The ca. 370 Ma Eastern Shore dykes include six single or multiple (two or three) parallel spessartite dykes that trend NNW in the Sheet Harbour area of eastern mainland Nova Scotia. Spessartite is a variety of calc-alkaline lamprophyre that characteristically occurs in dykes associated with granitoid rocks and gold mineralization in orogenic belts. Spessartite dykes typically contain crustal xenoliths and xenocrysts, a feature shown by three of the Eastern Shore dykes (Popes Harbour, Tuff Island, and Borgles Island). The Eastern Shore dykes are mineralogically and chemically typical of spessartite but show wide chemical variation and higher MgO, lower TiO2 and P2O5, and flatter chondrite-normalized rare-earth-element patterns than are typical of spessartite. The pair of dykes at Sober Island show internal variations that are evidence of magma evolution resulting from plagioclase and amphibole fractionation; the East Jeddore and Little Harbour Road and Coast dykes are similar to the least evolved Sober Island spessartite. The three xenolith/xenocryst-bearing dykes show anomalous chemical features such as more enrichment in light rare-earth elements (REE), higher Sr, Y, Zr, and Hf, and more varied compositions compared to the other dykes. The Popes Harbour dyke is characterized by low Ni. Despite these differences, mainly parallel chondrite-normalized REE patterns suggest that the Eastern Shore dykes are related and derived from hydrous large-ion-lithophile- and high-field strength-element-enriched garnet-bearing mantle-derived magma that experienced variable crustal contamination.

Trace fossils in the High Head Member display disparity thus far unique in lower Cambrian (upper Terreneuvian–Series 2) deep-water sedimentary rocks. This disparity is likely not because the organisms making trace fossils did not exist in other places but instead a result of the special preservation conditions—big exposures of tops of beds made of sediments of the right grain size and under modern-day weathering conditions that gradually are exposing trace fossils that would otherwise not be preserved or observable.

Two wide-angle seismic reflection/refraction profiles were acquired to determine the velocity characteristics of the Meguma terrane and adjacent Avalonia northeast of the Cobequid-Chedabucto Fault Zone (CCFZ) in eastern Canada. Line 99-1 is located along the Scotian margin whereas line 99-2 crosses the Scotian margin and onshore Nova Scotia and extends into the Gulf of St. Lawrence. Velocity models were derived by forward modelling of travel times. P-wave velocities of 5.5-6.0 km/s and 6.0-6.4 km/s are interpreted to be metasedimentary rocks of the Goldenville and Halifax groups and granitic rocks, respectively. This inference is based on comparison with laboratory velocities of a suite of rock samples, offshore sampling, links to onshore geology with multibeam bathymetry, and gravity modelling. On both lines a low velocity zone (LVZ) >350 km wide and up to 15 km thick is present at mid-crustal levels. The LVZ is not observed beneath onshore Nova Scotia or northeast of Orpheus Graben, the offshore extension of the CCFZ. The crustal thickness of the Meguma terrane varies between 31 and 38 km; in contrast, the Moho is at a depth of 41 km beneath Avalonia. The velocity of the lower crust on line 99-2 is 6.8-7.1 km/s beneath the LVZ and Avalonia, and 6.6 km/s beneath onshore Meguma terrane. Poisson's ratios calculated from P- and S-wave velocities are 0.19-0.23 in the Meguma terrane crust; in contrast, Poisson's ratios of 0.24-0.25 are indicated for Avalonian crust.

Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite-tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid-Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U-Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U-Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (delta 18O) are between +7.4 +/- 0.2%o and +9.3 +/- 0.3%o indicating significant involvement of the crust as the magma source or contaminant. If the high delta 18Ozrn values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have epsilon Hf(t) between -6.0 +/- 1.5 and +2.1 +/- 2.5. The new zircon U-Pb, O, and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. The data suggest that Devonian magmatism in the Meguma terrane post-dated the main orogenic event that caused folding and regional metamorphism and involved the same magma source and/or contaminants throughout the terrane.

Structural complexity of the Cape Breton Highlands is a key problem in reconstructing tectonic events in the northern Appalachian orogen. A new U-Pb thermal ionization mass spectrometry age of 428.53 +/- 0.16 Ma for metarhyolite in the Calumruadh Brook Formation shows that volcanic and sedimentary rocks were deposited before collision of the Aspy and Bras d'Or terranes along the Eastern Highlands shear zone. A new U-Pb laser ablation zircon age of 394 +6/-4 Ma confirms that peak metamorphism in the Middle River complex continued during convergence linked to late stages of the Acadian orogeny. The compressive tectonic environment evolved into a transpressional system after initial collision in the late Silurian and caused a repeated pattern of imbrication of units in the Aspy terrane in the hanging wall in the collision. The shear zones bounding the geological units are curvilinear and have south-directed kinematics, imbricating units and transporting higher grade rocks over lower grade rocks, and moving plutons upward relative to their host rocks during and shortly after intrusion. The vergence of imbrication is parallel to the direction of transpressional movement on the main Eastern Highlands shear zone. This geometry is present in Ordovician-Silurian rocks and repeated in Devonian plutonic rocks, indicating that the overall transpressional tectonic setting was a long-lived feature of the orogen. The shear zones localized late syn- to postdeformational plutons that intruded at ca. 375-370 Ma. By the latest Devonian, emplacement of the ca. 363 Ma Margaree and related plutons marked the beginning of extension in the central Cape Breton Highlands.

Abstract Avalonian sections in the Saint John area, southern New Brunswick, have long contributed to global understanding of Cambrian chronostratigraphy. A tuffaceous bed in the Ratcliffe Brook Formation (RBF) in the Somerset Street section dated at c. 531 Ma has traditionally been considered to post-date small shelly fossils attributed to the Watsonella crosbyi Zone in the Hanford Brook section. A fine-grained tuffaceous bed approximately 8 m stratigraphically lower in the Somerset Street section yields a chemical abrasion isotope dilution–thermal ionization mass spectrometry zircon age of 532.3 ± 0.3 Ma; a tuffaceous carbonate unit in the lower RBF in Hanford Brook gives an age of 531.5 ± 0.3 Ma. Crystal and crystal-lithic tuff beds near the top of the RBF yield ages of 520.3 ± 0.3 Ma (in Hanford Brook) and 519.1 ± 0.3 Ma (in Ratcliffe Brook). The new ages confirm the correlation between the Somerset Street and Hanford Brook sections based on acritarchs and make the association of small shelly fossils in the Hanford Brook section younger than 531 Ma. This result is relevant to ongoing discussions on the age of the base of undefined Cambrian Stage 2. The radiometric ages also support a young age for the upper part of the RBF, perhaps extending into Epoch 2.

The upper Ediacaran to lower Cambrian Castalia Group as originally defined comprises a basal sequence of clastic marine sedimentary rocks assigned to the Great Duck Island and Flagg Cove formations and an upper sequence of mainly mafic volcanic and volcaniclastic rocks of the Ross Island, North Head, Priest Cove, and Long Pond Bay formations. A few previously reported specimens of the long-ranging trace fossil Planolites in the Flagg Cove Formation were not inconsistent with the U–Pb age of 539.0 ± 3.3 Ma age for the Priest Cove Formation or the interpreted intrusive relationship between the Flagg Cove Formation and 535 ± 2 Ma Stanley Brook Granite.During a recent visit, abundant morphologically simple trace fossils, including Planolites, were recognized in strata south of Stanley Beach in Flagg Cove, together with vertically or obliquely oriented trace fossils more than 10 mm in diameter, and probable Teichichnus. The age of this association of trace fossils is post earliest Fortunian. More significantly, grey silty shale interbedded with the sandstone that contains the traces yielded organic-walled microfossils. The microfossils include the acritarch Micrhystridium spp of a type also found in the King Square Formation in the Saint John area. The microfossils suggest a Miaolingian (middle Cambrian) age for the Flagg Cove Formation, requiring that its relationship with the Stanley Brook Granite and Castalia Group needs to be re-examined. it also raises the possibility of correlation with middle Cambrian clastic sedimentary sequences exposed on mainland southern New Brunswick and elsewhere in the region.

The Park Spur pluton was emplaced in the Aspy terrane of the central Cape Breton Highlands at 374.2 ± 2.9 Ma (U–Pb zircon). It consists mainly of muscovite-biotite monzogranite with small areas of garnet-bearing muscovite monzogranite and abundant pegmatite and aplite dykes. On its northern margin the pluton intruded metamorphic rocks of the Ordovician–Silurian Cape North Group and associated orthogneiss and on the south it intruded low-grade metamorphic rocks of the Silurian Calumruadh Brook Formation. Deformation along the southern margin of the Park Spur pluton is consistent with emplacement during dextral transpression between the Bras d’Or and Aspy terranes. The Late Devonian age combined with S-type petrological characteristics show that the Park Spur pluton and nearby Canal pluton are related to the ca. 375 Ma Black Brook Granitic Suite, all interpreted to have been emplaced during later stages of the Acadian orogeny in Ganderia as a result of delamination.