Tectonic implications of 40Ar/39Ar mineral ages from late Precambrian – Cambrian plutons, Avalon composite terrane, southern New Brunswick, Canada

1992 ◽  
Vol 29 (11) ◽  
pp. 2445-2462 ◽  
Author(s):  
R. David Dallmeyer ◽  
R. Damian Nance
Keyword(s):  
New Brunswick ◽  
Quartz Diorite ◽  
Head Group ◽  
Low Grade ◽  
Marine Strata ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
Sedimentary Sequences ◽  
Stratigraphic Record ◽  
Isotope Correlation

Within the Avalon composite terrane exposed in southern New Brunswick, late Precambrian, low-grade volcanic–sedimentary sequences are juxtaposed against late Precambrian gneisses (Brookville Gneiss) and older platformal metasedimentary rocks (Green Head Group) along the Caledonia Fault. Both assemblages host petrographically similar suites of calc-alkalic dioritic and granodioritic plutons. Those intruding volcanic–sedimentary sequences (Caledonia terrane) record ca. 615–625 Ma crystallization ages typical of arc-related magmatism throughout the Avalon composite terrane. However, 40Ar/39Ar age data from stocks intruding gneisses and platformal metasedimentary rocks (Brookville terrane) suggest significantly younger crystallization ages.36Ar/40Ar versus 39Ar/40Ar isotope correlation ages recorded by hornblende are interpreted to closely date postmagmatic cooling within six plutons: Fairville Granite (547 ± 1 Ma); French Village Quartz Diorite (539 ± 2 and 537 ± 1 Ma); Rockwood Park Granodiorite (529 ± 2 and 523 ± 3.5 Ma); Musquash Granite (526 ± 2 Ma); Milkish Head Granite (Red Bridge pluton, 520 ± 1.5 Ma); Lepreau Diorite (Talbot Road pluton, 519 ± 2 Ma and Hansen Stream pluton, 518 ± 1.5 Ma. A hornblende isotope correlation age of 530 ± 2 Ma from penetratively foliated amphibolite within the French Village Quartz Diorite suggests that the magmatic activity was locally accompanied by ductile shear. Muscovite within granitic pegmatite in the Brookville Gneiss records a 40Ar/39Ar plateau age of 510 ± 1 Ma interpreted to date final phases of associated magmatic activity.Arc-related magmatism extending into the Cambrian contrasts with the characteristic tectono-stratigraphic record in the Avalon composite terrane where late Precambrian igneous rocks are overstepped by Cambrian–Ordovician shallow-marine strata with only a local and minor record of rift-related volcanic activity. Although the Brookville terrane shows affinities with the Avalon composite terrane during the late Precambrian, the 40Ar/39Ar age data suggest that it was isolated as a distinct tectono-stratigraphic element by the Early Cambrian.

40Ar/39Ar whole-rock phyllite ages from late Precambrian rocks of the Avalon composite terrane, New Brunswick: evidence of Silurian–Devonian thermal rejuvenation

1994 ◽  
Vol 31 (5) ◽  
pp. 818-824 ◽  
Author(s):  
R. David Dallmeyer ◽  
R. Damian Nance
Keyword(s):  
New Brunswick ◽  
Low Grade ◽  
Fine Grained ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
Minimum Age ◽  
Tectonic Contact ◽  
Age Constraints ◽  
Gas Fractions ◽  
Thermal Overprint

Several variably deformed and metamorphosed, late Precambrian volcanic–sedimentary successions have been recognized within the Avalon composite terrane exposed in the Caledonian Highlands of southern New Brunswick. Whole-rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest (ca. 600–635 Ma) Avalonian succession display similar, internally discordant 40Ar/39Ar age and apparent K/Ca spectra. Intermediate-temperature gas fractions were experimentally evolved solely from very fine grained, cleavage-aligned white micas. These yield apparent ages between ca. 430 and 410 Ma, and are interpreted to closely date a static Late Silurian – Early Devonian thermal rejuvenation.Evidence for a Silurian – Devonian thermal event has not been previously documented in Avalonian rocks of the Caledonian Highlands (Caledonia assemblage). However, a thermal overprint of similar age (ca. 400 Ma) is recorded by metamorphic muscovite in high-grade gneisses and platformal metasedimentary rocks (Brookville assemblage), which are in tectonic contact with the low-grade Caledonia assemblage. These potentially correlative thermal overprints may provide minimum age constraints on the juxtaposition of these contrasting tectono-stratigraphic assemblages, which are likely to have been palinspastically separate tectonic elements during the earliest Paleozoic.

Chronology of Cadomian tectonothermal activity in the baie de Saint-Brieuc (north Brittany), France: evidence from 40Ar/39Ar mineral ages

1991 ◽  
Vol 28 (5) ◽  
pp. 762-773 ◽  
Author(s):  
R. D. Dallmeyer ◽  
R. A. Strachan ◽  
R. S. D'Lemos
Keyword(s):  
West African ◽  
Quartz Diorite ◽  
Contact Aureole ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
The North ◽  
Granite Emplacement ◽  
Continental Arc ◽  
Armorican Massif ◽  
Isotope Correlation

The late Precambrian Cadomian Orogen exposed in the North Armorican Massif (northwest France) is a collage of displaced terranes that, in part, developed during amalgamation of continental-arc and marginal-basin complexes. 40Ar/39Ar mineral ages reported here place new constraints on the timing of Cadomian tectonothermal activity in the southern part of the St Brieuc terrane. In the baie de Saint-Brieuc area Brioverian supracrustal units were deformed, metamorphosed, and intruded by calc-alkaline plutonic complexes. Metamorphic hornblende from a metabasic amphibolite sheet within Brioverian rocks records an isotope correlation age of 568.4 ± 2.6 Ma (interpreted to date postmetamorphic cooling through appropriate argon closure temperatures). Similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the Penthièvre complex (567.5 ± 1.2 Ma) and the La Croix Gibat amphibolite (574.8 ± 2.1 Ma). Igneous hornblende from the late tectonic to posttectonic St Quay quartz diorite and muscovite from Brioverian metasedimentary rocks in the contact aureole record isotope correlation ages of ca. 565–570 Ma. These and a ca. 568 Ma isotope correlation age determined for hornblende from the foliated Fort de la Latte quartz diorite are interpreted to date postmagmatic cooling.The 40Ar/39Ar ages indicate that Cadomian tectonothermal activity within southern parts of the St Brieuc terrane occurred prior to ca. 570 Ma. This is markedly older than the ca. 540 Ma date previously suggested for peak Cadomian metamorphism and granite emplacement in the adjacent St Malo terrane and is consistent with palinspastic separation of the contrasting Cadomian elements until at least the latest Precambrian. A pre-570 Ma age for Cadomian tectonothermal activity in the St Brieuc terrane suggests correlation with similar-aged orogenic activity in other circum-Atlantic, late Precambrian Gondwanan marginal terranes (including southern portions of the Iberian massif and various sectors of the West African orogens).

40Ar/39Ar ages of detrital muscovite within early Paleozoic overstep sequences, Avalon composite terrane, southern New Brunswick: implications for extent of late Paleozoic tectonothermal overprint

1990 ◽  
Vol 27 (9) ◽  
pp. 1209-1214 ◽  
Author(s):  
R. D. Dallmeyer ◽  
R. D. Nance
Keyword(s):  
New Brunswick ◽  
Coarse Grained ◽  
Granitic Rocks ◽  
Late Paleozoic ◽  
Low Grade ◽  
Early Paleozoic ◽  
Late Precambrian ◽  
Pelitic Schist ◽  
Gas Fractions ◽  
Thermal Overprint

Concentrates of coarse-grained detrital muscovite from the Ratcliffe Brook Formation (lowermost Cambrian) display internally discordant 40Ar/39Ar age spectra. Gas fractions evolved at intermediate and high experimental temperatures record apparent ages of ca. 610–620 Ma. These are interpreted as dating initial cooling through temperatures appropriate for intracrystalline retention of 40Ar and may indicate derivation from mylonite zones developed within proximal late Precambrian granitic rocks. Gas fractions evolved at lower experimental temperatures record patterns of spectra discordance that suggest the constituent grains experienced partial, intracrystalline diffusive loss of 40Ar during a late Paleozoic, low-grade thermal overprint. A muscovite concentrate from pelitic schist beneath the allochthonous, latest Precambrian Cranberry Head granite records a 40Ar/39Ar plateau age of 318 ± 1 Ma. This is interpreted as closely dating Late Carboniferous thrust emplacement of the allochthon.

Age of the Brookville Gneiss and associated rocks, southeastern New Brunswick

1982 ◽  
Vol 19 (11) ◽  
pp. 2158-2166 ◽  
Author(s):  
William J. Olszewski Jr. ◽  
Henri E. Gaudette
Keyword(s):  
New Brunswick ◽  
Source Area ◽  
Head Group ◽  
Low Grade ◽  
Tectonic Event ◽  
Cape Breton Island ◽  
Eastern Margin ◽  
Saint John ◽  
Loss Event ◽  
Single Zircon

The Brookville Gneiss is a medium- to high-grade quartz–feldspar–biotite and hornblende–quartz–feldspar–biotite gneiss found north and northeast of Saint John, New Brunswick. The Green Head Group, a sequence of low-grade metasediments, surrounds the Brookville Gneiss. Analyses of zircons with euhedral to subhedral overgrowths and rounded to subrounded cores from the Brookville Gneiss yield an upper intercept age on concordia of 1641 Ma, considered to be the age of the source area for the zircons. The zircon analyses also indicate two Pb-loss events at approximately 780 and 370 Ma. These ages are confirmed by zircon analyses of a quartz diorite gneiss from Green Head Island, which yields ages of 827 and 333 Ma. A small euhedral single zircon from the Brookville Gneiss, believed to be formed during metamorphism, gives a concordant age of 814 Ma corresponding to the first Pb-loss event. Rb–Sr whole-rock analyses of a granite from the east side of Musquash Harbour southwest of Saint John give an age of 392 Ma and an initial Sr ratio of 0.7187 substantiating the second Pb-loss event.The results indicate that the Brookville Gneiss and Green Head Group are older than 800 Ma and probably younger than 1200 Ma. The zircon source area age (1641 Ma) and first Pb-loss event (800 Ma) are similar to ages found in rocks of the eastern margin of the Appalachian orogen from Massachusetts and Cape Breton Island, respectively. They suggest a setting and tectonic event correlated in time for the Late Precambrian of the eastern margin distinct from the younger so-called "Avalonian."

scholarly journals Influence of Titaniferous Phases on Tungsten Mineralizing Processes at the Giant Sisson Brook W-Mo Deposit, New Brunswick, Canada: Mineral-Chemical and Geochronological Assessment

Minerals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 637
Author(s):  
Aaron L. Bustard ◽  
Wei Zhang ◽  
David R. Lentz ◽  
Christopher R. M. McFarlane
Keyword(s):  
New Brunswick ◽  
Low Grade ◽  
Elemental Mapping ◽  
Metasedimentary Rocks ◽  
West Central ◽  
Icp Ms ◽  
Volcaniclastic Rocks ◽  
Acadian Orogeny ◽  
Host Rocks ◽  
Mineralizing Fluids

The Sisson Brook deposit is a low-grade, large-tonnage W-Mo deposit with notable Cu located in west-central New Brunswick, Canada, and is one of several W-Mo deposits in New Brunswick associated with fluids sourced from granitic plutons emplaced during the Devonian Acadian Orogeny. The younger Devonian-aged stockwork and replacement scheelite-wolframite-molybdenite (and chalcopyrite) mineralization straddles the faulted boundary between Cambro-Ordovician metasedimentary rocks with Ordovician felsic volcaniclastic rocks and the Middle Silurian Howard Peak Granodiorite, with dioritic and gabbroic phases. U-Pb dating of magmatic titanite in the host dioritic phase of the Howard Peak Granodiorite using LA ICP-MS resulted in a 204Pb-corrected concordant age of 432.1 ± 1.9 Ma. Petrologic examination of selected mineralization combined with elemental mapping of vein selvages using micro-XRF and metasomatic titanite and ilmenite grains using LA ICP-MS indicates that saturation of titaniferous phases influenced the distribution of scheelite versus wolframite mineralization by altering the aFe/aCa ratio in mineralizing fluids. Ilmenite saturation in Ti-rich host rocks lowered the relative aFe/aCa and led to the formation of scheelite over wolframite. Altered magmatic titanite and hydrothermal titanite also show increased W and Mo concentrations due to interaction with and/or saturation from mineralizing fluids.

Geometry and kinematics of a major crustal shear zone segment in the Appalachians of southern New Brunswick

1994 ◽  
Vol 31 (10) ◽  
pp. 1523-1535 ◽  
Author(s):  
Adrian F. Park ◽  
Paul F. Williams ◽  
Steven Ralser ◽  
Albert Léger
Keyword(s):  
New Brunswick ◽  
Shear Zone ◽  
Low Grade ◽  
Northern Boundary ◽  
Crystalline Complex ◽  
Late Precambrian ◽  
The North ◽  
Appalachian Orogen ◽  
Complex Forms ◽  
Geometry And Kinematics

In southern New Brunswick the Kennebecasis Fault follows the northern boundary of a crystalline portion of the late Precambrian – Cambrian Avalon terrane. This low-grade crystalline complex forms the basement to a series of Carboniferous through Triassic basins. This complex also contains a major shear zone relic that is largely flat lying but upturned adjacent to the fault, and that with it defines the Pocologan–Kennebecasis fault zone. The orientation of the main composite foliation (S1) and the included mineral (stretching) lineation (L1) indicate that this geometry is a primary feature of the shear zone, representing a linked pair of horizontal and vertical detachments bounding an allochthonous unit. Kinematic indicators show that this allochthon moved parallel to the strike of the north Appalachian orogen, with top towards the west or west-southwest. The bounding shear zone is not uniform, but consists of a mylonite–phyllonite adjacent to the detachment. The upturned segment of the shear zone has been the site of later, brittle reactivation, one episode of which is represented by the Kennebecasis Fault. The main shear zone relic relates to more fundamental events, such as the accretion of the Avalon terrane.

scholarly journals Geochemistry of Umm Rus gold - quartz veins, Central Eastern Desert Egypt. A new contribution

2001 ◽  
Vol 34 (3) ◽  
pp. 1139
Author(s):  
O. A. KAMEL ◽  
M. M. EL MAHALLAWI ◽  
H. M. HELMY
Keyword(s):  
Hybrid Zone ◽  
Eastern Desert ◽  
Quartz Diorite ◽  
Low Grade ◽  
Gold Content ◽  
Strongly Correlated ◽  
Quartz Veins ◽  
Central Eastern Desert ◽  
Pan African ◽  
Gold Bearing

Gold-bearing quartz veins of the Umm Rus area occur at the south-eastern contact of a Precambrian granodiorite cupola within younger gabbros of 573-615 Ma belonging to the Pan African orogenic belt. The rocks are intruded within low-grade metasediments. At such contact, a hybrid zone is developed characterized by the occurrence of quartz diorite which grades into diorite and meta-ferrogabro. A limited number of mineralized quartz veins cut the granodiorite-gabbro complex. Different alteration zones are developed in the vicinity of the quartz veins. The quartz veins have two main trends; NS and N30 E, the latter one is usaually gold-bearing. The mineralized parts of the veins commonly consist of highly sheared and banded smoky quartz, and the gold content depends on the relation with the dykes. The element is strongly correlated with As and Ag, but moderately with Cu. Near to intermediate and basic dykes, the contents of Au, Ag and As are noticably increased

scholarly journals The thrust contact between the Canastra and Vazante groups in the Southern Brasília Belt: structural evolution, white mica crystallinity and implications for the Brasiliano orogeny

2016 ◽  
Vol 46 (4) ◽  
pp. 567-583 ◽  
Author(s):  
Manuela de Oliveira Carvalho ◽  
◽  
Claudio de Morisson Valeriano ◽  
Pamela Alejandra Aparicio González ◽  
Gustavo Diniz Oliveira ◽  
...  
Keyword(s):  
Structural Evolution ◽  
White Mica ◽  
Low Grade ◽  
Kink Bands ◽  
Metasedimentary Rocks ◽  
Kübler Index ◽  
Crenulation Cleavage ◽  
Thrust Sheets ◽  
Brasiliano Orogeny ◽  
Carbonaceous Phyllite

ABSTRACT: Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the Southern Brasília Belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of contractional deformation, associated with low-grade metamorphism. The first two (D1 and D2) are ductile, while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slaty S1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed a crenulation cleavage (S2) that dips moderately to NW and is associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrusts indicate that the peak of metamorphism is pre or syn-thrusting.

Sequence stratigraphy of the late Carboniferous Clifton Formation, New Brunswick

2020 ◽  
Vol 57 (11) ◽  
pp. 1289-1304
Author(s):  
Brandon M. Keough ◽  
Olivia A. King ◽  
Matthew R. Stimson ◽  
Page C. Quinton ◽  
Michael C. Rygel
Keyword(s):  
New Brunswick ◽  
Sediment Supply ◽  
Sequence Stratigraphic ◽  
Marine Strata ◽  
Stratigraphic Framework ◽  
Carbonaceous Shales ◽  
Study Interval ◽  
Maritimes Basin ◽  
Sequence Boundaries ◽  
Maximum Flooding Surface

The Maritimes Basin of Atlantic Canada contains a rich record of Pennsylvanian cyclothems. Previous studies have focused on rapidly subsiding depocenters in the central part of the basin where Carboniferous successions feature cyclic alternations between terrestrial and marginal marine strata. In contrast, the Pennsylvanian Clifton Formation was deposited on the relatively stable New Brunswick platform and contains almost entirely terrestrial strata. Although early studies of the Clifton Formation noted a cyclic architecture, particularly within Member B, this unit has remained understudied. We provide a sedimentological and sequence stratigraphic framework for the lower 85 m of Member B and interpret our results relative to a broader regional framework. Near the base of the study interval, the highstand systems tract is composed of red floodplain mudrocks; overlying sequence boundaries are composed of calcretes and (or) channels. The transgressive systems tract and maximum flooding surface are represented by coals and aquatic bivalve-bearing mudrocks. Moving upward through the section, the architecture of the highstand systems tract remains largely unchanged while sequence-bounding paleosols become less well developed, the transgressive systems tract becomes thinner and eventually not preserved, and the maximum flooding surface is only occasionally preserved, possibly represented by carbonaceous shales. These changes in cyclic architecture may be attributed to changes in the magnitude of glacioeustatic fluctuations, climate, and (or) the accommodation/sediment supply ratio. The results of this study show that the Clifton Formation represents the terrestrial/proximal endmember for cyclicity in the Maritimes Basin and provide new insight into paleotopography as a possible control on cyclothem architecture.

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