it is not clear if subduction beneath the Virgilina arc was con- tinuous during the time frame between the two elements or if there was a hiatus in acti- vity (Fig. 2). We imply that subduction was continuous in Figure 10 mainly because rea- sonable explanations of a hiatus are elusive. Consequently, it appears that closure of the seaway between the Charlotte and Virgilina arcs led to collision and suturing of the Charlotte and Carolina terranes at by c. 550 Ma ( Barker et al., 1998). ...
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... Staal et al., 1998). The Kings Mountain sequence is shown in Figure 10 as lying along the westerly margin of this extensional system. As Carolinia migrated westward (modern coordinates) and Iapetus narrowed, it appears that it occuppied a lower plate setting, as no further magmatic activity took place in Carolinia during the early Paleozoic. ...
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... A cluster of geologic units with large As exceedance percentages occurs in the youngest portion of the Carolina Slate belt-the Albemarle arc ( Fig 2B)-that lies in a geographic region previous noted as having elevated As concentration in well water [13,14,24]. The Albemarle arc along with the rest of the Carolina Slate belt was a zone of suprasubduction that accreted to North America [29,30]. Other geologic events in these regions included intense metamorphism, folding, faulting, and igneous intrusive activity, resulting from collisions and rifting events associated that contribute to the complex geology of the Albemarle arc [31,32]. ...
... Additional rocks surrounding the Albemarle arc and influenced by it contain As exceedance percentages that are >5%. The Gold Hill Shear zone (CZph, 4 th greatest exceedance, 19.1%), a zone of deformation that marks the contact between the Carolina Slate belt and Charlotte belt, is hosted in rocks associated with the Cid and Tillery Formations [29]. Additionally, recent mapping efforts [38] have indicated that a geologic unit composed of undifferentiated Albemarle arc and Hyco arc sediments (CZmd, 14th greatest exceedance, 6.8%) in the eastern part of the Carolina Slate belt is also likely related to the Cid Formation. ...
... The northern (and older) part of the Carolina Slate belt, the Hyco arc, has significantly lesser exceedance percentages for As (<1.9%; S1 Table), supporting the geologic influence and spatial variability within the Carolina Slate belt [24]. With the exception of the Gold Hill shear zone, the geological units in the Charlotte belt, with its distinct geologic history from the Caroline Slate belt [29], have comparatively small exceedance percentages (<2.8%; S1 Table). ...
More than 200 million people worldwide, including 11 million in the US, are estimated to consume water containing arsenic (As) concentrations that exceed World Health Organization and US EPA standards. In most cases, the As found in drinking water wells results from interactions between groundwater and geologic materials (geogenic contamination). To that end, we used the NCWELL database, which contains chemical information for 117,960 private drinking wells across North Carolina, to determine the spatial distribution of wells containing As contaminated water within geologic units. Specific geologic units had large percentages (up to 1 in 3) of wells with water exceeding the EPA As maximum contaminant level (MCL, 10 μg/L), both revealing significant variation within areas that have been previously associated with As contamination and identifying as yet unidentified problematic geologic units. For the 19 geologic units that have >5% of wells that contain water with As concentrations in exceedance of 10 μg/L, 12 (63%) are lithogenically related to the Albemarle arc, remnants of an ancient volcanic island, indicating the importance of volcanogenic materials, as well as recycled (eroded and deposited) and metamorphosed volcanogenic material. Within geologic units, wells that have As concentrations exceeding 10 μg/L tended to have pH values greater than wells with As concentrations less than 10 μg/L, emphasizing the importance of the extent of interaction between groundwater and geologic materials. Using census information with the geologic-based exceedance percentages revealed the importance of regional geology on estimates of population at risk compared to estimates based on county boundaries. Results illustrate that relating As contamination to geologic units not only helps explain sources of geogenic contamination but sharpens the identification of communities at risk for exposure and further illuminates problematic areas through geologic interpretation.
... These arcs and adjacent terranes of different provenance, i.e., peri-Laurentian and Avalonia-type peri-Gondwanan crust , eventually were accreted to Laurentia during multiple events. Complex accretionary stages lasted until the Silurian (Kellett et al., 2017) and led to the usage of local names for some Late Ordovician and Silurian orogenies, such as the Cherokee orogeny of the Southern Appalachians (Hibbard et al., 2013) and the Salinic orogeny of the Northern Appalachians (e.g., Fyffe et al., 2012;Willner et al., 2018). ...
... The contiguous East Avalonia plate eventually became accreted at the SW edge of Eastern Europe (Torsvik and Rehnström, 2003), i.e., the Tornquist suture of the Arcto-European plate. This accretion was coeval with ongoing subduction-accretion tectonics affecting West Avalonian arc terranes at the active plateboundary zone of North America (Hibbard et al., 2013;van Staal et al., 2012). As mentioned above, there is no direct orogenic constraint pointing to a collisional contact between East Avalonia and the East European Craton. ...
New analytical and field techniques, as well as increased international communication and collaboration, have resulted in significant new geological discoveries within the Appalachian-Caledonian-Variscan orogen. Cross-Atlantic correlations are more tightly constrained and the database that helps us understand the origins of Gondwanan terranes continues to grow. Special Paper 554 provides a comprehensive overview of our current understanding of the evolution of this orogen. It takes the reader along a clockwise path around the North Atlantic Ocean from the U.S. and Canadian Appalachians, to the Caledonides of Spitsbergen, Scandinavia, Scotland and Ireland, and thence south to the Variscides of Morocco.
... Some of the latter rocks appear to be tuffaceous. The Albemarle Group was most likely deposited in an island arc environment with a more evolved crustal component during the Cambrian ( Hibbard et al. 2013). ...
... The Appalachians record a long development from an accretionary to a collisional orogen (e.g., van Staal et al., 2009;Hatcher, 2010;van Staal and Barr, 2012). The Southern and Central Appalachians include a series of Paleozoic terranes that were accreted before the final collision between Laurentia and Gondwana during several diachronous orogenies (Hatcher, 2010), i.e., Ordovician arc accretion (Cherokee orogeny 1 ), Late Devonian -Early Carboniferous diachronous zipper-style terrane accretion (Neoacadian orogeny), and Late Carboniferous to Early Permian collision between Laurussia 2 and Gondwana 1 The Cherokee and Taconic orogenies are coeval, but have been distinguished by Hibbard et al. (2013) to highlight the contrasting provenance of terranes accreted to Laurentia during Iapetus closure. Cherokee orogeny is used for the Southern and Central Appalachians to refer to the accretion of terranes of peri-Gondwana provenance, Taconic orogeny is used for the Northern Appalachians to refer to the accretion of terranes of peri-Laurentian provenance. ...
... Mineralized areas correspond to tectonic elements that cannot be correlated along the Appalachian orogen (Hatcher, 2010) and that are dominated by arc rocks that have formed and accreted at different time (e.g. Hibbard et al. (2007Hibbard et al. ( , 2013, Owens et al. (2013), Tull et al. (2014)). AS = Albemarle sequence; CCT = Cowrock and Cartoogechaye terranes; KMB = Kings Mountain Belt; WED = Weedowee-Emuchfaw-Dahlonega Belt. ...
... For instance, the Dahlonega and Chopawamsic belts of the Southern Appalachians, the Annieopsquatch accretionary tract, the Notre Dame and the Dashwood arcs, and the Baie Verte and the Lushs Bight oceanic tracts of the Northern Appalachians, and Midland Valley and Southern Upland of the Great Britain either formed on terranes or represent terranes that are derived from the Laurentian margin (e.g., Hibbard et al., 2007;van Staal, 2007;Hatcher, 2010;Chew and Strachan, 2013). Similarly, magmatic arcs on Carolinia of the Southern Appalachians, on Ganderia and Avalonia of the Northern Appalachians, and on Avalonia (Leinster terrane, Welsh Basin) in Variscan Europe formed on crust originally derived from the margin of Gondwana (e.g., Woodcock, 2002;van Staal, 2007;Hatcher, 2010;Hibbard et al., 2013). Common to these magmatic arcs is that there are (i) volcanic massive sulfide deposits in back-arc basins related to the formation of the arcs and/or (ii) structurally-controlled quartz-Au or quartz-sulfide-Au mineralization related to obduction of the arcs and later strike-slip movements along former sutures (Fig. 5). ...
The distribution of Au mineralization in the Appalachians and Variscides is irregular. Major segments of the belt do not show significant Au mineralization. Segments with major Au deposits, however, show a complex history of repeated endogenic and exogenic metal redistribution. Major sources for Au occurrences in the Appalachians and Variscides are Cambrian to Ordovician sedimentary rocks and Cambrian to Ordovician magmatic arcs. (i) Gondwana-derived Au forms paleo-placer deposits in Cambrian to Ordovician sedimentary rocks on stable continental crust and may be preserved in low-strain or upper plate domains of the Appalachians and Variscides. The erosion of these sediments during rifting of peri-Gondwana led to the redeposition of these Au-anomalous protoliths as fan and turbiditic sediments at the continent margin. (ii) The magmatic arcs are built on Laurentian or Gondwana crust that earlier had separated from the main continents. Gold mineralization is mainly bound to volcanic massive sulfide deposits that formed in suprasubduction zone ophiolites. Sedimentary rocks earlier deposited at the continent margin may significantly contribute to the Au budget of suprasubduction zone ophiolites. The early Paleozoic accretion and obduction of the magmatic arcs to Laurentia and Laurussia resulted in a first redistribution of Au, in part in close spatial relation with the older deposits, in part in relation to structural elements that were active during accretion. With the onset of the collision of the Armorican Spur (Gondwana) with Laurussia at c. 400–380 Ma, style of Au mineralization and redistribution becomes highly diverse within the plate boundary zone between Gondwana and Laurussia with (i) magmatic Au mineralization (New Brunswick), (ii) shear zone related mineralization (e.g., Southern Alleghanian, Newfoundland, Ireland, Scotland), and (iii) quartz-Au veins in greenschist to amphibolite facies metasedimentary rocks (Nova Scotia). Only in Maritime Canada Au mineralization is related to subduction, in all other areas Au mineralization is related to reactivation of strike-slip shear zones and to redistribution within older deposits. In areas of continental collision with subduction of continental crust, Au is restricted to shear-zone bound vein-type mineralization and to magmatic rocks in structurally high allochthonous units (Spain, Armorica, Central Bohemian Plutonic Complex). The age of Au mineralization in supra-subduction ophiolites is very variable along the Appalachians and Variscides and reflects the formation of oceanic crust followed by the accretion or obduction of these rocks. In contrast, shear-zone bound quartz-Au veins in low-grade metamorphic domains and in areas with older Au mineralization, as well as granite-bound Au mineralization, formed along the entire belt in distinct pulses that are controlled by reorganizations within the plate boundary system and by reactivations of old structures in different stress systems.
Phanerozoic reactivations of basement fault zones are documented in 5000m of basement core recovered from beneath the updip Atlantic Coastal Plain underlying the U.S. Department of Energy Savannah River Site. These basement fault zones are adjacent to the excised Rheic Ocean suture. C. 619 and 624 Ma metaintrusive rocks contain a mylonitic fabric and intrude foliated mafic metavolcanic rocks. At c. 305 Ma, granulite facies orthogneisses were thrust over amphibolite facies metaigneous rocks in the transpressive Tinker Creek nappe. The overturned limb of the nappe localizes the Dunbarton Triassic basin border fault. The border fault acted as a conduit for fluids in the Mesozoic and Cenozoic. C. 220±5 Ma, a potassium and silica metasomatic event affected SRS basement. A propylitic event flushed reducing fluids through rocks as young as Santonian. The remains of a Triassic subbasin were identified in the northwest part of the site. A Cretaceous and younger vein paragenesis overprints the previous events. More than thirty pseudotachylytes are found in SRS basement and are preferentially localized on metasomatized Alleghanian chloritic fractures. Pseudotachylyte post-dates mineralized fractures. The Pen Branch fault offsets the basement-Cretaceous unconformity and is present in c. 242 m of core between PBF-7-419 m and PBF-7-660.8 m. The Pen Branch Fault cross-cuts mineralized fractures and must postdate strike-normal zeolites.
The Boy Scout-Jones prospect is one of several molybdenum (Mo) prospects exposed in the Carolina superterrane of the southern Appalachians. Molybdenum mineralization at the Boy Scout-Jones prospect is hosted by quartz veins that occur in association with the late Paleozoic Medoc Mountain granitic stock. Petrographic, molybdenite, and pyrite chemistry studies were undertaken to better understand the origin of the Boy Scout-Jones Mo mineralization. Molybdenite, the sulfide which hosts the Mo, displays wavy lath-like textures and occurs in association with feldspars and sericite crystals within quartz veins. Pyrite, an abundant sulfide mineral encountered in this study that also occurs in association with feldspar, has a restricted composition comparable to that of pure pyrite. There is no correlation between Mo (55.31-60.64 wt.%) and elements such as Re (0.03-0.12 wt.%), W (0.01-0.11 wt.%), and Fe (0.01-0.18 wt.%) which are common substituents for Mo, probably suggesting either the highly variable nature of Re in molybdenite, and/or remobilization of the Mo during hydrothermal alteration of the prospect. The mineralogy at Boy Scout-Jones of molybdenite, feldspar, sericite, and pyrite, as well as concentrations of Mo and rhenium, are all consistent with phyllic alteration that originated as a porphyry Mo and/or porphyry copper-Mo deposit. The mineralization and alteration at this, and possibly other Halifax County molybdenum prospects in North Carolina, are likely related to the intrusion of the Medoc Mountain granite, and therefore, syngenetic.
The Halifax County complex (HCC) is a meta-ultramafic/metamafic body that crops out along the easternmost exposed part of the Carolina superterrane in northeastern North Carolina. Petrographic and mineral chemistry studies were undertaken to place some constraints on the evolution of the HCC. Halifax County Complex amphiboles are zoned, with hornblende cores and actinolitic rims. Feldspar minerals span the whole plagioclase- and potassium-feldspar spectrum. Evolved olivines (Fo69–75) are primary, and pyroxenes plot in the enstatite, pigeonite, augite, and diopside fields. Low TiO2 (<0.8 wt.%) clinopyroxenes and highly calcic plagioclases are consistent with origin of the HCC at an island arc setting. Chlorites are characterized by wide variations in their Si atoms per formula unit but have restricted total Fe concentrations. Potassium feldspar in the HCC likely originated during adularization or potassification. Chlorite thermometry yields temperatures of formation of 241–300 °C. Application of hornblende-plagioclase thermometers yields average temperatures of 648 °C consistent with amphibolite facies conditions as well as greenschist facies conditions, at pressures of up to 6.5 kbar. Both clinopyroxene and evolved olivine compositions are consistent with an island arc origin for the HCC. Amphibolite facies metamorphisms recorded by HCC rocks likely represent metamorphism of the HCC during arc–arc terrane collision, whereas greenschist metamorphism is interpreted to record the temperatures of thrusting of the HCC onto its present location at pressures of <3 kbar in Alleghanian times during the final assembly of the Appalachians. Results reported here have implications for the origin of comparable metamorphosed mafic-ultramafic rocks encountered along ancient orogenic belts worldwide.
