Growth and Impact of a Mafic–Silicic Layered Intrusion in the Vinalhaven Intrusive Complex, Maine

SynopsisThe country lying between the head of Loch Ainort and the northern end of the Blaven Range in central Skye forms part of a Tertiary igneous complex. Country rocks in the area are Jurassic sediments. The earliest igneous rocks are basalt lavas which show the effects of thermal metamorphism by a later intrusion of eucrite and gabbro. This latter, which is part of the Blaven mass, has features of a layered intrusion such as igneous lamination, repetition of layers rich in certain minerals and comparable textures. It may be correlated with zones of the Cuillin layered intrusion. The eucrites are cut by a cone sheet swarm. Adjacent to the eucrite is a vent breccia which contains eucrite blocks, is not cut by cone sheets and is, therefore, of later age than the eucrite. The major part of the area under discussion is formed from four granitic ring dykes and a hybrid suite with ring dyke form, all of which belong to the Western Redhills intrusive complex; in addition, part of a fifth granitic ring dyke, which probably belongs to the Eastern Redhills intrusive complex is included in the area. The granites are mainly fayalite-hedenbergite types with a variety of phenocrysts of felspar and features characteristic of high level intrusions such as granophyric texture and varying optical and chemical properties of the felspar indicating higher temperature modifications. Three new chemical analyses of the granites and one of ferrohedenbergitic pyroxene are presented. The granites may be regarded as partial remelts of the underlying basement gneiss and a simple investigation of thermal requirements indicates that the heat necessary for the partial melting could be provided by a mass of basic rock presumed from geophysical evidence to underlie the complex. Various acid and basic minor intrusions in the area are also described.

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The Kunene complex, Angola/Namibia: a composite massif-type anorthosite complex

Geological Magazine ◽

10.1017/s0016756800012371 ◽

1994 ◽

Vol 131 (5) ◽

pp. 579-591 ◽

Cited By ~ 33

Author(s):

Lewis D. Ashwal ◽

David Twist

Keyword(s):

Block Structure ◽

Layered Intrusion ◽

Coarse Grained ◽

Ultramafic Rocks ◽

Intrusive Complex ◽

Grenville Province ◽

Rock Types ◽

Ti Oxides ◽

Field Area ◽

Anorthosite Complex

AbstractThe c. 15000 km2, c. 2 Ga Kunene complex of southern Angola and northern Namibia is one of the world's largest occurrences of anorthositic rocks, rivalled only perhaps by the Lac St Jean massif of the Grenville Province in Quebec. We report here the results of a detailed field and laboratory study of a 100 km2 area in the northern part of the complex. Coarse grained (av. 1–2 cm) anorthosite and leucotroctolite are the predominant rock types, although colour index varies between 0 and 50, averaging about 10. Ultramafic rocks are totally absent. Typical mineralogy is: plagioclase (An57–76) + olivine(Fo64–71) + orthopyroxene(En65–74) + clinopyroxene ± Fe—Ti oxides ± apatite. Textures are dominantly massive, although weak, impersistent, magmatic lamination with nearvertical dip and unsystematic strike is also present. Other magmatic features include plagioclase and orthopyroxene megacrysts, block structure, mortar texture, and anorthositic dykes. Metamorphic effects are minimal or absent. All of these attributes are similar to those found in typical massif-type anorthosites. Since comparable features are present over large areas elsewhere in the complex, we suggest that Kunene should be considered analogous to a large, composite, massif-type anorthositic intrusive complex, rather than to a large, single or composite mafic layered intrusion such as Bushveld, as has been previously suggested or assumed. This interpretation is supported by satellite imagery, which shows the outlines of several individual anorthositic plutons, one of which clearly encompasses our field area.

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Ultramafic-alkaline-carbonatite complexes as a result of two-stage melting of mantle plume: evidence from the mid-paleoproterozoic Tiksheozero intrusion, Northern Karelia, Russia

Доклады Академии наук ◽

10.31857/s0869-56524864460-465 ◽

2019 ◽

Vol 486 (4) ◽

pp. 460-465

Author(s):

E. V. Sharkov ◽

A. V. Chistyakov ◽

M. M. Bogina ◽

O. A. Bogatikov ◽

V. V. Shchiptsov ◽

...

Keyword(s):

Fractional Crystallization ◽

Mantle Plume ◽

Large Igneous Province ◽

Intrusive Complex ◽

Incongruent Melting ◽

Isotopic Data ◽

Two Stage ◽

Similar Composition ◽

Igneous Province ◽

Alkaline Magmas

Tiksheozero ultramafic-alkaline-carbonatite intrusive complex, like numerous carbonatite-bearing complexes of similar composition, is a part of large igneous province, related to the ascent of thermochemical mantle plume. Our geochemical and isotopic data evidence that ultramafites and alkaline rocks are joined by fractional crystallization, whereas carbonatitic magmas has independent origin. We suggest that origin of parental magmas of the Tiksheozero complex, as well as other ultramafic-alkaline-carbonatite complexes, was provided by two-stage melting of the mantle-plume head: 1) adiabatic melting of its inner part, which produced moderately-alkaline picrites, which fractional crystallization led to appearance of alkaline magmas, and 2) incongruent melting of the upper cooled margin of the plume head under the influence of CO2-rich fluids that arrived from underlying zone of adiabatic melting gave rise to carbonatite magmas.

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The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/ggub.v181.5118 ◽

1999 ◽

pp. 103-112

Author(s):

Feiko Kalsbeek ◽

Lilian Skjernaa

Keyword(s):

Intrusive Complex ◽

The South ◽

Original Series ◽

Early Proterozoic ◽

West Greenland ◽

North East ◽

The North ◽

Southern Border ◽

Area North ◽

Igneous Layering

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., & Skjernaa, L. (1999). The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 103-112. https://doi.org/10.34194/ggub.v181.5118 _______________ The 2800 Ma Atâ intrusive complex (elsewhere referred to as ‘Atâ granite’ or ‘Atâ tonalite’), which occupies an area of c. 400 km2 in the area north-east of Disko Bugt, was emplaced into grey migmatitic gneisses and supracrustal rocks. At its southern border the Atâ complex is cut by younger granites. The complex is divided by a belt of supracrustal rocks into a western, mainly tonalitic part, and an eastern part consisting mainly of granodiorite and trondhjemite. The ‘eastern complex’ is a classical pluton. It is little deformed in its central part, displaying well-preserved igneous layering and local orbicular textures. Near its intrusive contact with the overlying supracrustal rocks the rocks become foliated, with foliation parallel to the contact. The Atâ intrusive complex has escaped much of the later Archaean and early Proterozoic deformation and metamorphism that characterises the gneisses to the north and to the south; it belongs to the best-preserved Archaean tonalite-trondhjemite-granodiorite intrusions in Greenland.

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