1. Oceanic Spreading Centers

2. Structure of a fast spreading center (East Pacific Rise ~ 10 cm/yr)

3. Detailed structure of the Axial Magma Lens Carbotte et al., 2013

4. Underwater eruptions

5. Slow Spreading Centers Mid-Atlantic Ridge (~ 2.5 cm/yr) Chapman conference, 2010

6. Dynamics of Spreading Blackman et al., 1996 Passive flow produces broad zone of high T, upwelling and melt production Active (Buoyancy-driven) flow produces focused zone of melt production

7. Seismic structure of the East Pacific Rise

8. Mantle structure and melting

9. Melt porosity and transport Node Tubule The seismic effect of melt is a function of melt porosity and geometry; not the rate of melting or extent of melting The effect of melt on velocity and Q is not well quantified by experiments Melt porosity and geometry also control the permeability Experimental evidence suggests melt permeability is high even for 1% melt; melt should be efficiently extracted Geochemical evidence from U-series disequalibria indicates that melt porosity is small M. Spiegelman website Transport by high porosity channels? Melt forms interconnected network even at low porosity Zhu et al [2011]

10. Melting at spreading centers

11. Mantle temperature controls on mid ocean ridges Ridge Depth Crustal Thickness Langmuir et al 1992

12. Significant variations between active backarcs – Lau slowest, and Mariana fastest Variations largely confined to the “ melt producing ” region - 40 to 100 km depth Mantle temperature variations between active backarcs Seismic Structure Major Element systematics Large solid symbols are basin averages (with error bars) Data from Kelley et al [2006], dry (< 0.65 wt % in melt) samples only Na 2 O and FeO corrected to equilibrium with Fo 90 olivine Wiens, Kelley, Plank, EPSL, 2006

13. Backarc spreading centers: Subducted water signature Tivey et al [2012] Variable slab influence on backarc spreading centers Eastern Lau Spreading Center