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Machias Seal Island in the northern Gulf of Maine consists of fine- to medium-grained weakly foliated quartz monzodiorite. Although previously inferred to be as young as Devonian, the quartz monzodiorite yielded an Ediacaran-Early Cambrian U-Pb (zircon) age of 542.0 ± 0.9 Ma. Typical Machias Seal Island quartz monzodiorite contains strongly zoned plagioclase (50%), about 30% mafic minerals (biotite and amphibole with relict cores of both ortho- and clinopyroxene, and 20% interstitial quartz and orthoclase. The average chemical composition (5 samples) has 60.6% SiO2, with relatively high Al2O3 (over 16%) and low K2O (2.8%). Overall, the chemical characteristics, including low Rb, Y, and Nb, are consistent with emplacement in a continental margin subduction zone. The quartz monzodiorite contains abundant ovoid metadioritic enclaves, likely of cognate origin. Age and compositional similarities strongly suggest correlation of Machias Seal Island quartz monzodiorite with the abundant ca. 550-525 Ma gabbroic to granitic plutons of the Brookville terrane on the mainland of southern New Brunswick. Its age is similar also to the ages of volcanic and some plutonic rocks on Grand Manan Island and in the New River terrane in mainland southern New Brunswick, strengthening the interpretation that all of these areas are part of Ganderia. Hence the Fundy Fault southeast of Machias Seal Island likely marks the boundary between Ganderia and Avalonia in the Gulf of Maine. [ABSTRACT FROM AUTHOR]

A major ductile high-strain zone up to 5 km in width can be traced for at least 70 km diagonally across the Avalonian Caledonia terrane of southern New Brunswick. A study of the northeastern part of this zone from the Prosser Mountain area in the northwest to the Point Wolfe River area west of Fundy National Park shows that both the ca. 630-620 Ma Broad River Group and associated plutons and the 560-550 Ma Coldbrook Group contain similar structural elements, related to a largely shared deformational 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 (Lm¹) is locally prominent, defined by biotite aggregates. The plutonic rocks have fabrics that developed during and soon after crystallization, including a foliation (S1) producing augen-gneiss with a prominent L-tectonite (Lm¹). S1 in the plutonic rocks 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 the mineral lineation (Lm¹) in both units shares a common orientation. 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. Kinematic indicators for F2 structures 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 older plutonic rocks implies a history of exhumation beginning under hot, anhydrous conditions during and soon after crystallization at ca. 620 Ma, followed by hydration during retrogression as plutonic rocks were tectonically emplaced into this crustal stack. The age of the later tectonic events is not yet well constrained, but could be as late as Carboniferous. [ABSTRACT FROM AUTHOR]

The northeastern part of Kaipokok Bay is located in the Makkovik Province of Labrador, in the boundary zone between the Kaipokok and Aillik domains. The Kaipokok domain is characterized by reworked Archean gneiss, ca. 2100 Ma mafic metavolcanic and supracrustal metasedimentary rocks, and ca. 1895-1870 Ma plutonic rocks. The Aillik domain to the southeast is characterized by metavolcanic and metasedimentary rocks of the ca. 1860 Ma Aillik Group and younger 1800 Ma (syn-Makkovikian), 1720 Ma (post-Makkovikian), and 1670-1640 Ma (Labradorian) plutonic rocks. In the study area, the Aillik Group is dominated by metasandstone with less abundant metaconglomerate and meta-rhyolite, and rare calc-silicate and mafic volcanic rocks. The largest plutons in the area are the ca. 1802 Ma Long Island Quartz Monzonite and Kennedy Mountain granite, part of the Kennedy Mountain Intrusive Suite of the Aillik domain. A U-Pb (zircon) age of 1800.6 ± 2.3 Ma for the Kennedy Mountain granite confirms that it is the same age as the Long Island Quartz Monzonite, as inferred by earlier workers in the area. Plutons of similar age (Drunken Harbour and Hares Islands granites) have been documented farther northwest in the Kaipokok domain. The presence of compositionally similar 1800 Ma plutons in both the Aillik and Kaipokok domains is consistent with tectonic models which show that the domains were juxtaposed by that time. These plutons have within-plate, A-type characteristics, and were likely emplaced during regional transpression that was focussed on the Kaipokok Bay shear zone between the Kaipokok and Aillik domains. Labradorian-age (1670-1640 Ma) plutonic rocks occur in both the Kaipokok and Aillik domains and range in composition from ultramafic to gabbro and granite. These plutons have diverse petrological characteristics and their ages are not well constrained. Their tectonic setting during emplacement is uncertain, as they are located far from the focus of Labradorian orogenic activity in the Grenville Province. [ABSTRACT FROM AUTHOR]

The Seal Island Pluton outcrops only on small islands located on the continental shelf 45 km south of Nova Scotia, although geophysical data indicate that the pluton is part of large granitoid units that cover thousands of square kilometres farther offshore. Based on the island outcrops, the Seal Island Pluton consists of biotite monzogranite and muscovite–biotite monzogranite of uncertain relative age. Metasedimentary xenoliths combined with characteristic magnetic patterns indicate that the pluton intruded the Cambrian–Ordovician Meguma Group. Compared with the biotite monzogranite, the muscovite–biotite monzogranite is higher in SiO2, more peraluminous, and more depleted in heavy rare-earth elements, and also has lower εNd (–1.39 versus +0.82), possibly the result of more contamination by Meguma Group sedimentary rocks. The biotite monzogranite yielded a Late Devonian U–Pb (zircon) age of 362.8 ± 0.7 Ma. Although the relatively minor petrological differences between the two units do not preclude a co-magmatic relationship, the muscovite–biotite monzogranite could be 10–15 Ma older than the biotite monzogranite, based on its petrological similarities to parts of the onshore ca. 376–372 Ma Shelburne and Port Mouton plutons. Comparison with granite samples in offshore drill core indicates that granitoid rocks similar to those exposed on Seal and surrounding islands form part of large plutons farther offshore in the Meguma terrane. The age and petrochemical data from both onshore and offshore plutons indicate that peraluminous granitoid rocks in the Meguma terrane were derived from similar sources over a span of at least 20 million years. Magma genesis may have been related to mantle upwelling and stepping back of the subduction zone to the southeast subsequent to docking of Meguma terrane with adjacent Avalonia. [ABSTRACT FROM AUTHOR]

New U–Pb zircon, titanite, and monazite ages reported here, along with existing age data, demonstrate that granitoid bodies in the northwestern segment of the Paleoproterozoic Makkovik Province, Labrador, are of three distinct ages. The redefined Island Harbour Bay plutonic suite consists of varied dioritic to granitic units that were syntectonically emplaced into Archean crust of the Kaipokok domain between ca. 1895 Ma and 1870 ± 2 Ma. This plutonism occurred during the early stages of the Makkovikian Orogeny in an obliquely convergent, Andean continental margin setting. The Hares Islands and Drunken Harbour granites form smaller, discrete plutons that were emplaced in or adjacent to the Island Harbour Bay plutonic suite at 1805 ± 5 Ma and 1791 ± 2 Ma, respectively, during dextral strike-slip deformation that accompanied accretion of an outboard juvenile terrane. Magmatic activity during this period was preferentially sited along active structural zones, but also occurred outside of these zones. The undeformed Blacklers Bight A-type granite was emplaced in the Kaipokok domain at 1716 ± 1 Ma, late in the development of the orogen. A-type granites of this age form a significant component of the southeastern Makkovik Province, and their generation is linked to mafic underplating and heterogeneous regional extension. The new age data support the conclusion of earlier workers that crustal growth via synorogenic and postorogenic plutonism was episodic, and allow, along with field and geochemical data, inferences to be made regarding the tectonic setting of individual plutonic events.Les nouveaux âges U–Pb sur du zircon, de la titanite et de la monazite, rapportés ici avec certaines données d'âge déjà existantes, démontrent que des amas granitoïdes dans le segment nord-ouest de la province de Makkovik, du Paléoprotérozoïque, au Labrador, sont de trois âges distincts. La suite plutonique Island Harbour Bay redéfinie comprend des unités dioritiques à granitiques variées qui ont été mises en place syntectoniquement dans la croûte archéenne du domaine Kaipokok il y a environ 1895 à 1870 ± 2 Ma. Ce plutonisme a eu lieu au cours des premiers stages de l'orogénie makkovikienne dans un environnement de marge continentale andin à convergence oblique. Les granites de Hares Islands et de Drunken Harbour forment de plus petits plutons distincts qui ont été mis en place dans la suite plutonique Island Bay Harbour ou adjacents à cette dernière respectivement à 1805 ± 5 Ma et 1791 ± 2 Ma, au cours d'une déformation dextre qui a accompagné l'accrétion d'un terrane juvénile extérieur. L'activité magmatique au cours de cette période était localisée surtout le long de zones structurales actives mais elle a aussi eu lieu en dehors de ces zones. Blacklers Bight, le granite non déformé de type A, a été mis en place dans le domaine de Kaipokok ca. 1716 ± 1 Ma, soit tard dans le développement de l'orogène. Des granites de type A de cet âge sont une composante significative de la province Makkovik du sud-est et leur génération est liée à une remontée de magma mafique sous les plaques et à une extension hétérogène régionale. Les nouvelles données d'âge supportent les conclusions de travailleurs précédents à savoir que la croissance de la croûte par du plutonisme syn- et post orogénique était épisodique et permettaient, avec les données de terrain et géochemiques, de tirer des conclusions sur l'environnement tectonique d'événements plutoniques individuels.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Basement rocks from the Continental Offshore Stratigraphic Test (COST) No. G-1 petroleum exploration well, Georges Bank, offshore Massachusetts, USA, show the first direct evidence for a fragment of Paleoproterozoic West African crust preserved along the eastern North American continental margin. Detrital zircon from two metawacke samples near the base of the core yielded ca. 3.05-1.90 Ga laser ablation-inductively coupled plasma-mass spectrometry dates, with a predominant 2.2-2.0 Ga population. This detrital zircon signature is consistent with that in the Taghdout Group of the Anti-Atlas region, which is part of the Paleoproterozoic passive margin rocks deposited directly on the Archean-Paleoproterozoic WAC shortly after its formation. African provenance has previously been recognized for the Suwannee and Meguma terranes in the southern and northern Appalachians, respectively. However, these areas represent Neoproterozoic-Paleozoic sedimentary basins, deposited well over a billion years after formation of the Paleoproterozoic WAC and cover rocks, including those in the COST No. G-1 well. The Paleoproterozoic rocks in the COST No. G-1 well were likely amalgamated with the North American margin during final closure of the Rheic Ocean and assembly of Pangea near the end of the Paleozoic. [ABSTRACT FROM AUTHOR]

The current division of the peri-Gondwanan realm of the northern Appalachian orogen into Avalonian and Ganderian components resolves some of the long-standing problems in reconciling terrane models in New Brunswick and Cape Breton Island with those in New England and Newfoundland. The similarity in Neoproterozoic history between Ganderia and Avalonia makes resolution of those components particularly challenging, especially because the Neoproterozoic components of Ganderia are so little exposed in Newfoundland and Maine. Complexity within each of Ganderia and Avalonia also contributes to the problem, as both consist of multiple Neoproterozoic terranes. The previously well-documented geological contrasts between Ganderia and Avalonia are supported further by recognition that Avalonia experienced systematic and pervasive 18O-depletion that did not affect Ganderia. This depletion may have been linked to hydrothermal alteration during rifting at ca. 560-550 Ma as Avalonia separated from Gondwana. U-Pb dating has shown that Neoproterozoic rocks are more widespread in both western Cape Breton Island and in the New River belt of southern New Brunswick than was previously recognized. From mainland southern New Brunswick, they appear to be offset to Grand Manan Island and the central Gulf of Maine. These Neoproterozoic Ganderian belts are separated from the also Neoproterozoic Ganderian Brookville-Bras d'Or terrane of southern New Brunswick and Cape Breton Island by the Silurian Kingston-Aspy arc. Geophysical studies suggest that the basements are different under these Ganderian Neoproterozoic belts, although all these areas produced granitoid rocks with negative epsilon Nd values, in contrast to the positive values characteristic of Avalonia. The original positions of Ganderia and Avalonia around Gondwana, the nature of their pre-Neoproterozoic basements, and their relationship to the now-adjacent Meguma remain major uncertainties. Geochemical, isotopic, and detrital zircon data from sedimentary and metasedimentary sequences in Avalonia suggest that older stratigraphic units of Avalonia had different and more continental and mature sources than the Upper Neoproterozoic and Lower Paleozoic cover. Those sources were not identical to those which provided similarly continental and mature sediment to Ganderia. Links between sources and basements in Ganderia and Meguma seem more likely than links between those areas and Avalonia. [ABSTRACT FROM AUTHOR]

The ca. 620 Ma Huntington Mountain pluton and East Bay Hills Group, which comprise part of the Avalonian Mira terrane, Cape Breton Island, Nova Scotia, Canada, are characterized by pervasive propylitic alteration (chlorite, epidote, sericite, and Fe-Ti oxides) and low δ18O values (-3.8 to +6.2‰). This alteration is a product of interaction with hydrothermal fluids of meteoric and/or meteoric-seawater mixed origin at -300 °C over a range of water/rock (w/r) ratios. Locally, the propylitic alteration was further overprinted by quartz-calcite-sericite alteration. Such samples have generally higher δ18OWR values (up to +9.5‰), reflecting interaction with evolved meteoric water at lower temperatures (-200 °C) and very low w/r ratios. The hydrothermal fluids responsible for widespread propylitic alteration of the Huntington Mountain-East Bay Hills complex (and regions beyond) likely entered the crust during initial rifting of the Mira terrane from Gondwana at ca. 575-550 Ma. [ABSTRACT FROM AUTHOR]

Unusual black sandstone beds of Cambrian age (~530 to 511 Ma) occur in the upper part of the Glen Falls Formation and the lower part of the overlying Hanford Brook Formation of the Saint John Group in the Saint John area of southern New Brunswick. The dark color of these beds has been attributed to phosphatic minerals and iron chlorite. The ubiquitous presence of phosphorous, an essential nutrient for life, is important as these rocks formed during the time of the "Cambrian Explosion" in the early evolution of life. This project focuses on mineralogy, origin, and depositional environment of the black sandstones, as well as their disputed stratigraphic relationships with overlying and underlying rocks, and the phosphorous cycling that took place during deposition. The study will investigate also the correlation between the evolution of life as recorded 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. 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 process 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 likely linked to sea-level rise at the Precambrian-Cambrian boundary and iron-redox cycling. These events allowed 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 have been compared for lateral and stratigraphic variations. Interpretations of seven lithofacies described in these outcrops suggest deposition was in a tidal barrier island environment to mid-to-distal shelf environment. Thin sections of samples have been cut and examined using both petrographic and scanning electron microscopy to aid in determining paragenesis. Results confirm that francolite occurs as firmgrounds, intraclasts, and coated grains. SEM-EDS was used to determine the chemical composition of the phosphorites. Five samples were sent to the Queen's Facility for Isotopic Research where stable isotope compositions for carbon (δ13C) are being determined by ICP-MS; these data will aid in the interpretation of depositional conditions. [ABSTRACT FROM AUTHOR]