Water-rock interactions in volcaniclastic sediments across the Izu-Bonin-Mariana Arc; comparison of sites U1438, U1201, 792 and 793.

Author(s): van der Land, Cees; Sena, C.; Loudin, L. C.; Zhang Zhaohui
Author Affiliation(s): Primary:
Newcastle University, Civil Engineering and Geosciences, United Kingdom
University of Aveiro, Portugal
University of New Hampshire, United States
Nanjing University, China
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The rapid deposition of volcanogenic sediments, highly susceptible to alteration by seawater has led to distinct pore water geochemical profiles throughout the sedimentary basins of the Izu-Bonin-Mariana Arc. Drilling at Site U1438, in the Amami-Sankaku Basin, recovered a 1300 m thick volcaniclastic section overlain by a 160 m thick section of sediments largely devoid of volcanic input. At Site U1438, 67 porewater samples were analyzed onboard for salinity, pH, oxidation-reduction potential and major and trace element concentrations. Here we focus on the depth profiles of elements which were also analyzed at Sites U1201, 792 and 793. Chloride and Bromide concentrations display similar trends; near constant in the upper 160 m and a linear downward increase to maximum concentrations from 600 mbsf onwards. This increase is likely caused by uptake of water by secondary minerals, resulting in chloride and bromide enrichment in the porewater. Calcium and magnesium porewater concentrations display opposite trends in the upper 440 m; the first increases from 11.5 to 140 mM, and the latter decreases from 53 mM until its depletion in the porewater. Leaching of Ca from the glass-rich sediments and underlying igneous basement are potential sources for Ca in the porewater, while Mg, Na and K presumably replace Ca through cation-exchange. Compared to Site U1438, similar trends of major elements concentration in the pore water were observed at the nearby Sites U1201 (serpentine mud volcano in the forearc of the Mariana subduction system), 792 and 793 (both in the Izu-Bonin forearc sedimentary basin). However, differences in depositional rates, thickness and age of the sedimentary basins, geothermal gradients and the influence of serpentine mud flows, have led to distinct pore water geochemical profiles.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Expedition 351; IODP Site U1201; IODP Site U1438; Integrated Ocean Drilling Program; Izu-Bonin Arc; Leg 126; Mariana Islands; Marine sediments; Micronesia; North Pacific; Northwest Pacific; ODP Site 792; ODP Site 793; Ocean Drilling Program; Oceania; Pacific Ocean; Philippine Sea; Sediments; Volcaniclastics; West Pacific
Coordinates: N305457 N322359 E1405317 E1395039
N322355 N322359 E1402249 E1402246
N310619 N310621 E1405217 E1405215
Record ID: 2015065266
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