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Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec Arc

Matthew I. Leybourne, Ulrich Schwarz-Schampera, Cornel E. J. de Ronde, Edward T. Baker, Kevin Faure, Sharon L. Walker, David A. Butterfield, Joseph A. Resing, John E. Lupton, Mark D. Hannington, Harold L. Gibson, Gary J. Massoth, Robert W. Embley, William W. Chadwick, Malcolm R. Clark, Christian Timm, Ian J. Graham and Ian C. Wright
Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec Arc
Economic Geology and the Bulletin of the Society of Economic Geologists (December 2012) 107 (8): 1669-1694

Abstract

The Monowai volcanic center is located at the midpoint along the approximately 2,530-km-long Tonga-Kermadec arc system. The Monowai volcanic center is comprised of a large elongate caldera (Monowai caldera area approximately 35 km (super 2) ; depth to caldera floor 1,590 m), which has formed within an older caldera some 84 km (super 2) in area. To the south of this nested caldera system is a large composite volcano, Monowai cone, which rises to within approximately 100 m of the sea surface and which has been volcanically active for the past several decades. Mafic volcanic rocks dominate the Monowai volcanic center; basalts are the most common rock type recovered from the cone, whereas basaltic andesites are common within the caldera. Hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone: (1) the summit of the cone, (2) low-temperature venting (<60 degrees C; Mussel Ridge) on the southwestern wall of the caldera, and (3) a deeper caldera source with higher temperature venting that has yet to be observed. The cone summit plume shows large anomalies in pH (a shift of -2.00 pH units) and delta (super 3) He (< or =358%), and noticeable H (sub 2) S (up to 32 mu m), and CH (sub 4) (up to 900 nm). The summit plume is also metal rich, with elevated total dissolvable Fe (TDFe up to 4,200 nm), TDMn (up to 412 nm), and TDFe/TDMn (up to 20.4). Particulate samples have elevated Fe, Si, Al, and Ti consistent with addition to the hydrothermal fluid from acidic water-rock reaction. Plumes extending from approximately 1,000- to 1,400-m depth provide evidence for a major hydrothermal vent system in the caldera. The caldera plume has lower values for TDFe and TDMn, although some samples show higher TDMn concentrations than the cone summit plume; caldera plume samples are also relatively gas poor (i.e., no H (sub 2) S detected, pH shift of -0.06 pH units, CH (sub 4) concentrations up to 26 nm). The composition of the hydrothermal plumes in the caldera have higher metal contents than the sampled vent fluids along Mussel Ridge, requiring that the source of the caldera plumes is at greater depth and likely of higher temperature. Minor plumes detected as light scattering anomalies but with no (super 3) He anomalies down the northern flank of the Monowai caldera most likely represent remobilization of volcanic debris from the volcano flanks. We believe the Monowai volcanic center is host to a robust magmatic-hydrothermal system, with significant differences in the style and composition of venting at the cone and caldera sites. At the cone, the large shifts in pH, very high delta (super 3) He% values, elevated TDFe and TDFe/TDMn, and the H (sub 2) S- and CH (sub 4) -rich nature of the plume fluids, together with elevated Ti, P, V, S, and Al in hydrothermal particulates, indicates significant magmatic volatile + or - metal contributions in the hydrothermal system coupled with aggressive acidic water-rock interaction. By contrast, the caldera has low TDFe/TDMn in hydrothermal plumes; however, elevated Al and Ti contents in caldera particulate samples, combined with the presence of alunite, pyrophyllite, sulfide minerals, and native sulfur in samples from Mussel Ridge suggest past, and perhaps recent, acid volatile-rich venting and active Fe sulfide formation in the subsurface.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 107
Serial Issue: 8
Title: Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec Arc
Affiliation: GNS Science, Lower Hutt, New Zealand
Pages: 1669-1694
Published: 201212
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 70
Accession Number: 2013-010685
Categories: Economic geology, geology of ore depositsIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus. incl. 6 tables, sketch maps
S36°00'00" - S26°00'00", W180°00'00" - W175°00'00"
S47°30'00" - S34°30'00", E166°30'00" - E178°30'00"
Secondary Affiliation: Bundesanstalt fuer Geowissenschaften und Rohstoffe, DEU, GermanyNOAA, USA, United StatesUniversity of Washington, USA, United StatesUniversity of Ottawa, CAN, CanadaLaurentian University, CAN, CanadaOregon State University, USA, United StatesNational Institute of Water and Atmospheric Research, NZL, New ZealandUniversity of Southampton, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201308
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