On the classification of the West Greenland anorthosites

Windley, Brian F.

doi:10.1007/bf01848777

Cited by 9 publications

(10 citation statements)

References 6 publications

(2 reference statements)

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“…Many large crystals, of which plagioclase is the most widespread, occur within coarse-grained metamorpbic mineral assemblages showing a variety of intensities of development of tectonic fabrics. Althougb similar large crystals were formerly tbougbt to be metamorphic porphyroblasts (Windley, 1967), tbey are here considered to be primary igncous erystals because they occur most abundantly wbere thc rocks are least deformed and igneous textures are best prcserved. Some have well developed crystal faces, and coarse-grained metamorphic mineral assemblages can be seen in various stages of growth around tbeie margins and along twin planes (fig.…”

Section: Stratigraphymentioning

confidence: 96%

“…They are most abundant in the Fiskenaesset region of South-West Greenland, where the anorthosite contains chromite layering (Ghisler, 1966). This feature led Windley (1966Windley ( , 1967 to conclude that the anorthosites and associated gabbroic rocks and amphibolites represent metamorphosed gravitystratified igneous rocks, and he called them the Fiskenaesset complex (Windley, 1969(Windley, , 1971.…”

Section: Introductionmentioning

confidence: 99%

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Igneous stratigraphy of Archaean anorthosite at Majorqap qâva, near Fiskenæsset, South-West Greenland

Myers¹

1975

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Majorqap qâva provides one of the best preserved examples of a major group of anorthosites and associated gabbroic rocks which are characterised by extremely calcic plagioclase and are widespread throughout the Archaean complex of Greenland. The anorthosite outcrop is part of a sheet of layered igneous cumulates which were deposited in a number of cycles from magma intruded into basic volcanic rocks. It consists of six major units which in upward succession are: lower gabbro (10 m), ultramafic (30 m), lower leucogabbro (60 m), middle gabbro (40 m), upper leucogabbro (60 m), and anorthosite (200 m). The lower four units are considered to represent sequences of plagioclase-pyroxene, olivine-pyroxene, plagioclase, and plagioclase-pyroxene cumulates respectively, and the upper two units are plagioclase cumulates with intercumulus hornblende and plagioclase respectively. Plagioclase is the most abundant cumulus mineral and extensively occurs as equant crystals 2 to 10 cm in diameter. The anorthosite outcrop is enclosed by gneiss which was derived by deformation from sheetlike granitic intrusions younger than the anorthosite complex. The gneiss was more duetile and partly cushioned the anorthosite complex from the ravages of later deformation and metamorphism by absorbing a greater amount of strain and recrystallisation.

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Section: Stratigraphymentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Igneous stratigraphy of Archaean anorthosite at Majorqap qâva, near Fiskenæsset, South-West Greenland

Myers¹

1975

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“…The Grenville belt of North America (Buddington 1939, Martignole & Schrijver 1970, McLelland & Isachsen 1985 and the anorthosite-granulite associations of western and southern Norway (Kolderup 1935, Barth 1935, Greenland (Windley 1967), Atlantic belt, Brazil (Wernick 1981), Angola, south-west Africa (Vermaak 1981), Mozambique belt, east Africa (Cahen et al 1984), West Australia and Antarctica (Herz 1969) are a few instances. The Grenville belt of North America (Buddington 1939, Martignole & Schrijver 1970, McLelland & Isachsen 1985 and the anorthosite-granulite associations of western and southern Norway (Kolderup 1935, Barth 1935, Greenland (Windley 1967), Atlantic belt, Brazil (Wernick 1981), Angola, south-west Africa (Vermaak 1981), Mozambique belt, east Africa (Cahen et al 1984), West Australia and Antarctica (Herz 1969) are a few instances.…”

Section: Concluding Remarks: the Eastern Ghats Type Metamorphismmentioning

confidence: 99%

“…For anorthosite-massif-granulite associations, such as at Bolangir in the Eastern Ghats, we may consider the following scenario. Variants of the continental rifting model in relation to anorthosites and granulites have been considered by Emslie (1978), Windley (1983) and Sandiford & Powell (1986). These melt fractions would rise into the crustal basement in the form of domed massifs, in response to a slowly developing tendency of the 'supercontinents' to fracture, rift and split apart--starting from the base upwards.…”

Section: Concluding Remarks: the Eastern Ghats Type Metamorphismmentioning

confidence: 99%

P-T -time history and thermal modelling of an anorthosite-granulite interface, Eastern Ghats metamorphic belt, India

Mukherjee

1989

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A pressure-temperature-time synthesis and a thermal model are presented for the anorthosite-massif-granulite interface near Bolangir, Orissa, India: a type area of the Eastern Ghats metamorphic belt. While the anorthosite pluton can be shown to have been forcefully intruded as a schlieren dome into the granulite cover, the calculated mineral equilibria of the interface suggest a P-T convergence at 620-740°C and 4.7-7 kbar and a nearly isobaric cooling in this pressure range under a cratonic overburden between 15 and 25 km. Parameterized model calculations suggest that a noritic anorthosite pluton of 7.5 and 10 km radius with 50% initial crystallinity and a lower crustal contact temperature in the region of 800°C would cool from the initial temperature of 1200°C to 850-900°C in about 20 Ma and then the cooling rate would fall dramatically to the order of 0.75°C Ma 1. Finite difference calculations of the heat conduction from the equilibrated anorthosite-granulite interface suggest that for some combinations of the thermal properties of the medium and the heat generation and uplift rates, boundary conditions based on an initial transient elevated geotherm produce a nearly isobaric cooling path. The initial prograde metamorphism of the granulites, the anorthosite invasion and the final cooling and P-T convergence of the anorthositegranulite interface have resulted in a composite overturned (anticlockwise) Y-shaped P-T-t configuration. It is suggested that this configuration is characteristic of the Eastern Ghats type metamorphic belt, representatives of which seem to be widespread in the Archaean to Proterozoic continental segments of North America, Scandinavia and parts of Africa, Western Australia and Antarctica. In contrast to the Alpine type belts, the Eastern Ghats type belts are much wider and thickly cratonized with low isostatic resilience (low uplift/exhumation rate) and have anorthosite intrusive cores acting as 'exotic' heat sources, resulting in characteristic anticlockwise overturned and forked Yshaped P-T-t loops.

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“…7). The cbromite-layered anortbosite is associated with a series of ultramafic rocks including bypersthene amphibolite, pyroxenite, peridotite and hornblendite (Windley, 1967(Windley, , 1969. Some of the rock types within the ultramafic series may contain sapphirine, corundum, spinel and gamet.…”

Section: Chromium Fiskenaessetmentioning

confidence: 99%