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Crustal magnetization of Brothers volcano, New Zealand, measured by autonomous underwater vehicles: / F. Caratori Tontini in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1571-1581 Titre : Crustal magnetization of Brothers volcano, New Zealand, measured by autonomous underwater vehicles: : geophysical expression of a submarine hydrothermal system Type de document : texte imprimé Auteurs : F. Caratori Tontini, Auteur ; B. Davy, Auteur ; Cornel E. J. de Ronde, Auteur Année de publication : 2013 Article en page(s) : pp. 1571-1581 Note générale : economic geology Langues : Anglais (eng) Mots-clés : Near-bottom  magnetic  anomaly;  Brothers  volcano;  crustal  magnetization Résumé : Near-bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at Brothers volcano, southern Kermadec arc, New Zealand. Crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields, one of which was unknown prior to our surveys. The magnetization pattern is consistent with a model of discrete, individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids. Differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1571.short [article] Crustal magnetization of Brothers volcano, New Zealand, measured by autonomous underwater vehicles: : geophysical expression of a submarine hydrothermal system [texte imprimé] / F. Caratori Tontini, Auteur ; B. Davy, Auteur ; Cornel E. J. de Ronde, Auteur . - 2013 . - pp. 1571-1581. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1571-1581 Mots-clés : Near-bottom  magnetic  anomaly;  Brothers  volcano;  crustal  magnetization Résumé : Near-bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at Brothers volcano, southern Kermadec arc, New Zealand. Crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields, one of which was unknown prior to our surveys. The magnetization pattern is consistent with a model of discrete, individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids. Differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1571.short

Detailed morphology and structure of an active submarine arc caldera / R. W. Embley in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1557-1570 Titre : Detailed morphology and structure of an active submarine arc caldera : Brothers volcano, Kermadec arc Type de document : texte imprimé Auteurs : R. W. Embley, Auteur ; Cornel E. J. de Ronde, Auteur ; S. G. Merle, Auteur Année de publication : 2013 Article en page(s) : pp. 1557-1570 Note générale : economic geology Langues : Anglais (eng) Mots-clés : Brothers  caldera  volcano;  submarine  frontal  arc.  morphology Résumé : A survey of the Brothers caldera volcano (Kermadec arc) with the autonomous underwater vehicle ABE has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity. Brothers volcano has formed between major SW-NE–trending faults within the extensional field of the Havre Trough. Brothers may be unique among known submarine calderas in that it has four active hydrothermal systems, two high-temperature sulfide-depositing sites associated with faulting on the northwestern and western walls (i.e., the NW caldera and W caldera hydrothermal sites, respectively), and gas-rich sites on the summits of the constructional cones that fill most of the southern part of the caldera (i.e., the Upper and Lower cone sites). The 3.0- × 3.4-km caldera is well defined by a topographic rim encompassing ∼320° of its circumference and which lies between the bounds of two outer half-graben–shaped faults in the northwest and southeast sectors. There is not a morphologically well defined continuous ring fault (at the map resolution), although near-vertical scarps are present discontinuously at the base of sections of the wall. The width of the wall varies from <200 m at its southwest portion to ∼750 m on its northern section. The widest part of the wall is its northwest sector, which also has the largest documented area of hydrothermal alteration and where sea-floor magnetization is lowest. In addition to primary northwest-southeast elongation and southwest-northeast structures caused by faulting within the regional back-arc strain field, there are also less well developed west-southwest–north-northeast regional structures intersecting the volcano that is apparent on the ABE bathymetry and at outcrop scale from submersible observations. Asymmetrical trap-door–style caldera collapse is considered a possible mechanism for the formation of the Brothers caldera. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1557.short [article] Detailed morphology and structure of an active submarine arc caldera : Brothers volcano, Kermadec arc [texte imprimé] / R. W. Embley, Auteur ; Cornel E. J. de Ronde, Auteur ; S. G. Merle, Auteur . - 2013 . - pp. 1557-1570. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1557-1570 Mots-clés : Brothers  caldera  volcano;  submarine  frontal  arc.  morphology Résumé : A survey of the Brothers caldera volcano (Kermadec arc) with the autonomous underwater vehicle ABE has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity. Brothers volcano has formed between major SW-NE–trending faults within the extensional field of the Havre Trough. Brothers may be unique among known submarine calderas in that it has four active hydrothermal systems, two high-temperature sulfide-depositing sites associated with faulting on the northwestern and western walls (i.e., the NW caldera and W caldera hydrothermal sites, respectively), and gas-rich sites on the summits of the constructional cones that fill most of the southern part of the caldera (i.e., the Upper and Lower cone sites). The 3.0- × 3.4-km caldera is well defined by a topographic rim encompassing ∼320° of its circumference and which lies between the bounds of two outer half-graben–shaped faults in the northwest and southeast sectors. There is not a morphologically well defined continuous ring fault (at the map resolution), although near-vertical scarps are present discontinuously at the base of sections of the wall. The width of the wall varies from <200 m at its southwest portion to ∼750 m on its northern section. The widest part of the wall is its northwest sector, which also has the largest documented area of hydrothermal alteration and where sea-floor magnetization is lowest. In addition to primary northwest-southeast elongation and southwest-northeast structures caused by faulting within the regional back-arc strain field, there are also less well developed west-southwest–north-northeast regional structures intersecting the volcano that is apparent on the ABE bathymetry and at outcrop scale from submersible observations. Asymmetrical trap-door–style caldera collapse is considered a possible mechanism for the formation of the Brothers caldera. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1557.short

Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera / Matthew I. Leybourne in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1649-1668 Titre : Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera Type de document : texte imprimé Auteurs : Matthew I. Leybourne, Auteur ; Cornel E. J. de Ronde, Auteur ; Richard J. Wysoczanski, Auteur Année de publication : 2013 Article en page(s) : pp. 1649-1668 Note générale : economic geology Langues : Anglais (eng) Mots-clés : sea-floor;  massive  sulfide  mineralization;  Caldera Résumé : Sea-floor imagery, volcanic rock, massive sulfide, and hydrothermal plume samples (δ3He, pH, dissolved Fe and Mn, and particulate chemistry) have been collected from the Rumble II West volcano, southern Kermadec arc, New Zealand. Rumble II West is a caldera volcano with an ∼3-km-diameter summit depression bounded by ring faults with a resurgent central cone. Rocks recovered to date are predominantly mafic in composition (i.e., basalt to basaltic andesite) with volumetrically lesser intermediate rocks (i.e., andesite). On the basis of its size, geometry, volcanic products, and composition, Rumble II West can be classified as a mafic caldera volcano. Rumble II West has a weak hydrothermal plume signature characterized by a small but detectable δ3He anomaly (25%). Time-series light scattering data though, obtained from vertical casts and tow-yos, do show that hydrothermal activity has increased in intensity between 1999 and 2011. Massive sulfides recovered from the eastern caldera wall and eastern flank of the central cone are primarily comprised of barite and chalcopyrite, with lesser sphalerite, pyrite, and traces of galena. The weak hydrothermal plume signal indicates that the volcano is in a volcanic-hydrothermal quiescent stage compared to other volcanoes along the southern Kermadec arc, although the preponderance of barite with massive sulfide mineralization indicates higher temperature venting in the past. Of the volcanoes along the Kermadec-Tonga arc known to host massive sulfides (i.e., Clark, Rumble II West, Brothers, Monowai, Volcano 19, and Volcano 1), the majority (five out of six) are dominantly mafic in composition and all but one of these mafic volcanoes form moderate-size to large calderas. To date, mafic calderas have been largely ignored as hosts to sea-floor massive sulfide deposits. That 75% of the presently known massive sulfide-bearing calderas along the arc are mafic in composition (the dacitic Brothers volcano is the exception) has important implications for sea-floor massive sulfide mineral exploration in the modern oceans and ancient rock record on land. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1649.short [article] Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera [texte imprimé] / Matthew I. Leybourne, Auteur ; Cornel E. J. de Ronde, Auteur ; Richard J. Wysoczanski, Auteur . - 2013 . - pp. 1649-1668. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1649-1668 Mots-clés : sea-floor;  massive  sulfide  mineralization;  Caldera Résumé : Sea-floor imagery, volcanic rock, massive sulfide, and hydrothermal plume samples (δ3He, pH, dissolved Fe and Mn, and particulate chemistry) have been collected from the Rumble II West volcano, southern Kermadec arc, New Zealand. Rumble II West is a caldera volcano with an ∼3-km-diameter summit depression bounded by ring faults with a resurgent central cone. Rocks recovered to date are predominantly mafic in composition (i.e., basalt to basaltic andesite) with volumetrically lesser intermediate rocks (i.e., andesite). On the basis of its size, geometry, volcanic products, and composition, Rumble II West can be classified as a mafic caldera volcano. Rumble II West has a weak hydrothermal plume signature characterized by a small but detectable δ3He anomaly (25%). Time-series light scattering data though, obtained from vertical casts and tow-yos, do show that hydrothermal activity has increased in intensity between 1999 and 2011. Massive sulfides recovered from the eastern caldera wall and eastern flank of the central cone are primarily comprised of barite and chalcopyrite, with lesser sphalerite, pyrite, and traces of galena. The weak hydrothermal plume signal indicates that the volcano is in a volcanic-hydrothermal quiescent stage compared to other volcanoes along the southern Kermadec arc, although the preponderance of barite with massive sulfide mineralization indicates higher temperature venting in the past. Of the volcanoes along the Kermadec-Tonga arc known to host massive sulfides (i.e., Clark, Rumble II West, Brothers, Monowai, Volcano 19, and Volcano 1), the majority (five out of six) are dominantly mafic in composition and all but one of these mafic volcanoes form moderate-size to large calderas. To date, mafic calderas have been largely ignored as hosts to sea-floor massive sulfide deposits. That 75% of the presently known massive sulfide-bearing calderas along the arc are mafic in composition (the dacitic Brothers volcano is the exception) has important implications for sea-floor massive sulfide mineral exploration in the modern oceans and ancient rock record on land. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1649.short

Metallogenesis and mineralization of intraoceanic arcs I: kermadec arc / Cornel E. J. de Ronde in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1521-1525 Titre : Metallogenesis and mineralization of intraoceanic arcs I: kermadec arc : introduction Type de document : texte imprimé Auteurs : Cornel E. J. de Ronde, Auteur ; D. A. Butterfield, Auteur ; M. I. Leybourne, Auteur Année de publication : 2013 Article en page(s) : pp. 1521-1525 Note générale : economic geology Langues : Anglais (eng) Mots-clés : intraoceanic  arcs;  kermadec  arc Résumé : The Kermadec intraoceanic arc marks the southernmost section of the Pacific Ring of Fire in the western Pacific region, a chain of mostly underwater volcanoes that stretches from north of Japan southward to New Zealand. The Kermadec arc, striking for 1,200 km from Monowai volcano to the North Island of New Zealand, represents the southern portion of the contiguous ~2,500-km Kermadec-Tonga arc (Fig. 1; de Ronde et al., 2003). The Kermadec arc is populated by almost 30 volcanic centers comprising single, large caldera or cone volcanoes, or less commonly, groups of relatively smaller cones (de Ronde et al., 2001, 2007; Graham et al., 2008). All of these volcanic centers lie to the west of the Kermadec Ridge in the southern and mid-parts of the arc—by up to 70 km in the case of Rumble II West—then merge with the Kermadec Ridge near the Kermadec islands around 30° S. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1521.extract [article] Metallogenesis and mineralization of intraoceanic arcs I: kermadec arc : introduction [texte imprimé] / Cornel E. J. de Ronde, Auteur ; D. A. Butterfield, Auteur ; M. I. Leybourne, Auteur . - 2013 . - pp. 1521-1525. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1521-1525 Mots-clés : intraoceanic  arcs;  kermadec  arc Résumé : The Kermadec intraoceanic arc marks the southernmost section of the Pacific Ring of Fire in the western Pacific region, a chain of mostly underwater volcanoes that stretches from north of Japan southward to New Zealand. The Kermadec arc, striking for 1,200 km from Monowai volcano to the North Island of New Zealand, represents the southern portion of the contiguous ~2,500-km Kermadec-Tonga arc (Fig. 1; de Ronde et al., 2003). The Kermadec arc is populated by almost 30 volcanic centers comprising single, large caldera or cone volcanoes, or less commonly, groups of relatively smaller cones (de Ronde et al., 2001, 2007; Graham et al., 2008). All of these volcanic centers lie to the west of the Kermadec Ridge in the southern and mid-parts of the arc—by up to 70 km in the case of Rumble II West—then merge with the Kermadec Ridge near the Kermadec islands around 30° S. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/8/1521.extract

Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec arc / H. A. Berkenbosch in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1613-1633 Titre : Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec arc Type de document : texte imprimé Auteurs : H. A. Berkenbosch, Auteur ; Cornel E. J. de Ronde, Auteur ; J. B. Gemmell, Auteur Année de publication : 2013 Article en page(s) : pp. 1613-1633 Note générale : economic geology Langues : Anglais (eng) Mots-clés : submarine  volcano;  black  smoker  chimneys;  Brothers  volcano Résumé : Brothers caldera volcano is a submarine volcano of dacitic composition, located on the Kermadec arc, New Zealand. It hosts the NW caldera vent field perched on the steep slope of the caldera walls and includes numerous, active, high-temperature (max 302°C) chimneys and a greater amount of dead, sulfide-rich spires. Petrographic studies of these chimneys show that three main zones can occur within the chimneys: a chalcopyrite-rich core, surrounded by a sulfate-dominated zone, which is in turn mantled by an external rind of Fe oxides, calcite, and silicates. Four chimney types are identified based on the relative proportions of the chalcopyrite and sulfate layers and the presence or absence of anhydrite. Two are Cu rich, i.e., chalcopyrite-sulfate and chalcopyrite-bornite chimneys, and two are Zn rich, i.e., sphalerite-barite and sphalerite-chalcopyrite. Chimney growth begins with the formation of a sulfate wall upon which sulfides precipitate. Later, zone refining results in a chalcopyrite-rich core with pyrite/marcasite and sphalerite occurring predominantly near the outer margins. In chalcopyrite-bornite chimneys, the chalcopyrite core rapidly loses permeability and limits the thickness of the surrounding sulfate layer. In these chimneys, bornite, chalcocite, and covellite form along the outer margin of the chalcopyrite zone as a result of oxidation by seawater. Zinc-rich chimneys display a more vertical zonation and their growth involves an upward-advancing barite cap followed by chalcopyrite deposition (if present) nearer the base. The vertical zonation and lack of anhydrite in these chimneys also implies that larger chalcopyrite and anhydrite deposits may exist subsea floor. The different chimney types are related to subsea-floor permeability, the amount of fluid mixing that occurs prior to venting, and heterogeneous fluid compositions. The occurrence of specular hematite and Bi or Au tellurides associated with chalcopyrite are consistent with magmatic contributions to the NW caldera vent site. These tellurides are the first gold-bearing phase to be identified in these chimneys, and the Bi-Au association suggests that gold enrichment up to 91 ppm is due to scavenging by liquid bismuth. The presence of tellurides in Brothers chimneys have implications for other telluride-bearing deposits, such those in the Urals. Likewise, other aspects of the mineralogy (i.e., textures) and zonation, including the implied subsea-floor deposition, presented here from an active, undeformed environment can aid in understanding ancient volcanogenic massive sulfide (VMS) deposits that have undergone various degrees of metamorphism. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1613.short [article] Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec arc [texte imprimé] / H. A. Berkenbosch, Auteur ; Cornel E. J. de Ronde, Auteur ; J. B. Gemmell, Auteur . - 2013 . - pp. 1613-1633. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1613-1633 Mots-clés : submarine  volcano;  black  smoker  chimneys;  Brothers  volcano Résumé : Brothers caldera volcano is a submarine volcano of dacitic composition, located on the Kermadec arc, New Zealand. It hosts the NW caldera vent field perched on the steep slope of the caldera walls and includes numerous, active, high-temperature (max 302°C) chimneys and a greater amount of dead, sulfide-rich spires. Petrographic studies of these chimneys show that three main zones can occur within the chimneys: a chalcopyrite-rich core, surrounded by a sulfate-dominated zone, which is in turn mantled by an external rind of Fe oxides, calcite, and silicates. Four chimney types are identified based on the relative proportions of the chalcopyrite and sulfate layers and the presence or absence of anhydrite. Two are Cu rich, i.e., chalcopyrite-sulfate and chalcopyrite-bornite chimneys, and two are Zn rich, i.e., sphalerite-barite and sphalerite-chalcopyrite. Chimney growth begins with the formation of a sulfate wall upon which sulfides precipitate. Later, zone refining results in a chalcopyrite-rich core with pyrite/marcasite and sphalerite occurring predominantly near the outer margins. In chalcopyrite-bornite chimneys, the chalcopyrite core rapidly loses permeability and limits the thickness of the surrounding sulfate layer. In these chimneys, bornite, chalcocite, and covellite form along the outer margin of the chalcopyrite zone as a result of oxidation by seawater. Zinc-rich chimneys display a more vertical zonation and their growth involves an upward-advancing barite cap followed by chalcopyrite deposition (if present) nearer the base. The vertical zonation and lack of anhydrite in these chimneys also implies that larger chalcopyrite and anhydrite deposits may exist subsea floor. The different chimney types are related to subsea-floor permeability, the amount of fluid mixing that occurs prior to venting, and heterogeneous fluid compositions. The occurrence of specular hematite and Bi or Au tellurides associated with chalcopyrite are consistent with magmatic contributions to the NW caldera vent site. These tellurides are the first gold-bearing phase to be identified in these chimneys, and the Bi-Au association suggests that gold enrichment up to 91 ppm is due to scavenging by liquid bismuth. The presence of tellurides in Brothers chimneys have implications for other telluride-bearing deposits, such those in the Urals. Likewise, other aspects of the mineralogy (i.e., textures) and zonation, including the implied subsea-floor deposition, presented here from an active, undeformed environment can aid in understanding ancient volcanogenic massive sulfide (VMS) deposits that have undergone various degrees of metamorphism. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1613.short

Radiometric dating of volcanogenic massive sulfides and associated iron oxide crusts with an emphasis on 226Ra/Ba and 228Ra/226Ra in volcanic and hydrothermal processes at intraoceanic arcs / Robert G. Ditchburn in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

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Sources of chalcophile and siderophile elements in kermadec arc lavas / Christian Timm in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

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Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec arc / Matthew I. Leybourne in Economic geology, Vol. 107 N° 8 (Décembre 2012) 

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