Search

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. Les secteurs des collines Creignish et du mont North dans le sud-ouest de l'ile du Cap-Breton sont principalement constitues de roches neoproterozo'iques typiques du terrane de Ganderian Bras d'Or. Les ages U-Pb sur zircon detritique de la formation de Blues Brook des collines Creignish presentes ici confirment une sedimentation survenue il y a au plus 600 Ma environ. Meme s'il est possible que certains elements de la formation soient beaucoup plus ages, les similarites des lithotypes et les observations sur le terrain laissent supposer que ce n'est pas le cas. Il est probable que la formation equivalente de Malagawatch dans le secteur du mont North de meme que les roches metasedimentaires a forte teneur de la formation de Melford et du complexe du chemin Chuggin dans les collines Creignish et le complexe de gneiss de la colline Lime dans le secteur du mont North representent les memes unites que la formation de Blues Brook ou des unites stratigraphiquement equivalentes. Les ages minimaux de toutes ces unites sont limites par les plutons syntectoniques et post-tectoniques transversaux, ages pour la plupart de 550 a 565 Ma, ce qui revele que les sediments se sont deposes, se sont metamorphises et deformes a lechelle regionale, et ont ete penetres par les plutons au cours dune periode de moins de 40 a 50 millions d'annees. L'assemblage de roches pelitiques, psammitiques et carbonatees signale qu'une marge passive dans un climat tropical s'est rapidement transformee en une marge continentale de type andeen active dans laquelle de volumineux plutons calco-alcalins dioritiques a granitiques se sont mis en place. Un tel passe sedimentaire et tectonique est caracteristique du terrane de Bras d'Or et constitue un trait que le terrane a en commun avec l'unite vraisemblablement correlative du terrane de Brookville dans le sud du Nouveau-Brunswick. [Traduit par la redaction], INTRODUCTION The Creignish Hills and North Mountain areas of western Cape Breton Island (Fig. 1) consist mostly of Neoproterozoic metasedimentary and plutonic rocks typical of the Bras d'Or terrane of [...]

The Partridge Island block is a newly identified tectonic element in the Saint John area of southern New Brunswick, located south of and in faulted contact with Proterozoic and Cambrian rocks of the Ganderian Brookville and Avalonian Caledonia terranes. It includes the Lorneville Group and Tiner Point complex. The Lorneville Group consists of interbedded volcanic and sedimentary rocks, subdivided into the Taylors Island Formation west of Saint John Harbour and West Beach Formation east of Saint John Harbour. A sample from thin rhyolite layers interbedded with basaltic flows of the Taylors Island Formation at Sheldon Point yielded a Late Devonian - Early Carboniferous U-Pb (zircon) age of 358.9 +6/-5 Ma. Petrological similarities indicate that all of the basaltic rocks of the Taylors Island and West Beach formations are of similar age and formed in a continental within-plate tectonic setting. West of Saint John Harbour, basaltic and sedimentary rocks of the Taylors Island Formation are increasingly deformed and mylonitic to the south, and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the Tiner Point complex. Based on magnetic signatures, the deformed rocks of the Tiner Point complex can be traced through Partridge Island to the eastern side of Saint John Harbour, where together with the West Beach Formation, they occupy a thrust sheet above a redbed sequence of the mid-Carboniferous Balls Lake Formation. The Tiner Point complex includes leucotonalite and aegirine-bearing alkali-feldspar granite with A-type chemical affinity and Early Carboniferous U-Pb (zircon) ages of 353.6 ± 5.7 and 346.4 [+ or -] 0.7 Ma, respectively. Based on similarities in age, petrological characteristics, alteration, iron oxide--copper-gold (IOCG)-type mineralization, and deformation style, the Partridge Island block is correlated with Late Devonian--Early Carboniferous volcanic- sedimentaryplutonic rocks of the Cobequid Highlands in northern mainland Nova Scotia. Deformation was likely a result of dextral transpression along the Cobequid-Chedabucto fault zone during juxtaposition of the Meguma terrane. Le bloc de Partridge Island est un element tectonique nouvellement identifie dans la region de Saint John du sud du Nouveau-Brunswick; il est situe au sud et dans un contact de faille avec des roches datant du Proterozoique et du Cambrien des terranes de Brookville (Ganderien) et de Caldonia (Avalonien). Le bloc comprend le Groupe de Lorneville et le complexe de Tiner Point. Le Groupe de Lorneville est forme de roches volcaniques et sedimentaires interlitees, subdivisees entre la Formation de Taylors Island a l'ouest du port de Saint John et la Formation de West Beach a l'est. Un echantillon de minces couches de rhyolite interlitees avec des ecoulements basaltiques de la Formation de Taylors Island a la pointe Sheldon a donne un age Devonien tardif - Carbonifere precoce de 358,9 +6/-5 Ma, determine par U-Pb sur zircon. Des similitudes petrologiques indiquent que toutes les roches basaltiques des formations de Taylors Island et de West Beach ont un age similaire et qu'elles ont ete formees dans un environnement continental a l'interieur d'une plaque tectonique. A l'ouest du port de Saint John, des roches basaltiques et sedimentaires de la Formation de Taylors Island sont de plus en plus deformees et mylonitiques vers le sud; elles sont aussi en partie interlitees tectoniquement avec des roches granitoides mylonitiques et des roches metasedimentaires accessoires du complexe de Tiner Point. En se basant sur les signatures magnetiques, les roches deformees du complexe de Tiner Point peuvent etre retracees a travers l'lle Partridge, jusqu'au cote est du port de Saint John ou, avec la Formation de West Beach, elles forment une nappe de charriage au-dessus d'une sequence de lits rouges de la Formation de Balls Lake (Carbonifere moyen). Le complexe de Tiner Point comprend des granites alcalins feldspathiques avec une tonalite leucocrate et de l'aegyrine qui ont une affinite chimique de type A; ils datent du Carbonifere precoce et ont des ages respectifs de 353,6 ± 5,7 et 346,4 ± 0,7 Ma determines par datation U-Pb sur zircons. En se basant sur les similitudes d'age, les caracteristiques petrologiques, l'alteration, la mineralisation de type IOCG (oxyde de fer, cuivre, or) et le style de deformation, le bloc de Partridge Island est correle avec les roches volcaniques sedimentaires plutoniques (Devonien tardif - Carbonifere precoce) des hautes terres de Cobequid dans le nord de la partie continentale de la Nouvelle-Ecosse. La deformation proviendrait d'une transpression dextre le long de la zone de failles Cobequid-Chedabucto durant la juxtaposition du terrane de Meguma. [Traduit par la Redaction], Introduction Southern New Brunswick consists of a collage of inferred peri-Gondwanan terranes and terrane fragments (Fig. 1), some of which may have been part of the microcontinent of Ganderia and [...]

Geochronology of detrital muscovite from the Lower Cretaceous of the central Scotian Basin has shown predominant supply of Meguma terrane detritus, including muscovite with Alleghanian (mid-Carboniferous to Permian) ages from the inner Scotian Shelf. In this study, 87 detrital muscovite grains from five wells in the eastern Scotian Basin, representing depositional ages from Tithonian to Early Albian, were dated by single-grain [sup.40]Ar/[sup.39]Ar techniques. Previous work shows that the provenance of this sediment was different from wells in the central Scotian Basin. Compared with the central Scotian Basin, the muscovite age populations from the eastern Scotian Basin have more (20% versus 7%) pre-Devonian ages, derived from inboard terranes of the Appalachians. In both the central and eastern Scotian Basin, most old grains are found in the Tithonian and the Aptian-Albian, with fewer in the Valanginian and almost none in the Kimmeridgian and the Hauterivian-Barremian. These data suggest rapid unroofing of the Meguma terrane in the Kimmeridgian and Hauterivian-Barremian and greater supply of sediment from Newfoundland to the eastern Scotian Basin in the Tithonian and Aptian-Albian. Compared with the central Scotian Basin, which has most ages in the range 340-300 Ma, the muscovite age populations from the eastern Scotian Basin have a higher proportion of 420-340 Ma and in particular 300-260 Ma ages. Such late Alleghanian overprinting of argon ages is very rare on land in Nova Scotia, but in the Maritimes Basin, this was the time of uplift and erosion of strata. La geochronologie de la muscovite detritique du centre du bassin Scotian (Cretace inferieur) montre un approvisionnement predominant de debris du terrane de Meguma, incluant de la muscovite presentant des ages alleghaniens (Cretace moyen a Permien) provenant de l'interieur de la plate-forme Scotian. Dans la presente etude, 87 grains de muscovite detritique de cinq puits dans l'est du bassin Scotian, representant des ages de deposition du Tithonien a l'Albien precoce, ont ete dates selon les technique [sup.40]Ar/[sup.39]Ar sur des grains uniques. Des travaux anterieurs montrent que la provenance de ces sediments differait de celle de puits dans le centre du bassin Scotian. Compare avec le centre du bassin Scotian, les populations d'age de la muscovite de l'est du bassin Scotian etaient plus pre-devoniennes (20 % p/r 7%), provenant de terranes internes des Appalaches. Dans le centre et l'est du bassin Scotian, la plupart des plus anciens grains provenaient du Tithonien et de l'Aptien-Albien, peu du Valanginien et presque aucun du Kimmeridgien et du Hauterivien-Barremien. Ces donnees suggerent que le degagement rapide du terrane de Meguma au Kimmeridgien et a l'Hauterivien-Barremien et un plus grand approvisionnement de sediments de Terre-Neuve vers l'est du bassin Scotian au Tithonien et a l'Aptien-Albien. Compare au centre du bassin Scotian, dont la plupart des ages se situent dans la plage 340-300 Ma, les populations de muscovite de l'est du bassin Scotian ont une plus grande proportion d'ages dans la plage 420-340 Ma et particulierement 300-260 Ma. Une telle surimpression d'ages argon de l'Alleghanien est tres rare sur la masse terrestre de la Nouvelle-Ecosse; cependant, dans le bassin des Maritimes, c'etait le moment du soulevement et de l'erosion des strates., Introduction The geochronology of single grains of detrital muscovite is a powerful tool for identifying sediment provenance (Adams and Kelley 1998). Muscovite is abraded and comminuted during transport and is [...]

Single-grain ages of detrital muscovite from 15 sand(stone) samples from the Lower Carboniferous Horton Group and the Lower Cretaceous Chaswood Formation of central Nova Scotia were used to infer the nature of the Early Carboniferous unroofing of the Meguma terrane and the reworking of Carboniferous rocks in the Early Cretaceous. In the western Windsor Basin, a sample from the oldest Horton Group rocks yielded ages principally between ca. 400 and 380 Ma, suggesting that most of the muscovite present came from the metamorphic rocks of the Meguma terrane but was variably reset by the intrusion of the South Mountain Batholith at ca. 380 Ma. Other samples in this part of the basin show partial post-depositional resetting. Younger Horton Group metamorphic rocks in the eastern Windsor Basin contain many grains with ages of ca. 370-360 Ma, suggesting derivation from the central core of the South Mountain Batholith or the Musquodoboit Pluton. Horton Group sandstones from the western part of the St. Marys Basin contain muscovite derived from the Liscomb Complex along with metamorphic muscovite variably reset by the intrusion of this complex. In general, our data suggest predominant northward dispersion of muscovite from the Meguma terrane to the Horton Group and a lack of axial transport along the Horton grabens through central Nova Scotia, a pattern compatible with tectonic models in which the Meguma terrane is ramped over the Avalon terrane. Muscovite ages obtained for the Chaswood Formation compare well with those from the Horton Group rocks in the western St. Marys Basin. These rocks may have been exposed to rapid erosion by reactivation of the Cobequid-Chedabucto fault zone in the Early Cretaceous and the resulting sediments were perhaps transported to depositional sites along northeast- trending faults. Unlike the detrital monazites in these rocks, there is no evidence that any of the detrital muscovites came from distal sources outside the Meguma terrane. Des grains uniques de muscovite detritique de 15 echantillons de sable(gres) du Groupe de Horton (Carbonifere inferieur) et de la Formation de Chaswood (Cretace inferieur) du centre de la Nouvelle-Ecosse ont ete utilises pour deduire la nature de l'erosion du terrane de Meguma au Carbonifere precoce et le remaniement des roches carboniferes au Creetace; precoce. Dans le bassin Windsor occidental, un echantillon des roches les plus anciennes du Groupe de Horton a surtout donne des ages d'environ 400-380 Ma, suggerant que la plus grande partie de la muscovite presente provienne de roches metamorphiques du terrane de Meguma mais qu'elle a ete; reajustee par l'intrusion du batholite de South Mountain vers 380 Ma. D'autres echantillons de cette partie du bassin montrent un reajustement partiel post-deposition. Des roches metamorphiques plus jeunes du Groupe de Horton dans la partie orientale du bassin de Windsor peuvent contenir des grains ayant des ages d'environ 370-360 Ma, suggerant une provenance du noyau central du batholite de South Mountain ou du pluton de Musquodoboit. Les gres du Groupe de Horton de la partie ouest du bassin de St. Marys contiennent de la muscovite provenant du complexe de Liscomb en plus de muscovites metamorphiques reajustees de maniere variable par l'introduction de ce complexe. En general, nos donnees suggerent une dispersion de la muscovite surtout vers le nord a partir du terrane de Meguma vers le Groupe de Horton et un manque de transport axial le long des grabens Horton a travers le centre de la Nouvelle-Ecosse, un patron compatible avec les modeles tectoniques dans lesquels le terrane de Meguma est charrie par-dessus le terrane d'Avalon. Les ages de la muscovite obtenus pour la Formation de Chaswood se comparent bien a ceux obtenus des roches du Groupe de Horton dans l'ouest du bassin St. Marys. Ces roches peuvent avoir subi une erosion rapide par la reactivation de la zone de faille Cobequid-Chedabucto au Cretace; precoce et les sediments qui en ont decoule ont ete transported vers des sites de deposition le long de failles a tendance nord-est. A la difference des monazites detritiques dans ces roches, il n'existe pas de preuves que quelconque des muscovites detritiques provienne de sources distales a l'exteerieur du terrane de Meguma. [Traduit par la Redaction], Introduction The Meguma terrane is the most outboard terrane of the Canadian Appalachians (Fig. 1). It is a peri-Gondwanan continental margin fragment that docked with the Avalon terrane in the [...]

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 quartzitepebble 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. Nous rapportons des ages determines sur des grains uniques de muscovite detritique provenant d'echantillons de gres de cinq localites du sud du Nouveau-Brunswick et du sud-est de l'ile du Cap Breton, en Nouvelle-E cosse, ainsi que de deux clastes de quartzite d'un conglomerat de galets-quartzite qui se retrouve sous les unites de gres echantillonnees au Nouveau-Brunswick. Les plus anciens grains detritiques ont ete retrouves dans l'un des clastes de quartzite; leur plage d'age, d'environ 650-630 Ma, est definie non seulement par des analyses sur grains uniques mais aussi par une datation ponctuelle (au moyen d'un laser UV) a l'interieur d'un seul gros grain, suggerant que ces grains proviennent d'une seule source. Le second claste de quartzite avait une texture blastomylonitique avec des grains lenticulaires << mica fish >> et la plupart des ages pour la muscovite avaient ete partialement reinitialises a ~550 Ma a partir des ages originaux ~650-630 Ma. Les courbes de distribution de l'age, obtenues pour les echantillons de gres, suggerent la presence de muscovite ayant conserve l'age original de la source; cependant, la plupart des grains ont ete reinitialises par le meme evenement survenu a ~550 Ma qui a reinitialise les ages de la muscovite dans le second claste de quartzite. Selon nous, la source de quartzite qui a produit les deux clastes serait aussi la source de la muscovite dans les roches avaloniennes, datant du Cambrien, des provinces maritimes canadiennes. La roche source originale etait probablement une unite de roche granitique ou metamorphique situee relativement pres du site de deposition du quartzite protolithe, mais la source reelle est inconnue et aucun << candidat >> potentiel n'affleure localement. L'evenement de reinitialisation survenu il y a ~550 Ma pourrait etre relie aux stades initiaux de transtension regionale associee a la creation du rift entre l'Avalonie et le Gondwana. [Traduit par la Redaction], Introduction For many years, U-Pb ages of detrital zircon grains have been used to infer the provenance of sedimentary units. More recently, Haines et al. (2004), among others, also have [...]

Abstract: The Tertiary (Paleogene and Neogene) geological record in south-central Canadian Cordillera is dominated by the 350-400 km wide, lower Eocene volcanic arc and the overlying Miocene-Recent back-arc lavas that [...]

40Ar/39Ar dating of hornblende, muscovite, and orthoclase from southeastern Quebec provides new constraints on the timing, grade, and regional extent of Taconian and Acadian metamorphism in the Canadian Appalachians. Muscovite ages reveal that the Taconic orogeny occurred at ca. 463 Ma throughout the region. Lack of reset amphibole indicates that the metamorphic grade did not exceed greenschist facies. Acadian metamorphism, with a peak of

Geochronology of detrital muscovite from the Lower Cretaceous of the central Scotian Basin has shown predominant supply of Meguma terrane detritus, including muscovite with Alleghanian (mid-Carboniferous to Permian) ages from the inner Scotian Shelf. In this study, 87 detrital muscovite grains from five wells in the eastern Scotian Basin, representing depositional ages from Tithonian to Early Albian, were dated by single-grain 40Ar/39Ar techniques. Previous work shows that the provenance of this sediment was different from wells in the central Scotian Basin. Compared with the central Scotian Basin, the muscovite age populations from the eastern Scotian Basin have more (20% versus 7%) pre-Devonian ages, derived from inboard terranes of the Appalachians. In both the central and eastern Scotian Basin, most old grains are found in the Tithonian and the Aptian-Albian, with fewer in the Valanginian and almost none in the Kimmeridgian and the Hauterivian-Barremian. These data suggest rapid unroofing of the Meguma terrane in the Kimmeridgian and Hauterivian-Barremian and greater supply of sediment from Newfoundland to the eastern Scotian Basin in the Tithonian and Aptian-Albian. Compared with the central Scotian Basin, which has most ages in the range 340-300 Ma, the muscovite age populations from the eastern Scotian Basin have a higher proportion of 420-340 Ma and in particular 300-260 Ma ages. Such late Alleghanian overprinting of argon ages is very rare on land in Nova Scotia, but in the Maritimes Basin, this was the time of uplift and erosion of strata. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Single-grain ages of detrital muscovite from 15 sand(stone) samples from the Lower Carboniferous Horton Group and the Lower Cretaceous Chaswood Formation of central Nova Scotia were used to infer the nature of the Early Carboniferous unroofing of the Meguma terrane and the reworking of Carboniferous rocks in the Early Cretaceous. In the western Windsor Basin, a sample from the olde.st Horton Group rocks yielded ages principally between ca. 400 and 380 Ma, suggesting that most of the muscovite present came from the metamorphic rocks of the Meguma terrane but was variably reset by the intrusion of the South Mountain Batholith at ca. 380 Ma. Other samples in this part of the basin show partial post-depositional resetting. Younger Horton Group metamorphic rocks in the eastern Windsor Basin contain many grains with ages of ca. 370-360 Ma, suggesting derivation from the central core of the South Mountain Batholith or the Musquodoboit Pluton. Horton Group .sandstones from the western part of the St. Marys Basin contain muscovite derived from the Liscomb Complex along with metamorphic muscovite variably reset by the intrusion of this complex. In general, our data suggest predominant northward dispersion of muscovite from the Meguma terrane to the Horton Group and a lack of axial transport along the Horton grabens through central Nova Scotia, a pattern compatible with tectonic models in which the Meguma terrane is ramped over the Avalon terrane. Muscovite ages obtained for the Chaswood Formation compare well with those from the Horton Group rocks in the westem St. Marys Basin. These rocks may have been exposed to rapid erosion by reactivation of the Cobequid-Chedabucto fault zone in the Early Cretaceous and the resulting sediments were perhaps transported to depositional sites along northeasttrending faults. Unlike the detrital monazites in these rocks, there is no evidence that any of the detrital muscovites came from distal sources outside the Meguma terrane. [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]

Latest Devonian to Early Carboniferous igneous rocks along the Cobequid shear zone of central Nova Scotia record a complex history of intrusion, volcanism, deformation, and hydrothermal alteration. Twenty new 40Ar/39Ar age determinations have been made on biotite and hornblende separates from rocks that constrain these events. The mafic plutons of the Cobequid shear zone are synchronous with the previously dated granitoid plutons (363–355 ± 4 Ma), with the exception of the younger Folly Lake gabbro (355–350 ± 4 Ma). High temperature shear deformation continued along the Cobequid shear zone during this entire period of pluton emplacement. Several samples from mylonitic and hydrothermally altered rocks with dates ca. 340 Ma indicate renewed movement along the Cobequid shear zone at this time, accompanied by minor magmatism. Younger ∼330–320 Ma ages reflect final movement along the Rockland Brook fault resulting in mid-Namurian uplift of the Cobequid Highlands. Following this regional Alleghenian event, there was no significant motion on the northern faults of the Cobequid shear zone and deformation moved southward to the Cobequid fault and its continuation in the Hollow and Chedabucto fault zones. Hydrothermal alteration, probably driven by a mid-crustal gabbro heat source, was widespread along the Cobequid and Rockland Brook faults in the early Carboniferous, resulting in albitization, potassic alteration, and iron mineralization. [ABSTRACT FROM AUTHOR]

We report [sup 40] Ar/[sup 39] Ar age spectrum and laserprobe data for primary magmatic or fluido-magmatic muscovite minerals from the Port Mouton pluton, one of several weakly peraluminous peripheral plutons in the Meguma terrane, southwestern Nova Scotia. Laserprobe data from the cores of thin grain fragments suggest that this pluton cooled rapidly following intrusion at 373 ± 1 Ma, the U–Pb monazite age. The rims of thicker more complete grains record ages of 315–325 Ma, even in cases where there have been no apparent changes in grain rim chemistry and where deformation is minimal. The observed age gradients may be the result of prolonged reheating during the Late Carboniferous Alleghanian Orogeny or, alternatively, the result of rapid cooling at this time to temperatures below the closure value for muscovite rims. Conventional age spectra obtained from muscovite separates record neither the older intrusion age nor the younger reset–cooling age. Instead, these intermediate ages appear to reflect the averaging of intragrain (core–rim) age variations in thick grains and thus have no chronological significance. For these Port Mouton muscovite minerals, the record of initial cooling appears to reside only in certain limited regions of a given grain, a record that can be recovered by the laserprobe technique applied to carefully prepared subgrain fragments. A contrast in the early tectono-thermal histories of plutonic rocks in southwestern Nova Scotia relative to those in the northeast may be the result of perturbation by a mantle plume.Nous rapportons des données de sonde à laser et de plage d'âge [sup 40] Ar/[sup 39] Ar pour des muscovites primaires magmatiques ou de fluides magmatiques provenant du pluton de Port Mouton, un parmi plusieurs plutons périphériques faiblement hyperalumineux dans le terrane de Meguma, au sud-ouest de la Nouvelle-Écosse. Les données de sondes à laser du centre de fragments à grain mince suggèrent que ce pluton s'est refroidi rapidement après son intrusion il y a 373 ± 1 Ma, soit l'âge de la monazite U–Pb. Les bordures de grains plus épais et plus complets enregistrent des âges de 315–325 Ma, même dans les cas où il n'y a aucun changement apparent dans la chimie du bord du grain et où la déformation est minimale. Les gradients d'âges observés peuvent être le résultat d'un réchauffement prolongé au cours de l'orogenèse alléghanienne au Carbonifère tardif ou, alternativement, le résultat d'un refroidissement rapide à cette époque à des températures sous la valeur limite pour les bordures de muscovite. Les spectres d'âge conventionnels obtenus de feuillets de muscovite n'enregistrent ni l'âge de l'intrusion la plus vieille ni l'âge plus jeune de reprise/refroidissement. Ces âges intermédiaires semblent plutôt refléter la moyenne de variations d'âges intra-grains (centre–bordure) dans les grains épais et ainsi n'ont aucune signification chronologique. Pour ces muscovites de Port Mouton, l'enregistrement du refroidissement initial semble ne résider que dans certaines régions limitées d'un grain donné, une donnée qui peut être déterminée par la technique de la sonde à laser appliquée à des fragments soigneusement préparés de sous-grains. Un contraste dans les historiques tectono-thermiques précoces des roches plutoniques dans le sud-ouest de la Nouvelle-Écosse par rapport à celles au nord-est peut découler d'une perturbation par un panache du manteau.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Presents a correction to the study "A Comparative [sup40]Ar/[sup39]Ar Conventional and Laserprobe Study of Muscovite From Port Mouton Pluton, Southwest Nova Scotia," published in the 2001 issue of the "Canadian Journal of Earth Science,"

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]