A seismological perspective on fluid transport in the Cascadia subduction zone
Abstract
Cascadia represents an end-member in terms of thermal characteristics for subduction zones. Because it involves one of the youngest and warmest subducted plates on earth, it was predicted that the downgoing plate had to undergo dehydration at unusually shallow depths, yet until recently this hypothesis had not been thoroughly tested. Here, we review seismic imaging results from the past decade showing clearly that along the length of the subduction zone, the subducted crust loses the bulk of its water at depths < 40-50 km as its hydrated metabasalts progressively transform into dry eclogite under increasing pressure and temperature. This depth estimate is supported by geodynamic models, petrological data, and magnetotelluric results, and it contrasts with colder subduction zones where eclogitization is observed at average depths of ~100 km. These results raise interesting questions regarding other observations in the Cascadia subduction zone. First, Cascadia possesses a clearly defined volcanic arc that sits above the ~90 km depth-contour of the subduction interface, which means that some amount of water is entrained at depths greater than that where eclogitization occurs; second, the slab in central and southern Oregon is aseismic despite evidence that it is undergoing dehydration, which suggests that dehydration reactions may not always cause seismicity in the slab.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T12A..06R
- Keywords:
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- 7240 Subduction zones (1207;
- 1219;
- 1240);
- 7270 Tomography (6982;
- 8180);
- 8104 Continental margins: convergent;
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413);
- 8185 Volcanic arcs