Manioc : Portail | resultats 1 - 20 pour la recherche: island arc

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : If the net flux to the island arc crust is primitive arc basalt, the evolved composition of most arc magmas entails the formation of complementary thick ultramafic keels at the root of the island arc crust. Dunite, wehrlite, and Cr-rich pyroxenite from the Jijal complex, constituting the Moho transition zone of the Kohistan paleo–island arc (northern Pakistan), are often mentioned as an example of high-pressure cumulates formed by intracrustal fractionation of mantle-derived melts, which were later extracted to form the overlying mafic crust. Here we show that calculated liquids for Jijal pyroxenites-wehrlites are strongly rare earth element (REE) depleted and display flat or convex-upward REE patterns. These patterns are typical of boninites and are therefore unlike those of the overlying mafic crust that have higher REE concentrations and are derived from light rare earth element (LREE)–enriched melts similar to island arc basalt. This observation, along with the lower 208Pb/204Pb and 206Pb/204Pb ratios of Jijal pyroxenites-wehrlites relative to gabbros, rejects the hypothesis that gabbros and ultramafic rocks derive from a common melt via crystal fractionation. In the 208Pb/204Pb versus 206Pb/204Pb diagram, ultramafic rocks and gabbros lie on the same positive correlation, suggesting that their sources share a common enriched mantle 2 (EM2) signature but with a major depleted component contribution for the ultramafic rocks. These data are consistent with a scenario whereby the Jijal ultramafic section represents a Moho transition zone formed via melt-rock reaction between subarc mantle and incoming melt isotopically akin to Jijal gabbroic rocks. The lack in the Kohistan arc of cogenetic ultramafic cumulates complementary to the evolved mafic plutonic rocks implies either (1) that a substantial volume of such ultramafic cumulates was delaminated or torn out by subcrustal mantle flow from the base of the arc crust in extraordinarily short time scales (0.10–0.35 cm/yr), or (2) that the net flux to the Kohistan arc crust was more evolved than primitive arc basalt.
ISSN: 0091-7613

hal-00406688
https://hal.archives-ouvertes.fr/hal-00406688
DOI : 10.1130/G23675A.1

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Emancipation in the West Indies : a six months's tour in Antigua, Barbadoes, and Jamaica, in the year 1837
Auteur(s) : Thome, James Armstrong (1813-1873) Kimball, Joseph Horace (1813-1838)
Auteurs secondaires : American Anti-Slavery Society
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Strain modes within the forearc, arc and back-arc domains in the Izu (Japan) and Taiwan arc-continent collisional settings
Auteur(s) : Lallemand, Serge
Auteurs secondaires : Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)

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Histoire généralle des Indes occidentales, et Terres-Neuves qui jusques à présent ont esté descouvertes, augmentee en ceste cinquiesme edition de la description de la nouvelle Espagne, & de la grande ville de Mexicque, autrement nommee, Tenuctilan: composee en espagnol par François Lopez de Gomara, & traduite en françois par le S. de Genillé Mart. Fumée
Auteur(s) : López de Gómara, Francisco (1511-1566)
Auteurs secondaires : Fumée Genillé, Martin (1540-1590)
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Negro slavery, or A view of some of the more prominent features of that state of society, as it exists in the United States of America and in the colonies of the West Indies, especially in Jamaica
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Narrative of a five years' expedition against the revolted negroes of Surinam in Guiana, on the wild coast of South America from the year 1772 to 1777, elucidating the history of that country and describing its productions... with an account of the Indians of Guiana and negroes of Guinea... Tome 2
Auteur(s) : Stedman, John Gabriel (1744-1797)
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Une histoire des colonies anglaises aux Antilles: de 1649 à 1660 : thèse présentée à la faculté des lettres de l'Université de Paris
Auteur(s) : Watts, Arthur Pryor (18..-19..)
Auteurs secondaires : Université de Paris (1896-1968). Faculté des lettres
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L'Amérique angloise, ou Description des isles et terres du roi d'Angleterre, dans l'Amérique. Avec de nouvelles cartes de chaque isle & terres
Auteur(s) : Blome, Richard (16..-1705)
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The history, civil and commercial, of the British colonies in the West Indies. Volume II
Auteur(s) : Edwards, Bryan (1743-1800)
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