Themicrostructurewasstudiedon three orthogonal sections. The microstructural shape analysis suggests an axial fabric which is confirmedbytexture analysis. Commonly, anorthosites form at the tops of modally graded layers on the scale of several meters up to 100 meters or more. Grain size (typically <1 cm) is characteristically smaller than the massif-type or Archean anorthosites, and textures vary from orthocumulates with tabular crysts of plagioclase to adcumulates having equant polygonal grains.
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From theFiskenæsset complex, W. Greenland. Myers (1985) Stratigraphy and structure of the Fiskenæsset complex, West Greenland.Grønl. Geol.Unders. Bull 150. Photograph courtesy John Myers. Winter (2001) An Introduction toIgneous and Metamorphic Petrology. Prentice Hall.
3.2- Les roches des terres lunaires. Une anorthosite à structure grenue rapportée par la mission Apollo 17, on y observe, des feldspaths gris d'anorthite et des 25 Jun 2020 The zone is essentially a homoclinal, neritic layered series, but one which varies from pristine igneous cumulate textures in some places to highly. Anorthosite /ænˈɔːrθəsaɪt/ is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar, with a minimal mafic component.
2019-07-31 · The gabbro, leucogabbro, and anorthosite units of the sill largely retain their primary igneous textures and minerals, REE and HFSE compositions, and Sm–Nd and Pb isotope signatures. These geochemical and petrographic data indicate that these units of the Bird River Sill crystallised from a hydrous, Ca- and Al-rich tholeiitic magma that fractionated from a hydrous primitive arc tholeiitic Request PDF | Neutron diffraction pole figures of geological anorthosite textures | Texture investigations on geological anorthosite specimens with the triclinic plagioclase-type structure have 310 KOLKER AND LINDSLEY: LATE PLUTON IN LARAMIE ANORTHOSITE COMPLEX texture. Mafic clots resembling those in Maloin MSY have been observed in a Quebea quartz mangerite, interpreted by Philpotts (1981) as segregations of immiscible Fe-rich melt.
Spinifex texture is commonly said to result from extremely fast cooling, but recent research points instead to a steep thermal gradient, in which olivine conducts heat so rapidly that its crystals grow as wide, thin plates instead of its preferred stubby habit. osti.gov journal article: lunar anorthosite 15415: texture, mineralogy, and metamorphic history. blastoporphyritic texture deﬁned by antiperthitic plagioclase phenocrysts set in a well recrystallized ﬁne-grained mosaic of Fe-rich orthopyroxene Fe-rich clinopyroxene, ilmenite with or without fay-alitic olivine. The proportion of ferromagnesian minerals increases from anorthosite to ferrodiorite through leuconorites L'anorthosite est une roche ignée intrusive formée de 90% ou plus de feldspath plagioclase et 10% ou moins de minéraux mafiques comme le pyroxène, l'olivine, l'ilménite et la magnétite. L'anorthosite a communément une texture grenue, souvent pegmatitique. Some of the rock at this location remains strong and competent, but much of it has a brittle crumbly or chalky texture as weathering has begun the process of breaking it down into clay. Many of the anorthosite samples returned by astronauts from the Moon have a similar crumbly texture, not because of weathering by water but due to impact shock and shattering by meteorite bombardment.
A wet anorthosite deformed at dry conditions (T ~675-700°C) was dynamically recrystallised. Continuous bands of recrystallised grains developed a texture yet
20 nov. 2012 2.6 Textures observées dans la Suite anorthositique de Vallant . 2.13 Texture porphyroclastique des plagioclases dans une anorthosite
Compositions (An(50+10)), textures (lathy plagioclase) and settings (emplaced into continental rather than oceanic crust) effectively distinguish Proterozoic from
Dans l'Anorthosite (gabbro très riche en plagioclase) d'Ankafotia au Sud de (en "Lumière Naturelle") montre que la texture coronitique est polyminérale. Sedimentation structures, microscopic textures and the phase petrology provide conclusive evidence of the igneous origin of the rocks and of the crystal
A coarse-grained crystalline rock consisting mostly of calcic plagioclase (>90%, usually labradorite) with. Roche magmatique plutonique hololeucocrate, à texture grenue, composée de 80 à 90 % de plagioclases (andésine, labrador, bytownite) et d'un peu de
L'anorthosite est une roche magmatique de structure phanéritique, composée principalement Elles se distinguent des anorthosites protérozoïques par leur texture et leur composition minéralogique. Leur trait le plus caractéristique
7 May 1971 Nearly monomineralic anorthosite, with plagioclase Anso.
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9). Cognate anorthosite inclusions also occur in other plume-related ocean-island basalts such as at Hawaii, and in island-arc volcanic rocks such as those in Japan and the Lesser Antilles. Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic 2017-06-18 Figure 20-1a.
Abstract. Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a
The dominant texture is ‘Nodular’ troctolite, in which amoeboid olivine oikocrysts 10–20 cm in diameter are spaced 20–30 cm apart within a matrix of anorthosite ( Woussen et al., 1988; Figs 1 and 2 ). The oikocrysts consist of a single or possibly a few olivine crystals with abundant chadocrysts of plagioclase.
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There are two 2010-01-01 · Free Online Library: Igneous structure and texture of the ~1.3 Ga Hosenbein anorthosite pluton (Nain, Labrador) and implications for the crystallization of massif-type anorthosite.(Report) by "Atlantic Geology"; Earth sciences Crystal structure Case studies Models Crystallization Research Crystals Structure Magma Natural history Plutonic rocks Observations Properties The textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite. Such textures have been quantified in a troctolite–anorthosite from the Proterozoic Lac-St-Jean anorthosite complex, Canada.
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The exploitation of anorthosite for industrial The rock type is anorthosite, a cumulate rock made mostly of plagioclase. Cumulate rocks typically have the same minerals about the same size. In this case, grain textures look somewhat annealed, possibly because of deformation and annealing when it was still very hot. Stillwater Complex, Montana. Plane/cross-polarized light, field width is 6 mm. STW-37 Anorthite is a rare member of the Feldspar group.Italian Localities include Monte Somma, Mount Vesuvius; Val Schiesone, Sondrio; and Val Di Fassa, Trento. Japan produces excellent crystals thinly coated with a dark layer of lava at Miyaki Jima (Miyaki Island), Tokyo Prefecture.