New constraints on the geometry of the Lac Bouchette gabbro – anorthosite from magnetotellurics and magnetics

Kellett, Richard

doi:10.1139/e95-110

Cited by 6 publications

(1 citation statement)

References 29 publications

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“…The Raudot intrusion, however, is separated from the parautochthon to the north by the Hart Jaune Fault and from the allochthonous Hart Jaune terrane to the south by a shear zone. Kish (1968) described the intrusion as an intrusive sheet or laccolith, but the structural position of the Raudot intrusion suggests it may be similar to the Lac Bouchette gabbro-anorthosite body (Kellett 1995), which is a thin, tectonically transported sheet sandwiched between an allochthonous terrane to the south and the parautochthon to the north in the western Grenville.…”

Section: Brien and Raudot Cumulate Rocksmentioning

confidence: 99%

Contrasting Si-saturation in troctolite-anorthosite intrusions along the Manicouagan corridor of the Abitibi-Grenville transect

Francis

Scowen²,

Panneton

et al. 2000

Can. J. Earth Sci.

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A survey of troctolite-anorthosite complexes along the Manicouagan corridor of the Abitibi-Grenville Lithoprobe transect reveals the existence of two distinct crystallization sequences in their cumulate rocks. In two intrusions (Brien and Raudot), olivine crystallized first, followed by plagioclase, Fe-oxides, and then clinopyroxene; and magmatic orthopyroxene is absent. In five other intrusions (Lucie, Tétépisca, Blache, Baie-Comeau, and Pentecôte), plagioclase and olivine are followed by orthopyroxene, and then clinopyroxene. These two distinct crystallization sequences correlate with compositional differences in gabbroic marginal rocks and dykes associated with the intrusions. The Raudot intrusion exhibits a fine-grained gabbroic margin that is Fe-and Al-rich, but Si-poor and nepheline normative. In contrast, the marginal rocks of the Blache, Baie-Comeau, and Pentecôte intrusions are typically gabbronorites that are poorer in Fe and richer in Si. Dyke rocks cutting this latter group of intrusions share these compositional characteristics and are typically orthopyroxene normative. The differences between the two types of intrusions appear to reflect the degree of Si-saturation of their parental magmas with respect to the troctolite divide. Together, the array of estimated parental magma compositions of the troctolite-anorthosite intrusions mimics that of Tertiary picritic magmas. The low forsterite (Fo) contents in olivine and the late appearance of clinopyroxene in the cumulates of the intrusions may reflect the interaction of mantle-derived parental magmas with relatively juvenile feldspathic crust.Résumé : Un levé des complexes de troctolite-anorthosite dans le corridor Manicouagan, le long du transect d'AbitibiGrenville du projet Lithoprobe, révèle l'existence de deux séquences de cristallisation dans leurs unités à cumulats. Dans deux intrusions, (Brien et Raudot), l'olivine a cristallisé en premier, suivie du plagioclase, des oxydes de fer et finalement du clinopyroxène; il y a absence d'orthopyroxène magmatique. Dans cinq autres intrusions (Lucie, Tétépisca, Blache, Baie-Comeau et Pentecôte), le plagioclase et l'olivine sont suivis par l'orthopyroxéne, et ensuite le clinopyroxène. Ces deux séquences de cristallisation distinctes sont mises en corrélation avec les différences de composition des roches gabbroïques en bordure des intrusions et avec les dykes qui leur sont associés. L'intrusion de Raudot montre une bordure gabbroïque à grain fin qui est riche en Fe et Al, mais pauvre en Si et néphéline normative. D'autre part, les roches de la bordure des intrusions de Blache, Baie-Comeau et Pentecôte sont typiquement des gabbronorites plus pauvres en Fe et plus riches en Si. Les roches formant les dykes qui recoupent ce dernier groupe d'intrusions ont en commun les mêmes caractères de composition et typiquement de l'orthopyroxène normatif. Les différences entre les deux types d'intrusions reflètent probablement le degré de saturation en Si de leurs magmas parentaux en rapport avec la séparation de la trocto...

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Section: Brien and Raudot Cumulate Rocksmentioning

confidence: 99%

Contrasting Si-saturation in troctolite-anorthosite intrusions along the Manicouagan corridor of the Abitibi-Grenville transect

Francis

Scowen²,

Panneton

et al. 2000

Can. J. Earth Sci.

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Mantle fabric at multiple scales across an Archean–Proterozoic boundary, Grenville Front, Canada

Frederiksen

Ferguson

Eaton

et al. 2006

Physics of the Earth and Planetary Interiors

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Crustal‐scale shortening and extension across the Grenville Province of western Québec

Martignole¹,

Calvert²

1996

Tectonics

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A deep seismic reflection survey shot in 1993 crosses almost the full width of the Grenville Province in western Québec. The seismic transect provides a very clear image of the crust‐mantle boundary and the most precise definition to date of the various Grenvillian terranes. The crust is around 44 km thick beneath the Grenville Front but thins rapidly to 36 km some 60 km to the southeast; it is also notable that the greatest crustal thickness of 50 km occurs at the southeast end of the transect, far from the inferred location of the main Grenvillian collision. The Grenville Front zone, in which NW directed thrusting at about 1 Ga was followed by SE directed extension, is defined by discontinuous, SE dipping reflections, which extend down to the Moho. To the southeast, the overlying migmatitic Archean parautochthon, almost half of the transect, is characterised instead by NW dipping reflectors extending into the lower crust. These reflectors are in turn truncated to the southeast by a 12‐km‐thick zone of intense SE dipping reflections, the Baskatong crustal ramp. The base of the allochthonous terranes (Allochthon Boundary Thrust) is likely located at this ramp, which flattens out at around 30‐km depth into the base of the relatively transparent intermediate crust. A highly reflective upper crustal deck corresponding to rocks of the Mont‐Laurier terrane was thrust over the Baskatong crustal ramp and is represented further to the northwest by the klippelike Cabonga allochthon. The synformal, transparent Morin anorthosite‐charnockite complex belongs to the same upper crustal level. Ramp anticlines and the overriding basal thrust of the upper allochthons demonstrate the NW directed propagation of tectonic transport during the Grenvillian orogeny, involving deformation and displacement along the Baskatong ramp with a relay into the Grenville Front zone. Postaccretional extension appears to have been primarily accommodated along the latter two crustal discontinuities thinning the crust immediately south of the Grenville Front and affecting the crust up to 350 km away from the front.

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New constraints on the geometry of the Lac Bouchette gabbro – anorthosite from magnetotellurics and magnetics

Cited by 6 publications

References 29 publications

Contrasting Si-saturation in troctolite-anorthosite intrusions along the Manicouagan corridor of the Abitibi-Grenville transect

Contrasting Si-saturation in troctolite-anorthosite intrusions along the Manicouagan corridor of the Abitibi-Grenville transect

Mantle fabric at multiple scales across an Archean–Proterozoic boundary, Grenville Front, Canada

Crustal‐scale shortening and extension across the Grenville Province of western Québec

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