The action of water films at Å-scales in the Earth: Implications for the Nankai subduction system

IODP Expedition 348 Shipboard Party

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

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 Å. 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 Å 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.

Original languageEnglish (US)
Pages (from-to)266-276
Number of pages11
JournalEarth and Planetary Science Letters
Volume463
DOIs
StatePublished - Apr 1 2017

Fingerprint

subduction
Earth (planet)
porosity
ultrafiltration
Ions
ion
Water
clays
Ultrafiltration
fluid
water
fluids
ions
drilling
Fluids
clay
subduction zone
compression
Drilling
tremors

Keywords

  • ion dehydration
  • nanofilms
  • overpressuring
  • pore fluid evolution
  • porosity evolution
  • ultrafiltration

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

The action of water films at Å-scales in the Earth : Implications for the Nankai subduction system. / IODP Expedition 348 Shipboard Party.

In: Earth and Planetary Science Letters, Vol. 463, 01.04.2017, p. 266-276.

Research output: Contribution to journalArticle

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title = "The action of water films at {\AA}-scales in the Earth: Implications for the Nankai subduction system",
abstract = "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 {\AA}. 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 {\AA} 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.",
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author = "{IODP Expedition 348 Shipboard Party} and Brown, {Kevin M.} and Dean Poeppe and Matthew Josh and Sample, {James C} and Emilie Even and Demian Saffer and Harold Tobin and Takehiro Hirose and Kulongoski, {J. T.} and Sean Toczko and Lena Maeda",
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AU - IODP Expedition 348 Shipboard Party

AU - Brown, Kevin M.

AU - Poeppe, Dean

AU - Josh, Matthew

AU - Sample, James C

AU - Even, Emilie

AU - Saffer, Demian

AU - Tobin, Harold

AU - Hirose, Takehiro

AU - Kulongoski, J. T.

AU - Toczko, Sean

AU - Maeda, Lena

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AB - 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 Å. 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 Å 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.

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