Borehole Observatories on the Mariana Forearc: A Window Into Dynamic Processes Within a Subduction Channel
Abstract
As the Pacific Plate subducts and warms, fluids trapped in the pores and minerals of the Pacific Plate are liberated. These fluids ascend and chemically react with the overriding Philippine Plate to produce a slurry of serpentinite mud and fluids that are very alkaline (with a pH up to 12.5), yet support microbial life. This slurry sporadically ascends faults west of the Mariana Trench in the Mariana forearc and discharges at the seafloor, producing the largest mud volcanoes on Earth, some spanning 50 km in diameter and several kilometers in height. Thus, the slurry that reaches the seafloor provides a window into processes that occur deep within the subduction channel. During International Ocean Discovery Program (IODP) Exp. 366 material was recovered from three serpentinite mud volcanoes in the Mariana forarc and installed cased boreholes with subsurface screens on each of the summits. These boreholes represent a transect of study sites perpendicular to the trench that provide the foundation for sampling fluids and materials with increasing temperature and pressure within the subduction channel as the Pacific Plate descends.
We are funded to deploy a CORK-Lite in each of the three summit boreholes to provide a structure that will enable the community to collect fluids, conduct in situ experiments, and monitor temporal characteristics to elucidate a range of hydrologic, geochemical, and microbial processes. Planned sampling strategies will test a model of abiotic methane formation in the subduction channel, constrain the extent of serpentinization during the initial stages of subduction, set limits on potential microbial metabolic capabilities, and resolve water-rock reactions and solute sources within the subduction channel. We will also assess the permeability of flow paths within the three serpentinite mud volcanoes, each of which shows a different stage of activity from recent cm-thick serpentinite mud flows to large slump failures with associated debris flows on the flank of seamount. The deployment of CORK-Lites will leave infrastructure available to the international scientific community for a range of geochemical, microbiological, hydrologic, and geophysical studies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V51G0212W
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8185 Volcanic arcs;
- TECTONOPHYSICS;
- 8413 Subduction zone processes;
- VOLCANOLOGY