Interdisciplinary Groups: Interplay between mantle and crustal processes

Moderator: Roger Buck

Participants (list your name here):
    •    Spahr Webb
    •    Chris Russo
    •    Jeff Standish
    •    Scott White
    •    David Graham
    •    Laurent Montesi
    •    Mike Perfit
    •    Adam Goss
    •    Allison Fundis
    •    Hal Johnson
    •    Garrett Ito
    •    Dorsey Wanless
    •    Ian Ridley
    •    Milene Cormier
    •    Danielle Stroup
    •    Dan Curewitz
    •    Robert Weekly
    •    Lowell
    •    Eunseo Choi
    •    Dennis Geist

Discussion topics (list ideas and suggestions here):
    •    Spatial and temporal distributions of geochemical signatures
    •    How do faults influence magma transport?
    •    What controls the width and segmentation of the neovolcanic zone?
    •    The extent to which primary magmas interact with, and are modified by, the crust during ascent and eruption, based on studies at the ISS scale.
    •    Over what temporal and spatial scales do magma compositions change and what do they tell us about magmatic processes.

Discussed the importance of process-driven scientific investigations that integrate targeted observations and quantitative models.

Recent progress in modeling
L. Montesi: Models of melt migration in the mantle toward mid-ocean ridge segments with realistic geometries are being used to address observations of crustal thickness, bathymetry, and gravity near transforms in a range of environments spanning a wide range of spreading rates.

E. Choi and R. Buck: Constraints on mantle viscosity from topographic predictions of 2D models of extension and magmatism. Diking simulated by introducing a pressurized crack, which accommodates some extension but also feeds surface topography to simulate erupted lavas. One study is to use predictions of topography to examine mantle viscosity. With high mantle viscosity (~10^20-10^21 Pas) due to dehydrated mantle, then the topography is unrealistic. Low viscosities are needed for realistic topography.

A. Olive Numerical models of turbulent hydrothermal circulation above a magma lens with strongly temperature-dependent permeability are used to study how fluid convection effects the overlying temperature structure as well as properties/segmentation of the magma lens. Results pertain to the wavelengths of circulation cells, and how they influence temperatures in the melt lens, partial crystallization and even segmentation of the AMC.

T. Crone Poroelastic fluid flow models are being used to constrain permeability in young oceanic crust. Simulations include tidal loading and changes in stress due to poro-elastic response. The phase delay between tidal load at the surface and stress changes in the upper 1.5 km of the crust are sensitive to permeability. Predictions are compared with observations of microseismicity to learn about the permeability structure of the oceanic rust.

B. Lowell: Models of thermal & chemical interaction between hydrothermal fluids & magma. Heat balance between hydrothermal circulation (heat sink) and magmatic heat supply used to estimate the energy balance of the hydrogeologic system. Other models simulate the net effects of two-phase flow to study the evolution of fluid phases in the hydrothermal system (Chlorine, quartz solubility). Other efforts are being done to study the relationship between focused and diffuse flow. Questions discussed include, what is the path of fluid flow and how heat is loss from the magma (is all heat lost right above the magma lens or is it mined by hydrothermal flow along the sides of the magma storage zone over a range of depths)?

J. Conder: Numerical models are being done to study the evidence for along-trench flow from changes in composition and shear-wave splitting directions along the Lau Spreading center. Rapid, along-trench flow of tens of cm/yr is needed to explain the shear-wave splitting variations along Central Lau Spreading Center? Future work to study seismic anisotropy beneath ELSC.

R. Buck, M. Behn, G. Ito: Origin of faulting and large-scale morphology of the mid-ocean ridges. Models now can simulate the interplay between magmatism, faulting, and their interaction through tectono-magmatic cycles. This provides an opportunity for making ties between surface topography with observations of seafloor geology, volcanology, seismic structure in the crust, and petrology.
Buck, W. R., L. L. Lavier, and A. N. B. Poliakov (2005), Modes of faulting at mid-ocean ridges, Nature, 434, 719-723.
Behn, M. D. and G. Ito (2008), Magmatic and tectonic extension at mid-ocean ridges: 1. Controls on fault characteristics, Geochem. Geophys. Geosys., 9, Q09O12, doi:10.1029/ 2008GC001970.
Ito, G. and M. D. Behn (2008), Magmatic and tectonic extension at mid-ocean ridges: 2. Origin of axial morphology, Geochem. Geophys. Geosys. 9, Q08O10, doi:10.1029/ 2008GC001965

S. Carbotte: Evidence from seismic and topographic suggests dike intrusions—not far field extension—are responsible for forming the axial graben at the Juan de Fuca Ridge
Carbotte, S. M., R. S. Detrick, H. A., J. P. Canales, J. Babcock, G. Kent, E. Van Ark, M. Nedimovic, and J. Diebold (2006), Rift topography linked to magmatism at the intermediate spreading Juan de Fuca Ridge, Geology, 34, 209-212, doi:210.113/G21969.1.

Discussion

Construction of the crust, extrusives, dikes, gabbros, Moho transition zone.
How is melt distributed in the lower crust and how does it accrete? (gabbro).