Deformational behaviour of migmatites and problems of structural analysis in migmatite terrains

Mclellan, Eileen L.

doi:10.1017/s001675680002923x

Cited by 39 publications

(22 citation statements)

References 21 publications

(30 reference statements)

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“…2), indicates that the belt of metasediments has maintained its structural coherency during anatexis. Viscous folding in rocks with greater than 30~01% partial melting, as described by McLellan (1984), resulting in scattering of structural element orientations, has not occurred to any great extent.…”

Section: Kilometre-scale Plutonic Bodiesmentioning

confidence: 97%

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: Kilometre-scale Plutonic Bodiesmentioning

confidence: 97%

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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“…However, we are fortunate in having some easily available reviews on which to base a revised opinion (King, 1965;McLellan, 1984;Ashworth, 1985;Olsen, 1985;and Brown, 1993). The origin of migmatites is not so easily solved as was once thought.…”

Section: Preamblementioning

confidence: 99%

The Nature and Origin of Granite

Pitcher¹

1997

199

127

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“…Previous structural studies of migmatites have used classic field methods, melt topology analysis or fabric analysis. Field studies have highlighted the complex geometric relationships between leucosome, mesosome, and melanosome [e.g., McLellan , 1983; Passchier et al , 1990; Hopgood , 1998]. Melt topology analysis has provided a better understanding of the leucosome distribution with respect to the principal strain axes [ Brown et al , 1999; Vernon and Paterson , 2001; Barraud et al , 2001].…”

Section: Introductionmentioning

confidence: 99%

Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites

et al. 2003

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[1] The rheological behavior of the lower to middle continental crust during orogenic deformation is poorly understood. Migmatite, common at this crustal level, remains difficult to analyze from a structural viewpoint because of pervasive recrystallization. We present new anisotropy of magnetic susceptibility (AMS) data from 217 specimens of migmatites of the Superior Province in Minnesota with the aim of investigating its potential as a petrofabric tool. Quarry exposures provide the ideal sampling playground for such a study. The migmatites are coarse grained, are granitic to tonalitic in composition, and display a centimeter-scale compositional layering. The layering and the regional foliation are subhorizontal to shallowly dipping to the NE. Mineral lineations are difficult to observe due to recrystallization but trend around 70°N with gentle plunges. Magnetic properties are carried mainly by multidomain (MD) primary magnetite grains ranging in size from 20 to 200 mm. The magnetic susceptibilities are generally high, around (5-10) Â 10 À3 SI. The degree of magnetic anisotropy is large, between 1.2 and 1.3. The principal axes of the AMS ellipsoids coincide with those of the finite strain, and the degree of anisotropy broadly correlates with the mineral fabric intensity. This study is the first detailed investigation of magnetic fabrics in migmatites. These preliminary results suggest that the AMS technique is an easy and powerful tool for the petrofabric analysis of migmatites.

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Deformational behaviour of migmatites and problems of structural analysis in migmatite terrains

Cited by 39 publications

References 21 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

The Nature and Origin of Granite

Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites

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