Oceanic Spreading Centers

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

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

Underwater eruptions

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

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

Seismic structure of the East Pacific Rise

Mantle structure and melting

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]

Melting at spreading centers

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

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

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