Title

Mariana melting and thermal structure

Mariana melting and thermal structure

James A. ConderDept. of Earth and Planetary

SciencesWashington University

James A. ConderDept. of Earth and Planetary

SciencesWashington University

Subduction system melting & thermal componentsSubduction system melting & thermal components

From Zyzzy2 on Wikipedia (aka Bob Stern)

backarcbackarc arcarc forearcforearc slabslab

First order thermal controlsFirst order thermal controls

Convergence rate moderate/?

Backarc spreading slow/cold Slab age

old/cold

Geophysical constraints

Geophysical constraints

Wiens, Kelley, and Plank, 2006

Mariana mantle is relatively cool

Mariana mantle is relatively cool

Secondary thermal controlsSecondary thermal controls

Forearc depth extent

2D vs 3D flow 3D/warm?

Temperature-difference gridsfor different numerical modelsTemperature-difference gridsfor different numerical models

Conder, 2005, PEPI

Temp-dep viscosity - isoviscous Yield strength - Temp-dep visc

- Seismicity begins west of Big Blue Seamount

-Shallow seismicity ends at ~55 km depth

Courtesy of Erica Emry

60

40

20

80

Seismicity with depth near Big Blue (18ºN)

serpentinized forearc: receiver functions

serpentinized forearc: receiver functions

Tibi and Wiens, submitted

Yield strengthYield strength

+ serpentine+ serpentine

SSTs Top 350m above wet

basalt solidus

Likely extent of crustal

dewatering

Basalt facies & solidus from Hacker et al., 2003

“…melting of fluid-saturated subducted sediment or basalt in normal, steady-state subduction may be inevitable, rather than impossible.”Kelemen et al., 2003

Kincaid and Griffiths mantle motion

Kincaid & Griffiths, 2003

RollbackRollback

SlabtemperaturesSlabtemperatures

Melting

Decompression meltingDecompression melting + rehydration to 120km+ rehydration to 120km

Wedge melting structureWedge melting structure

Melting

+ rehydration to 200km+ rehydration to 200km+ rehydration to 120km+ rehydration to 120km

Wedge melting structureWedge melting structure

Crustal addition rateCrustal addition rate

Diamalanta et al., 2002Tori-Shima (Izu), 2002

Backarc-Arc relationship

Backarc-Arc relationship

Pagan vs.

Guam

Pagan vs.

Guam

Pagan seismic attenuation structurePagan seismic attenuation structure

Pozgay, 2007

Pagan Backarc Spreading moviePagan Backarc Spreading movie

Pagan melt structure

Pagan melt structure

Backarc-Arc relationship

Backarc-Arc relationship

Pagan vs.

Guam

Pagan vs.

Guam

Guam Backarc Spreading movieGuam Backarc Spreading movie

SummarySummary• Forearc/Slab: Serpentinization of the deep Mariana forearc

mantle extends the decoupling zone defining the forearc, potentially leading to warmer slab surface temperatures and possible slab melting.

• Arc: Melting beneath the Mariana arc may have significant contributions from multiple mechanisms: decompression melting ~20 km3/Myr/km; decomp+flux ~45; decomp+flux+slab <~ 50.

• Backarc: Arc and backarc melting have a history of intermixing with melting loci that become more distinct and less intermingled as spreading matures. Pagan is in the latter stages with distinct melting loci for arc and backarc. Melting loci are less distinct near Guam with more intermixing of melting regimes.

• Forearc/Slab: Serpentinization of the deep Mariana forearc mantle extends the decoupling zone defining the forearc, potentially leading to warmer slab surface temperatures and possible slab melting.

• Arc: Melting beneath the Mariana arc may have significant contributions from multiple mechanisms: decompression melting ~20 km3/Myr/km; decomp+flux ~45; decomp+flux+slab <~ 50.

• Backarc: Arc and backarc melting have a history of intermixing with melting loci that become more distinct and less intermingled as spreading matures. Pagan is in the latter stages with distinct melting loci for arc and backarc. Melting loci are less distinct near Guam with more intermixing of melting regimes.

Anatahan, N. Mariana, 2003