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The MacCodrum Formation is a classical "lower" Cambrian unit in southeastern Cape Breton Island stratigraphy, described since the 1800s. The age of this formation and its correlation with other Avalonian Cambrian units in eastern Newfoundland and southern New Brunswick have remained uncertain through numerous revisions. Here we present U-Pb CA-TIMS ages from an ash bed in the basal part of the MacCodrum Formation in its type-section on MacCodrum Brook that fix the maximum time of deposition at 531.86 ± 0.34 Ma. Organic-walled microfossils sampled throughout the MacCodrum Formation type-section yield acritarch taxa identifying the Asteridium–Comasphaerdium Zone, whereas the first acritarchs of the Skiagia–Fimbriaglomerella Zone appear in the overlying Canoe Brook Formation in other sections. The radiometric age and acritarch zonation place the MacCodrum Formation in the upper Fortunian, Cambrian Stage 2. Among trace fossils in the MacCodrum Formation, the meandering trace fossil Didymaulichnus dailyi comb. nov. is of particular note and morphologically identical to the type material from the lower part of the Ratcliffe Brook Formation in New Brunswick. The new radiometric and biostratigraphic data presented here provide the first firm constraints on the age of the MacCodrum Formation and enable more precise correlation with sections in southern New Brunswick and eastern Newfoundland. [ABSTRACT FROM AUTHOR]

As a result of new geological mapping, the Goldenville and Halifax groups in the eastern Meguma terrane have been divided into formations. They have a total stratigraphic thickness of about 7750 m and correspond to only the upper half of the Goldenville Group and lower half of the Halifax Group in the northwestern and southeastern areas of the terrane. The revised stratigraphy combined with compiled and new whole-rock major and trace element and Sm–Nd isotopic analyses enable more detailed documentation of the chemical changes with stratigraphy that were demonstrated in previous studies. Based on chemical compositions, the protolith compositions of the analysed samples range from lithic arenite to wacke to shale. Major and trace element characteristics are consistent with deposition in an active continental margin, basins associated with island arcs, or most likely at a passive continental margin with volcanic rocks in the source area. Chemical compositions show a scattered but overall increasing abundance of lithophile elements such as La and Th with stratigraphic position. Epsilon Nd(t) values become increasingly negative up-section, and depleted mantle model ages become increasingly older. The data are consistent with increased mixing between sediments derived from Mesoproterozoic upper crustal sources and sediments derived from a magmatic arc. These data are consistent with published detrital zircon patterns which show increasing amounts of ca. 2 Ga zircon with decreasing age, and with a source area comprising a Pan-African (800–540 Ma) volcanic arc and/or active margin magmatism and mainly Eburnean crust, most likely in the West African craton. [ABSTRACT FROM AUTHOR]

The first "Geological Highway Map of Nova Scotia" was published by the Atlantic Geoscience Society (AGS) in 1980, with subsequent revised editions published in 1990 and 2005. Like earlier editions, the fourth edition shows the current road system of Nova Scotia superimposed on underlying bedrock geological units. The map is intended to encourage people to observe and better understand the diverse geological features that are responsible for the renowned scenic beauty of the province, evident as they travel around the province or visit viewpoints, parks, and coastal sections. In addition to a significantly updated and revised geological map at a scale of 1:620 000, the front side of the map includes a legend (Table of Rock Units) that uses a simplified version of the 2021 International Chronostratigraphic Chart as the time scale. Units are divided into four areas: southern mainland, northern mainland, southeastern Cape Breton Island, and northwestern Cape Breton Island. Also included is information on how to use the map, a symbols key, representative block diagrams, and a long list of geological sites of interest. Current and past mining and quarrying activities with commodities are also highlighted. The reverse side provides more detailed maps and site descriptions for selected areas that are well known and publicly accessible, including Joggins, the Cabot Trail, the Parrsboro-Five Islands area, Scots Bay-Burntcoat Head, Yarmouth-Cape St. Marys, Arisaig, Halifax, and Louisburg. The descriptions emphasize rock types, minerals, fossils, structural features, landforms, and glacial history. In addition, the map highlights sites that are more hazardous than others where caution should be exercised and where special collection permits are required. The map is a traveller's companion to a second new AGS Special Publication "Journey Through Time - Places of Geological Significance in New Brunswick and Prince Edward Island". [ABSTRACT FROM AUTHOR]

The White Rock Formation is the lowermost formation of the Rockville Notch Group, an assemblage of Silurian-Devonian rocks preserved in five areas along the northwestern margin of the Meguma terrane of Nova Scotia. The formation consists mainly of mafic and felsic metavolcanic rocks, interlayered with and overlain by marine metasedimentary rocks. Felsic metatuff has now been dated from four locations near both the bottom and top of the volcanic pile and yielded a narrow age range (with errors) of about 446-434 Ma. These dates confirm a 30 Ma hiatus after deposition of the Early Ordovician Hellgate Formation in the underlying Halifax Group. This hiatus is coeval with the 'Sardian gap' in the Lower Palaeozoic of peri-Gondwanan Europe. The metavolcanic-metasedimentary assemblage is overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses; some of the latter were previously interpreted to be Ordovician tillite, an interpretation no longer viable. New detrital zircon data from metasedimentary samples indicate that the major sediment sources for the White Rock Formation have ages of ca. 670-550 and ca. 2050 Ma, similar to ages from the underlying Goldenville and Halifax groups. A smaller population of Mesoproterozoic zircon grains indicates that the Meguma terrane interacted with a terrane composed mainly of Mesoproterozoic crust during the Silurian and Devonian. The occurrence of the 'Sardian gap' and the detrital zircon record constrain the palaeoposition of the Meguma terrane to have been close to Cadomia and West Africa in the Early Cambrian to Early Silurian. [ABSTRACT FROM AUTHOR]

Pre-Mesozoic rocks on Grand Manan Island are divided into two groups; an older Grand Manan Group of early Ediacaran or older age, and a younger Castalia Group, considered to be latest Ediacaran to earliest Cambrian. The Castalia Group as it is currently 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 assigned to the Ross Island, North Head, Priest Cove and Long Pond Bay formations. A maximum age for the Castalia Group is ca. 600 Ma, based on the presence of volcanic clasts in conglomerate of the Great Duck Island Formation that are derived from the underlying Ingalls Head Formation (ca. 618 Ma). Additional age constraints include a U-Pb age of 539 ± 3 Ma for felsic tuff from the Priest Cove Formation and a minimum age of earliest Cambrian based on an assumed intrusive relationship between the ca. 535 Ma Stanley Brook Granite and the Flagg Cove Formation. However, stratigraphic relationships are generally poorly known due to intense deformation and thrusting, and most contacts are faulted. The Flagg Cove Formation consists of quartzose sandstone and green to dark grey silty shale, previously reported to contain rare trace fossils (Planolites) in strata along Flagg Cove. A sequence of sandstone and silty shale containing abundant morphologically simple trace fossils, including Planolites, at the south end of Stanley Beach in Flagg Cove recently yielded organic walled microfossils (Micrhystridium sp.) of a type also found in the King Square Formation in the Saint John area. This suggests a much younger (Miaolingian) age for the Flagg Cove Formation, indicating that its relationship with the Stanley Brook Granite and inclusion in the Castalia Group need to be re-evaluated. [ABSTRACT FROM AUTHOR]

Amygdaloidal basaltic flows of the Ashfield Formation were encountered in two drill holes in areas of positive aeromagnetic anomalies in the Carboniferous River Denys Basin in southwestern Cape Breton Island, Nova Scotia. One sample of medium-grained basalt yielded a plateau age of 201.8 ± 2.0 Ma, similar to the U-Pb and 40Ar/39Ar crystallization ages from basaltic flows and dykes in the Newark Supergroup. A second sample of zeolite-bearing basalt yielded a discordant age spectrum and a younger age of ca. 190 Ma, which is interpreted to date a widespread hydrothermal event related to zeolite formation. Whole-rock chemical data show that the Ashfield Formation basalt is low-Ti continental tholeiite, consistent with its within-plate tectonic setting. Chemically, it resembles basaltic flows in the Mesozoic Fundy and Grand Manan basins exposed in southern Nova Scotia and eastern New Brunswick and elsewhere in Central Atlantic Magmatic Province (CAMP). The age and geochemical data from the Ashfield Formation provide the first evidence for early Mesozoic CAMP volcanism in Cape Breton Island and demonstrate that the event was more widespread in Nova Scotia than previously thought, which has implications for its continuity and extent elsewhere within CAMP. [ABSTRACT FROM AUTHOR]

The Bras d'Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks has varied detrital zircon signatures from laser ablation inductively coupled plasma mass spectrometry U-Pb zircon dating, but combining three or more samples yielded representative age spectra that support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d'Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d'Or terrane, the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semipelitic samples from correlative units in the eastern Bras d'Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semipelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims, which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d'Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d'Or terrane and form in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d'Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 and 540 Ma. [ABSTRACT FROM AUTHOR]

The Creignish Hills and North Mountain areas of southwestern Cape Breton Island consist mostly of Neoproterozoic rocks typical of the Ganderian Bras d'Or terrane. U-Pb ages presented here for detrital zircon in the Blues Brook Formation of the Creignish Hills confirm a depositional age no greater than about 600 Ma. Although it is possible that some components of the formation are much older, similarities in rock types and field relations suggest that this is not the case. It is likely that the equivalent Malagawatch Formation of the North Mountain area, as well as high-grade metasedimentary rocks of the Melford Formation and Chuggin Road complex in the Creignish Hills and Lime Hill gneiss complex in the North Mountain area, represent the same or stratigraphically equivalent units as the Blues Brook Formation. The minimum ages of all of these units are constrained by cross-cutting syn- and post-tectonic plutons with ages mostly between 565 and 550 Ma, indicating that sediments were deposited, regionally metamorphosed, deformed, and intruded by plutons in less than 40-50 million years. The assemblage of pelitic, psammitic, and carbonate rocks indicates that a passive margin in a tropical climate was quickly changed to an active Andean-type continental margin in which voluminous calcalkaline dioritic to granitic plutons were emplaced. This sedimentary and tectonic history is characteristic of the Bras d'Or terrane and is shared by its likely correlative, the Brookville terrane in southern New Brunswick. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Brookville terrane represents ca. 650Ma passive margin of Puncoviscana Ocean. [•] Formed on Proto-Andean-Caribbean edge of Amazonia. [•] Dominated by Meso- and Paleoproterozoic detrital zircon ages. [•] Active margin in Late Neoproterozoic-Cambrian. [•] Separated in mid-Cambrian to become the foundation of Ganderia. [ABSTRACT FROM AUTHOR]

We present data on the pressure and temperature (P–T) conditions experienced by metamorphic rocks of the Meguma Terrane, Nova Scotia, Canada, also utilizing three‐dimensional microstructural data on one sample to better constrain the mechanisms that controlled garnet crystallization. Inverse and forward thermodynamic modelling place peak P–T conditions in the southwestern Meguma Terrane at ~650°C and 4.5 kbar. Interpretation of these results with petrographic observations and previous P–T constraints across the terrane suggests that amphibolite facies metamorphism occurred during the Devonian Neoacadian orogeny (406–388 Ma). Integration of quantitative 3D textural data with an estimated metamorphic heating rate of <5°C/Myr is consistent with amphibolite facies metamorphism resulting from tectonic loading during the Neoacadian orogeny, though the exact nature of the orogeny is still not well understood. Further, the intrusion of granitic plutons into the Meguma metasediments at 373 Ma likely locally drove metamorphic recrystallization (polymetamorphism). The 3D size, shape, and location of garnet crystals in one sample reveal that the rate‐limiting step for garnet crystallization was likely the diffusion of aluminium through the intergranular matrix at length scales less than the mean nearest neighbour distance between garnet crystals. Nucleation was aided by epitaxial overgrowth onto a muscovite substrate, though it appears there may have been a decoupling between minerals providing a substrate and those providing nutrients during garnet growth. [ABSTRACT FROM AUTHOR]

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.

Detailed geological mapping of the Goldenville and Halifax groups in metropolitan Halifax Regional Municipality, Nova Scotia, resulted in two-fold subdivision of both groups. The Goldenville Group was divided into the metasandstone (feldspathic wacke)-dominated Taylors Head formation and the overlying, metasiltstone-dominated, Mn-rich Beaverbank formation. The Halifax Group was divided into the Cunard formation, dominated by sulphide-rich slate, and the overlying Bluestone formation, consisting of mainly metasiltstone and metasandstone. Lithogeochemical and petrological studies resulted in the characterization of the Beaverbank, Cunard, and Bluestone formations as potential acid-producing units with pyrrhotite as the main iron-sulphide mineral. The presence of acid rock drainage (ARD) is governed by bulk-rock chemical composition and mineral assemblage. To test the predictability of ARD production, a portable XRF instrument was used to obtain relatively inexpensive whole-rock and sulphur data that were used in conjunction with conventional XRF analyses and acid-base accounting tests. Results from the three methods compare favourably. Use of the portable XRF instrument facilitates a timely and cost-effective approach to predicting ARD but does not replace the legally mandated acid-base accounting procedure. [ABSTRACT FROM AUTHOR]

Regional mapping and petrological studies have led to revision of the Cambrian-Ordovician stratigraphy in southwestern Nova Scotia. The Goldenville and Halifax formations have been elevated to groups, and formations have been defined in each group. In the northwestern part of the area, the Goldenville Group is divided into the metasandstone-dominated Church Point formation and the overlying metasiltstone-dominated Bloomfield formation. The Church Point formation contains a metasiltstone unit (High Head member) with a distinctive trace-fossil assemblage characteristic of the Early Cambrian, consistent with detrital U-Pb zircon ages. The detrital U-Pb zircon data also suggests that the Goldenville Group below the High Head member is Early Cambrian but allows the Goldenville Group to extend into the Neoproterozoic. Units in the overlying Halifax Group are the slate-rich Acacia Brook formation and overlying metasandstone-dominated Bear River formation. In the southeastern part of the area, southeast of the Chebogue Point shear zone, the lowestmost unit in the Goldenville Group is a fine-grained metasandstone-slate package termed the Moses Lake formation. It is overlain by a thickly bedded, medium-grained metasandstone-dominated unit termed the Green Harbour formation that is similar in appearance to the Church Point formation. The upper part of the Goldenville Group consists of thinly bedded metasandstone/metasiltstone termed the Government Point formation. No equivalent unit is recognized in the northwestern area. The uppermost part consists of Mn-rich metasiltstone of the Moshers Island formation that is stratigraphically equivalent to the Bloomfield formation, although the latter lacks the characteristic Mn-rich beds. Units in the overlying Halifax Group include the black slate-rich Cunard formation and overlying grey slate-dominated Feltzen formation. The upper part of the Government Point formation farther east has yielded early Middle Cambrian trilobite fossils of Acado-Baltic affinity. The upper parts of the Bear River formation in the northwestern area and Feltzen formation in the southeastern areas locally contains the Early Ordovician graptolite Rhabdinopora flabelliformis, suggesting that the underlying Acacia Brook, Cunard, Bloomfield, and Moshers Island formations are Middle to Late Cambrian, and that a significant unconformity exists between the Halifax Group and the overlying Silurian White Rock Formation. A revised minimum thickness for the combined Goldenville and Halifax groups is 11 km. [ABSTRACT FROM AUTHOR]

Detrital zircon ages from the lower part of the Late Proterozoic(?) to Middle Cambrian Goldenville Group in the Meguma terrane of Nova Scotia suggest derivation from local sources in the Avalonian and Pan-African orogens on the margins of Early Cambrian Gondwana. Samples from near the top of the group show a broader distribution, including ages back to Archean. The εNd data show a corresponding trend, from slightly positive in the lower Goldenville Group to highly negative in the upper Goldenville Group and overlying Upper Cambrian to Lower Ordovician Halifax Group. The trends are consistent with deposition of the lower part of the Meguma succession in a rift, in which uplifted rift-flanks were the main source of the early basin fill, whereas subsequent thermal subsidence of rift margins allowed for more widespread sediment sourcing in younger units. The rift was possibly located between Gondwana and Avalonia, and may have been the locus for separation of Avalonia from Gondwana to form part of the Rheic Ocean. [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]

Examines the evolution of the Kingston orogenic belt in New Brunswick. Formation of a continental margin volcanic arc; Collision between the Kingston arc and a continental block; Complexity of the central part of the orogen.

Zircon grains from metasiltstone beds in the Precambrian Ashburn Formation were dated to constrain the age of the stromatolite Archaeozoon acadiense. The largest group of analyzed grains consists of mostly well-rounded detrital zircon no younger than 1060 Ma with significant peaks at about 1200–1100, 1500, 1800, 2050, and 2700 Ma, as well as a few Mesoarchean ages. A second population of apparently euhedral grains gives ages in the range 680–400 Ma. The distribution of detrital zircon ages along with field relationships suggest that the Ashburn and Martinon formations are proximal and distal parts of the Green Head Group, respectively, and hence a previously reported maximum depositional age of ca. 602 ± 8 Ma for the Martinon Formation also applies to stromatolite in the Ashburn Formation. Paleozoic zircon recovered from the Ashburn Formation cannot be detrital because the rocks were intruded and contact metamorphosed by the Golden Grove Plutonic Suite at ca. 550–525 Ma. The Paleozoic zircon grains were found in four independently processed samples and have also been seen in other studies in the region, showing that they are not due to laboratory contamination. Zircon formed during younger magmatic activity may have been transported in hydrothermal fluids and emplaced into these metasedimentary rocks in veins. A single euhedral zircon recovered from an atypically thick vein gave an age of 659 ± 33 Ma. Hydrothermally transported zircon might provide a window into younger igneous processes for which evidence is not otherwise preserved in this and other areas. [ABSTRACT FROM AUTHOR]

The paper 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf' (Romer et al., published in 2011) describes six samples of which four are from the Meguma Supergroup of Nova Scotia. Previous work indicates that these samples are Cambrian and that they were deposited in a deep-water turbidite basin ('Megumia'), not on the Avalonian shelf. The geochemical data support models for Mn concentration, involving oxidation and reduction in a sedimentary environment but do not constrain water depth. Likely correlatives are in the Cambrian of North Wales and not in the European localities sampled by the authors. [ABSTRACT FROM AUTHOR]

Paleomagnetic results and a U–Pb baddeleyite age from the Silurian Mavillette gabbroic sill in southwest Nova Scotia, Canada, provide new evidence about the Paleozoic tectonic evolution of the Meguma terrane. The Mavillette gabbro sill intruded ca. 440–430 Myr old bimodal rift-related metavolcanic and metasedimentary rocks of the White Rock Formation in the Silurian–Devonian Rockville Notch Group. The 426.4 ± 2.0 Ma Mavillette gabbro age is notably younger than the ca. 440 Ma magmatism, but is part of a geochemically defined suite of within-plate sills and volcanic rocks of the Rockville Notch Group with ages as young as Early Devonian. Paleomagnetic investigation of 13 sites distributed along the Neoacadian (ca. 390 Ma) synclinal limbs of the Mavillette sill reveal magnetization directions that fail a fold test and therefore postdate Silurian emplacement of the gabbro. The post-folding remanence has a mean direction of D = 153.4, I = 17.1°; α95 = 6.5° (n = 12 sites), with corresponding paleopole 31.9 °S, 325.2 E; dp = 3.5°, dm = 6.7° that resembles a pervasive late Carboniferous Kiaman overprint magnetization in North America, but is rotated significantly 22.2° ± 8.1° counter-clockwise (CCW). Mavillette remanence acquisition likely occurred in concert with fluid mobilization related to Alleghanian deformation, recorded locally by ca. 320 Ma muscovite 40Ar–39Ar ages. Previously published paleomagnetic results from the Meguma terrane also have Carboniferous remanence directions with similar ∼24° CCW discordance. The regional CCW rotation of the southwest Meguma terrane post-dates this ca. 320 Ma tectonothermal remanence acquisition event, likely recording the development of an oroclinal bend of the Meguma terrane during the Alleghanian orogeny. [ABSTRACT FROM AUTHOR]

The Margaree pluton extends for >40 km along the axis of the Ganderian Aspy terrane of northern Cape Breton Island, Nova Scotia. The pluton consists mainly of coarse-grained megacrystic syenogranite, intruded by small bodies of medium-grained equigranular syenogranite and microgranite porphyry, all locally displaying rapakivi texture. The three rock types have similar U–Pb (zircon) ages of 363 ± 1.6, 364.8 ± 1.6, and 365.5 ± 3.3 Ma, respectively, consistent with field and petrological evidence that they are coeval and comagmatic. The rare earth elements display parallel trends characterized by enrichment in the light rare earth elements, flat heavy rare earth elements, moderate negative Eu anomalies, and, in some cases, positive Ce anomalies. The megacrystic and rapakivi textures are attributed to thermal perturbation in the magma chamber caused by the mixing of mafic and felsic magma, even though direct evidence of the mafic magma is mainly lacking at the current level of exposure. Magma evolution was controlled by fractionation of quartz, K-feldspar, and Na-rich plagioclase in molar proportions of 0.75:0.12:0.13. The chemical and isotopic (Sm–Nd) signature of the Margaree pluton is consistent with the melting of preexisting continental crust that was enriched in heat-producing elements, likely assisted by intrusion of mantle-derived mafic magma during Late Devonian regional extension. The proposed model involving magma mixing at shallow crustal levels in a cryptic silicic-mafic magma chamber during post-Acadian extension is consistent with models for other, better exposed occurrences of rapakivi granite in the northern Appalachian orogen. [ABSTRACT FROM AUTHOR]

The Trafalgar Plutonic Suite intruded metasedimentary rocks of the Goldenville and Halifax groups in the northeastern part of the Meguma terrane of southern Nova Scotia at about 374 Ma, based on previously published U-Pb and 40Ar/39Ar mineral ages. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular or porphyritic) and modal mineralogy (quartz diorite/tonalite, granodiorite, monzogranite, and syenogranite). The granodiorite, monzogranite, and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the quartz diorite/tonalite plutons show mineralogical and chemical variation, both within and between plutons. The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The quartz diorite/tonalite plutons are varied but chemically resemble minor Devonian mafic intrusions elsewhere in the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has chemical characteristics of volcanic-arc to syn-collisional granitoid rocks and likely has experienced extensive contamination by metasedimentary material as documented by previous studies of plutons in the Meguma terrane. The minor quartz diorite/tonalite plutons are additional examples of the mafic rocks that have been proposed in tectonic models of the Meguma terrane to have facilitated melting of the lower crust to generate granodioritic parent magmas, followed by crystal fractionation and extensive contamination by metasedimentary material. [ABSTRACT FROM AUTHOR]

Field, petrological, dating, and structural studies in the central Cape Breton Highlands have led to new understanding of the complex history related to convergence between the Aspy and Bras d'Or terranes along the Eastern Highlands shear zone in the late Devonian. The Park Spur pluton (PSP) was emplaced in the Aspy terrane in the early Late Devonian (ca. 375 Ma, U-Pb zircon). Its age combined with S-type petrological characteristics and abundant pegmatite and aplite show that it is co-magmatic with the Black Brook Granitic Suite and satellite plutons that characterize the northern Aspy terrane. These widespread plutons may have formed by crustal melting caused by subducted slab failure. On its northern margin the PSP intruded high-grade Ordovician-Silurian metamorphic rocks of the Cape North Group at mesozonal depth (>10 km), consistent with its petrological features and abundant pegmatite and aplite dykes. On its southern margin the PSP was synchronously deformed in the east-west-trending Park Spur Road shear zone and juxtaposed in a southerly direction over the low-grade metasedimentary and metavolcanic rocks of the Ordovician-Silurian Calumruadh Brook Formation (CBF). Ongoing dextral transpression between Aspy and Bras d'Or terranes reactivated the north-south-trending Central Highlands shear zone, on which the higher- grade Middle River metamorphic suite and Silurian Taylors Barren pluton to the west were transported upward relative to the adjacent CBF and PSP. By about 365 Ma, convergence had mainly ended, as evidenced by shallow emplacement of the ca. 363 Ma Margaree pluton in an extensional setting. [ABSTRACT FROM AUTHOR]

The Cambrian syn-rift strata preserved in western Avalonia provide a distinctive example of how unconformity-bounded sequences are diachronous throughout proximal to marginal rift branches. Terreneuvian--Miaolingian third-order sequences of the Caledonian Highlands, New Brunswick, Canada, reflect a complex interplay among syn-rift tectonic events, denudation pulses, and sea-level fluctuations. Unconformably overlying the early, rift-related volcanosedimentary Coldbrook Group (ca. 560-550 Ma), the Ratcliffe Brook, Glen Falls, Hanford Brook, and Forest Hills Formations can be subdivided into two transgressive systems tract (TST)--highstand systems tract (HST) sequences (each ~10 m.y.) and an incomplete TST sequence that are separated by stratigraphic gaps. They reflect uplift and tilting events affecting the basement, transgressive and drowning surfaces, and condensed sections. Arid to semi-arid climatic episodes are supported by the excellent preservation of mafic to felsic volcanic clasts in non-marine breccias and conglomerates, which are derived from the Ediacaran basement, and the local precipitation of marine gypsum through the evaporation of pore fluids. Early Miaolingian episodes of microbial/ shelly carbonate production preserved precipitates of coeval evaporite (gypsum pseudomorphs after drusy mosaics of calcite) and ikaite (glendonitic, star-shaped aggregates and crusts). Both minerals, traditionally considered to be indicators of contrasting climate conditions, potentially co-occur in temperate-water substrates recording high rates of microbial activity. The early rift phases preserved in the western Avalonian rift transect comprise stepwise uplift and unroofing of rift shoulders, which are related to diachronous, angular discordances and paraconformities bounded by syntectonic slope-apron deposits. Facies homogenization was attained during Miaolingian times as a result of generalized flooding, sealing of paleotopographies, and blanketing with monotonous offshore-dominant shales. [ABSTRACT FROM AUTHOR]

Abstract Geologically diverse fault-bounded crustal slices form the present-day southern margin of Ganderia in southern New Brunswick. One such slice, the Pocologan metamorphic suite (PMS), was previously shown to contain high-pressure metamorphic rocks and interpreted as part of the forearc of the adjacent Silurian Kingston arc terrane. In this study, the protolith age of metasedimentary rocks in the PMS has been constrained by U-Pb dating of detrital zircon to less than about 470 Ma. The age spectrum is dominated by 500 to 600 Ma ages and sparse older ages, typical of other Lower Paleozoic sedimentary components of Ganderia. An orthogneiss sample yielded a U-Pb concordia age of 433.5 ± 0.7 (2σ) Ma, interpreted as the igneous crystallization age and further supporting a link to the Kingston arc. Electron-microprobe dating of monazite from mica-schist samples yielded a mean age of 388.3 ± 2.8 (2σ) Ma, an older population at about 417 Ma, and older detrital grains at 450 Ma. Pseudosection modeling and quartz-in-garnet barometry showed that garnet cores in these mica-schist samples formed at 7 kbar and 550 °C; similar modeling combined with phengite geobarometry showed a second event at similar pressure but higher temperature. This event was followed by pressure decrease to 5 kbar and slight cooling, when biotite and staurolite porphyroblasts formed. Mylonitization started at the peak of the second metamorphic event and ended during early exhumation. The P-T and monazite age data suggest that the PMS was metamorphosed in the Early Devonian by burial to middle-lower crustal levels during the collision of Avalonia with Ganderia and metamorphosed again about 30 million years later, also at middle-lower crustal levels, during dominantly transcurrent tectonic activity. During this time different crustal slices were juxtaposed to form the PMS and probably the entire fault-bounded Ganderian and Avalonian terrane assembly in southern New Brunswick. [ABSTRACT FROM AUTHOR]

In 1998, the Nova Scotia Department of Natural Resources began a major bedrock mapping initiative in the Meguma Group of southern Nova Scotia to produce a series of 1:50 000-scale geological bedrock maps. As a result of mapping, combined with follow-up geological studies, a redefinition of its stratigraphy is now justified. As previously proposed, the lower metasandstone-dominated Goldenville Formation and upper slate-dominated Halifax Formation should be formally elevated to 'group' status. 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 Meguma Supergroup can be divided into two distinct stratigraphic packages separated by the Chebogue Point shear zone (CPSZ). In the Digby-Yarmouth area (west and northwest of the CPSZ), the lower part of the Goldenville Group is the metasandstone-dominated Church Point Formation, whereas the upper part consists of metasiltstone of the Bloomfield Formation. Units in the overlying slate-rich Halifax Group are the Acacia Brook Formation and overlying Bear River Formation. East of the CPSZ in the Pubnico-Chester area the lowest unit in the Goldenville Group is a metasandstone/slate package termed the Moses Lake Formation. The Moses Lake Formation is overlain by the metasandstone-dominated Green Harbour Formation, which is similar in appearance to the Church Point Formation. The middle part of the Goldenville Group consists of metasandstone/metasiltstone assigned to the Government Point Formation. No equivalent unit is recognized in the Digby-Yarmouth area. The upper part consists of Mn-rich metasiltstone of the Moshers Island Formation. Although this unit appears to be the stratigraphic equivalent to the Bloomfield Formation, no Mn-rich beds have been found west of the CPSZ. Units in the overlying slate-rich Halifax Group include the Cunard and overlying Feltzen formations. The Church Point Formation of the Goldenville Group contains a metasiltstone unit (High Head Member) with a distinctive trace fossil assemblage characteristic of the boundary between the Neoproterozoic and Phanerozoic, suggesting that the Goldenville Group below this member extends into the Neoproterozoic. The upper part of the Government Point Formation has yielded early Middle Cambrian trilobite fossils of Acado-Baltic affinity. The upper part of the Bear River and Feltzen formations locally contains the Early Ordovician graptolite Rhabdinopora flabelliformis, suggesting that the underlying Acacia Brook, Cunard, Bloomfield, and Moshers Island formations are Middle to Late Cambrian, and that a significant unconformity exists between the Halifax Group and the overlying late Ordovician-Early Silurian White Rock Formation. A revised minimum thickness for the Meguma Group is 10 km. One of the most significant obstacles to formalizing the proposed stratigraphy in the Meguma Supergroup is gaining acceptance of the new subdivisions among geologists. Hence, establishment of a joint working group is proposed to reach consensus on the proposed divisions and avoid confusion in the geological literature. [ABSTRACT FROM AUTHOR]

Granitoid plutons are a major component of pre-Carboniferous rocks in Cape Breton Island and knowledge of the time and tectonic setting of their emplacement is crucial for understanding the geological history of the island, guiding exploration for granite-related economic mineralization, and making alongorogen correlations. The distribution of these plutons and their petrological characteristics have been used in the past for recognizing both Laurentian and peri-Gondwanan components in Cape Breton Island, and for subdividing the peri-Gondwanan components into Ganderian and Avalonian terranes. However, ages of many plutons were assumed on the basis of field relations and petrological features compared to those of the relatively few reliably dated plutons. Seventeen new U-Pb (zircon) ages from igneous units reported here provide enhanced understanding of the distribution of pluton ages. Arc-related plutons in the Aspy terrane with ages of ca. 490 to 475 Ma likely record the Penobscottian tectonomagmatic event recognized in the Exploits subzone of central Newfoundland and New Brunswick but not previously recognized in Cape Breton Island. Arc-related Devonian plutonic activity in the same terrane is more widespread, continuous, and protracted (445 Ma to 395 Ma) than previously known. Late Devonian magmatism in the Ganderian Aspy terrane is similar in age to that in the Avalonian Mira terrane (380 to 360 Ma) but the tectonic settings are different. In contrast, magmatic activity in the Bras d'Or terrane is almost exclusively arc-related in the Late Ediacaran (580 to 540 Ma) and rift-related in the Late Cambrian (520 to 490 Ma). The new data support the terrane distinctions previously documented. [ABSTRACT FROM AUTHOR]

In the Wolfville and Bear River areas pre-Carboniferous rocks of the Goldenville, Halifax, and Rockville Notch groups are intruded by mafic sills (Type I and Type II) that have similar chemistry but different textures, alteration, and mineralogy. Type I sills appear to be penecontemporaneous with the country rock deposition based on field relations but there are no conclusive geochronological data for the sills. The relationship between Type I and Type II sills is not clearly understood and their respective effects on the country rock have not been investigated. Field mapping of sills in the Wolfville area shows that sills range from 1 to 65 m in thickness and are concordant with bedding. All the sills have sharp bottom contacts with the country rock but only larger sills have sharp top contacts. The larger sills are generally homogeneous from bottom to top and show poorly developed cleavage along their bottom contacts with the country rocks. Some of the smaller sills have vesicular textures and convolute margins along their top contacts. Contact aureoles at the margins of the sills are variable in thickness and some appear to be silicified. Further field mapping and petrographic work will focus on mineralogical changes from bottom to top in the sills and comparisons among different sills, as well as the extent and mineralogy of the contact aureoles in contrast to the country rock unaffected by the sills. Laser Ablation ICP-MS U-Pb analysis will be used to determine the zircon crystallization and apatite cooling ages for the sills. [ABSTRACT FROM AUTHOR]

Volcanic rocks of the lower Mississippian Fountain Lake Group and related plutonic rocks form a linear belt trending NW-SE through the northeastern Cobequid Highlands of northern mainland Nova Scotia. The volcanic rocks, with an exposed stratigraphic thickness of about 7 km and strike length of 35 km, include basalt and minor intermediate rocks but are dominated by rhyolite. Ten previously reported U-Pb zircon ages range from about 358 Ma to 353 Ma. LiDAR imagery shows topographic features that are useful to identify individual flow units and faults. Petrographic study of 88 thin sections showed that the rhyolite displays a diverse spectrum of spectacular textures, from welded to non-welded lithic, crystal, and ash tuff, and from spherulitic to flow-banded in the welded tuff samples. Texture has no apparent correlation with flow unit or chemistry. Silica contents in 14 basalt samples and 62 rhyolite samples range from 45 to 52% and 70 to 78%, respectively. The basalt is subalkalic and has chemical characteristics, including REE patterns, typical of continental tholeiite. The rhyolite is metaluminous to peraluminous, but not peralkaline, with chemical characteristics typical of within-plate A-type magma derived from crustal melting. Chondrite-normalized REE patterns in rhyolite samples are relatively flat and high, ranging from 100 to 1000 times chondritic values with variable but large Eu anomalies. As reported in earlier work, the rhyolite can be divided based on chemistry into low Zr and high Zr groups, the latter with higher REE contents, but correlations with most other chemical characteristics, stratigraphic position, magnetic susceptibility, or texture have not yet been recognized. [ABSTRACT FROM AUTHOR]

The Meguma terrane of mainland Nova Scotia underwent regional greenschist to amphibolite facies metamorphism between ca. 410 and 380 Ma. The relationships between deformation and metamorphism in the northeastern Meguma terrane are not well understood, a problem further complicated by the presence of voluminous granitic intrusions (some of which are deformed). The plutons produced contact metamorphic aureoles that overprinted regional metamorphic mineral assemblages in some areas. This study is focused on the area between Trafalgar and Country Harbour with the objective of documenting and interpreting the mineralogy, deformation history, and pressure-temperature conditions recorded in the rocks to help contribute to the understanding of the relative timing and conditions of deformation and metamorphism in the northeastern Meguma terrane. The highest grade regional metamorphic rocks in the study area are garnet-staurolite-biotite-muscovite schist, in which fabrics indicate that the metamorphism was pre- and syn-deformational in most areas but may be post-deformational in others. Additionally, andalusite schist, andalusite-cordierite schist, and gneiss occur in contact aureoles around plutons. Forward and inverse thermodynamic modeling suggest temperatures from ~500°C to ~550°C and pressures ranging between ~3.5 kbar and ~4.5 kbar in the main metasedimentary assemblages of the study area. Temperatures are up to ~600°C in contact aureoles at similar pressure conditions. However, the fabrics and overprinting relationships in the contact aureole rocks show that contact metamorphism predated the deformation, and therefore potentially predated regional metamorphism. This result is surprising because the sequence of events has previously been interpreted to be the opposite, suggesting that the events are diachronous across the area. The implication is that the Chedabucto fault system may have had a major influence on the sequence of metamorphism and deformation in this part of the Meguma terrane, related to juxtaposition with Avalonia. [ABSTRACT FROM AUTHOR]

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. • Seismic reflection/refraction, gravity, and rock density/velocity data were obtained. • Two velocity/depth models were generated onshore and offshore of Nova Scotia, Canada. • Both models show an extensive low-velocity zone in the offshore Meguma terrane. • Meguma terrane has crustal structure different from that of adjacent Avalonia. • Avalonia extends only 30 km under Meguma terrane in faulted contact. [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]

Cambrian to Ordovician metamorphosed clastic sedimentary rocks of the Meguma terrane have no correlatives elsewhere in Atlantic Canada but are similar to successions in North Wales. In the Meguma terrane, the Cambrian Goldenville Group, dominated by sandstone, is overlain by the Halifax Group, consisting mainly of fine-grained slate and siltstone. Within the Halifax Group widespread Furongian black slate units are overlain by greyer units with rare Early Ordovician fossils, assigned to the laterally equivalent Bear River, Feltzen, Bluestone Quarry, Lumsden Dam and Glen Brook formations. The type section of the Bluestone Quarry Formation, here defined, is on Halifax Peninsula, where four constituent members are recognized; the type section of the Lumsden Dam Formation is here defined in the Lumsden Dam region near Wolfville. Detrital zircons extracted from a sample of the Lumsden Dam Formation show a range of ages similar to those displayed by the underlying Goldenville Group, including abundant Neoproterozoic zircon representing Avalonian or Pan-African sources, and a prominent group of peaks between 1.95 and 2.2 Ga, probably representing sources in West Africa. A sample from the Glen Brook Formation east of Halifax shows a similar distribution. In contrast to the correlative Welsh successions, no influx of Mesoproterozoic zircon is seen in Early Ordovician samples, suggesting that, if the two basins were in close proximity in the Cambrian, they had diverged by the Early Ordovician, possibly as a result of strike-slip motion along the margin of Gondwana. [ABSTRACT FROM AUTHOR]

We present the first description of organic-walled microfossils from Cambrian strata of the Bourinot belt, central Cape Breton Island. Age-diagnostic acritarchs have been recovered from the Dugald and MacMullin formations and from probable levels within the upper part of the Eskasoni Formation, which permit detailed correlations with acritarch-based zones in Newfoundland and Spain. The assemblage of acritarchs from the Dugald Formation confirms earlier assignments to the early middle Cambrian eteminicus Zone, but it also indicates that the upper part of the formation belongs to the hicksi Zone of the Drumian Stage. Acritarchs from the MacMullin Formation provide the first biostratigraphic evidence that this unit extends into the forchhammeri Zone of the Guzhangian Stage. These acritarchs are present in the lower part of the MacMullin Formation, putting into question earlier identification of hicksi Zone trilobites in this unit and raising the possibility of an unconformity. The data from the Bourinot belt provide additional evidence for the biostratigraphic utility of acritarchs in the Cambrian Acado-Baltic province. [ABSTRACT FROM AUTHOR]

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]

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]

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 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]

The White Rock Formation in the Yarmouth area of the Meguma terrane of southern Nova Scotia consists mainly of mafic tuffaceous rocks with less abundant mafic flows, epiclastic and clastic sedimentary rocks, and minor intermediate and felsic crystal tuff. It is divided into seven map units that appear to young from west to east, inconsistent with a previously assumed synclinal structure. The White Rock Formation is flanked on both northwest and southeast by mainly the Cambrian to Lower Ordovician Halifax Formation; the western contact is interpreted to be a sheared disconformity, whereas the eastern contact appears to be a major brittle fault and shear zone that juxtaposes different crustal levels. The granitic Brenton Pluton forms a faulted lens within the eastern shear zone. A felsic tuff from the upper part of the White Rock Formation yielded a U–Pb zircon age of 438[sup +3] [sub –2] Ma, identical within error to published ages for the Brenton Pluton and felsic volcanic rocks near the base of the White Rock Formation in the Torbrook area of western Nova Scotia. The chemical characteristics of the mafic volcanic rocks and associated mafic intrusions consistently indicate alkalic affinity and a continental within-plate setting. The felsic volcanic rocks and Brenton Pluton have chemical characteristics of within-plate anorogenic granitic rocks, and the pluton is interpreted to be comagmatic with the felsic volcanic rocks. The igneous activity may have occurred in response to extension as the Meguma terrane rifted away from Gondwana in the latest Ordovician to Early Silurian. Epsilon Nd values are similar to those in voluminous Devonian plutonic rocks of the Meguma terrane, and the magmas appear to have been derived from similar sources.La Formation de White Rock dans la région de Yarmouth du terrane de Meguma, au sud de la Nouvelle-Écosse, comprend surtout des roches mafiques tufacées et, en quantités moindres, des coulées mafiques, des roches sédimentaires épiclastiques et clastiques ainsi que des quantités mineures de tufs cristallins intermédiaires et felsiques. La formation est divisée en sept unités cartographiques qui sembleraient de plus en plus jeunes d'ouest en est, ce qui est incompatible avec une présumée structure anticlinale définie antérieurement. Au nord-ouest et au sud-est de la Formation de White Rock on retrouve surtout la Formation de Halifax (Cambrien à Ordovicien inférieur); le contact ouest est interprété comme une discordance tronquée alors que le contact est semble être une faille majeure cassante et une zone de cisaillement qui juxtapose divers niveaux de la croûte. Le pluton granitique de Brenton forme une lentille faillée à l'intérieur de la zone de cisaillement est. Un tuf felsique de la partie supérieure de la Formation de White Rock a donné un âge U–Pb, sur zircon, de 438[sup +3] [sub –2] Ma, identique, à l'intérieur de la marge d'erreur, aux âges publiés pour le pluton de Brenton et des roches volcaniques felsiques à proximité de la base de la Formation de White Rock, dans la région de Torbrook, de l'ouest de la Nouvelle-Écosse. Les caractéristiques chimiques des roches volcaniques mafiques et des intrusions mafiques associées indiquent constamment une affinité alcaline et une mise en place continentale à l'intérieur d'une plaque. Les roches volcaniques felsiques et le pluton de Brenton ont des caractéristiques chimiques de roches granitiques anorogéniques à l'intérieur de la plaque et on interprète le pluton comme étant comagmatique avec les roches volcaniques felsiques. L'activité ignée peut découler d'une réaction à l'extension alors que le terrane de Meguma s'éloignait de Gondwana entre l'Ordovicien terminal et le Silurien précoce. Les valeurs ℇ[sub Nd] sont semblables à celles dans les volumineuses roches plutoniques dévoniennes du terrane de Meguma et les magmas semblent provenir de sources semblables.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Devonian granitoid plutons comprise a major part of the bedrock of northwestern Maine representing the magmatic expression of the Acadian orogeny in this part of the northern Appalachian orogen. They are petrographically diverse with minerals characteristic of both I- and S-type granites, in some cases within the same intrusion, and some are compositionally zoned. New LA-ICP-MS ages presented here elucidate the timing and duration of this magmatism. The earliest phase of granitoid magmatism began around 410-405 Ma with the emplacement of the Flagstaff Lake Igneous Complex, and the presence of contemporaneous mafic rocks suggests that mantle-derived magmas were also produced at this time. Late Devonian ages, ca. 365 Ma, for many intrusions, such as the Chain of Ponds and Songo plutons, reveal that magmatism continued for 45 million years during which compositionally diverse I- and S-type magmas were produced. In addition, there is evidence that intrusive activity was prolonged within some plutons, for example the Rome-Norridgewock pluton and the Mooselookmeguntic Igneous Complex, with 10-15 myr between intrusive units. The new ages suggest a break in magmatism between 400 Ma and 390 Ma apparently separating Acadian magmatism into early and late pulses. The production of lower crustal I-type magmas appears to have been concentrated later, ca. 380-365 Ma, although several S-type granitoids were also emplaced during this period. These Late Devonian plutons display abundant zircon inheritance with ages around 385 Ma, which suggests that the crust was experiencing enhanced thermal perturbations during this extended timeframe. The new data for granitoid plutons in northwestern Maine are consistent with tectonic models for other parts of Ganderia which propose initial flat slab subduction followed by slab breakoff and delamination. [ABSTRACT FROM AUTHOR]

New U-Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 ± 5 Ma and 622 ± 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from crosscutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartzfeldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 ± 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U-Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560-550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a "supereruption/supervolcano" environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560-550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 ± 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 ± 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane. [ABSTRACT FROM AUTHOR]

Although a variety of trace and body fossils have been described from the Cambrian strata in the stratotype section (global stratotype section and point) of the Precambrian–Cambrian boundary in the Burin Peninsula, Newfoundland, a detailed analysis of its organic‐walled microfossils has been missing. The basal Cambrian Treptichnus pedum Ichnozone of the Chapel Island Formation is dominated by leiosphaerids and filamentous sheaths. The appearance of Granomarginata approximates the base of the overlying Rusophycus avalonensis Ichnozone. Common process‐bearing acritarchs, represented by small Asteridium and Comasphaeridium, first appear in the middle of the overlying Random Formation, and a more diverse acritarch assemblage at its top. The Random Formation also yields small carbonaceous metazoan fossils, the first report of this type of fossil in this formation. The initial low diversity of phytoplankton in the basal Cambrian strata, a holdover from Ediacaran extinctions, indicated that they have limited potential for precise global correlation of the global stratotype section and point. The pattern of increasing diversity of acritarchs through the lower Fortunian strata lagged behind and was potentially a response to the Cambrian radiation of metazoans, as most clearly represented by ichnofossils. The timing of phytoplankton radiation reflects a dynamic lag driven by metazoan‐induced changes in early Cambrian food webs. [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]

Diverse and well-preserved acritarchs are reported from the type section of the Cambrian Hanford Brook Formation at Hanford Brook, southern New Brunswick. This section fills an important gap in acritarch studies by providing the first detailed picture of changing acritarch associations close to the traditional lower-middle Cambrian boundary in Avalonia. Acritarchs from the St Martins Member, at the base of the succession, include Skiagia ciliosa, Heliosphaeridium notatum, H. longum and Liepaina plana and suggest attribution to Cambrian Stage 4. Acritarchs from the Somerset Street Member, in the middle of the formation, include Eliasum llaniscum and Comasphaeridium silesiense. This information adds new biochronological context to an ash bed in the Somerset Street Member previously dated as c. 510 Ma or 508 Ma, and to the endemic trilobites from the same member, including Protolenus elegans. It also places absolute ages on the basal range of stratigraphically important acritarchs. Both the acritarch assemblage and the radiometric age are consistent with a position very close to the traditional lower-middle Cambrian transition and likely within Cambrian Stage 5. Acritarchs from the Long Island Member, at the top of the succession, include additional taxa demonstrating assignment to Cambrian Stage 5. Both the Somerset Street and Long Island members probably correlate with the Morocconus notabilis Zone. The new acritarch species Retisphaeridium striatum Palacios is described. New data are presented on acritarchs from the upper part of the Hell's Mouth Formation, Wales, and correlation proposed with the Long Island Member. [ABSTRACT FROM AUTHOR]

40Ar/39Ar in situ UV laser ablation of white mica, Rb–Sr mineral isochrons and zircon fission track dating were applied to determine ages of very low- to low-grade metamorphic processes at 3.5±0.4 kbar, 280±30°C in the Avalonian Mira terrane of SE Cape Breton Island (Nova Scotia). The Mira terrane comprises Neoproterozoic volcanic-arc rocks overlain by Cambrian sedimentary rocks. Crystallization of metamorphic white mica was dated in six metavolcanic samples by 40Ar/39Ar spot age peaks between 396±3 and 363±14 Ma. Rb–Sr systematics of minerals and mineral aggregates yielded two isochrons at 389±7 Ma and 365±8 Ma, corroborating equilibrium conditions during very low- to low-grade metamorphism. The dated white mica is oriented parallel to foliations produced by sinistral strike-slip faulting and/or folding related to the Middle–Late Devonian transpressive assembly of Avalonian terranes during convergence and emplacement of the neighbouring Meguma terrane. Exhumation occurred earlier in the NW Mira terrane than in the SE. Transpression was related to the closure of the Rheic Ocean between Gondwana and Laurussia by NW-directed convergence. The 40Ar/39Ar spot age spectra also display relict age peaks at 477–465 Ma, 439 Ma and 420–428 Ma attributed to deformation and fluid access, possibly related to the collision of Avalonia with composite Laurentia or to earlier Ordovician–Silurian rifting. Fission track ages of zircon from Mira terrane samples range between 242±18 and 225±21 Ma and reflect late Palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid-absent conditions during rifting prior to opening of the Central Atlantic Ocean. [ABSTRACT FROM PUBLISHER]

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]