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Numerical simulation of cool hydrothermal processes in the upper volcanic crust beneath a marine sediment pond: North Pond, North Atlantic Ocean

Citation

Price, Adam N.; Fisher, Andrew T.; Stauffer, Philip H.; Gable, Carl W. (2022), Numerical simulation of cool hydrothermal processes in the upper volcanic crust beneath a marine sediment pond: North Pond, North Atlantic Ocean, Dryad, Dataset, https://doi.org/10.7291/D1G67P

Abstract

Low temperature hydrothermal systems hosted in the volcanic oceanic crust are responsible for ~20% of Earth's global heat loss. Marine sediment ponds comprise an important type-setting on young ridge flanks where hydrothermal circulation advectively extracts lithospheric heat, but the nature of coupled fluid-heat transport in these settings remains poorly understood. Here we present coupled (fluid-heat) numerical simulations of ocean crustal hydrogeology in and below North Pond, a sediment pond on ~8 Ma seafloor of the North Atlantic Ocean. Two- and three-dimensional simulations show that advective transport beneath North Pond is complex and time-varying, with multiple spatial and temporal scales, consistent with seafloor and borehole observations. A unidirectional, single-pass flow system is neither favored nor needed to match the spatial distribution of seafloor heat flux through North Pond sediments. When the permeability of the crustal aquifer is relatively high (10-10 to 10-9 m2), simulations can replicate much of the observed variability and suppression of seafloor heat flux, and can explain basement overpressures and transient perturbations in pressure and temperature in the upper volcanic crust. Simulation results can also help explain heterogeneity in pore fluid chemistry and microbiology in the crust. Although driven by the same physical processes, the dynamics of hydrothermal circulation below North Pond are different from those seen on "discharge-dominated" ridge flanks, where the permeability and exposed area of isolated basement outcrops control the extent of regional heat extraction.

Methods

These data are input files for the numerical simulation code Finite Element Heat and Mass Transfer Code (FEHM; https://fehm.lanl.gov/). This dataset complements the publication titled "Numerical Simulation of Cool Hydrothermal Processes in the Upper Volcanic Crust Beneath a Marine Sediment Pond: North Pond, North Atlantic Ocean" published in the Journal of Geophysical Research: Solid Earth. The data here are model input files for the numerical code Finite Element Heat and Mass Transfer Code (FEHM) for the simulation of coupled fluxes of fluid and heat beneath the sedimented pond, North Pond in the North Atlantic Ocean. These files represent the characteristic simulation of permeability for each of the resulting aquifer thicknesses simulated 100, 300, 600, and 1000m.

Usage Notes

The following zipped file contains input files for FEHM (https://fehm.lanl.gov) numerical model. Please visit https://github.com/lanl/FEHM for buildFile and source code.

The file structure is as follows:

   |-2D
   |---aq300
   |-----p10
   |-----p11
   |-----p9
   |---aq600
   |-----p10
   |-----p11
   |-----p9
   |-3D
   |---aq100
   |-----p9
   |---aq1k
   |-----p10
   |---aq300
   |-----p10
   |-----p11
   |-----p12
   |-----p9
   |---aq600
   |-----p10
   |-----p11
   |-----p12
   |-----p9
   |---cond

Where the uppermost directory contains either 2- or 3-dimensional simulation geometries. The next subdirectory denotes the aquifer thickness simulated (aq1k = aquifer thickness 1000m, etc..) and one directory for a simulation with conductive physics. The next subdirectories denote the aquifer permeability simulated (p9 = aquifer permeability 10E-9).

Within those directories are the following input files:
*.area - List of external nodes and cross-sectional areas in xyz.
*.cond - Thermal conductivity by node in xyz.
*.dat - Main FEHM control file. Used to specify files to read, boundary conditions, output type and frequency, and runtime parameters.
*.fehm - List of node numbers and coordinates, followed by element numbers and constituent nodes in each.
*.files - control file
*.flow - Flow file for use with FLOW macro, setting depth-dependent hydrostatic boundary condition at mesh top.
*.hflx - Heatflux file for use with HFLX macro, setting heatflow input at mesh bottom.
*.iap - Initial ambient pressure file, list of hydrostatic pressure by node based on ambient thermal conditions.
*.ini - Initial conditions used for simulation.
*.perm - Permeability by node in xyz.
*.ppor - Compressibility by node (scalar).
*.rock - Grain density, specific heat, and porosity by node.
*.stor - Node volume and mesh connectivity data for all nodes.
*.zone - List of zones and all constituent nodes. Includes materials and any additional specified zones (faults, conduits, etc.).
*_material.zone - List of material zones and all constituent nodes.
*_outside.zone - List of zones describing external surfaces of the mesh, and all constituent nodes.

The format of all of these input files can be found in the FEHM user manual (http://www.lanl.gov/orgs/ees/fehm/docs/FEHM_UM_V3.3.0.pdf)

Finally, file: "nist120-1800.out" is a lookup table for density, viscosity, enthalpy, and respective derivatives with respect to temperature and pressure for pure water at pressures 20-180 MPa and temperatures 0 - 1800ºC based on NIST STEAM tables (https://webbook.nist.gov/chemistry/fluid/).

The data columns are as follows:
Column 1 = Pressure (MPa)
Column 2 = Temperature (ºC)
Column 3 = Density (g/m3)
Column 4 = ∆Density / ∆Pressure
Column 5 = ∆Density / ∆Temperature
Column 6 = Enthalpy / 1000
Column 7 =  ∆Enthalpy / ∆Pressure / 1000
Column 8 =  ∆Enthalpy / ∆Temperature / 1000
Column 9 =  Viscosity
Column 10 =  ∆Viscosity / ∆Pressure
Column 11 =  ∆Viscosity / ∆ Temperature

This file is symbolically linked to all the above directories as "run.wpi". FEHM will not run without this symbolic link.

Funding

National Science Foundation, Award: OIA-0939564

National Science Foundation, Award: OCE-1924384