Structural Reconnaissance of the Green Head Group Saint John, New Brunswick

Nance, Douglas C.

doi:10.4095/111209

Cited by 5 publications

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“…Clastic and dolomitic units are highly fractured, exhibit little lateral continuity, and occur as variably sized boudins in the mylonitic calcite marbles. Extreme warping of marble layering around these boudins and the local preservation of pristine pre-deformational structures and textures indicate the high ductility of the calcite marble (Nance, 1982). Hence, the formation names of Wardle (1978) are not used, in favor of the broader Ashburn Formation.…”

Section: Green Head Groupmentioning

confidence: 99%

Geology of the Brookville Terrane, southern New Brunswick, Canada

White¹,

Barr²

1996

Special Paper 304: Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic

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The Brookville terrane of southern New Brunswick includes late Precambrian rocks of the Green Head Group, Brookville Gneiss, and Dipper Harbour volcanic unit, and numerous Late Proterozoic to Cambrian granitoid plutons. The Neoproterozoic(?) Green Head Group is a mainly low-grade carbonate-pelite sequence, interpreted to have been deposited on a passive continental margin. It is in faulted contact along a ductile shear zone with the Brookville Gneiss, composed of low-pressure paragneiss, amphibolite, and tonalitic to granodioritic orthogneiss, with minor marble and quartzite. The paragneiss has a maximum depositional age of ca. 640 Ma; the orthogneiss has an igneous crystallization age of ca. 605 Ma, and regional amphibolite facies metamorphism occurred at ca. 564 Ma. The ages indicate that the gneiss is younger than the Green Head Group, but the original relationship between these units is uncertain. The Late Proterozoic Dipper Harbour volcanic unit consists of rhyolitic to andesitic tuffs and rhyolitic flows, with minor interlayered siltstone and marble, preserved in Carboniferous thrust sheets in the southwestern part of the terrane.Plutonic units in the Brookville terrane are dioritic to syenogranitic, I-type, calcalkaline suites with U-Pb zircon and titanite crystallization ages from ca. 555 Ma. to 537 Ma. They are interpreted to have formed in a continental margin subduction zone and appear to represent a more shallow crustal level in the southwest, where they are associated with volcanic rocks of the Dipper Harbour volcanic unit, than in the northeast, where they intrude the Brookville Gneiss and Green Head Group.The Brookville terrane is a late Precambrian to Cambrian tectonostratigraphic terrane, separate from Avalon terrane sensu stricto, and is correlated with the Bras d'Or terrane of Cape Breton Island and areas with rocks of similar age in the Hermitage Flexure of southern Newfoundland.

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Section: Green Head Groupmentioning

confidence: 99%

Geology of the Brookville Terrane, southern New Brunswick, Canada

White¹,

Barr²

1996

Special Paper 304: Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic

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“…The Green Head Group and Brookville Gneiss have been affected by several episodes of ductile deformation and metamorphism (Wardle 1978;Nance 1982). However, they are tectonically separated by a major ductile shear zone (termed informally the MacKay Highway shear zone) that precludes direct correlation of specific tectonic and/or thermal events.…”

Section: Structural Geometrymentioning

confidence: 99%

“…1990). Locally retrograde greenschist facies metamorphic assemblages predominate throughout the Green Head Group (Wardle 1978;Nance 1982), with quartz-albite-muscovite-actinolite-epidoteklinozoisite 2 biotite metasiltstones, muscovite/sericite-chlorite-quartz * biotite phyllites, and calcite-tremolite-epidote-muscovite-quartz f phlogopite calc-silicate rocks accompanying more common, essentially monomineralic (calcite, dolomite, quartz) metacarbonates and quartzites. Cross-cutting mafic dykes in the Green Head Group are usually low grade amphibolites with actinolitic hornblende-chlorite-albiteepidote-sericite-quartz biotite.…”

Section: Structural Geometrymentioning

confidence: 99%

“…These form essentially upright, close structures which plunge at moderate angles to the south-west (Figure 5b) and have axial traces in excess of 0.5 km in length (Nance 1982). West of Drury Cove (Figure 6), the regional orientation of SdSGHl is controlled by two megascopic F G H Z folds in which intense fracturing parallel to the steeply east-dipping axial surfaces has virtually destroyed the SdSGHl fabric at the fold closures.…”

Section: Dgh Structuresmentioning

confidence: 99%

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Structural and ⁴⁰Ar/³⁹Ar mineral age constraints for the tectonothermal evolution of the Green Head Group and Brookville Gneiss, southern New Brunswick, Canada: Implications for the configuration of the Avalon composite terrane

Nance

Dallmeyer

1994

Geological Journal

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In the late Precambrian Avalon composite terrane of the Canadian Appalachians, the local juxtaposition of Avalonian successions against gneiss complex-platformal metasedimentary rock associations of uncertain relationship to the Avalonian overstep sequence has raised importad i u d o n s about the configuration of the composite terrane. Typical of this relationship is the juxtapostion of Avalonia:. arc-related packages (Caledonia assemblage) with the migmatitic Brookville Gneiss and metacarbonate-quartzite Green Head Group (Brookville assemblage) along the Caledonia Fault in southern New Brunswick. Polyphase deformation of the predominantly greenschist facies Green Head Group accompanied development of a regional ductile shear zone that separates the group from the amphibolite facies Brookville Gneiss. Heterogeneous ductile flow in carbonate rocks and the development of a regional foliation was followed by NW-directed shortening and the local development of a penetrative axial planar fabric that intensifies towards the shear zone. Associated structural elements suggest regional dextral transpression, consistent with the metamorphic contrast across the shear zone. Steeply plunging east-west folds may record younger, sinistral movement on associated NE-SW faults. Deformation coincident with metamorphic culmination in the Brookville Gneiss produced a gneissic foliation that was later deformed to produce widespread minor folds of sheath-like geometry. These folds are best developed proximal to the shear zone where they locally document dextral shear, and probably include several generations that overlap early phases of deformation of the Green Head Group. Kinematic indicators within the gneiss are predominantly dextral. '6Ar?oAr versus "Ar/JOAr isotope-correlation ages recorded by metamorphic hornblende suggest that regional cooling of the Brookville Gneiss through ca. 500°C occurred a t ca. 540 Ma. providing a minimum age for initial deformation and concomitant metamorphic culmination in the gneiss. aAr/J9Ar plateau ages for metamorphic muscovite suggest cooling through ca. 375°C at ca. 500-520 IMa, providing a minimum age for progressive deformation in both lithotectonic sequences. Low temperature age discordance in the muscovite spectra suggest partial rejuvenation in the mid-and late Palaeozoic.Protracted Cambrian tectonothermal activity in the Brookville assemblage contrasts with the Avalonian tectonostratigraphic record of the Caledonia assemblage in which late Precambrian arc-related packages are overstepped by Cambrian-Ordovician shallow marine strata. Significant Cambrian separation between the two assemblages is therefore suggested, despite Precambrian similarities in their tectonothermal evolution. Separation as a consequence of terrane dispersal is suggested. and may imply a significant rearrangement of the Avalon composite terrane at this time. Final juxtaposition of the two assemblages pre-dates their shared late Palaeozoic rejuvenation, and may correspond to an earlier, mid-Palaeozoic thermal overprint...

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“…With the exception of contact zones bordering the Brookville gneiss, where sillimanite-bearing pelitic assemblages are locally developed, the bulk of the Green Head Group lies within the greenschist facies as demonstrated by the coexistence of dolomite + quartz in carbonates and muscovite + chlorite ---biotite in clastics (Wardle 1978;Nance 1982). However, stable assemblages are commonly those of the retrograde metamorphism of higher grade phases some of which are thought to reflect an earlier regional metamorphism while others define contact metamorphic aureoles around late Precambrian plutons of the Golden Grove suite.…”

Section: Green Head Groupmentioning

confidence: 99%

Late Precambrian-Early Palaeozoic evolution of part of the Avalon terrane in southern New Brunswick, Canada

Nance

1990

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An important Proterozoic to early Ordovician record of the Avalon terrane is exposed between the Wheaton Brook Fault and the Bay of Fundy in southern New Brunswick, Canada. Ductilely mobilized tonalitic ?basement of possibly Helikian age (Brookville gneiss) a platform carbonate-quartzite cover (Green Head Group) containing ?mid-Riphaean stromatolites. ?Unconformably overlying carbonate slump breccias and turbidites (Martinon Formation) are interpreted to record the collapse of this platform and may be broadly contemporary with minor mafic magmatism and a mid-Hadrynian (c. 800 Ma) tectonothermal event apparently recorded in the Brookville gneiss. However, the association may equally reflect the onset of late Hadrynian (c. 625-550 Ma) subduction recorded in calc-alkaline granitoid plutonism (Golden Grove suite) and associated arc-related volcanism (Coldbrook Group). The broadly coeval? emplacement of bimodal sheeted dykes (Kingston complex) appears to have occurred under conditions of sinistral transtension suggesting subduction was oblique. Mafic dykes are mainly continental tholeiites and the complex is interpreted to represent the floor of a volcanic arc rift. Major ductile shear zones of dextral sense, which border the dyke complex, may record late Precambrian rift closure but were active in the mid-Palaeozoic. Post-tectonic 'Eocambrian' volcanogenic redbeds and continental rift volcanics pass disconformably into Cambro-Ordovician sandstones and shales of the Saint John Group which contain shallow-marine Acado-Baltic fauna of the Iapetus cycle and represent an overstep sequence to Avalon's Precambrian evolution. Termination of subduction and the tectonic transition to Cambro-Ordovician platformal conditions lacks evidence of a major collisional event. Instead, they coincide with the break-up of a late Precambrian supercontinent that was responsible for the inception of the Iapetus cycle and are likely to reflect the major plate reorganizations that would accompany such an event.

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Structural Reconnaissance of the Green Head Group Saint John, New Brunswick

Cited by 5 publications

References 0 publications

Geology of the Brookville Terrane, southern New Brunswick, Canada

Geology of the Brookville Terrane, southern New Brunswick, Canada

Structural and ⁴⁰Ar/³⁹Ar mineral age constraints for the tectonothermal evolution of the Green Head Group and Brookville Gneiss, southern New Brunswick, Canada: Implications for the configuration of the Avalon composite terrane

Late Precambrian-Early Palaeozoic evolution of part of the Avalon terrane in southern New Brunswick, Canada

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Structural Reconnaissance of the Green Head Group Saint John, New Brunswick

Cited by 5 publications

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Geology of the Brookville Terrane, southern New Brunswick, Canada

Geology of the Brookville Terrane, southern New Brunswick, Canada

Structural and 40Ar/39Ar mineral age constraints for the tectonothermal evolution of the Green Head Group and Brookville Gneiss, southern New Brunswick, Canada: Implications for the configuration of the Avalon composite terrane

Late Precambrian-Early Palaeozoic evolution of part of the Avalon terrane in southern New Brunswick, Canada

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Structural and ⁴⁰Ar/³⁹Ar mineral age constraints for the tectonothermal evolution of the Green Head Group and Brookville Gneiss, southern New Brunswick, Canada: Implications for the configuration of the Avalon composite terrane