Migmatitic structures and solid-state diapirism in orthogneiss domes, eastern Grenville Province, Canada
Published:January 01, 2004
Félix Gervais, Léopold Nadeau, Michel Malo, 2004. "Migmatitic structures and solid-state diapirism in orthogneiss domes, eastern Grenville Province, Canada", Gneiss Domes in Orogeny, Donna L. Whitney, Christian Teyssier, Christine S. Siddoway
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In the Aguanish Complex of the eastern Grenville Province, foliation trajectories, along with the contacts between migmatized orthogneissic sheets, define kilometer-scale 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 flanking shear bands (melt-filled 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.