Superposed Neoproterozoic and Silurian magmatic arcs in central Cape Breton Island, Canada: geochemical and geochronological constraints

2000 ◽  
Vol 137 (2) ◽  
pp. 137-153 ◽  
Author(s):  
J. D. KEPPIE ◽  
J. DOSTAL ◽  
R. D. DALLMEYER ◽  
R. DOIG
Keyword(s):  
New Brunswick ◽  
New England ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Zircon Age ◽  
Cape Breton Island ◽  
Northern Margin ◽  
Element Abundances ◽  
Southern New England ◽  
Cape Breton

Isotopic and geochemical data indicate that intrusions in the eastern Creignish Hills of central Cape Breton Island, Canada represent the roots of arcs active at ∼ 540–585 Ma and ∼ 440 Ma. Times of intrusion are closely dated by (1) a nearly concordant U–Pb zircon age of 553±2 Ma in diorites of the Creignish Hills pluton; (2) a lower intercept U–Pb zircon age of 540±3 Ma that is within analytical error of 40Ar/39 Ar hornblende plateau isotope-correlation ages of 545 and 550±7 Ma in the River Denys diorite; and (3) an upper intercept U–Pb zircon age of 586±2 Ma in the Melford granitic stock. On the other hand, ∼ 441–455 Ma 40Ar/39 Ar muscovite plateau ages in the host rock adjacent to the Skye Mountain granite provide the best estimate of the time of intrusion, and are consistent with the presence of granitic dykes cutting the Skye Mountain gabbro–diorite previously dated at 438±2 Ma. All the intrusions are calc-alkaline; the Skye Mountain granite is peraluminous. Trace element abundances and Nb and Ti depletions of the intrusive rocks are characteristic of subduction-related rocks. The ∼ 540–585 Ma intrusions form part of an extensive belt running across central Cape Breton Island, and represent the youngest Neoproterozoic arc magmas in this part of Avalonia. Nearby, they are overlain by Middle Cambrian units containing rift-related volcanic rocks, which bracket the transition from convergence to extension between ∼ 540 and 505/520 Ma. This transition varies along the Avalon arc: 590 Ma in southern New England, 560–538 Ma in southern New Brunswick, and 570 Ma in eastern Newfoundland. The bi-directional diachronism in this transition is attributed to northwestward subduction of two mid-ocean ridges bordering an oceanic plate, and the migration of two ridge–trench–transform triple points. Following complete subduction of the ridges, remnant mantle upwelling along the subducted ridges produced uplift, gravitational collapse and the high-temperature/low-pressure metamorphism in the arc in both southern New Brunswick and central Cape Breton Island. The ∼ 440 Ma arc magmatism in the Creignish Hills extends through the Cape Breton Highlands and into southern Newfoundland, and has recently been attributed to northwesterly subduction along the northern margin of the Rheic Ocean.

U – Pb zircon date from Avalonian Cape Breton Island and geochronologic calibration of the Early Ordovician

1997 ◽  
Vol 34 (5) ◽  
pp. 724-730 ◽  
Author(s):  
Ed Landing ◽  
Samuel A. Bowring ◽  
Kathleen L. Davidek ◽  
Richard A. Fortey
Keyword(s):  
New Brunswick ◽  
Eastern Cape ◽  
Associated Fauna ◽  
Zircon Age ◽  
Cape Breton Island ◽  
Early Ordovician ◽  
Cape Breton ◽  
Fossil Evidence ◽  
North Wales ◽  
Saint John

A U–Pb zircon date of 483 ± 1 Ma is recorded from an uppermost Tremadoc K-bentonite from the Chesley Drive Group on McLeod Brook, eastern Cape Breton Island. The associated fauna, with the trilobite Peltocare rotundifrons, is also known from the Reversing Falls section in Saint John, New Brunswick, and the traditional reference of the latter section to the Arenig is incorrect. A 483 ± 1 Ma age is significantly older than a U – Pb zircon age reported from the classical base of the Arenig Series in north Wales and about 10 Ma older than strata regarded herein as upper Arenig in central Newfoundland. If the global standard for the base of the Arenig is defined at the Tetragraptus approximatus Zone base, then the base of the type Arenig in Wales is younger than the latter horizon. The McLeod Brook occurrence is from an uppermost Tremadoc (Hunnebergian Stage) interval that has been removed below the unconformity in north Wales. The age of the Tremadoc –Arenig series boundary remains uncertain; however, a tentative estimate that it is significantly younger than 483 Ma is suggested by fossil evidence.

scholarly journals New and noteworthy records of Orthoptera and allies in the Maritimes and the Îles-de-la-Madeleine, Quebec

2014 ◽  
Vol 127 (4) ◽  
pp. 332 ◽  
Author(s):  
Paul M. Catling ◽  
Donald F. McAlpine ◽  
Christopher I. G. Adam ◽  
Gilles Belliveau ◽  
Denis Doucet ◽  
...  
Keyword(s):  
Nova Scotia ◽  
New Brunswick ◽  
Prince Edward Island ◽  
Forficula Auricularia ◽  
Cape Breton Island ◽  
Cape Breton ◽  
La Madeleine

Chortophaga viridifasciata, Forficula auricularia, Melanoplus stonei, Scudderia furcata furcata, Scudderia pistillata, and Trimerotropis verruculata from Prince Edward Island and Doru taeniatum, Melanoplus punctulatus, Orchelimum gladiator, and Spharagemon bolli from New Brunswick are new provincial records. Other records of interest include the endemic Melanoplus madeleineae from Île d’Entrée in the Îles-de-la-Madeleine, Quebec; Trimerotropis verruculata from the Îles-de-la-Madeleine, Quebec; and Chortophaga viridifasciata, Stethophyma lineatum, and Tetrix subulata, new for Cape Breton Island, Nova Scotia. The ranges of Conocephalus brevipennis, Tetrix arenosa angusta, Tetrix ornata, and Tetrix subulata are significantly extended in New Brunswick. A previously unpublished record from 2003 of Roeseliana roeselii (Metrioptera roeselii) is the earliest report of this European introduction to the Maritimes.

Upper Precambrian through Lower Cambrian of Cape Breton Island: faunas, paleoenvironments, and stratigraphic revision

1991 ◽  
Vol 65 (4) ◽  
pp. 570-595 ◽  
Author(s):  
Ed Landing
Keyword(s):  
Lower Cambrian ◽  
Volcanic Rocks ◽  
Depositional Sequence ◽  
Cape Breton Island ◽  
Tectonic History ◽  
Small Shelly Fossils ◽  
Cape Breton ◽  
Local Erosion ◽  
Lake Formation ◽  
Random Block

Latest Precambrian through Early Cambrian tectonic history and stratigraphy are comparable in southeastern Cape Breton Island and the western Placentia–Bonavista axis, southeastern Newfoundland. The lithostratigraphic nomenclature of southeastern Newfoundland is used for this interval in Cape Breton Island. Upper Precambrian volcanic rocks of the Forchu Group (=“Giant Lake Complex,’ designation abandoned) are unconformably overlain by uppermost Precambrian through lowest Cambrian strata termed the “Morrison River Formation’ (designation abandoned). This depositional sequence consists of three formations: 1) red beds through tidalites of the Rencontre Formation (to 279+ m; =“Kelvin Lake Formation,’ designation abandoned); 2) prodeltaic clastics of the Chapel Island Formation (to 260 m); and 3) macrotidal quartzites of the Random Formation (to 71 + m). Post-Random block faulting and 300 m of local erosion took place prior to onlap of the “MacCodrum Formation’ (abandoned). Siliciclastic mudstones of the lower “MacCodrum’ are re-assigned to the middle Lower Cambrian Bonavista Group. Sub-trilobitic faunas from the Bonavista Group include “Ladatheca’ cylindrica from the West Centre Cove Formation(?) and higher diversity faunas (23 species) in the Camenella baltica Zone of the Cuslett and Fosters Point Formations. Trilobite-bearing, upper Lower Cambrian (Branchian Series) strata (Brigus Formation, =upper “MacCodrum’ and overlying “Canoe Brook’ Formations) unconformably overlie the Placentian Series in Cape Breton Island, southeastern Newfoundland, Shropshire, and, probably, eastern Massachusetts. Correlations based on small shelly fossils indicate an earlier appearance of trilobites in Avalon than on the South China Platform. Twenty-six species are illustrated. Halkieria fordi n. sp., the conodont(?) “Rushtonites’ asiatica n. sp., and the zhijinitid(?) Samsanoffoclavus matthewi n. gen. and sp. are described. Ischyrinia? sp. may be the oldest ischyrinoid rostroconch.

Tectonic setting and regional correlation of Ordovician–Silurian rocks of the Aspy terrane, Cape Breton Island, Nova Scotia

1991 ◽  
Vol 28 (11) ◽  
pp. 1769-1779 ◽  
Author(s):  
Sandra M. Barr ◽  
Rebecca A. Jamieson
Keyword(s):  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Volcanic Arc ◽  
Cape Breton Island ◽  
Metasedimentary Rocks ◽  
Tectonic History ◽  
Cape Breton ◽  
Metavolcanic Rocks ◽  
High Grade Metamorphism ◽  
Arc Setting

Interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of Ordovician to Silurian age are characteristic of the Aspy terrane of northwestern Cape Breton Island. These rocks were affected by medium- to high-grade metamorphism and were intruded by synkinematic granitoid orthogneisses during Late Silurian to Early Devonian times. They were intruded by posttectonic Devonian granitic plutons and experienced rapid Devonian decompression and cooling. The chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic-arc setting. The volcanic rocks of the Aspy terrane differ from many other Silurian and Silurian–Devonian successions in Atlantic Canada, which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within-plate settings, and are somewhat younger than the Aspy terrane sequences. Aspy terrane units are most similar to Ordovician–Silurian volcanic and metamorphic units in southwestern Newfoundland, including the La Poile Group and the Port aux Basques gneiss. Together with other occurrences of Late Ordovician to Early Silurian volcanic-arc units, they indicate that subduction-related compressional tectonics continued into the Silurian in parts of the northern Appalachian Orogen. The complex Late Silurian – Devonian tectonic history of the Aspy terrane may reflect collision with the southeastern edge of a Grenvillian crustal promentory.

Provenance of detrital muscovite in Cambrian Avalonia of Maritime Canada: 40Ar/39Ar ages and chemical compositions

2009 ◽  
Vol 46 (3) ◽  
pp. 169-180 ◽  
Author(s):  
Peter H. Reynolds ◽  
Sandra M. Barr ◽  
Chris E. White
Keyword(s):  
New Brunswick ◽  
Age Distribution ◽  
Chemical Compositions ◽  
Rock Unit ◽  
Original Source ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Single Grain ◽  
Maritime Canada ◽  
Age Range

We report single-grain ages for detrital muscovite separated from sandstone samples from five localities in southern New Brunswick and southeastern Cape Breton Island, Nova Scotia, and from two quartzite clasts from a quartzite-pebble conglomerate that underlies the sampled sandstone units in New Brunswick. The oldest detrital grains were found in one of the quartzite clasts; their age range, ca. 650−630 Ma, is defined not only by the single-grain analyses but also by spot dating (using a UV laser) within a single large grain, suggesting that these grains came from a single source. The second quartzite clast has a blastomylonitic fabric with muscovite “fish,” and most of the muscovite ages have been partially reset (at ca. 550 Ma) from the original ca. 650–630 Ma ages. The age distribution plots obtained for the sandstone samples suggest the presence of muscovite that still retains the original source age, but most of the grains have been partially reset by the same ca. 550 Ma event that reset muscovite ages in the second quartzite clast. We suggest that the quartzite source that produced the two clasts was also the source of muscovite in the Avalonian Cambrian rocks of Maritime Canada. The original source rock was likely a metamorphic or perhaps granitic rock unit situated relatively proximal to the site of deposition of the quartzite protolith, but the actual source is not known, and locally, no potential candidates are exposed. The resetting event at ca. 550 Ma may be linked to initial stages of regional transtension associated with rifting of Avalonia from Gondwana.

Birth of the Avalon arc in Nova Scotia, Canada: geochemical evidence for ∼700–630 Ma back-arc rift volcanism off Gondwana

1998 ◽  
Vol 135 (2) ◽  
pp. 171-181 ◽  
Author(s):  
J. D. KEPPIE ◽  
J. DOSTAL
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Benioff Zone ◽  
Calc Alkaline ◽  
Cape Breton Island ◽  
Mafic Rocks ◽  
Cape Breton ◽  
Arc Setting ◽  
Oceanic Island Basalts ◽  
Back Arc

Central Cape Breton Island in Nova Scotia, Canada, is host to ∼700–630 Ma felsic and associated mafic volcanic rocks that are relatively rare in other parts of the Avalon Composite Terrane, occurring elsewhere only in the Stirling Block of southern Cape Breton Island and in parts of eastern Newfoundland. The mafic rocks of central Cape Breton Island are typically intraplate tholeiitic basalts generated by melting of a garnet-bearing mantle source. They lack a continental trace element and εNd imprint although they were emplaced on continental crust; they resemble oceanic island basalts. Contemporaneous volcanism in the Stirling Block is calc-alkaline and formed in a volcanic arc setting. In the absence of evidence for an intervening trench complex or suture, it may be inferred that the central Cape Breton tholeiites formed in a back-arc setting relative to the Stirling Block. This rifting may represent the initial stages of separation of an Avalonian arc from western Gondwana. The arc rifted further between ∼630–610 Ma when the younger Antigonish-Cobequid back-arc basin formed. Subsequently, the extensional arc became convergent, telescoping the back-arc basin. Northwestward migration of calc-alkaline arc magmatism may be related to shallowing of the associated Benioff zone through time.

40Ar/39Ar ages of detrital muscovite within Lower Cambrian and Carboniferous clastic sequences in northern Nova Scotia and southern New Brunswick: implications for provenance regions

1997 ◽  
Vol 34 (2) ◽  
pp. 156-168 ◽  
Author(s):  
R. D. Dallmeyer ◽  
J. D. Keppie ◽  
R. D. Nance
Keyword(s):  
Nova Scotia ◽  
New Brunswick ◽  
Lower Cambrian ◽  
Source Region ◽  
Regional Distribution ◽  
Coarse Grained ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Meguma Terrane

Detrital muscovite from lowermost Cambrian sequences exposed in the Avalon Composite Terrane in Nova Scotia and New Brunswick record 40Ar/39Ar plateau ages of ca. 625–600 Ma. These are interpreted to date times of cooling in source areas. The regional distribution of coarse-grained detrital muscovite in Lower Cambrian rocks of Avalonian overstep sequences suggests a source region of dimensions considerably larger than any presently exposed in Appalachian segments of the Avalon Composite Terrane. Late Proterozoic tectonic reconstructions locate the Avalon Composite Terrane adjacent to northwestern South America, thereby suggesting a possible source within Late Proterozoic PanAfrican – Brasiliano orogens. Detrital muscovite from clastic sequences of the proximally derived, Lower Carboniferous (Tournaisian) Horton Group and the more distal Upper Carboniferous (Westphalian D – Stephanian) Pictou Group in Nova Scotia records 40Ar/39Ar spectra that define plateau ages of ca. 390–380 Ma (Horton Group) and and ca. 370 Ma (Pictou Group). Finer grained fractions from samples of the Horton Group display more internally discordant age spectra defining total-gas ages of ca. 397–395 Ma. A provenance for the finer muscovite may be found in southern Nova Scotia where Cambrian–Ordovician turbidites of the Meguma Group display a regionally developed micaceous cleavage of this age. The ca. 390–380 Ma detrital muscovites probably were derived from granite stocks presently exposed in proximal areas of northernmost Cape Breton Island. A more distal source for the ca. 370 Ma detrital muscovites in the Pictou Group is suggested by its original extensive distribution, although a local, possibly recycled, source may also have been present. The presence of only 400–370 Ma detrital muscovite suggests a rapidly exhumed orogenic source with characteristics similar to those of crystalline rocks presently exposed in the Cape Breton Highlands and (or) the Meguma Terrane.

Geophysical evidence for the extent of the Avalon zone in Atlantic Canada

1979 ◽  
Vol 16 (3) ◽  
pp. 552-567 ◽  
Author(s):  
Richard T. Haworth ◽  
Jean Pierre Lefort
Keyword(s):  
New Brunswick ◽  
Fracture Zone ◽  
Volcanic Rocks ◽  
Magnetic Anomalies ◽  
Seismic Velocities ◽  
Northern Boundary ◽  
Southern Limit ◽  
Grand Banks ◽  
Magnetic Pattern ◽  
Cape Breton

Precambrian volcanic rocks exposed in structural highs of the Avalon zone of Newfoundland are marked by high magnetic anomalies whose continuity offshore permits recognition of the extent of the Avalon zone, particularly on the Grand Banks. South of Newfoundland and in the Gulf of St. Lawrence, where the magnetic pattern is less well defined, the Avalon platform can also be recognized by the existence of seismic velocities of the order of 6.6 km s−1, which are apparently associated with volcanic rocks. The magnetic Collector Anomaly running eastwards from Cape Breton across the southern Grand Banks is the southern limit of these Avalonian markers, while the northern boundary follows a serrated path (the offsets apparently caused by a series of northwest-trending faults) from the Belle Isle Fault in New Brunswick to the Hermitage and Dover Faults in Newfoundland, thence to the western end of the Charlie Fracture zone. These Avalonian boundaries provide markers for the constraint of pre-drift continental reconstructions.

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