Migmatitic structures and solid-state diapirism in orthogneiss domes, eastern Grenville Province, Canada

Abstract

In the Aguanish Complex of the eastern Grenville Province, foliation trajectories, along with the contacts between migmatized orthogneissic sheets, defi ne kilometerscale domes. We present a detailed structural analysis of three of these domes with an emphasis on the distribution of the principal stretching axes derived from conjugate fl anking shear bands (melt-fi lled extensional shear bands). Noteworthy structural elements formed synchronously with the development of the domes are (1) maximum and minimum stretching axes are distributed tangentially along the envelopes of domes and radially toward the cores of domes, respectively; (2) a radial distribution of elongation lineations in the core of the most exposed dome; (3) the local convergence of lineations and fold axes toward a vertical triple junction of foliation trajectories located between two of these domes and the adjacent supracrustal trough; and (4) the development of a horizontal foliation, overprinting a steeply dipping fabric, in the core of the most exposed dome. We argue that a melt-enhanced, solid-state diapiric model best explains the aforementioned features. At the regional scale, we suggest that this diapiric process resulted from the lateral escape of the thermally softened granitic middle-crust of the Aguanish Complex, which was pushed up to compensate for the sagduction (gravity-sinking) of the denser overlying Wakeham Group, previously overloaded by the emplacement of voluminous gabbroic sills. In turn, the thermal softening of the middle granitic crust can be related to the coupled effects of thermal blanketing by the gabbroic sills and underplating of hot anorthosite-mangerite-charnockite-granite magmas associated with the intrusion of a large Grenvillian anorthositic complex.

Large-scale flat-lying isoclinal folding in extending lithosphere: Santa María de la Alameda dome (Central Iberian Massif, Spain)

“…In spite of that, second-order domes and basins in the core of this dome may account for multiple granitoid intrusions or convection within magmatic bodies (Bouchez and Diot, 1990;Weinberg, 1997), thus suggesting contribution of diapirs (currently unexposed) in the development of the dome (e.g., Gervais et al, 2004). Likewise, local evidences of incipient diapirism in the migmatized domain (Figs.…”

Southern continuation of the Wakeham Group and Robe-Noire mafic suite (eastern Grenville Province) from hydrocarbon-targeted seismic reflection data on Anticosti Island, Quebec, Canada

“…6) enlarges the regional extent of these units characterized by shallow dips and simple open folding. Moreover, the strong contrast between the structural style imaged on seismic and documented both in the Saint-Jean domain to the west (Gobeil et al 2003) and in gneiss complexes to the east (Gervais et al 2004) indicate that the sedimentary succession of the Wakeham Group is most probably detached from its underlying highgrade basement (Fig. 6).…”

“…1), the Lac-à-l'Aigle and Saint-Jean domains are composed of gneiss and abundant intrusions of various types (granitoid, gabbro, gabbronorite, anorthosite). East of Havre Saint-Pierre, the Natashquan domain consists of the relatively low-metamorphic grade Wakeham Group characterized by greenschist facies assemblages, with possible subgreenschist facies locally, rising to amphibolite facies near its margins and surrounded both to the west and east by high grade metamorphic complexes composed mainly of Pinwarian (1.53-1.45 Ga) orthogneiss exhibiting more complex ductile deformation (Gobeil et al 2003;Gervais et al 2004).…”

“…This trough corresponds to a regional N-S trending synform with a subvertical axial plane and deforms both the supracrustal D r a f t rocks and the mafic sills. Metamorphic grade observed at the surface varies from greenschist facies in the core of the the Davy Trough to amphibolite facies towards the margin of the Wakeham Group, where it is largely in fault contact with the surrounding gneisses of the Natashquan domain (Camion 1990;Martignole et al 1994;Gobeil et al 2003; Gervais et al 2004). The Natashquan domain is cut by several plutonic bodies of 1.50 Ga felsic orthogneisses (Wodicka et al 2003), and includes minor scattered paragneiss units and numerous scattered and discontinuous mafic dikes less than 10 m thick (Gobeil et al 2003).…”

“…The Natashquan domain is cut by several plutonic bodies of 1.50 Ga felsic orthogneisses (Wodicka et al 2003), and includes minor scattered paragneiss units and numerous scattered and discontinuous mafic dikes less than 10 m thick (Gobeil et al 2003). East of the Wakeham Group the amphibolite-facies gneisses have been pervasively deformed into series of dome structures (Gervais et al 2004).…”