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Hydrothermal breccia textures and processes / R. Cas in Economic geology, Vol. 106 N° 3 (Mai 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 3 (Mai 2011) . - pp. 437-450 Titre : Hydrothermal breccia textures and processes : lisca Bianca Islet, Panarea Volcano, Aeolian Islands, Italy Type de document : texte imprimé Auteurs : R. Cas, Auteur ; G. Giordano, Auteur ; F. Balsamo, Auteur Année de publication : 2011 Article en page(s) : pp. 437-450 Note générale : Géologie Economique Langues : Anglais (eng) Mots-clés : Hydrothermal  system  Panarea  volcano  Italy Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Panarea is a largely submarine to partly subaerial Quaternary lava dome complex-stratovolcano with a long-lived, active, shallow hydrothermal system, located in the Aeolian Islands volcanic arc of southern Italy. The emergent top of the volcano forms a small archipelago, made up of calc-alkaline basaltic andesite to rhyolite lava domes (ca. 150–20 ka). We document the facies outcropping on Lisca Bianca islet, Panarea archipelago, based on grain size, clast fabric, and degree of hydrothermal alteration, identifying coherent facies, boulder breccia facies, cobble breccia facies, pebble breccia facies, and pervasively altered andesite facies (alunite-marcasite-sulfur). The breccias all have ubiquitous jigsaw-fit clast textures, and are variably hydrothermally altered. The breccias are interpreted as hydrothermal breccias and are distinguished from primary volcanic facies based on their distinguishing characteristics. The breccias formed through a cyclical process, involving the following: stage 1: progressive build-up of fluid pressure toward the level of the tensile strength of the host andesite; stage 2: incipient fracturing of the andesite when fluid pressure approaches and then exceeds the tensile strength of the andesite under critical fracturing conditions; stage 3: pervasive fracturing of the host andesite, leading to an increase in permeability as a network of fractures develops; stage 4: declining pressure, with fluid flow rates that lead to infilling and sealing of fractures by natroalunite, thereby reducing permeability, leading to progressive build-up of fluid pressure again, and the beginning of a new cycle. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/cgi/content/abstract/106/3/437 [article] Hydrothermal breccia textures and processes : lisca Bianca Islet, Panarea Volcano, Aeolian Islands, Italy [texte imprimé] / R. Cas, Auteur ; G. Giordano, Auteur ; F. Balsamo, Auteur . - 2011 . - pp. 437-450. Géologie Economique Langues : Anglais (eng) in Economic geology > Vol. 106 N° 3 (Mai 2011) . - pp. 437-450 Mots-clés : Hydrothermal  system  Panarea  volcano  Italy Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Panarea is a largely submarine to partly subaerial Quaternary lava dome complex-stratovolcano with a long-lived, active, shallow hydrothermal system, located in the Aeolian Islands volcanic arc of southern Italy. The emergent top of the volcano forms a small archipelago, made up of calc-alkaline basaltic andesite to rhyolite lava domes (ca. 150–20 ka). We document the facies outcropping on Lisca Bianca islet, Panarea archipelago, based on grain size, clast fabric, and degree of hydrothermal alteration, identifying coherent facies, boulder breccia facies, cobble breccia facies, pebble breccia facies, and pervasively altered andesite facies (alunite-marcasite-sulfur). The breccias all have ubiquitous jigsaw-fit clast textures, and are variably hydrothermally altered. The breccias are interpreted as hydrothermal breccias and are distinguished from primary volcanic facies based on their distinguishing characteristics. The breccias formed through a cyclical process, involving the following: stage 1: progressive build-up of fluid pressure toward the level of the tensile strength of the host andesite; stage 2: incipient fracturing of the andesite when fluid pressure approaches and then exceeds the tensile strength of the andesite under critical fracturing conditions; stage 3: pervasive fracturing of the host andesite, leading to an increase in permeability as a network of fractures develops; stage 4: declining pressure, with fluid flow rates that lead to infilling and sealing of fractures by natroalunite, thereby reducing permeability, leading to progressive build-up of fluid pressure again, and the beginning of a new cycle. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/cgi/content/abstract/106/3/437