Earth’s Deep Water Cycle

Earth’s Deep Water Cycle Suzan van der Lee Northwestern University

Feng et al. (2007); Van der Lee and Wiens (EDWC) mantle wedge seismically slow and wet, dry below?

Rupke et al. (EDWC) Mantle outgassing 90% efficient; at least 10% stays in mantle, and likely more in slab

Song and Helmberger (EDWC) lvz on 410 (red o) right next to “normal” mantle (white o)

Karato et al. (EDWC) melt on 410 from upwelling saturated wadselyite, but…

Predicted melt layer thinner than observed lvz < 7 km wd-->ol transition thickens with increasing H2O at undersaturated conditions Hirschmann et al. (EDWC)

5 4 velocity 0 4 0 5 5 5 0 0 0 5 3 2 1 3 1 2 0 p p m 2 0 0 p p m 5 0 0 p p m 1 0 0 0 p p m Phase transition interval (km) Calculations at D=20 suggest that ol-->wd transition can be very thick at only 0.1 wt % water >25 km (after Wood, 1995)

z z z z z z z z z z z z z z z z z z z z z z z z z z z H H H H H H H H H H H H H H H H H H H H H H H H H H H 5 2 5 5 2 5 5 5 2 5 5 5 5 5 5 2 4 6 2 2 1 6 3 2 7 6 5 7 1 3 5 3 7 4 3 2 2 1 5 4 3 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 = = = = = = = = = = = = = = = = = = = = = = = = = = = f f f f f f f f f f f f f f f f f f f f f f f f f f f 410 410 ) m k ( h t p e d 660 660 Water would thus be an explanation for puzzling receiver functions, but… VSL, Italy PAB, Spain KEG, Egypt

<15 km Hirschmann et al. (EDWC) With D=5 and 0.1 wt % H2O transition would be less than 15 km thick

V low and Q very low in mantle wedge --> water V low, but Q high below 200 km --> warm Conder and Wiens (2006); Roth et al. (1999); Van der Lee and Wiens (EDWC)

Separate effects of water from other effects Shito et al. (EDWC)

Water above 400 km, from upwelling TZ or from slab Still some trade-off btw w and T Shito et al. (EDWC)

Use other seismic measurements to evaluate the relative role of w and T, such as transition-zone discontinuity properties: Smyth and Jacobsen (2006)

Braunmiller et al. (EDWC) TZ thickens but ol-->wd does not: deep SAm mantle dry (or saturated)

Suetsugu et al. (EDWC) Vp and 660: >1 wt % water near slab

410, 520, and Vs: >0.2 wt % water Courtier and Revenaugh (EDWC)

VdLee & Frederiksen (2005) Grand (2002) low Vs: < 1 wt% water low Vs above slab in top of lower mantle

Inoue et al. (EDWC) Experiments show that Shy-B is stable in TZ and cool slab

Komabayashi (EDWC) Calculations show that abc phases are stable throughout upper mantle in cool slab; breakdown occurs in top of lower mantle.

Hydrous TZ likely less dense than dry TZ, and: Water lowers the viscosity by 4-5 orders of magnitude, at least above 300 km. Hydrous mantle can well up and hydrate lithosphere. Karato and Jung (2003); Karato (EDWC)

Deformation model Temperature and water-sensitive yield and thermal-mechanical feedback Mid Atlantic ridge Ocean continent Boundary Sediment loading Seafloor age turned into temperatures 70 km thick Lithosphere cross section shown Regenauer-Lieb et al. (2001)

Regenauer-Lieb et al. (2001) wet rheology dry rheology time 0 km -- lithosphere 100 km -- lithosphere breaks only in wet conditions; subduction of dense lithosphere enabled.

-- 0 km -- continent(N America) continent(N America) subducting plate(Atlantic?) subducting plate(Farallon) -- 660 km -- Connecting past and future episodes of subduction 200-300 m.y.

Connecting past and future episodes of subduction

Present

Deep water cycle may sustain plate tectonics over many Gy. • Water in mantle is detectable in various ways • seismic V from tomography or triplication branches • Q/attenuation • discontinuity depths and properties • More work is needed • mineral physics: elasticity at p, T, and C • seismology: benchmarking, denser data (USArray!) Conclusions

Earth’s Deep Water Cycle