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| Titel |
The influence of isotropic and anisotropic crustal permeability on hydrothermal flow at fast spreading ridges |
| VerfasserIn |
Jörg Hasenclever, Lars Rüpke, Sonja Theissen-Krah, Jason Morgan |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135831
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| Publikation (Nr.) |
 EGU/EGU2016-16742.pdf |
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| Zusammenfassung |
| We use 3-D numerical models of hydrothermal fluid flow to assess the magnitude and spatial
distribution of hydrothermal mass and energy fluxes within the upper and lower oceanic crust.
A better understanding of the hydrothermal flow pattern (e.g. predominantly on-axis above
the axial melt lens vs. predominantly off-axis and ridge-perpendicular over the entire
crustal thickness) is essential for quantifying the volume of oceanic crust exposed to
high-temperature fluid flow and the associated leaching and redistribution of economically
interesting metals.
The initial setup of all 3-D models is based on our previous 2-D studies (Theissen-Krah et
al., 2011), in which we have coupled numerical models for crustal accretion and
hydrothermal fluid flow. One result of these 2-D calculations is a crustal permeability field
that leads to a thermal structure in the crust that matches seismic tomography data at the East
Pacific Rise. Our reference 3-D model for hydrothermal flow at fast-spreading ridges predicts
the existence of a hybrid hydrothermal system (Hasenclever et al., 2014) with two interacting
flow components that are controlled by different physical mechanisms. Shallow on-axis flow
structures develop owing to the thermodynamic properties of water, whereas deeper off-axis
flow is strongly shaped by crustal permeability, particularly the brittle–ductile transition.
About ∼60% of the discharging fluid mass is replenished on-axis by warm (up to 300oC)
recharge flow surrounding the hot thermal plumes. The remaining ∼40%, however,
occurs as colder and broader recharge up to several kilometres away from the ridge
axis that feeds hot (500–700oC) deep off-axis flow in the lower crust towards the
ridge. Both flow components merge above the melt lens to feed ridge-centred vent
sites.
In a suite of 3-D model calculations we vary the isotropic crustal permeability to quantify
its influence on on-axis vs. off-axis hydrothermal fluxes as well as on along-axis
hydrothermal activity. We also explore the effect of anisotropic permeability that is likely to
be a feature of the diking region above the melt lens where the repeated emplacement of
meter-size dikes should lead to higher permeability in vertical and along-ridge direction and
to lower permeability across the ridge. We further study the effect of along-ridge
depth-variations of the axial melt lens on the distribution of hydrothermal vent sites. |
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