CTO Annual Meeting, Nov. 8, 2006 An integrated view of subduction zones from geochemistry, seismology, and dynamics Reported by Mike Gurnis

CTO Annual Meeting, Nov. 8, 2006 Emerging threads from CTO studies of subduction Observational controls on slab dip, Carl Tape, M. Gurnis, H. Kanamori & M. Simons Evidence for a Low Velocity Layer above the Japan slab, Min Chen, J. Tromp, D. Helmberger & H. Kanamori Full mass and energy coupling in subduction modeling, Laura Baker, Paula Smith, P. Asimow & M. Gurnis Subduction zone evolution and low viscosity wedges and channels, Vlad Manea & M. Gurnis

CTO Annual Meeting, Nov. 8, 2006 Controls on slab dip inferred from subduction zone parameters Simple view of plate forces predicts that slab dip should increase with plate age (A) and that dip should decrease with convergence velocity (V cmp ) Much of our understanding harks back to Jarrard (1986), a multiple linear regression analysis that has been missing in recent studies A new analysis has been needed: –more, revised data (plate velocities, age of slabs, age of subduction zones) –Multiple linear regression The new multiple regression analysis suggests that: –For intermediate depths (<125km), dip is controlled by A, over-riding plate type, distance to boundary edge, and the age of the subduction zone, but not V cmp. –For deep depths (>125km), dip is controlled by V cmp and the age of the subduction zone, but not A. Carl Tape

CTO Annual Meeting, Nov. 8, 2006 Carl Tape Predicted Observed

CTO Annual Meeting, Nov. 8, 2006 Study of the Japan slab structure Min Chen

CTO Annual Meeting, Nov. 8, 2006 Study of the Japan slab structure Japanese Hi-net array. High sensitivity of a wide & broad array with component stations Compare waveforms to those calculated with many 2-D FDM and 3-D SEM Used 2 deep focus events with simple sources (589 km, Mw=6.4; 492 km, Mw=6.1) Waveforms from tomography models or simple tabular, high velocities slabs do not produce prominent secondary arrivals Min Chen

CTO Annual Meeting, Nov. 8, 2006 Study of the Japan slab structure FD model of SH-waves Min Chen

CTO Annual Meeting, Nov. 8, 2006 Study of the Japan slab structure Low Velocity Layer (LVL) above the slab produces secondary arrivals Polarity reversal of later arriving phases indicates a low velocity waveguide Waveform change is dependent on LVL depth; only depths ~300km fit for all distances Preferred LVL has -14% shear velocity reduction with a thickness of 20 km Tradeoffs between LVL thickness and velocity contrast Deeper than 150 km, layer may be serpentinized peridotite Min Chen

CTO Annual Meeting, Nov. 8, 2006 I. 2-D ConMan variable viscosity thermal flow model solves conservation of mass, energy, and momentum II. pHMELTS (adiabat_1ph) a thermodynamically-based melting and solid equilibration model that takes into account water in both hydrous and nominally-anhydrous minerals, and in melts pHMELTS: Asimow et al. (2004); based on pMELTS (Ghiorso et al., 2002) and with the adiabat_1ph front-end by Smith & Asimow (2005) achieved through an iterative, particle-based feedback mechanism: full coupling between two separate models: initial distribution of 40,000 Lagrangian particles captures steady-state thermal and velocity conditions Laura Baker & Paula Smith

CTO Annual Meeting, Nov. 8, 2006 Laura Baker & Paula Smith

CTO Annual Meeting, Nov. 8, 2006 Southeastern Costa Rica Subduction Zone: 90.0 mm/yr convergence rate, 30 degree slab dip, 15 Ma slab thermal age, 30 km over-riding lithosphere Laura Baker & Paula Smith

CTO Annual Meeting, Nov. 8, km 200 km Laura Baker & Paula Smith

CTO Annual Meeting, Nov. 8, 2006 Subduction zone evolution and low viscosity wedges and channels Vlad Manea

CTO Annual Meeting, Nov. 8, 2006 Low Viscosity Wedges (LVW) versus No LVW Vlad Manea

CTO Annual Meeting, Nov. 8, 2006 Vlad Manea

CTO Annual Meeting, Nov. 8, 2006 Low viscosity channels (LVC) have much the same effects as LVW Vlad Manea

CTO Annual Meeting, Nov. 8, 2006 If the weakening is confined to shallow depths, then slab dip decreases and leads to flat lying subduction Vlad Manea

CTO Annual Meeting, Nov. 8, 2006 Some important points & ideas to pursue Slab dip is not simply controlled by plate age & convergence; subduction zone age may be even more important Low Velocity Layers may be a pervasive feature above slabs and the Japan LVL extends to ~300 km depth The coupling of thermodynamics and fluid dynamics suggest that Low Viscosity Channels (LVCs) can form above slabs through slab dehydration The strength of LVCs can change slab dip The depth of mantle wedge weakening can lead to divergent evolutionary pathways: Shallow LVCs can lead to flat slabs while deep LVW/LVCs to steep slabs

CTO Annual Meeting, Nov. 8, 2006 Extra Slides

CTO Annual Meeting, Nov. 8, 2006 Carl Tape

CTO Annual Meeting, Nov. 8, 2006 Predicted Observed Carl Tape

CTO Annual Meeting, Nov. 8, 2006 Study of the Japan slab structure From Min Chen

CTO Annual Meeting, Nov. 8, 2006 Central Costa Rica Subduction Zone: 87.0 mm/yr convergence rate, 45 degree slab dip, 18 Ma slab thermal age, 30 km over-riding lithosphere Laura Baker & Paula Smith

CTO Annual Meeting, Nov. 8, 2006 Vlad Manea