Mélange

Mélange
Melange from Narooma, Australia

In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies. Large-scale melanges formed in active continental margin settings generally consist of altered oceanic crustal material and blocks of continental slope sediments in a sheared mudstone matrix. The mixing mechanisms in such settings may include tectonic shearing forces, ductile flow of a water-charged or deformable matrix (such as serpentinite), sedimentary action (such as slumping, gravity-flow, and olistostromal action), or some combination of these. Some larger blocks of rock may be as much as 1 km across. Smaller-scale localized melanges may also occur in shear or fault zones, where coherent rock has been disrupted and mixed by shearing forces.

Examples include the Franciscan Formation along the Coast Ranges of central and northern California and the Bay of Islands ophiolite complex in Newfoundland. The Gwna Mélange in the UK extends through Anglesey and the Llŷn Peninsula onto Bardsey Island in North Wales. The Northern Palawan melange distributed in Minilog Island, west coast of Inabamalaki Island, west coast of El NIdo town; Cudugman Point on Bacuit Bay, in the islands of the Cuyo Group of Islands. It consists of a jumble of various rock types contained in a matrix of grey-green slaty mudstone and siltstone.

Before the advent of plate tectonics in the early 1970s, it was difficult to explain mélanges in terms of known geological mechanisms. A particularly troubling paradox was the occurrence of blueschist blocks (low temperature and high pressure metamorphic rocks) in direct contact with graywacke (a coarse sandstone with lithic fragments) that was deposited in a sedimentary environment. Mélange occurrences are associated with thrust faulted terranes in orogenic belts. A mélange is formed in the accretionary wedge above a subduction zone. The ultramafic ophiolite sequences which have been obducted onto continental crust are typically underlain by a mélange. Both tectonic and sedimentary processes can form mélange. Olistostromes are mélanges formed by gravitational sliding under water, with accumulation of the flow as a semi fluid body without bedding planes.

Etymology

The term mélange in English language is a loan word from French, used to mean mixture of disparate components (what would be referred to in the sciences as a heterogeneous mixture). Its derivation, and therefore to some extent its connotation, is similar to Mêlée [1][2]. Mélange is the modern form of the Old French noun meslance, which comes from the infinitive mêler, meaning "to mix".

References

  • Blatt, Harvey and Robert Tracy (1996), Petrology, 2nd ed., Freeman (pp. 178, 514), ISBN 0-7167-2438-3.
  • Hsu, K.J., 1970, Preliminary report and geologic guide to Franciscan melanges of the Morro Bay - San Simeon area, San Luis Obispo County, California: California Geological Survey Special Publication 35.
  • Raymond, L.A., 1984, Classification of melanges: Geological Society of America, Special Paper 198, p. 7-20.
  • British Geological Survey: "Geology of the country around Aberdaron," HMSO, London (1993), ISBN 011 884487 3

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  • mélange — [ melɑ̃ʒ ] n. m. • 1538 n. f.; meslinge 1380; de mêler 1 ♦ Action de mêler, de se mêler. Faire, opérer un mélange, le mélange de divers éléments. ⇒ alliage, alliance, assemblage, association, combinaison, fusion, mixtion, 1. union. Doser les… …   Encyclopédie Universelle

  • mélangé — mélange [ melɑ̃ʒ ] n. m. • 1538 n. f.; meslinge 1380; de mêler 1 ♦ Action de mêler, de se mêler. Faire, opérer un mélange, le mélange de divers éléments. ⇒ alliage, alliance, assemblage, association, combinaison, fusion, mixtion, 1. union. Doser… …   Encyclopédie Universelle

  • Melange — Mélange Un mélange est une association de deux ou plusieurs substances solides, liquides ou gazeuses qui n interagissent pas chimiquement. Le résultat de l opération est une préparation aussi appelée mélange. Les substances mélangées sont… …   Wikipédia en Français

  • Melange — Sf Mischung , österr. Milchkaffee per. Wortschatz fremd. Erkennbar fremd (18. Jh.) Entlehnung. Entlehnt aus frz. mélange, Abstraktum zu frz. mêler mischen (meliert).    Ebenso nndl. melange, ne. mélange, nfrz. mélange. ✎ DF 2 (1942), 97.… …   Etymologisches Wörterbuch der deutschen sprache

  • Melange — may refer to: Mélange, a geological breccia above a subduction zone environment Wiener Melange, a Viennese specialty coffee, similar to cappuccino Melange (fictional drug) or spice, a fictional drug in Frank Herbert s Dune series This… …   Wikipedia

  • Melange — tambien es una especialidad vienesa de cafe, similar al cappuccino. Melange es el nombre ficticio de una droga especia central a la Saga de Dune, una serie de novelas de Ciencia Ficcion creada por Frank Herbert. El sabor de la especia melange es… …   Enciclopedia Universal

  • mélangé — mélangé, ée (mé lan jé, jée) part. passé de mélanger. Différents ingrédients mélangés ensemble. •   Buvez encore avec plaisir les derniers verres du vin trop mélangé de cette vie ; soyez heureux, si on peut l être, VOLT. Lett. Richelieu, 6 juin… …   Dictionnaire de la Langue Française d'Émile Littré

  • melange — (n.) 1650s, from Fr. mélange (15c.), from mêler to mix, mingle, from O.Fr. mesler (see MEDDLE (Cf. meddle)) …   Etymology dictionary

  • mélange — /fr. meˈlã1/ [vc. fr., dal v. mêler «mescolare»] s. m. inv. 1. (di colori) mescolanza, misto 2. filato di vari colori FRASEOLOGIA caffè mélange, caffè viennese …   Sinonimi e Contrari. Terza edizione

  • melange — ► NOUN ▪ a varied mixture. ORIGIN French mélange, from mêler to mix …   English terms dictionary

  • Mélange — (fr., spr. Melangsch), Mischung, Gemengsel; Mélanges, Schriften vermischten Inhalts …   Pierer's Universal-Lexikon

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