Petrogenesis and paleotectonic history of the Wild Bight Group, an Ordovician rifted island arc in central Newfoundland

Swinden, H S; Jenner, George A.; Fryer, Brian J.; Hertogen, Jan; Roddick, J. C.

doi:10.1007/bf00678987

Cited by 61 publications

(30 citation statements)

References 57 publications

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“…16), suggesting that the enrichment in 147 Sm/ 144 Nd in the basalts and the lower ε Nd (500) value in the Tb-2 samples are not due to crustal contamination. Rather, the Nd isotope data are compatible with mixing of a depleted mantle component (DM, characterized by time-integrated LREE depletion) with a more fertile mantle component (FM, characterized by slight to moderate LREE enrichment but positive ε Nd ), such as one derived by relatively small degrees of partial melting (1%-7%) of an OIB-like mantle (Swinden et al, 1990). In this model, the Tb-2 samples, characterized by more enriched LREE and less positive ε Nd than the Tb-1 basalt, would have a higher proportion of the FM component in the mantle source (Fig.…”

Section: Mafi C Volcanic Rocksmentioning

confidence: 94%

The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition--Implications for the rifting of Ganderia

Schulz

Stewart

Tucker

et al. 2008

Geological Society of America Bulletin

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The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the westernmost of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia.U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ± 0.8 Ma) and overlying Castine Volcanics (503.5 ± 2.5 Ma) are Middle Cambrian in age. Two tholeiitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava fl ows and as sills in both units, has depleted La and Ce ([La/Nd] N = 0.53-0.87) values, fl at heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantlenormalized diagrams. In contrast, type Tb-2 basalt, present only in the Castine Volcanics, has slightly enriched LREE ([La/Yb] N = 1.42-2.92) values and no Th or Ta anomalies. Both basalt types have strongly positive ε Nd (500) values (Tb-1 = +7.9-+8.6; Tb-2 = +5.6-+7.0) and relatively enriched Pb isotopic compositions ( 206 Pb/ 204 Pb = 18.037-19.784; 207 Pb/ 204 Pb = 15.531-15.660; 208 Pb/ 204 Pb = 37.810-38.817). The basalts have compositions transitional between recent normal and enriched midocean-ridge basalt, and they were probably derived by partial melting of compositionally heterogeneous asthenospheric mantle. Two types of rhyolite also are present. Type R-1 rhyolite, which mostly occurs as tuffs interlayered with basalt in the Ellsworth Schist, is calc-alkaline and characterized by relatively low REE, Zr, and Hf contents, enriched LREE ([La/Yb] N ~3-6), positive Th and negative Ta anomalies, ε Nd (500) values near zero (+0.5 to −0.9), and relatively unradiogenic Pb isotope values ( 206 Pb/ 204 Pb = 18.845; 207 Pb/ 204 Pb = 15.625; 208 Pb/ 204 Pb = 38.626). The data suggest that R-1 rhyolite magma was likely derived by mixing of basalt with melts from a relatively depleted crustal source. Type R-2 rhyolite, which mostly occurs as lava fl ows and domes in the Castine volcanics, is tholeiitic and characterized by enriched REE with fl at patterns ([La/Yb] N = 1-2.5), moderate negative Eu anomalies (Eu/Eu* = 0.3-0.5), enriched Th, small negative Ta anomalies, and ε Nd (500) (+5.8-+7.5) and Pb isotope ( 206 Pb/ 204 Pb = 19.175-19.619; 207 Pb/ 204 Pb = 15.605-15.649; 208 Pb/ 204 Pb = 38.834-38.851) values that overlap those of the tholeiitic basalts. The data suggest that R-2 rhyolite magma was derived by the partial melting of hydrothermally...

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Section: Mafi C Volcanic Rocksmentioning

confidence: 94%

The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition--Implications for the rifting of Ganderia

Schulz

Stewart

Tucker

et al. 2008

Geological Society of America Bulletin

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“…ence of arc-type volcanics of Arenig age in the Exploits Subzone (Swinden et al, 1990;O 'Brien, 1993), together with the composite oceanic assemblages of the Notre Dame Subzone, suggest, but do not prove, subsequent southeast-dipping subduction near the Red Indian Line (Fig. 9b) as hypothesized by H. Williams et al (1988), although Dec and Swinden (1994) cast some doubt on this model.…”

Section: Nw Sementioning

confidence: 94%

“…Such subduction would consume early Arenig and older oceanic crust to the north west and build a west-facing volcanic arc. Transition from arc-type to non-arc volcanics in the Exploits Zone has been documented by Swinden et al (1990) and dated by O'Brien and coworkers (O'Brien, 1993;Hughes and O'Brien, 1994) as late Arenig or Llanvirn. This transition suggests open ing of a back-arc basin (Fig.…”

Section: Nw Sementioning

confidence: 99%

The northeastern end of the Dunnage Zone in Newfoundland

Currie

1995

atgeol

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The northeastern end of the Dunnage Zone comprises the Notre Dame Subzone, bounded to the southeast by the Red Indian Line, and the Exploits Subzone bounded to the southeast by the GRUB Line, the boundary of the Dunnage Zone against the Gander Zone. The Notre Dame Subzone consists of diverse, fault-bounded assemblages of Arenig and older rocks unplaced in oceanic settings. The Exploits Subzone includes four fault-bounded belts distinguished by their Silurian stratigraphies (Badger, Botwood, Duder [new] and Indian Islands belts). All exhibit Ashgill-Llandovery, southeast-vergent sinistral thrusting which emplaced a fragment of the Botwood Belt on the Indian Islands Belt. Progressive post-Wenlock Silurian deformation produced dcxtral faults and upright folds east of the Dog Bay Line, a Silurian terrane boundary, whereas west of the line it produced northwest-vergent folds. Late Silurian to Devonian brittle sinistral motion modified the Red Indian and GRUB lines. Structural and stratigraphic observations suggest early Arenig obduction of the margin of the Exploits Subzone onto the Gander Zone followed by eastward subduction of old ocean crust (Notre Dame Subzone), along the Red Indian Line, produced a west-facing volcanic arc. Arc rifting in late Arenig time produced an active back-arc basin. Rapid basin filling and structural inversion, accompanied by eastward thrusting began in Ashgill time, probably due to arrival of Laurentia at the subduction zone. Remnants of the back-arc basin were closed by westward subduction in Llandovery and Wen lock time. Continent-continent contact, accompanied by further compression and extrusion of wedge-shape fragments between conjugate faults, occurred in late Silurian time. RÉSUMÉ L'extremité nord-est de la zone de Dunnage cnglobe la sous-zone de Notre-Dame, délimitée au sud-est par la ligne Red Indian, et la sous-zone d'Exploits, délimitée au sud-est par la ligne GRUB, qui délimitée la zone de Dunnage contre la zone de Gander. La sous-zone de Notre-Dame est constitutée des assemblages varies limités par des failles de la série Arenig et les roches plus âgées placées dans des milieux océaniques. La sous-zone d'Exploits comprend quatre ceintures limitées par des failles qui se distinguent par leurs stratigraphies du Silurien (ceintures de Badger, de Botwood, de Duder [nouvelle] et des ties Indian). Toutes exposent les séries Ashgill et Llandovery, une poussée séncstre de déversement au sud-est qui a placé un fragment de la ceinture de Botwood sur la ceinture des iles Indian. Une déformation progressive postérieure à la sine Wenlock du Silurien a produit des failles dextres et des plis droits à l'est de la ligne de Dog Bay, une formation géologique frontière du Silurien, tandis qu'à l'ouest de la ligne, elle a produit des plis se déversant vers le nord-ouest. Un mouvement sénestre de rupture du Silurien supérieur au Dévonien a modifié les lignes Red Indian et GRUB. Des observations structurales et stratigraphiques laissent supposer qu'une obduction de L'Arenig infeérieure de la marge de la sous-zone d'Exploits sur la zone de Gander, suivie par une subduction en direction est de l'ancienne croute océanique (sous-zone de Notre-Dame), le long de la ligne Red Indian, a produit un arc volcanique faisant face à l'ouest. La distension de Pare vers la fin de la peériode de l'Arenig a produit un bassin arriere-arc actif. L'inversion structural et le remplissage rapides du bassin, accompagnes d'une poussée vers Test, ont débuté au cours de la période de l'Ashgill, probablement par suite de l'arrivée du bouclier laurentien dans la zone de subduction. Les lambeaux d'érosion du bassin arriere-arc ont été bloqués par la subduction en direction ouest au cours des series Llandovery et Wenlock. Un contact intercontinental, accompagne d'une compression et d'une extrusion ultérieures de fragments en biseau entre des failles synchrones, est survenu pendant le Silurien supérieur [Traduit par la rédaction]

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“…Figure 6 depicts the geographic distribution of Nd and Sr isotopic data from this study together with isotopic data from previous studies for comparison Eby, 1984b;1985a;1985b; However, in the following sections the concentrations of mobile elements such as Rb, Sr, K, Ca, and Ba (Schiano et al, 1993;Swinden et al, 1990) are used for petrogenetic interpretations. Thus, a discussion of the robustness of the concentrations of these elements is warranted.…”

Section: Nd Sr Pb and Hf Isotopesmentioning

confidence: 99%

“…The higher degree of scatter in the Sr isotope data compared to the Nd isotope data likely reflects the greater mobility of Sr (Bienvenu et al, 1990;Swinden et al, 1990) and the greater variability of Sr contents among the contaminants (shales, limestones, schists) compared to Nd.…”

Section: Fractional Crystallization and Accumulationmentioning

confidence: 99%

Tracages isotopiques de l'origine et de l'évolution des magmas en milieu continental :

Roulleau¹

2010

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Petrogenesis and paleotectonic history of the Wild Bight Group, an Ordovician rifted island arc in central Newfoundland

Cited by 61 publications

References 57 publications

The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition--Implications for the rifting of Ganderia

The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition--Implications for the rifting of Ganderia

The northeastern end of the Dunnage Zone in Newfoundland

Tracages isotopiques de l'origine et de l'évolution des magmas en milieu continental :

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