13. Core-Scale Permeability of an Actively Venting, Felsic-Hosted Hydrothermal System: the PACMANUS Hydrothermal Field1

L.B. Christiansen2 and G.J. Iturrino3


Permeability of the ocean crust is one of the most crucial parameters for constraining submarine fluid flow systems. Active hydrothermal fields are dynamic areas where fluid flow strongly affects the geochemistry and biology of the surrounding environment. There have been few permeability measurements in these regions, especially in felsic-hosted hydrothermal systems. We present a data set of 38 permeability and porosity measurements from the PACMANUS hydrothermal field, an actively venting, felsic hydrothermal field in the eastern Manus Basin. Permeability was measured using a complex transient method on 2.54-cm minicores. Permeability varies greatly between the samples, spanning over five orders of magnitude. Permeability decreases with both depth and decreasing porosity. When the alteration intensity of individual samples is considered, relationships between depth and porosity and permeability become more clearly defined. For incompletely altered samples (defined as >5% fresh rock), permeability and porosity are constant with depth. For completely altered samples (defined as <5% fresh rock), permeability and porosity decrease with depth. On average, the permeability values from the PACMANUS hydrothermal field are greater than those in other submarine environments using similar core-scale laboratory measurements; the average permeability, 4.5 x 10–16 m2, is two to four orders of magnitude greater than in other areas. Although the core-scale permeability is higher than in other seafloor environments, it is still too low to obtain the fluid velocities observed in the PACMANUS hydrothermal field based on simplified analytical calculations. It is likely that core-scale permeability measurements are not representative of bulk rock permeability of the hydrothermal system overall, and that the latter is predominantly fracture controlled.

1Christiansen, L.B., and Iturrino, G.J., 2004. Core-scale permeability of an actively venting, felsic-hosted hydrothermal system: the PACMANUS hydrothermal field. In Barriga, F.J.A.S., Binns, R.A., Miller, D.J., and Herzig, P.M. (Eds.), Proc. ODP, Sci. Results [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/193_SR/202/202.htm>. [Cited YYYY-MM-DD]

2U.S. Geological Survey, 345 Middlefield Road, MS 421, Menlo Park CA 94025, USA. lchristi@usgs.gov

3Borehole Research Group, Lamont-Doherty Earth Observatory, Columbia University, PO Box 1000, 61 Route 9W, Palisades NY 10964, USA.

Initial receipt: 4 May 2003
Acceptance: 18 June 2004
Web publication: 1 September 2004
Ms 193SR-202