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Equilibration during mantle melting: a fractal tree model.
1Department of Geology and Geophysics, Woods Hole Oceanographic Institute, Woods Hole, MA 02543, USA.
Summary
Deep mantle melts retain their geochemical signatures by traveling rapidly through fractal magma networks. This fractal transport prevents chemical reequilibration, preserving evidence of deep melting processes.
Area of Science:
- Geochemistry
- Mantle Petrology
- Geophysical Fluid Dynamics
Background:
- Oceanic basalts often display trace element signatures indicative of melting at significant depths where garnet is stable.
- Ascent via porous flow risks obliterating these deep-source geochemical signatures due to reequilibration at shallower mantle depths.
Purpose of the Study:
- To investigate how deep mantle melt geochemical signatures are preserved during ascent.
- To determine if fractal magma transport networks can facilitate rapid melt ascent and minimize reequilibration.
Main Methods:
- Analysis of fractal network properties analogous to natural systems (rivers, vascular systems).
- Modeling magma ascent through a fractal network with conduits combining by twos.
- Calculating scaling of radius and flow velocity with network generation.
Main Results:
- A fractal magma "tree" structure allows for rapid magma transport, minimizing diffusive chemical contact with the host matrix.
- Melts experience limited reequilibration within hundreds of meters of their source in such networks.
- Deep geochemical signatures (<100 km) can be effectively delivered to the surface.
Conclusions:
- Fractal magma networks are crucial for preserving the geochemical signatures of deep mantle melting.
- Rapid ascent through fractal conduits prevents significant chemical alteration, allowing melts to represent local mantle domains.