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Does strong slab-parallel flow exist in the mantle wedge?. Thanks to: David Abt, Catherine Rychert, Mariela Salas, Laura Martin, Alexis Walker (Brown University) Geoff Abers, Laura Auger, Ellen Syracuse, Terry Plank (Boston University) J. Marino Protti, Victor Gonzalez - PowerPoint PPT Presentation
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Does strong slab-parallel flow exist in the mantle wedge?
Thanks to: David Abt, Catherine Rychert, Mariela Salas, Laura Martin, Alexis Walker (Brown University)Geoff Abers, Laura Auger, Ellen Syracuse, Terry Plank (Boston University)J. Marino Protti, Victor Gonzalez(OVSICORI, Universidad Nacional)Wilfried Strauch, Pedro Perez, Allan Morales(INETER)MARGINS
Kneller et al. (2005)
Lassak et al. (2006)
Fischer et al. (2000)
Examine:• Local S splitting• Paths outside wedge corner
Where is strongly 3D flow required?
Terms:
2D = wedge corner flow coupled to surface plate motions
3D = strong slab-parallel flow
Local S splitting fast directions relative to arc strike
Region fore-arc beyond arc• Ryukyu (Long & van der Hilst, 2006) //• Cascadia (Currie et al., 2004) //• Honshu (Nakajima & Hasegawa, 2005) // normal• Aleutians (Yang et al., 1995) //• Izu Bonin (Anglin & Fouch, 2005) variable• N. New Zealand (Morley et al., 2006) // normal & N• Tonga (Smith et al., 2001) // rotation to normal• Marianas (Pozgay et al., in prep.) // rotation to normal• Alaska (Christensen & Abers, in prep.) normal //• Kamchatka (Levin et al., 2004) normal //• S. America (Polet et al., 2000) variable• S. America (Anderson et al., in prep.) // • Nicaragua/Costa Rica (Abt et al., in prep.) normal? // + complexity
HonshuNakajima and Hasegawa (2004)
Consistent with 2D corner flow With B-fabric in wedge corner
TongaSmith et al. (2001)
Arc-// in wedge corner, BUT gradual rotation to arc-normal in back-arcNot consistent with melt-free 2D corner flow
After Turner and Hawkesworth (1998)
Rose Diagrams - plotted at station
Spatial Averaging
Marianas - Pozgay et al. (in prep.)
Arc-// in wedge corner, but stays arc-// beyond arcNot consistent with melt-free 2D corner flow
Kamchatka - Levin et al. (2004)
Arc-normal in wedge corner, arc-// beyond arcNot consistent with melt-free 2D corner flow
Chile/ArgentinaAnderson et al. (in prep.)
Arc-// beyond arcNot consistent with simple 2D corner flow
Costa Rica & Nicaragua - TUCAN ExperimentAbt et al. (in prep.)
Costa Rica & Nicaragua - TUCAN ExperimentAbt et al. (in prep.)
Costa Rica & Nicaragua - TUCAN ExperimentAbt et al. (in prep.)
Inversion: • model: 70% single xtal olivine, 30% single xtal opx• parameters: olivine a-axis azimuth, plunge & strength • split waveform for each path in successive blocks• calculate synthetic splitting at surface• invert residuals (data - synthetic splitting) using iterative damped least-squares method
Inversion: • model: 70% single xtal olivine, 30% single xtal opx• parameters: olivine a-axis azimuth, plunge & strength • split waveform for each path in successive blocks• calculate synthetic splitting at surface• invert residuals (data - synthetic splitting) using iterative damped least-squares method
Inversion: • model: 70% single xtal olivine, 30% single xtal opx• parameters: olivine a-axis azimuth, plunge & strength • split waveform for each path in successive blocks• calculate synthetic splitting at surface• invert residuals (data - synthetic splitting) using iterative damped least-squares method
SKS splitting indicates additional arc-// fast anisotropy below and farther into back-arc
Hypotheses for anisotropy sampled by local S
Beyond arc:• 2D corner flow + melt fabric• 3D flow around slab edge (or tear)• Flow along slab driven by changes in slab dip• Upwelling/downwelling beneath arc (Behn & Hirth)
Fore-arc:• Direction controlled by flow +/- B-fabric• But watch for upper plate, slab contributions
2D corner flow
Cagnioncle et al. (2006)
2D corner flow + melt fabric
Cagnioncle et al. (2006)
Oriented melt with arc-// strike (melt LPO effects not required)
• Marianas, Tonga, C. America require broader melting zones
• C. America SKS?
3D flow around slab edge
Kincaid et al. (2006)
In cross section is corner flow
Trench parallel Partial trench parallel
Kincaid et al. (2006)
No rollback
Rollback:No more corner flow
Slab translates
Kincaid et al. (2006)
3D flow around slab edge
Challenge:
Need slab-// flow over 500 km from slab edge, close to slab- enhance with slab dip changes
- enhance with low viscosities in mantle wedge
Supported by:
Geochemical evidence for flow around corner
After Turner and Hawkesworth (1998)
Tonga Costa Rica/Nicaragua
Herrstrom et al. (1995), Abratis & Woerner (2001), Feigenson (2004) - signature of Galapagos hotspot
3D flow around slab edge
Mehl et al. (2003)
Challenge:
Need slab-// flow over 500 km from slab edge, close to slab- enhance with slab dip changes
- enhance with low viscosities in mantle wedge
Supported by:
Geochemical evidence for flow around corner
In situ LPO data from Talkeetna arc
Upwellings or downwellings beneath arc
Behn and Hirth(this meeting)
Upwellings or downwellings beneath arc
Behn and Hirth(this meeting)
• Hard to match width of arc-// fast zone
• May explain 3D variations in anisotropy resolved in C. America
Feedbacks
Broader melt zones required in flow, T, melting models
If anisotropy = 2D corner flow + melt
If anisotropy = flow parallel to slab
Need 3D flow, T, melting models
velocity & attenuation images
Feedbacks
Broader melt zones required in flow, T, melting models
If anisotropy = 2D corner flow + melt
If anisotropy = flow parallel to slab
Need 3D flow, T, melting models
velocity & attenuation images
Marianas
C. America
Tonga
Conder and Wiens (2006)
Feedbacks
Broader melt zones required in flow, T, melting models
If anisotropy = 2D corner flow + melt
If anisotropy = flow parallel to slab
Need 3D flow, T, melting models
velocity & attenuation images
V, Q (T, volatiles, melt, grain size, dislocations)
V, Q (T, volatiles, melt, grain size, dislocations)