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The article discusses a field trip which highlights the unique geology of the Meguma terrane of southern Nova Scotia, the most easterly component of the northern Appalachian orogen. The Meguma terrane is described as a thick package of Early Cambrian to Early Ordovician turbiditic metasandstone and slate, locally overlain unconformably by a thin sequence of slate, quartzite and volcanic rocks. It suggests that the Meguma terrane was formed in a rift between Gondwana and Avalonia as shown by the stratigraphic differences across the Chebogue Point shear zone together with similarities to Avalonian detrital zircon populations, juvenile Nd isotopic compositions and sparse faunal evidence indicating Avalonian affinity.

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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. [ABSTRACT FROM AUTHOR]

Mesoproterozoic metaplutonic rocks in northern Cape Breton Island, Nova Scotia, occur in a tectonic inlier within the Appalachian orogen. Although they have been multiply metamorphosed and variably deformed, the petrology and geochemistry of these rocks provide insight into the tectonomagmatic evolution of easternmost Laurentia. Anorthosite, syenite, and granitoid plutons (1100–980 Ma) intruded the Sailor Brook and Polletts Cove River gneisses. New Nd isotopic data are presented from a biotite-rich part of the Sailor Brook gneiss (εNdi = −0·7), two anorthosite samples (εNdi = +2·1 and +2·8), and a charnockite unit (εNdi = −0·4). New U–Pb zircon data from the anorthosite yield 207Pb/206Pb ages between 975 and 1095 Ma. Disrupted U–Pb systematics preclude a unique age interpretation, but the ∼1095 Ma single-grain date is a minimum age for the anorthosite. Field relations, major and trace-element geochemistry, and isotopic characteristics indicate that the anorthosite and charnockite were probably coexisting melts, but not differentiates of a single parent magma. The lithological and chemical characteristics of the Lowland Brook Syenite are similar to those of a contemporaneous belt of ultrapotassic plutons in the southern Grenville Province, and both have the chemical characteristics of certain modern continental-margin arc magmas. These data indicate that the Mesoproterozoic units in the Blair River inlier were juvenile crustal additions to eastern Laurentia during Grenville-related orogenic events. [ABSTRACT FROM PUBLISHER]

Reports that Pb isotopic data from the Blair River Complex of leached feldspars on Breton Island, Nova Scotia, Canada are consistent with an old source region ultimately derived from the mantle and contaminated by sialic crust. Geological setting and sample distribution; Analytical methods; Pb Isotopic data; Oxygen isotopic data; Pb and O isotopic variations in Cape Breton Island; Regional comparisons; Conclusions.

The Cheticamp area of western Cape Breton Island is located in the Aspy terrane, part of the Ganderia realm of the northern Appalachian orogen. Equivalent parts of Ganderia in Newfoundland and New Brunswick are well known for their mainly volcanic-hosted metallic mineral deposits, and hence the Cheticamp area potentially has similar deposits. Mineral occurrences (Zn, Cu, Pb, Fe, As, Au) around Faribault Brook east of Cheticamp have been exploration targets since the 1890s, and are hosted by rocks generally assigned to the Ordovician-Silurian Jumping Brook Metamorphic Suite (JBMS). Subsequent geochronological work in the 1990s in the area showed that at least some of the metasedimentary and metavolcanic rocks of the JBMS could be Late Neoproterozoic, and similar in age to the ca. 550 Ma Cheticamp Pluton. However, no new mapping or petrological studies had been undertaken since then to assess the significance of these new age data. During the summer of 2007, an area of ∼180 km² that included all of the known mineral occurrences in the Faribault Brook area was mapped at a scale of 1:20 000, and geophysical data were incorporated in constructing a revised geological map of the area. Recent trenches not available to earlier workers were examined, as well as all available drill core from the area in the core storage facility at Stellarton. Mineralization was observed in mafic and felsic metavolcanic units, as well as in associated metasedimentary rocks. Unit names follow as much as possible those established by earlier workers, and include the Faribault Brook metavolcanic unit, Dauphinee Brook schist, Barren Brook schist, George Brook amphibolite, and Corney Brook schist. The Faribault Brook metavolcanic unit is mainly mafic flows with less abundant felsic flows and mafic tuff. The George Brook amphibolite appears to represent higher grade metavolcanic rocks. The Dauphinee Brook schist is fine-grained and pelitic, whereas the Barren Brook schist is coarser grained and has a higher quartz content. The Corney Brook schist is higher grade and includes metasedimentary and meta-igneous units; it may be similar to or part of the Pleasant Bay Complex. The contact between the Dauphinee Brook schist of the Jumping Brook metamorphic suite and the Cheticamp Pluton is intrusive, at least in part, rather than a nonconformity or fault as suggested in some earlier interpretations, based on recently exposed outcrop. Hence at least part of the Jumping Brook Metamorphic Suite is older than ca. 550 Ma. However, felsic porphyry that hosts mineralization at some locations (e.g., Galena Mine) is Silurian based on published U-Pb (zircon) ages. Similar lithology is observed at the Mountain Top Adit where is seems to be extrusive rather than intrusive as at the Galena Mine occurrence. [ABSTRACT FROM AUTHOR]

The Caledonian Highlands consist mainly of volcanic, sedimentary, and plutonic rocks formed in a continental margin magmatic arc complex in combination with later extensional tectonic events over a span of at least 70 million years in the late Neoproterozoic. The southern and eastern parts of the highlands are dominated by the Broad River Group, an assemblage of ca. 620 Ma rocks, including intermediate and felsic tuff, chloritic phyllite, and arkosic sandstone and conglomerate. Plutonic rocks of inferred ca. 620 Ma age occur in spatial association with the Broad River Group, and show a wide range in composition from gabbro and diorite to tonalite, granodiorite, and granite. The ca. 560-550 Ma Coldbrook Group forms most of the western part of the highlands, but also extends into the eastern part, where it is inferred to originally have had an unconformable relationship with the underlying Broad River Group. Typical Coldbrook Group rocks include intermediate to felsic lapilli tuff, dacitic to rhyolitic flows and plugs, laminated tuffaceous siltstone, amygdaloidal basalt flows, and coarse clastic sedimentary rocks. Circa 560-550 Ma plutons are widespread throughout the central and western parts of the Caledonian Highlands intruded into the lower units of the Coldbrook Group. Most consist of syenogranite with less abundant diorite and gabbro. A major high-strain zone up to 5 km in width can be traced for at least 70 km diagonally across the highlands from at least the Big Salmon River area in the southwest to the Caledonia Mountain area in the northeast. In this zone, both the Broad River Group and associated plutons and the Coldbrook Group contain similar structural elements, related to a largely shared deformation history. Some of this history is apparent also in the 560-550 Ma plutonic rocks. A pervasive foliation (S1) lies parallel to bedding (S0), and although evidently composite (S0-1) in the Broad River Group, this fabric is very heterogeneous in the younger Coldbrook Group, where low strain enclaves are widespread. No folds have been seen of an F1 generation, and no reversals of facing or vergence are apparent. A mineral lineation (L1m) is locally prominent. The plutonic rocks have early fabrics, including a foliation (S1) producing augen-gneiss with a prominent L-tectonite (L1m). S1 also includes a schistosity associated with the growth of white mica and breakdown of feldspar. Geometry suggests that S1 in the granites is related to S0-1 in the supracrustal rocks, and L1m in both units shares a common orienta tion. S1 and S0-1 are crenulated by a strong second cleavage (S2) axial planar to folds (F2), the large-scale expression of which is an asymmetric synform containing a belt of Coldbrook Group rocks lying between Stuart Mountain and Point Wolfe River. Kinematic indicators suggest an overall top-to-the-southeast motion along thrusts that stack units of Broad River Group, Coldbrook Group, and plutonic rocks. Fabric development in the plutonic rocks implies a history of exhumation beginning under hot, anhydrous conditions, followed by hydration during retrogression as plutonic rocks were tectonically emplaced into this crustal stack. The youngest deformation features are brittle fractures filled with pseudotachylite. The age of these tectonic events is not yet well constrained, but could be as young as Carboniferous. [ABSTRACT FROM AUTHOR]

Unusual black sandstone beds of Cambrian age (~530 to 511 Ma) occur in the Saint John area of southern New Brunswick. These beds are located in the Saint John Group and occur in the upper part of the Glen Falls Formation and the lower part of the overlying Hanford Brook Formation. The dark color of these beds has been attributed to the presence of phosphate minerals and iron chlorite. The presence of phosphorous, an essential nutrient for life, is important in these rocks as they span the time of the early evolution of life. The research of this project focuses on mineralogy, origin, and depositional environment of the black sandstones, as well as their disputed stratigraphic relationships with the overlying and underlying rocks, and the phosphorous cycling that took place during deposition that may have influenced the early evolution of life. No study prior to this has conducted the correlation between the evolution of life in the Saint John group and the appearance of phosphorite. Phosphorite is defined as a marine sedimentary rock with equal to or greater than 18% P2O5. The sedimentary phosphate mineral is francolite, (Ca5 (PO4,CO3)3F). The origin of phosphorite involves phosphorous in particulate organic matter being transferred to sediment, followed by diagenetic degradation and dissolved inorganic phosphorous being released from the organic matter to sedimentary pore waters, causing the precipitation of francolite. This produces phosphorite hardgrounds, as well as individual grains or concretions that become reworked, forming concentrated phosphorite beds. The phosphorite that occurs in the Glen Falls and Hanford Brook formations was probably linked to the sea-level rise at the Cambrian-Precambrian boundary and iron-redox. These events would have allowed for more phosphorous to be available for life forms. Fifty-two samples were collected from outcrops in and around the Saint John area and stratigraphic sections were logged for each location. The stratigraphic sections are being compared for lateral and stratigraphic variations. Thin sections of samples have been cut and examined for petrographic features using both petrographic and scanning electron microscopy to aid in determining paragenesis. SEM-EDS was used to determine the composition of the phosphorite. Five samples were sent to the Queen's Facility for Isotopic Research where stable isotope compositions for carbon (13C) and oxygen (18O) can be determined through ICP-MS, giving redox potential and temperature of precipitation, respectively. Future work includes further examination of polished thin sections under the scanning electron microscope as well as cathode luminescence to determine paragenesis. [ABSTRACT FROM AUTHOR]

The area offshore southeastern Cape Breton Island is inferred to be part of the Mira terrane, a component of the Avalonia realm of the northern Appalachian orogen. The Scatarie Ridge Magnetic Anomalies (SRMA) are a prominent belt, approximately 100 km long by 25 km wide, of northeast- trending magnetic anomalies that characterize this area. Magnetic values typically range from 300 to 600 nT; however, the centres of the anomalies reach highs of 900 nT to 1400 nT. In addition, positive gravity anomalies correspond approximately to the area of the magnetic anomalies, with gravity values ranging from 10 to 30 mGal. Like other parts of Avalonia, the onshore part of the Mira terrane is characterized by prominent linear total field magnetic anomalies that appear to be related to the linear belts of Neoproterozoic volcanic, sedimentary, and plutonic rocks that form much of the terrane. The Canso Fault is interpreted to offset the Mira terrane to southern New Brunswick, 100 km to the north, relative to mainland Nova Scotia, suggesting the possibility that the area of the SRMA offshore southeastern Cape Breton Island could correlate with the Antigonish Highlands. The purpose of the study is to investigate the source(s) of the anomalies utilizing magnetic, gravity, and seismic data, and to determine whether the offshore anomalies are caused by Neoproterozoic Mira terrane units, other Avalonian units such as those of the Antigonish Highlands, or some other as yet unrecognized sources. The high magnitude of the offshore anomalies is in contrast to lower surrounding signatures caused by widespread Carboniferous sedimentary basins and crustal thinning associated with the Orpheus Graben to the south. Lithoprobe East seismic interpretations suggested that the adjacent Meguma terrane has been thrust over the Avalon terrane, with the Orpheus Graben marking the suture zone between the two terranes. In the onshore, this boundary is marked by the Cobequid-Chedabucto fault system, but its position in the offshore (north or south of the Orpheus Graben) is somewhat uncertain. The area is further complicated by the recognition of Carboniferous detachment faulting on Isle Madame in the southernmost part of Cape Breton Island, and the possibility that Meguma terrane basement extends into that area. This study will evaluate and model the source(s) of the offshore anomalies, based on a compilation of existing magnetic, gravity, and seismic data. The models will be constrained by physical property data (i.e., specific gravity, magnetic susceptibility) measured in samples collected from relevant onshore areas in the Mira terrane and offshore exploration wells. Stratigraphic units in the models will be constrained by interpretations of industry and Lithoprobe East seismic lines in the study area. The modelling will ascertain the depth and extent of the anomalies source(s). By providing a better interpretation of the offshore geological units, this study should help to decipher the geology of the area and whether or not the Mira terrane units exposed onshore extend out under the shelf. [ABSTRACT FROM AUTHOR]

Neoproterozoic though Cambrian clastic sedimentary and/or metasedimentary rocks occur in the Hammondvale Metamorphic Suite (> ca. 620 to <680 Ma) and Broad River (ca. 620 Ma), Coldbrook (ca. 560-542 Ma) and Saint John (ca. 540-490 Ma) groups in the Avalonian Caledonia terrane of southern New Brunswick. The petrographic, major and trace element chemical, and Nd isotopic compositions of the sedimentary rocks provide constraints on the provenance and tectonic setting of these units and hence on the tectonic evolution of this typical part of Avalonia. Nd isotopic and whole-rock chemical data show that the Hammondvale Metamorphic Suite and metasedimentary rocks of the Broad River Group have negative εNd values, were derived from recycled sedimentary and mafic igneous sources, and were deposited in intra-arc basins as part of the ca. 620 volcanic-arc complex. In contrast, sedimentary rocks of the Coldbrook Group show generally positive εNd values and likely were derived from Avalonian felsic to intermediate igneous sources and deposited in rift basins associated with 560-550 Ma arc extension. Samples from the overlying Saint John Group have felsic to mafic igneous sources, but are characterized by negative εNd values and likely were deposited as part of a newly forming passive margin sequence. Many metasedimentary and sedimentary samples from the Hammondvale Metamorphic Suite, Broad River Group, and Saint John Group fall outside the normal Nd isotopic range for Avalonian igneous rocks, whereas Coldbrook Group samples fall mainly in the typical Avalonian igneous Nd isotopic range, suggesting a substantially larger Avalonian crustal component in their evolution. Based on their mostly positive εNd values, the sedimentary units in the Coldbrook Group were most likely derived from associated volcanic units as well as the older Broad River Group igneous units. The more negative εNd values for samples from the Hammondvale Metamorphic Suite and Broad River Group indicate a large, isotopically mature source from more interior locations in Gondwana. Based on overlapping detrital muscovite ages and similar Nd isotopic values, the lower Saint John Group units were derived from the Hammondvale Metamorphic Suite, whereas the middle to upper units, which have more evolved Nd isotopic values, appear to require a source outside of the Caledonia terrane. [ABSTRACT FROM AUTHOR]

The Scatarie Ridge Magnetic Anomalies (SRMA) form a prominent northeast-trending belt, 100 km long by 25 km wide, on the Scotian Shelf southeast of Cape Breton Island. The area is inferred to be part of the Mira terrane, a component of the Avalonia realm of the northern Appalachian orogen. The magnetic anomalies range from 300 nT to 600 nT with the centres reaching highs of 1000 nT. Associated with the magnetic anomalies are positive gravity anomalies that range from 10 to 30 mGal. This study used forward-modeling software to model magnetic and gravity data to investigate possible sources of the SRMA. The interpretations are constrained by physical property data measured in samples collected from onshore areas, and by multichannel seismic lines collected by PetroCanada and the Geological Survey of Canada Frontier Geoscience Project (Lithoprobe East). Using the second derivative magnetic map, the SRMA has been resolved into a linear anomaly trending east-northeast and two large magnetic aureoles located north of the central part of the SRMA. Forward potential field models indicate that the southern margin of the linear anomaly is the northern margin of the Orpheus Graben. A south-dipping fault separates rocks of the Meguma terrane to the south from rocks of the Avalon terrane to the north of the graben. The Meguma terrane is modeled as one unit with average density of 2750 kg/m³ and average magnetic susceptibility of 2x10-3 SI. The offshore Avalon terrane has been modeled as five geological units based on differences in magnetic susceptibility and density, in the range of 10x10-3 to 20x10-3 SI and 2600 to 2700 kg/m³, respectively. Upper crustal units beneath the Avalon terrane offshore have higher susceptibility and lower density than units beneath the onshore Mira terrane, suggesting that the offshore area is a different part of Avalonia, perhaps equivalent to the Antigonish Highlands or the eastern part of Avalon terrane in Newfoundland. The source of the large linear anomaly is interpreted to be a belt of mafic volcanic rocks at a depth of 6-15 km in the offshore Avalon terrane. The large magnetic aureoles have associated gravity anomalies indicating that they are caused by granite plutons and magnetic rocks in the surrounding contact metamorphic aureoles. In the Gabarus Bay area, similar magnetic aureoles are associated with the Devonian Deep Cove granite and other intrusions. Two granitic bodies south of the Orpheus Graben in the Meguma terrane have densities and magnetic susceptibilities similar to Devonian plutons in the adjacent onshore part of the Meguma terrane. [ABSTRACT FROM AUTHOR]

Cambrian sedimentary rocks in the Saint John area of New Brunswick are assigned to the Saint John Group, and divided into (from oldest to youngest) the Ratcliffe Brook, Glen Falls, Hanford Brook, Forest Hills, Kings Square, Silver Falls, and Reversing Falls formations. The lowermost four formations are preserved only in fault-bounded slivers along the northern and, to a lesser extent, southern margins of the Cambrian belt in Saint John, and in folds associated with thrusting in the Mystery Lake area. Most of the exposed area of the Saint John Group is intensely folded Kings Square Formation. The overlying Silver Falls and Reversing Falls formations are preserved only locally in synclinal keels. The Ratcliffe Brook Formation is age-equivalent to the Chapel Island Formation in eastern Newfoundland and likely extends back into the Ediacaran Period of the Late Neoproterozoic. Redbeds in the Ratcliffe Brook Formation differ from similar rocks in the underlying Seeley Beach Formation of the Coldbrook Group (equivalent to the Rencontre Formation of eastern Newfoundland) in containing abundant detrital muscovite and less abundant pyroclastic material. New 40Ar/39Ar data from the detrital muscovite indicates a maximum age of ca. 620 Ma, and a minimum age of 550 Ma. The depositional age of the upper part of the Ratcliffe Brook Formation is constrained by a U-Pb (zircon) age of ca. 531 Ma from an ash horizon, previously published by Isachsen and others. As originally defined, the overlying Glen Falls Formation consisted of grey to white quartz arenite and overlying black phosphatic and glauconitic quartz arenite. Based on paleontological evidence, only the white quartz arenite is considered to be equivalent to the lithologically similar Random Formation of eastern Newfoundland, whereas the upper phosphatic and glauconitic part is included with the Hanford Brook Formation. Laser ablation MC-ICPMS analysis of 100 detrital zircons from the white quartz arenite in the Glen Falls Formation yielded a nearly unimodal age population with a peak at ~540 Ma, similar to the age of zircon grains in the dated ash unit in the underlying Ratcliffe Brook Formation. The age of the Hanford Brook Formation is constrained to Late Early Cambrian by fossils and also by a U-Pb (zircon) age of ca. 511 Ma from an ash horizon, previously published by Landing and others. The unconformably overlying Forest Hills Formation is mainly shale, equivalent to the Middle Cambrian Chamberlains Brook and Manuels River formations in eastern Newfoundland. The Kings Square Formation consists of interbedded, muscovite-rich, fine-grained sandstone, shale, and siltstone, and is equivalent to the Middle to Upper Cambrian MacLean Brook Group of Cape Breton Island. The overlying Upper Cambrian to lower Ordovician Silver Falls and Reversing Falls formations have been assigned to the Chesley Drive Group by some other workers. Nd isotopic data indicate that the provenance changed during deposition from more juvenile sources in the Seeley Beach, Ratcliffe Brook, and Glen Falls formations to more evolved sources in the Late Cambrian part of the sequence. [ABSTRACT FROM AUTHOR]

The easternmost tectonic element of the northern Appalachian orogen, the Meguma terrane, traditionally includes the Cambrian--Ordovician Goldenville and Halifax formations (Meguma Group) and the younger White Rock and Torbrook formations, intruded by mainly Devonian plutonic units and overlain by Carboniferous and younger rocks. Recent mapping in the Meguma Group, combined with petrographic and chemical studies, has resulted in re-evaluation of its stratigraphy, tectonic setting, and provenance. As previously proposed, the lower metasandstone-dominated Goldenville Formation and upper slate-dominated Halifax Formation should be formally elevated to "group" status, because the new mapping has demonstrated that both formations can themselves be subdivided into formations and members. Thus, the Meguma Group will be elevated to a "supergroup". The redefined Goldenville Group consists of massive metasandstone with minor interbeds of metasiltstone and slate (Church Point, Green Harbour, Tangier, and Taylor Head formations), and grades upwards into thinly bedded metasandstone, metasiltstone, and silty slate (Government Point Formation). The uppermost unit (Moshers Island and Beaverbank formations) is characterized by numerous Mn-rich calcareous concretions. Units in the overlying slate-rich Halifax Group include the lower Acacia Brook/Cunard formations and the upper Bear River/Feltzen/Glen Brook formations. The Church Point Formation of the Goldenville Group contains a distinctive metasiltstone unit (High Head member) with abundant trace fossils, including the early Cambrian deepwater ichnofossil Oldhamia. The stratigraphically lowermost exposed unit in the Goldenville Group is located 3 km in stratigraphic thickness below the High Head member. This metasandstone unit yielded 555 Ma detrital zircon, providing a maximum depositional age for the exposed part of the Goldenville Group. The upper part (Tancook member) of the Government Point Formation of the Goldenville Group has yielded an early Middle Cambrian shelf-lithofacies trilobite faunule of Acado-Baltic affinity. In the overlying Halifax Group, the upper part of the Bear River Formation locally contains the graptolite Rhabdinopora flabelliformis and acritarch species that are Early Ordovician. The gap in age between this formation and the overlying late Ordovician--Early Silurian White Rock Formation indicates that a significant unconformity exists between the Halifax Group and White Rock Formation. Protoliths of the metasandstone units in the Goldenville and Halifax groups were predominantly feldspathic wacke to arenite. Preliminary whole-rock geochemical data from this clastic material suggest that the Meguma Supergroup was deposited near an active or recently active continental margin, and not at an Atlantic-style passive continental margin as previously assumed. This interpretation is further supported by the presence of numerous syn-depositional mafic sills of within-plate chemical character along the northwestern section of the Meguma Supergroup, suggesting that deposition was in a rift environment, possibly related to Late Neoproterozoic to early Paleozoic separation of the Meguma terrane from Gondwana. The lowest exposed metasandstone bed contains a detrital zircon population that is almost exclusively Late Neoproterozoic, indicating an age-homogeneous source area. In contrast, a sample from the Tancook member yielded a broad spectrum of detrital zircon ages extending back into the Archean, suggesting that the source area had changed significantly by the time (Middle Cambrian) when that member was being deposited. [ABSTRACT FROM AUTHOR]