The action of water films at A-scales in the Earth; implications for the Nankai subduction system

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doi: 10.1016/j.epsl.2016.12.042
Author(s): Brown, Kevin M.; Poeppe, Dean; Josh, Matthew; Sample, James; Even, Emilie; Saffer, Demian; Tobin, Harold; Hirose, Takehiro; Kulongoski, J. T.; Toczko, Sean; Maeda, Lena
Integrated Ocean Drilling Program, Expedition 348 Scientists
Author Affiliation(s): Primary:
University of California at San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States
Other:
Commonwealth Scientific and Industrial Research Organisation, Australia
Northern Arizona University, United States
Osaka City University, Japan
Pennsylvania State University, United States
University of Wisconsin at Madison, United States
Japan Agency for Marine-Earth Science and Technology, Japan
U. S. Geological Survey, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.463, p.266-276. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendix. 41 refs.; illus., incl. sect.
Summary: Water properties change with confinement within nanofilms trapped between natural charged clay particles. We investigated nanofilm characteristics through high-stress laboratory compression tests in combination with analyses of expelled pore fluids. We utilized sediments obtained from deep drilling of the Nankai subduction zone at Site C0002 of the Integrated Ocean Drilling Program (IODP). We show that below 1-2 km, there should be widespread ultrafiltration of migrating fluids. Experiments to >∼100 MPa normal compression collapse pores below a few ion monofilm thicknesses. A reduction towards a single condensing/dehydrating ion monofilm occurs as stresses rise >100-200 MPa and clay separations are reduced to <10-20 A. Thus, porosity in high mineral surface area systems only consists of double and single monofilms at depths below a few km leaving little room for either bulk water or the deep biosphere. The resulting semipermeable properties result in variable segregation of ions and charged isotopes and water during active flow. The ultrafiltration and ion dehydration processes are coupled in that both require the partial immobilization of ions between the charged clay surfaces. The general effect is to increase salinities in residual pore fluids at depth and freshen fluids expelled during consolidation. Cessation of nanofilm collapse to a near constant ∼17 A below 2 km depth at Nankai supports the contention for the onset of substantial geopressuring on the deeper seismogenic fault. The properties of monofilm water, thus, have considerable implications for the deep water properties of subduction zones generating major tremor and Mw 8+ earthquakes. Indeed, the combined effects of advective flow, ultrafiltration, diffusion, and diagenesis could provide a unifying explanation for the origins of overpressuring and pore water geochemical signals observed in many natural systems.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 18 Geophysics, Solid-Earth; Alkali metals; Boreholes; Clay minerals; Compression; Consolidation; Dehydration; Expedition 348; Experimental studies; Fluid pressure; Hydration; IODP Site C0002; Integrated Ocean Drilling Program; Ions; Isotopes; Kumano Basin; Metals; NanTroSEIZE; Nankai Trough; Nanofilms; North Pacific; Northwest Pacific; O-18; Overpressure; Oxygen; Pacific Ocean; Pore water; Porosity; Potassium; Salinity; Sheet silicates; Silicates; Sodium; Stable isotopes; Subduction zones; Thickness; Ultrafiltration; West Pacific
Coordinates: N331800 N331801 E1363801 E1363800
Record ID: 2017037301
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands