Age of the granulite-facies metamorphism of the Wilmington Complex, Delaware-Pennsylvania Piedmont

Grauert, B.; Wagner, Mary Emma

doi:10.2475/ajs.275.6.683

Cited by 35 publications

(8 citation statements)

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“…These features clearly point to a magmatic origin. Crystals grown during high-grade metamorphic events are usually multi-facetted with an oval shape (e.g., Grauert and Wagner 1975;Kro¨ner et al 1994). The occurrence of complex internal structures of older zircon crystals, such as those shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Ion microprobe (SHRIMP) dating of detrital zircon grains from quartzites of the Eckergneiss Complex, Harz Mountains (Germany): implications for the provenance and the geological history

Geisler

Vinx

Martin-Gombojav

et al. 2005

Int J Earth Sci (Geol Rundsch)

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The Eckergneiss Complex (EGC) is a geologically unique medium-to high-grade metamorphic unit within the Rhenohercynian domain of the Mid-European Variscides. A previously, poorly defined conventional lower U-Pb intercept age of about 560 Ma from detrital zircons of metasedimentary rocks has led to speculations about an East Avalonian affinity of the EGC. In order to unravel the provenance and to constrain the age of the sediment protolith, we carried out sensitive high-resolution ion microprobe U-Pb analyses on detrital zircons from five different EGC quartzite occurrences. The obtained age spectrum indicates a SW Baltica provenance of the detritus. Sveconorwegian ages between 0.9-1.2 Ga are particularly well represented by analyses from metamorphic recrystallization/alteration zones penetrating into igneous zircon. Cadomian (PanAfrican) ages, which might reflect a metamorphic event, could not be substantiated. Instead, zircons of igneous origin yielded concordant Lower Devonian and Silurian ages of 410±10, 419±10, and 436±6 Ma (1r), implying that sedimentation of the EG protolith must have taken place after 410±10 Ma. The lower age limit of the EGC metamorphism is constrained by 295 Ma intrusion ages of the adjacent, nonmetamorphosed Harzburg Gabbronorite and Brocken Granite. Sedimentation and metamorphism must thus have taken place between about 410 Ma and 295 Ma. Given that this time span coincides with most of the sedimentation within the virtually nonmetamorphosed (lowest grade) Rhenohercynian in the Harz Mountains, including the direct vicinity of the EGC, along with the high-grade metamorphism, the EGC can hardly be seen as uplifted local basement. A possible candidate for the root region is an easterly, concealed marginal segment of the Rhenohercynian domain of the Variscides, which is tectonically overridden and suppressed by the Mid-German Crystalline Rise during continent collision. However, based on the concept of strike-slip movement of Variscan terranes with different P-T-t histories as a result of postaccretion intraplate deformation, the EGC could also represent a fault-bounded complex with an origin located far east or south east of the present location.

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Section: Resultsmentioning

confidence: 99%

Ion microprobe (SHRIMP) dating of detrital zircon grains from quartzites of the Eckergneiss Complex, Harz Mountains (Germany): implications for the provenance and the geological history

Geisler

Vinx

Martin-Gombojav

et al. 2005

Int J Earth Sci (Geol Rundsch)

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“…The Pennsylvania Piedmont is underlain by numerous Grenvillian (Grauert et al, 1973a, b;Grauert and Wagner, 1975;Wagner and Crawford, 1975) basement blocks, the CambrianOrdovician passive margin metacarbonate and metaclastic sequences, a vast region of low-to high-grade schist of the Wissahickon Formation in the east and Octoraro Formation in the west, and metasiliciclastic rocks of the Peters Creek Formation in the central Piedmont. Three broad catagories of regional deformation and metamorphism are evident in specific parts of the Piedmont: (1) granulite and amphibolite facies metamorphism in the basement massifs is interpreted to be Grenvillian (Wagner and Crawford, 1975;Crawford and Crawford, 1980;Wagner and Srogi, 1987); (2) regional metamorphism and napperelated penetrative deformation in the Wissahickon, Octoraro and Peters Creek Formations is presumed to be Taconian (Lapham and Bassett, 1964;Wise, 1970;Folland and Muessig, 1978;Crawford and Crawford, 1980;Crawford and Mark, 1982;Wagner and Srogi, 1987); and (3) lower amphibolite to lower greenschist facies metamorphism and deformation is related to late Paleozoic regional dextral transpression that is confined to discrete steeply dipping shear zones and certain structural blocks between the shear zones (Lapham and Bassett, 1964;Crawford and Crawford, 1980;Valentino et al, , 1995.…”

Section: Geologic Settingmentioning

confidence: 98%

Interaction between Paleozoic strike-slip and thrust shear zones in the Philadelphia structural block, central Appalachian Piedmont

Valentino¹,

Valentino²,

Lamport³

1999

The Mid-Atlantic Piedmont: Tectonic Missing Link of the Appalachians

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The Philadelphia structural block in the Piedmont of Pennsylvania is dissected by a network of Paleozoic shear zones that cross-cut Taconic metamorphic zones and structures. The Wissahickon Formation (pelitic and semipelitic schist) was intruded by the Springfield granodioritic pluton, and the northern margin of the pluton was later intensely sheared in a northwest-dipping mylonite zone (here named the Llanerch thrust zone). Kinematic analysis revealed oblique reverse displacement in a due south direction on the Llanerch thrust. The direction of thrusting is parallel to the Crum Creek shear zone that is the boundary of the Springfield pluton on the western margin where the thrust is intersected. Sinistral offset of metamorphic zones in the Wissahickon Formation approximately 3-4.5 km occurs across the Crum Creek shear zone. The mapped width of the kyanite zones is relatively uniform along strike within the Wissahickon Formation of the hanging wall block north of the Llanerch thrust zone. The first sillimanite zone is very narrow due to truncation along the thrust; the second sillimanite zone lies in the footwall. Based on the structural thickness of the metamorphic zones, the heave on the Llanerch thrust is calculated to be a minimum of 1.5 km. Development of the Llanerch thrust was largely controlled by horizontal movement of the wedge of rock between the Rosemont zone and the Springfield pluton, causing part of the Wissahickon Formation to be thrust over toward the south. Parallel movement direction of the transcurrent Crum Creek zone and the Llanerch thrust suggests the structures are cogenetic. If this is the case, the amount of displacement across the southern segment of the Crum Creek zone must be 1.5 km greater than displacement across the northern segment of the zone to account for the contractional deformation on the Llanerch thrust wedge. Using metamorphic zones in the Wissahickon Formation, a complex palinspastic reconstruction of the postTaconic shear zones places the Wilmington Complex (root of the Taconic magmatic arc) directly adjacent to the West Chester massif (Laurentian Grenville basement) sometime during the middle to late Paleozoic.

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“…Because of the Cambrian or older age of the rocks, the granulite-facies metamorphism (suggested to be of Taconian age by Grauert and Wagner, 1975), the presence of anorthositic rocks, and the structural position adjacent to the Chopawamsic terrane (whether above or below), it is possible that the Wilmington terrane might be an extension of the Goochland terrane. The Wilmington terrane could have amalgamated with the Chopawamsic and Potomac terranes either in the Penobscottian or Taconian events.…”

Section: Deformational and Metamorphic Eventsmentioning

confidence: 99%

“…DEFORMATIONAL AND METAMORPHIC EVENTS-Granulite-facies metamorphism and associated deformation is suggested to be Taconian (Grauert and Wagner, 1975).…”

Section: Deformational and Metamorphic Eventsmentioning

confidence: 99%

“…REFERENCES-Brown and Van der Voo (1983); Grauert and Wagner (1975); Poland and Muessig (1978); Horton and others (1989a); Rao and Van der Voo (1980); Wagner and Srogi (1987); Ward (1959) NA42: SUSSEX TERRANE TERRANE BOUNDARIES-The Sussex terrane (Fig. 1), as named by Horton and others (1989a), lies entirely beneath sediments of the Atlantic Coastal Plain in Virginia and Maryland.…”

Section: Deformational and Metamorphic Eventsmentioning

confidence: 99%

See 1 more Smart Citation

Terranes and overlap sequences in the Central and Southern Appalachians, an expanded explanation for part of the Circum-Atlantic terrane map

Horton¹,

Drake²,

Rankin³

1994

Open-File Report

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Age of the granulite-facies metamorphism of the Wilmington Complex, Delaware-Pennsylvania Piedmont

Cited by 35 publications

References 0 publications

Ion microprobe (SHRIMP) dating of detrital zircon grains from quartzites of the Eckergneiss Complex, Harz Mountains (Germany): implications for the provenance and the geological history

Ion microprobe (SHRIMP) dating of detrital zircon grains from quartzites of the Eckergneiss Complex, Harz Mountains (Germany): implications for the provenance and the geological history

Interaction between Paleozoic strike-slip and thrust shear zones in the Philadelphia structural block, central Appalachian Piedmont

Terranes and overlap sequences in the Central and Southern Appalachians, an expanded explanation for part of the Circum-Atlantic terrane map

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