Migmatite structures in the Central Gneiss Complex, Boca de Quadra, Alaska

Mclellan, Eileen L.

doi:10.1111/j.1525-1314.1988.tb00437.x

Cited by 96 publications

(44 citation statements)

References 51 publications

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“…Lack of deformation during melting would presumably result in development of opthalmitic migmatites (McLellan, 1983) or possibly sporadic stromatic migmatites of the type described by , 1986. McLellan (1988) described migmatites similar to those observed here and inferred shear-induced segregation of partial melt, the migmatite structural style being a function of variation in the amount of differential stress. McLellan (1988) applied equations derived by Ramsay (1982) to document volume loss in melanocratic bands adjacent to leucosome-filled shears separating mesosome boudins.…”

Section: Mechanism Of Melt Segregationsupporting

confidence: 80%

“…McLellan (1988) described migmatites similar to those observed here and inferred shear-induced segregation of partial melt, the migmatite structural style being a function of variation in the amount of differential stress. McLellan (1988) applied equations derived by Ramsay (1982) to document volume loss in melanocratic bands adjacent to leucosome-filled shears separating mesosome boudins. Though this approach may be applied to Koettlitz Group migmatites, lack of melanosome development adjacent to shear-zone-hosted leucosomes suggests leucosome material was derived from outside the shear.…”

Section: Mechanism Of Melt Segregationsupporting

confidence: 80%

“…Furthermore, analysis of small-scale stromatic migmatites alone fails to address the larger role of migmatites, especially the extent of leucosome mobility and the structural controls on the movement of leucosome material. Studies with a structural emphasis that attempt to address these problems are comparatively rare (but see McLellan, 1983McLellan, , 1988Wickham, 1987b).…”

Section: Migmatites-previous Work and Problemsmentioning

confidence: 99%

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Segregation of leucogranite microplutons during syn‐anatectic deformation: an example from the Taylor Valley, Antarctica

Allibone¹,

Norris²

1992

Journal Metamorphic Geology

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A suite of migmatites in uppermost amphibolite facies schists of the Koettlitz Group exposed in the Taylor Valley, Antarctica, provides direct evidence of the behaviour of partially molten rock during syn-anatectic deformation. The geometry of the migmatites is directly related to their position relative to the hinge of a kilometre-scale antiform. Migmatitic rocks on the fold limbs are characterized by extensional shears and fractures, filled with leucosome material, that intersect the pervasive foliation and millimetre-thick stromatic leucosomes. Vein-and dyke-like leucosomes become more common and thicker from the limb to the hinge region of the antiform. Rocks characterized by high leucosome-to-rock ratios near the antiform hinge are xenolithic in appearance. Major parasitic folds within the hinge contain leucogranite 'microplutons' up to 50 m across beneath refractory 'cap-rock' layers.Angular boudinage structures in schists surrounded by leucosomes indicate a relatively low yield strength in the leucosome, which is compatible with a molten rather than solid leucosome. Leucogranitebearing extensional shears and fractures indicate that repeated extensional fracturing and shearing promoted by high fluid (melt) pressure is an important mechanism of melt segregation. Dilation in the hinges of developing folds aids the migration of melt into fold hinges and the development of 10-50-m-wide 'microplutons' of xenolith-rich leucogranite.Lack of vapour-absent melting and consequent low melt-to-rock ratios allowed the Koettlitz Group to maintain its structural coherency on a kilometre scale. Consequently, leucosome 'microplutons' did not exceed 50m in width, and therefore observed leucosomes have not contributed to the development of adjacent plutonic-scale granitoids.

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Section: Mechanism Of Melt Segregationsupporting

confidence: 80%

Section: Mechanism Of Melt Segregationsupporting

confidence: 80%

Section: Migmatites-previous Work and Problemsmentioning

confidence: 99%

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Segregation of leucogranite microplutons during syn‐anatectic deformation: an example from the Taylor Valley, Antarctica

Allibone¹,

Norris²

1992

Journal Metamorphic Geology

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“…Leucosomes contain euhedral grains of alkali feldspar and zoned plagioclase with interstitial quartz, suggesting the former presence of melt [e.g., Brown, 2002, 2003;Sawyer, 2001;Holness, 2008]. Furthermore, leucosome material (inferred former melt) collected in dilatant structural sites such as boudin necks, shear bands, and fold hinges [McLellan, 1984[McLellan, , 1988Brown, 1994;Burg and Vanderhaeghe, 1993;Brown and Solar, 1998]. Therefore, microstructural characteristics agree with field observations suggesting that deformation in the Naxos migmatites took place in the presence of melt.…”

Section: Migmatitic Core Of the Naxos Domesupporting

confidence: 76%

Viscoplastic flow in migmatites deduced from fabric anisotropy: An example from the Naxos dome, Greece

et al. 2010

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[1] Many migmatites represent crystallized partially molten crust and therefore record the mechanisms and pathways of orogenic crustal flow. Field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric in migmatites due to obscured flow fabrics or protracted deformation. In the Naxos dome (Greece), we test the anisotropy of magnetic susceptibility (AMS) as a tool for recovering mineral fabric symmetry and the kinematic axes of flow in migmatites. Measurements of 155 migmatite samples yield dominantly low values (<300 × 10 −6 [SI]) of bulk magnetic susceptibility (K m ) consistent with biotite being the dominant carrier of the AMS. Higher values of K m , thermomagnetic, hysteresis, and microstructural data, however, suggest a ferromagnetic contribution from magnetite in a subset of samples (N = 15). Using electron backscatter diffraction (EBSD) analysis, we establish the correspondence of the biotite subfabric with the AMS and structural fabric of the Naxos migmatites. EBSD data from biotite suggests that magnetic lineation in these dominantly paramagnetic migmatites arises from a zone axis orientation of biotite crystals organized about the direction of viscoplastic flow. Over a range of spatial scales, migmatitic foliation and magnetic foliation are well correlated. The magnetic lineation recovered by AMS displays a coherent organization despite the heterogeneous structure and composition of the Naxos migmatites. These data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow. Furthermore, our study demonstrates the utility of the AMS method for studying the dynamics of partially molten orogenic crust.

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“…Beaucoup d'auteurs (Flemming et White 1984;McLellan 1988;Brown 1994;Barbey et al 1996;Hobson et al 1998;Sawyer et al 1999) ont noté que les leucosomes dans la plupart des granulites sont contrôlés structuralement, et que leur orientation peut être reliée à la déformation à l'échelle régionale ou locale. Par conséquent, les observations suggèrent que la localisation du fondu et l'orientation des canaux de fondu (les leucosomes) sont contrôlées d'une certaine manière par la distribution des roches fertiles (fusion aux basses températures) et par l'orientation des contraintes tectoniques respectant l'anisotropie locale (foliation, litage).…”

Section: Contrôle Lithologique Versus Structural/tectonique à L'échelunclassified

Caractérisation et transfert des magmas felsiques dans la croûte moyenne à profonde :

Bonnay¹

2001

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Migmatite structures in the Central Gneiss Complex, Boca de Quadra, Alaska

Cited by 96 publications

References 51 publications

Segregation of leucogranite microplutons during syn‐anatectic deformation: an example from the Taylor Valley, Antarctica

Segregation of leucogranite microplutons during syn‐anatectic deformation: an example from the Taylor Valley, Antarctica

Viscoplastic flow in migmatites deduced from fabric anisotropy: An example from the Naxos dome, Greece

Caractérisation et transfert des magmas felsiques dans la croûte moyenne à profonde :

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