Trench-parallel fast axes of seismic anisotropy due to fluid-filled cracks in subducting slabs

David Healy, Steven M. Reddy, Nicholas E. Timms, Erin M. Gray, Alberto Vitale Brovarone

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

Subducting slabs experience deformation and metamorphism as they descend into the upper mantle. The presence of hydrous minerals gained through the interaction with sea water at mid-ocean ridges, transform faults or the outer rise ensures that dehydration reactions will be important at deeper levels. We describe field evidence for brittle hydrofracture in previously subducted rocks from the Western Alps, with a free aqueous fluid phase produced by dehydration reactions in the host blueschists and serpentinites. The protracted history of dehydration reactions, ductile deformation, fluid flow and brittle vein formation in these rocks implies that fluid-filled cracks are continuously produced within the dehydration window. The presence of abundant fluid-filled cracks at these depths has important implications for the seismic anisotropy generated within slabs, which has largely been overlooked. The effects of fluid-filled crack damage on the elastic properties of a blueschist and serpentinite within the slab at depth have been modelled, and show a significant rotation of the fast axes of P and S1 waves to be trench-parallel for receiving stations in the forearc, above the dehydrating portion of the slab. This model provides an alternative explanation for supra-subduction zone seismic anisotropy that does not require high-stress, high-water conditions, or trench-parallel flow in the supra-subduction zone mantle wedge.

Original languageEnglish
Pages (from-to)75-86
Number of pages12
JournalEarth and Planetary Science Letters
Volume283
Issue number1-4
Early online date25 Apr 2009
DOIs
Publication statusPublished - 15 Jun 2009

Fingerprint

seismic anisotropy
Dehydration
dehydration
trench
slab
slabs
crack
Anisotropy
cracks
Cracks
anisotropy
blueschist
Fluids
fluid
fluids
subduction zone
Transform faults
Earth mantle
Rocks
rocks

Keywords

  • shear wave splitting
  • high pressure metamorphism
  • vein
  • serpentinite
  • dehydration
  • eclogite

Cite this

Trench-parallel fast axes of seismic anisotropy due to fluid-filled cracks in subducting slabs. / Healy, David; Reddy, Steven M.; Timms, Nicholas E. ; Gray, Erin M. ; Vitale Brovarone, Alberto.

In: Earth and Planetary Science Letters, Vol. 283, No. 1-4, 15.06.2009, p. 75-86.

Research output: Contribution to journalArticle

Healy, David ; Reddy, Steven M. ; Timms, Nicholas E. ; Gray, Erin M. ; Vitale Brovarone, Alberto. / Trench-parallel fast axes of seismic anisotropy due to fluid-filled cracks in subducting slabs. In: Earth and Planetary Science Letters. 2009 ; Vol. 283, No. 1-4. pp. 75-86.
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