The Cabot Fault Zone (CFZ) in the western Newfoundland Appalachian orogen is a long-lived crustal-scale tectonic zone that separates the Corner Brook Lake block (CBLB) of the internal Humber Zone from the Dashwoods block of the western Dunnage Zone. The two blocks comprise different tectonostratigraphic assemblages and had distinct Early Palaeozoic tectonic histories. Using field and microscopic observations, five phases of deformation have been recognized in the CFZ, demonstrating a progressive evolution of the tectonic zone from mid-crustal levels (D1 gneisses and D2 mylonites) to shallow-crustal levels (D5 cataclasites). Inte-grating available geochronological data, the CFZ has recorded a protracted history of dominant oblique-dextral transcurrent movement, as evidenced by well-developed Late Ordovician-earliest Silurian (post-Taconic) D1 and late Early Silurian to Early Devonian (post-Salinic) D2 fabrics. Large-scale (i.e., 100s of km) of Early Palaeo-zoic orogen-parallel movement along the CFZ can explain the present-day juxtaposition of the distinct CBLB and the Dashwoods block. Such large-scale orogen-parallel motion implies that presently neighbouring terranes could have been far apart during convergence and ocean closures, which has significant implications for tectonic interpretation of the Early Palaeozoic evolution of the Newfoundland Appalachian orogen.
The Early Ordovician subvolcanic Gibson intrusive complex, located near Woodstock, New Brunswick, Canada, is composed of the main Gibson pluton, and mineralized marginal (satellite) stocks at Connell Mountain, Bulls Creek, and the tuffisitic diatreme at Sharp Mountain. The high-level Connell Mountain hornblende-plagioclase porphyritic tonalite stock (similar to 100 MPa) is a small cupola, 1500 m north of the main Gibson pluton, and hosts low-grade porphyry copper mineralization (23 Mt at 0.18% Cu). These intrusions are calc-alkalic, metaluminous, and magnesian, with low TiO2 (0.16 to 0.38 wt.%) and Zr (67 to 92 ppm), and low Nb (4.3-7.7 ppm) and Ta (<0.5 ppm), low Y (5 to <20 ppm) and Yb (1.0 to 2.9 ppm), which are consistent with adakitic slab failure magmatic rocks. Sulphur isotopic compositions of pyrite and chalcopyrite from the porphyry and altered sedimentary rocks range from delta S-34 = +9.3 to +12.5 parts per thousand (n = 8), indicating derivation from carbonaceous sulphidic metasedimentary rocks of the Cambrian-Ordovician Woodstock Group. The crystallization age of the Connell Mountain tonalite (474.5 +1/-4 Ma, U-Pb zircon, previously published) is similar to a previously determined U-Pb zircon age of the Gibson granodiorite, which is coeval with the volcanic-dominated Meductic Group (470-477 Ma) located just to the west. Three Re-Os model ages of 475.6 +/- 1.2, 475.8 +/- 1.2, and 476.5 +/- 1.2 Ma from three textural varieties of molybdenite at Connell Mountain (Re = 333, 642, and 1562 ppm) yield a weighted average model age of 475.9 +/- 1.1 Ma indistinguishable from those earlier zircon U-Pb ages, so the porphyry and Cu mineralization at Connell Mountain are related to a hypabyssal phase of the Gibson Granodiorite that is exposed (part of the Gibson Intrusive Complex).
The species Archimylacris acadica Scudder, first described from Nova Scotia (Canada), is the type species of the genus Archimylacris and the family Archimylacridae. It is re-described based on historical drawings and a coeval new specimen from the same geographic area, the Maritimes Basin of eastern Canada from Robertson Point (Sunbury Creek Formation) in central New Brunswick. A precise diagnosis of the genus and the species and an emended diagnosis of the family Archimylacridae are given. This new specimen and the type specimen of Archimylacris lubnensis are proposed as reference specimens for the missing holotype of Archimylacris acadica. Paleobiogeographically and stratigraphically, archimylacrids appeared suddenly in the fossil record of the paralic Appalachian Basin with no evolutionary forerunners yet discovered; they became common in the paralic Variscan foreland basins in northern Europe. They are so far unknown from contemporaneous entomofaunas of Cathaysia, from the Angara biotic province, and from Gondwana.
Pygocephalomorphs are fossil eumalacostracans with a shrimp to lobster-like morphology, known from the Late Devonian (Famennian) to the early Permian (Cisuralian; Artinskian). In the late Paleozoic, pygocephalamorphs formed an important component of marginal marine, brackish and freshwater communities. Several species, including species of Tealliocaris and Pygocephalus, have been described from the Carboniferous of Canada, in particular from the Pennsylvanian. A revision of Pygocephalus from the Carboniferous of Nova Scotia, Canada, is proposed based on original material described by Copeland and on undescribed material from the Joggins Fossil Cliffs UNESCO World Heritage Site. The presence of three taxa is confirmed: Pygocephalus cooperi, Pygocephalus cf. cooperi and Pygocephalus dubius. The pygocephalomorphs of Joggins Fossil Cliffs, and more generally Nova Scotia, were likely benthic walkers based on their leg morphology and the paleoichnological evidence. A comparison of the studied assemblages with previously known assemblages from the Mississippian of Canada shows a faunal turnover among these assemblages, which could reflect paleoenvironmental changes in Atlantic Canada during the Carboniferous and thus various ecological affinities among taxa. We also observed three types of microstructures on the shield of Pygocephalus dubius: canal-like pores, which are most probably organule canals, setal attachment site, and polygonal reticular ornamentation.
The Eight Mile Brook Plutonic Suite (EMBPS) consists of co-mingled gabbroic, syenitic, and granitic rocks that intruded Tonian rocks of the Mount Thom Formation and Mount Ephraim Plutonic Suite at the southeastern edge of the Mount Ephraim block in the Cobequid Highlands. It is unconformably overlain by or in faulted contact with Carboniferous sedimentary rocks. In situ dating of zircon in three samples by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) yielded Early Ordovician concordia and weighted mean 207Pb/238U ages of about 480 Ma. Age and chemical similarities among the EMBPS, West Barneys River Plutonic Suite in the Antigonish Highlands, and the Cape Porcupine Complex near the Strait of Canso suggest that all are closely related and formed by magma fractionation processes during an event that occurred between ca. 481 and 466 Ma based on previously published U-Pb zircon ages from thermal ionization mass spectrometry. The magmatism may be a far-field effect of subduction, a localized area of extension, or a hot spot. Chemical and age differences between these plutonic suites and the bimodal volcanic Dunn Point and McGillivray Brook formations in the northwestern Antigonish Highlands suggest that the magmatism in these units may not be directly related. Minor gabbroic and syenitic intrusions in the northern Antigonish Highlands are undated but show chemical differences from the dated magmatic rocks and hence may not be related.
A U-Pb LA-ICP-MS zircon study was conducted on 22 rock samples from offshore southeastern Nova Scotia, Canada, to investigate the nature of the pre-Mesozoic basement and the provenance of the overlying syn-rift Late Triassic Eurydice Formation of the Scotian Basin. Detrital zircon signatures from five offshore basement metasedimentary samples are consistent with those of the Meguma terrane. Three granitoid samples yielded ca. 381-358 Ma crystallization ages, consistent with felsic plutons of the onshore Meguma terrane. These results confirm that the Meguma terrane underlies the Scotian Basin. An isotopically evolved granodiorite yielded a ca. 576 Ma crystallization age and is interpreted as basement to the Meguma terrane. Its temporal, isotopic, and geochemical similarities to igneous rocks of the Ouarzazate Group in the Anti-Atlas of Morocco suggest that the Meguma terrane likely initiated in a Cadomian back-arc basin of northwest Africa. Detrital zircon signatures from the Eurydice Formation suggest that the late Ediacaran-Ordovician Meguma Supergroup was its primary sediment source, and absence of Silurian to Devonian zircon ages suggests that the rift-related Rockville Notch Group of the northwestern part of the Meguma terrane was not a source and likely absent below the Scotian Basin. The Rockville Notch Group was previously interpreted to represent rifting between Gondwana and the Meguma terrane. We interpret the ca. 576 Ma granodiorite as representing rifting between Gondwana and the Meguma terrane, and the Rockville Notch Group as Silurian rifting of an outboard Cadomian arc from the Meguma terrane.
A narrow (<1 m) fine- to medium-grained lamprophyre dyke intruded Neoproterozoic monzodiorite on the eastern side of Machias Seal Island in the northern Gulf of Maine about 19 km southwest of the island of Grand Manan, New Brunswick, Canada. The dyke is near-vertical and trends 015° to 025°, with two shoreline exposures about 680 m apart assumed to be the same dyke. The dyke is notably dark and dense, with a granular broken surface. Thin sections reveal abundant euhedral outlines of olivine pseudomorphs in a groundmass of small (<0.2 mm) grains of brown amphibole (kaersutite) and augite, with ocelli and interstitial patches of albite, calcite, and analcite. The olivine phenocrysts have been completely replaced by chlorite, whereas other ferromagnesian minerals remain unaltered. Accessory minerals include abundant needle-shaped apatite, magnetite, and cubic pyrite. Another small dyke on the western side of the island is less mafic, non-porphyritic, and consists of fine- to medium-grained plagioclase and clinopyroxene, which are highly altered; we interpret it to be unrelated to the lamprophyre dyke to the east. Whole-rock chemistry shows that the lamprophyre dyke is camptonite, similar to some Mesozoic lamprophyre dykes of Maritime Canada and New England, USA, of which the nearest example is about 110 km to the southwest in coastal Maine. Laser fusion 40Ar/39Ar analyses of single kaersutite crystals (n = 12) yield an age distribution with a single, well-defined mode of ca. 468 Ma; incremental heating analyses of small aliquots of crystals show evidence of some radiogenic 40Ar loss and yield a mean plateau age of 478.7 ± 1.9 Ma. This Early Ordovician age and the accompanying uncertainty are interpreted to represent the time of crystallization for the camptonite dyke. The camptonite of Machias Seal Island is older than other Paleozoic and Mesozoic mafic dykes in the region. It is interpreted to be the product of partial melting of a metasomatised mantle during the Penobscot orogeny.
The Dry River Diorite is one of the few mafic bodies spatially associated with the White Mountain Batholith of New Hampshire, USA. However, new U–Pb zircon geochronology reveals a 119.92 ± 0.62 Ma emplacement age for the diorite, considerably younger than the ca. 200–180 Ma batholith and indicates that it is instead a member of the younger White Mountain Magma Series (ca. 130–100 Ma) of the New England–Quebec province. The diorite is mildly silica undersaturated, with chondrite-normalized REE and spider diagram patterns that indicate ocean island basalt compositions. Several tectonic discrimination diagrams indicate the magmas have within-plate basaltic compositions. Ce/Yb versus La/Ta and Sm/Yb versus La/Sm values indicate the magmas are 2–5% partial melts of garnet peridotites. ƐNd and initial 87Sr/86Sr values range between 4.27 to 3.44 and 0.7036 to 0.7040 respectively. All these geochemical characteristics are identical to those of the mafic rocks of eastern Monteregian Hills and the Ossipee complex basalts of central New Hampshire. Modeling of the Dry River Diorite as the mafic endmember of the felsic rocks of the younger White Mountain Magma Series indicates that the felsic rocks contain up to 50% crustal endmember. Previous high-precision geochronological studies indicated a relatively brief period of magmatism across this region and have argued that observed age progressions of continental magmatism are consistent with the Great Meteor Hotspot hypothesis for their formation. The age produce here for the Dry River Diorite is consistent with this trend’ however, the younger-than-predicted age is likely the result of Pb-loss or complex geological factors. Although the Cretaceous magmatic rocks in this region do not easily fit a linear age progression as a simple hotspot model might predict, the confluence of geodynamic processes that have shaped this region over 200 myr are not simple and require a high standard of verification for any one hypothesis. Whether these magmas resulted from complex hotspot dynamics, asthenospheric upwelling, or some other mechanism or combination of mechanisms requires a clear path to deconvolve the role each process had in shaping the magmatic history we can now observe. The new geochronologic data we present is consistent with other ca. 120 Ma, geographically proximal plutons in the region and therefore consistent with the age progression a hot spot model would predict for a large fraction of the Cretaceous magmatism observed across the region; however this does not preclude other models, e.g., edge-driven convection, for parsimoniously explaining magmatism in the region that does not conform to this track.
Due to the rapid evolution of dinoflagellates, their fossil cysts are reliable age markers in the Mesozoic and Cenozoic. The Scotian Margin contains a well-developed succession of Mesozoic strata that accumulated during the opening of the North Atlantic Ocean. We focus on Lower Cretaceous conventional cores 4 to 13 from the Panuke B-90 well, which yield significant dinoflagellate cyst (dinocyst) assemblages. Four intervals from the section are defined based on associated lithologies, and in each interval the palynological assemblages broadly reflect changes in paleoenvironmental setting. Dinocyst occurrences and associated key bioevents are used to refine age. In the marginal marine Interval 1, the co-occurrence of Odontochitina operculata and Tenua anaphrissa and the first occurrence (FO) of Pseudoceratium retusum indicate an early Barremian age. Above the dominantly terrestrial Interval 2, the FOs of Palaeoperidinium cretaceum and Cerbia tabulata suggest a late Barremian age for the terrestrial to marine Interval 3. Near the boundary between Interval 3 and marine Interval 4, a Cerbia tabulata acme and the FO of Aptea cf. polymorpha, as well as the last occurrence (LO) of Muderongia microperforata, confirm an early Aptian age. Accordingly, the Upper Member of the Missisauga Formation is Barremian to lower Aptian and the overlying Naskapi Member of the Logan Canyon Formation is lower Aptian; the presence of the early Aptian ammonite Deshayesites provides further age constraint. The key dinocyst bioevents from Panuke B-90 conventional cores are an important contribution to the ongoing Mesozoic event-stratigraphic framework for the Scotian Margin.
The northeastern and eastern parts of the ca. 425-416 Ma Mount Peyton Intrusive Suite in north-central Newfoundland, Canada, host several Au-Ag-Sb-bearing mineralized zones associated with fracture systems and narrow quartz veins mantled by wide, potassic (sericite-muscovite) alteration envelopes bearing arsenopyrite and locally pyrite and stibnite. The Yellow Fox zone is hosted in a medium-grained and plagioclase-porphyritic, granophyric-textured biotite +/- hornblende I-type transitional to A2-type monzogranite in the northeastern part of the intrusive suite that is cut by rectilinearly fractured, muscovite-arsenopyrite-pyrite-rutile-alteration zones. This alteration occurs in an similar to 100 m long by 30 m wide, north-trending bleached and rusty alteration zone characterized by three distinct fracture sets: (1) a widely spaced, roughly east-west barren set; (2) a prominent north-trending 5-20 cm spaced set accompanied by abundant muscovite and disseminated arsenopyrite + pyrite; and (3) a weakly-developed, north-northeast-trending set that locally hosts a few narrow (<4 cm) stibnite-quartz-arsenopyrite veins with arsenopyrite mainly confined to the quartz vein margins and intensely altered to supergene scorodite and goethite. Relative to unaltered granite, both muscovite-pyrite-arsenopyriterutile-altered monzogranite and stibnite-quartz-arsenopyrite-veined monzogranite are anomalous in many metals (Sb <11.1 wt.%; As < 4.5 wt.%; Au <59.4 g/t; Ag < 73g/t; Pb <5.5 wt.%; Zn <7 wt.%; Cd <717 ppm). The altered host rock yielded a crystallization age of 422.3 +/- 1.3 Ma (CA-ID-TIMS U-Pb zircon), overlapping in error with two 40Ar/39Ar incremental-heating ages of 422.4 +/- 0.2 Ma and 422.9 +/- 0.6 Ma for muscovite from the same altered monzogranite. The coincident ages indicate that monzogranite crystallization and alteration were synchronous and therefore intrusion-related and formed broadly contemporaneously with proximal, mineralogically similar, intrusion-hosted mineralization in the region. Undated Au-Ag-As-Sb mineralization in the adjacent surrounding country rocks may also have been coeval. Fracturing, release of hydrothermal + magmatic fluids from deeper seated intrusions, and mineralization occurred during the final stages of monzogranite crystallization, which is interpreted to be associated with transient lithospheric extension that preceded north-to northwest-directed oblique Acadian thrusting, folding, and proximal orogenic Au mineralization in the Early Devonian (ca. <415 Ma).
The Cretaceous Period was a time generally of high sea levels, peaking in the Cenomanian and Turonian. With sea-level rise, the extent of shelf seas expanded, providing broad opportunities for plankton such as cystproducing dinoflagellates, which reached their maximum species richness during the Cretaceous. Because of their abundance, species richness, rapid evolution and distinctive morphology, organic-walled dinoflagellate cysts (dinocysts) have become the most important palynological index fossils for the period. Dinocysts are almost exclusively marine, and marine successions are extensive through the Cretaceous and across the Arctic. Spores and pollen (miospores), which are almost exclusively of terrestrial origin, are less prominent as index fossils in the Early Cretaceous: taxa tend to be long-ranging and taxonomy poorly constrained. However, with the advent of angiosperms and the increasing diversity and distinctiveness in the Late Cretaceous, pollen become more useful biostratigraphically upsection. Extensive zonation schemes based on palynomorphs have been proposed from Arctic Canada, Greenland and northern Russia, but they tend to be disparate, with little commonality or mutual correlation. For that reason, we have chosen to identify Cretaceous palynological bioevents (palynoevents) that potentially extend around the Arctic. We have identified 187 bioevents: 99 first occurrences and 87 last occurrences and 129 involving dinocysts and 58 involving miospores. The bioevents have been calibrated insofar as possible to independent age control, such as biozonation schemes based on ammonites and bivalves. The relationships of each event to stages and key fossil zonal schemes is shown on chronostratigraphic plots using the 2020 version of TimeScale Creator (R).
Geological Carbon Storage (GCS) is an essential climate mitigation strategy, enabling the long-term storage of carbon dioxide (CO2) in deep subsurface formations. Offshore Atlantic Canada offers significant potential due to favourable geology, extensive subsurface data, and infrastructure from past hydrocarbon development. Major sedimentary basins such as the Scotian, Jeanne d'Arc, and Orphan contain structural traps, thick saline aquifers, and effective caprock seals that are critical for secure CO2 storage. Successful GCS depends on robust geological modelling workflows that incorporate subsurface heterogeneity, trapping mechanisms, and containment integrity. This paper reviews the foundational components of geological models - structural, stratigraphic, geometric, and topological frameworks - combined with numerical simulators to predict plume migration, pressure evolution, and geochemical interactions. Modelling supports all project stages, from site screening to post-injection monitoring, and is guided by parameters such as capacity, injectivity, containment, and storage efficiency. In ternational offshore analogs such as Sleipner, Sn & oslash;hvit, Northern Lights, Tomakomai, and Porthos provide valuable lessons in infrastructure reuse, regulatory development, and public engagement. These projects highlight the importance of tailored monitoring and verification plans, hub-based infrastructure models, and early-stage demonstration projects to build public trust. Offshore Atlantic Canada faces unique challenges including complex structural geology, overpressure zones, and salt tectonics, necessitating detailed technical evaluation. Recommended actions include high-resolution geologic modelling, probabilistic capacity assessments, and the creation of a regional carbon storage atlas. As regulatory frameworks evolve and carbon management becomes increasingly urgent, offshore Atlantic Canada is well-positioned to become a leader in safe, large-scale geological CO2 storage.
Analysis of multibeam sonar and LiDAR data permits interpretation of submarine landforms in eastern Northumberland Strait, part of the St. Lawrence Estuary system, eastern Canada. Landforms are interpreted in the light of multiple forcing mechanisms, principally: (1) glaciation; (2) postglacial relative sea-level fluctuations; (3) spatial variability of tidal currents; and (4) modern sea-ice impact. Bedrock exposures testify to relatively thin glacial sediments. Glacial landforms comprise ribbed moraines and glacial meltwater channels. The study area was emergent in the early Holocene, as evidenced by fluvial channels and former lakes in the Cape Tormentine area. Today, spatially varying tidal forces are strong determinants of geomorphology, and several landforms zones are identified: (1) tidal-swept zones at Abegweit Passage and Caribou, characterized by seafloor scour and scattered bedform fields; (2) the area of weak tidal circulation between the Abegweit and Caribou zones - a low-relief sediment depocenter with littoral zone ridge-and-runnel beach systems, and estuaries; (3) transition zones located between the central depocentre and the tidal-current zones feature sediment drifts; (4) the tidal gyre at East Point, Prince Edward Island, which has formed Milne Bank; and (5) an area east of Caribou, where weaker tidal forces and stronger wave influence are evidenced by alongshore transport embayments between Milne Bank and Souris and the east-facing coast north of Cape Bear, where sediment is trapped in compartments isolated from one another. Modern sea-ice disturbance of the seabed (range -1 to -8 m) is most extensive in the Pictou Banks area.
Recent amendments to the North American Stratigraphic Code enable the renaming of offensive or inappropriate unit names. Although the Province of New Brunswick has commenced the identification and renaming of culturally inappropriate geographic features, the use of offensive toponyms presents a problem in the naming of geological units. Names of eight geological units and structures in New Brunswick are culturally inappropriate or offensive. Following the guidelines in the amended Stratigraphic Code, replacement names for these problematic units and structures are proposed herein.
The tectonic evolution of the northern Appalachian orogen is typically organized into orogenic episodes. The Taconian orogeny includes latest Cambrian to Late Ordovician arc-continent collision. Subsequent polarity reversal led to Silurian accretion of Ganderian terranes during Salinian orogenesis. The Acadian orogeny comprises Pridoli to Middle Devonian deformation attributed to accretion of West Avalonia to Laurentia. The term Neo-Acadian was coined by Robinson for Late Devonian to Mississippian shortening in New England, ca. 370-350 Ma, but the Indigenous-derived name Quaboagian was subsequently favoured for this episode. The "Neoacadian" later became associated with Meguma terrane docking, but clear convergent deformation in the Meguma terrane falls outside the original Neo-Acadian interval. Folding of strata in the Meguma terrane from ca. 409 Ma, concurrent with Acadian deformation, occurred in a different tectonic environment; emplacement of subduction-related plutons followed at mainly ca. 379-372 Ma. The ca. 370-350 Ma interval saw uplift of the Meguma terrane, local plutonism, and deposition of the Horton Group in a basin-and-range setting, whereas the crust beneath the Gulf of St. Lawrence thinned to less than half normal thickness during Maritimes Basin development. These anorogenic transtensional basins were probably connected with Quaboagian shortening in New England via dextral strike-slip. Shortening and inversion resumed after ca. 330 Ma, associated with dextral transpression, docking the Meguma terrane close its present-day position. The misuse of "Neoacadian orogeny" leads to misconceptions about timing of accretion of the Meguma terrane and about ca. 370-350 Ma tectonics in Atlantic Canada, which involved extension not shortening. We recommend that the term be abandoned in favour of Quaboagian and restricted to convergence in New England. Earlier deformation in the Meguma terrane may be attributed to the Kejimkujic orogeny.
New zircon U-Pb, Lu-Hf and trace element laser ablation inductively coupled mass spectrometry (LA-ICP-MS) data are presented for ten Ediacaran granitoid samples from the New England Avalon terrane, and from possibly exotic blocks of southeastern Massachusetts and Rhode Island, USA. Crystallization ages of the analyzed samples are ca. 611-577 Ma, with nine samples between ca. 611 Ma and ca. 588 Ma. These overlap with previously published ca. 620-589 Ma ages of granitoid rocks and ca. 597-584 Ma ages of volcanic complexes in the northern part of the terrane, where volcanism occurred immediately after plutonism. A granite that cuts sedimentary and volcanic rocks with a previously determined maximum depositional age of ca. 613 Ma in southern Rhode Island yielded a zircon chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS) date of 609.30 +/- 0.22 Ma. Volcanism therefore occurred between ca. 613 Ma and ca. 609 Ma, and ca. 10 myr prior to that in the northern part of the New England Avalon terrane. This area may be part of the previously interpreted exotic Newport Block. Zircon epsilon Hf-(t) values of all samples are -2.8-6.0, with ca. 1.23-0.96 Ga T-DM1 Hf model ages. These values are also consistent with published epsilon Hf-(t) values between -3.1 and 5.9 of nine published plutonic and volcanic rocks. Zircon trace element geochemistry data show mostly mixed continental arc and oceanic island signatures. The Eu/Eu* values are mostly 0.1-0.7, suggesting similar to 30-80 km crustal thicknesses. The exception is a sample southeast of the Nauset magnetic anomaly on the southeastern tip of Massachusetts, which has the highest zircon Sigma REE values, mostly Nb/Hf >0.001, generally low Eu/Eu* values, and high epsilon Hf-(t) values, all suggestive of a within-plate/anorogenic/rift setting. The new data provide a valuable reference data set, guiding future studies on the New England Avalon terrane and/or adjacent exotic blocks and on similar crustal domains elsewhere.
Bathymetric surveys of two small lakes in Newfoundland, located in different environments and separated by hundreds of kilometres, were carried out using two different survey methods-ground penetrating radar (GPR) and sound navigation and ranging (sonar). The different structures of these two disparate ponds were found to be related to the differing geology and degrees of anthropogenic influence at the two locations. In addition, the study outlined the strengths and limitations of the two survey methods. Tipping's Pond, on the outskirts of the town of Corner Brook in western Newfoundland, is a sinkhole in a popular recreation area. It is roughly square with an area of 1.6 km(2) and is slightly salty, making it largely impenetrable by radar. Bathymetric surveys with a salinity-impervious fish-finder sonar system revealed Tipping's Pond to be bowl-shaped and more than 25 m deep in the centre. Grassy Pond, 3 km inland from the Trans-Canada Highway in eastern Newfoundland, is within an undeveloped area accessible by snowmobile in the winter. It has an irregular, elongated shape 1.2 km(2) in area and is very fresh. As well as determining the bathymetry, GPR was able to determine the depth of a soft sediment layer overlying till, and to image structures within the soft sediments. The top of the sediment layer is undulating and shallow (<2.9 m deep) whereas the base of the sediments overlies sub-basins about 8 m deep.
High precision CA-ID-TIMS U-Pb zircon dates presented here establish 627.68 ± 0.66 Ma (2s internal uncertainty) Diorite at Rowley and associated granite near Topsfield, Massachusetts as the earliest arc-related magmatic rocks recognized so far in the Southeastern New England Avalon Zone. Granite dated at 609.10 ± 0.18 Ma on the southern extremity of this terrane in Newport, Rhode Island corresponds in age to previously dated Dedham Granite that is widespread in the vicinity of Boston, Massachusetts. Slightly younger diorite (605.48 ± 0.21 Ma) in an upfaulted block west of Boston clusters with previous dates from the Milford and Fall River granites, and Westwood Granite re-dated at 595.17 ± 0.50 Ma proves to be co-eval with Lynn-Mattapan volcanic rocks. LA-ICPMS age spectra from the same samples (except Westwood Granite) also show inherited components. The Ediacaran crystallization ages for the southeastern New England suite overlap LA-ICPMs ages from numerous samples in the Nova Scotia's Cobequid and Antigonish Highlands. These ages both reinforce previous comparisons between these terranes and reveal patterns of incremental intrusion like those documented for continental arc-related plutons of the western United States. Mesoproterozoic and older inherited components in both cases reflect West Avalonian origins as a series of volcanic arcs developed on metasedimentary deposits that detached from the Timanide margin of Baltica. By the time <630 Ma Jeffers block tuffs and Topsfield Granite acquired Cryogenian xenocrysts, these terranes were drifting towards collision with Ganderia, precluding Baltica provenance for ~680-640 Ma zircon. The source of this inheritance remains unresolved.
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.
