Geochemical constraints on fluid-rock reactions, fluid sources, and flow pathways along the IODP Expedition 375 transect; Northern Hikurangi Margin

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Author(s): Solomon, Evan A.; Huepers, Andre; Luo Min; Malie, Pierre R.; Saffer, Demian M.; Torres, Marta E.; Wallace, Laura M.; Petronotis, Katerina E.; Barnes, Philip; Pecher, Ingo Andreas; LeVay, Leah J.
International Ocean Discovery Program, Expedition 375 Scientists
Author Affiliation(s): Primary:
University of Washington, School of Oceanography, Seattle, WA, United States
University of Bremen, Germany
Shanghai Ocean University, China
Université Montpellier, France
Pennsylvania State University, United States
Oregon State University, United States
University of Texas at Austin, United States
International Ocean Discovery Program, United States
National Institute of Water & Atmospheric Research, New Zealand
University of Auckland, New Zealand
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Changes in physical and mineralogical properties with depth as sediments are subducted and the associated evolution of pore fluid pressure, composition, and fluid flow are intimately linked to fault slip behavior at subduction zones. Pore water solute concentrations and isotope ratios are sensitive tracers of fluid-rock reactions, fluid sources, and flow pathways, and their depth profiles provide constraints on the rates of diagenetic reactions and the formation of authigenic minerals. Thus, pore water geochemistry is an essential tool for investigating the physical, chemical, and hydrologic conditions associated with shallow slow slip at subduction zones. Here, we present a synthesis of the IODP Expedition 375 geochemical results to date. The pore water geochemical profiles along the drilling transect reflect a range of processes including organic matter diagenesis, authigenic carbonate mineral precipitation, volcanic ash/silicate mineral diagenesis, fluid flow, and non-steady state sedimentation. Site U1518 penetrates an active splay fault near the deformation front. Despite observations of elevated heat flow in this region, there is no clear geochemical evidence of modern fluid flow along the splay fault. Pore water chemical profiles in the hanging wall sediments are characteristic of early diagenesis of organic matter and volcanic ash. There is a clear repetition of the diagenetic sequence observed in the hanging wall below the fault zone in the footwall. The repetition of the early diagenetic sequence in the footwall indicates recent underthrusting and active displacement along the fault. Modeling of the diffusional solute gradients across the fault zone is in progress, and estimates of the time of underthrusting and the average slip rate will be presented. Site U1520 sampled the sedimentary sequence on the incoming Pacific Plate and Site U1519 penetrated a mid-slope sedimentary basin. Stacked Z-shaped profiles of alkalinity, ammonium, and bromide at Sites U1520 and U1519 clearly indicate non-steady state sedimentation and the rapid, repeated burial of older early diagenetic sequences at both sites. Evidence for contemporary lateral fluid flow within the Cretaceous volcaniclastic sediments and in situ pore water freshening under the low geothermal gradient at Site U1520 will also be discussed.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Crust; Geochemistry; Hikurangi Margin; Hikurangi Trough; IODP Site U1518; IODP Site U1519; IODP Site U1520; International Ocean Discovery Program; Lithosphere; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Plate tectonics; South Pacific; Southwest Pacific; Subduction; Subduction zones; West Pacific
Coordinates: S385133 S385133 E1785346 E1785346
S384338 S384338 E1783654 E1783651
S385810 S385810 E1790756 E1790756
Record ID: 2019050450
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