International Ocean Discovery Program; Expedition 376 preliminary report; Brothers arc flux; 5 May-5 July 2018

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doi: 10.14379/iodp.pr.376.2019
Author(s): de Ronde, Cornel E. J.; Humphris, Susan E.; Höfig, Tobias W.; Brandl, Philipp A.; Cai Lanlan; Cai Yuanfeng; Caratori Tontini, Fabio; Deans, Jeremy R.; Farough, Aida; Jamieson, John W.; Kolandaivelu, Kannikha; Kutovaya, Anna; Labonté, Jessica M.; Martin, Andrew J.; Massiot, Cécile; McDermott, Jill M.; McIntosh, Iona M.; Nozaki, Tatsuo; Pellizari, Vivian H.; Reyes, Agnes G.; Roberts, Stephen; Rouxel, Olivier; Schlicht, Lucy E. M.; Seo, Jung Hun; Straub, Susanne M.; Strehlow, Karen; Takai, Ken; Tanner, Dominique; Tepley, Frank J., III; Zhang, Chao
International Ocean Discovery Program, Expedition 379 Scientists, College Station, TX
Author Affiliation(s): Primary:
GNS Science, Marine Geoscience, New Zealand
Other:
Woods Hole Oceanographic Institution, United States
Texas A&M University, United States
GEOMAR-Helmholtz Centre for Ocean Research Kiel, Germany
Xiamen University, China
Nanjing University, China
University of Southern Mississippi, United States
Kansas State University, United States
Memorial University of Newfoundland, Canada
Virginia Polytechnic Institute and State University, United States
Rheinisch-Westfälische Technische Hochschule Aachen, Germany
Texas A&M University-Galveston, United States
Cardiff University, United Kingdom
Lehigh University, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Universidade de Sao Paulo, Brazil
University of Southampton, United Kingdom
University of Hawaii at Manoa, United States
University of Bremen, Germany
Inha University, South Korea
Lamont-Doherty Earth Observatory, United States
University of Wollongong, Australia
Oregon State University, United States
Leibniz University of Hannover, Germany
Source: Preliminary Report - International Ocean Discovery Program, Vol.376, 49p. Publisher: International Ocean Discovery Program, College Station, TX, United States. ISSN: 2372-9562
Note: In English. 44 refs.
Summary: Volcanic arcs are the surface expression of magmatic systems that result from the subduction of mostly oceanic lithosphere at convergent plate boundaries. Arcs with a submarine component include intraoceanic arcs and island arcs that span almost 22,000 km on Earth's surface, the vast majority of which are located in the Pacific region. Hydrothermal systems hosted by submarine arc volcanoes commonly contain a large component of magmatic fluid. This magmatic-hydrothermal signature, coupled with the shallow water depths of arc volcanoes and their high volatile contents, strongly influences the chemistry of the fluids and resulting mineralization and likely has important consequences for the biota associated with these systems. The high metal contents and very acidic fluids in these hydrothermal systems are thought to be important analogs to numerous porphyry copper and epithermal gold deposits mined today on land. During International Ocean Discovery Program (IODP) Expedition 376 (5 May-5 July 2018), a series of five sites was drilled on Brothers volcano in the Kermadec arc. The expedition was designed to provide the missing link (i.e., the third dimension) in our understanding of hydrothermal activity and mineral deposit formation at submarine arc volcanoes and the relationship between the discharge of magmatic fluids and the deep biosphere. Brothers volcano hosts two active and distinct hydrothermal systems: one seawater influenced and the other affected by magmatic fluids (largely gases). A total of 222.4 m of volcaniclastics and lavas was recovered from the five sites drilled, which include Sites U1527 and U1530 in the Northwest (NW) Caldera seawater-influenced hydrothermal field; Sites U1528 and U1531 in the magmatic fluid-influenced hydrothermal fields of the Upper and Lower Cones, respectively; and Site U1529, located in a magnetic low that marks the West (W) Caldera upflow zone on the caldera floor. Downhole logging and borehole fluid sampling were completed at two sites, and two tests of a prototype turbine-driven coring system (designed by the Center for Deep Earth Exploration [CDEX] at Japan Agency for Marine-Earth Science and Technology [JAMSTEC]) for drilling and coring hard rocks were conducted. Core recovered from all five sites consists of dacitic volcaniclastics and lava flows with only limited chemical variability relative to the overall range in composition of dacites in the Kermadec arc. Pervasive alteration with complex and variable mineral assemblages attest to a highly dynamic hydrothermal system. The upper parts of several drill holes at the NW Caldera hydrothermal field are characterized by secondary mineral assemblages of goethite + opal-A + zeolites that result from low-temperature (<150°C) reaction of rock with seawater. At depth, NW Caldera Site U1527 exhibits a higher temperature (∼250°C) secondary mineral assemblage dominated by chlorite + quartz + illite + pyrite. An older mineral assemblage dominated by diaspore + quartz + pyrophyllite + rutile at the bottom of Hole U1530A is indicative of acidic fluids with temperatures of ∼230°-320°C. By contrast, the alteration assemblage at Site U1528 on the Upper Cone is dominated by illite + natroalunite + pyrophyllite + quartz + opal-CT + pyrite, which attests to high-temperature reaction of rocks with acid-sulfate fluids derived from the disproportionation of magmatic SO2. These intensely altered rocks exhibit extreme depletion of major cation oxides, such as MgO, K2O, CaO, MnO, and Na2O. Furthermore, very acidic (as low as pH 1.8), relatively hot (=247°C) fluids collected at depths of 160, 279, and 313 meters below seafloor (mbsf) in Hole U1528D have chemical compositions indicative of magmatic gas input. In addition, preliminary fluid inclusion data provide evidence for involvement of two distinct fluids: phase-separated (modified) seawater and an ∼360°C hypersaline brine, altering the volcanic rock and potentially transporting metals in the system. The material and data recovered during Expedition 376 provide new stratigraphic, lithologic, and geochemical constraints on the development and evolution of Brothers volcano and its hydrothermal systems. Insights into the consequences of the different types of fluid-rock reactions for the microbiological ecosystem elucidated by drilling at Brothers await shore-based studies.
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; Boreholes; Brothers Volcano; Cores; Dacites; Expedition 376; Hydrothermal alteration; Hydrothermal conditions; Hydrothermal vents; IODP Site U1528; IODP Site U1529; IODP Site U1530; IODP Site U1531; Igneous rocks; International Ocean Discovery Program; Island arcs; Kermadec Islands; Lava; Metasomatism; Mineral assemblages; Ocean floors; Pacific Ocean; South Pacific; Submarine volcanoes; Volcanic rocks; Volcaniclastics; Volcanoes; Water-rock interaction; West Pacific Ocean Islands
Coordinates: S345200 S345200 E1790300 E1790300
S345300 S345300 E1790400 E1790400
S345300 S345300 E1790400 E1790400
S345200 S345200 E1790300 E1790300
S345300 S345300 E1790400 E1790400
Record ID: 2019054352
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.