Microtomography of Partially Molten Rocks: Three-Dimensional Melt Distribution in Mantle Peridotite

Abstract

The permeability of the upper mantle controls melt segregation beneath spreading centers. Reconciling contradictory geochemical and geophysical observations at ocean ridges requires a better understanding of transport properties in partially molten rocks. Using x-ray synchrotron microtomography, we obtained three-dimensional data on melt distribution for mantle peridotite with various melt fractions. At melt fractions as low as 0.02, triple junctions along grain edges dominated the melt network; there was no evidence of an abrupt change in the fundamental character of melt extraction as melt fraction increased to 0.2. The porosity of the partially molten region beneath ocean ridges is therefore controlled by a balance between viscous compaction and melting rate, not by a change in melt topology.

The influence of source heterogeneity on the U–Th–Pa–Ra disequilibria in post-glacial tholeiites from Iceland

“…Since the Iceland lavas show evidence for compositional variation created within melt channels (Maclennan et al, 2007;Stracke et al, 2003b;Maclennan, 2008b;Stracke and Bourdon, 2009;Koornneef et al, 2012), a dynamic melting model where melts do not re-equilibrate with their surrounding matrix appears most appropriate for interpreting the U-series data in Icelandic rocks Kokfelt et al, 2003;Bourdon et al, 2005Bourdon et al, , 2006Prytulak and Elliott, 2009;Stracke et al, 2003aStracke et al, , 2006Stracke and Bourdon, 2009). Moreover, recent experiments show that melts form interconnected melt networks at small degrees of melting (Zhu et al, 2011), suggesting that channelized melt transport may already be established during the initial stages of partial melt-ing. The dynamic melting model, developed by McKenzie (1985), assumes that melts produced in the upwelling mantle 'escape' the solid residue after a critical threshold porosity is reached, with no further chemical interaction between the solid and melt (channelled melt flow).…”

Composition of the Oceanic Crust

“…As melt fraction increases, the melt will eventually spread along grain edges, forming an interconnected network (e.g., Zhu et al, 2011). Once melt fraction reaches 0.02-3%, depending on interfacial free energies, permeability increases rapidly and the melt will be expelled upward by a combination of buoyancy, melting rate, and compaction (Von Bargen and Waff, 1986;Wark et al, 2003;Zhu et al, 2011).…”

Kinetics of melting in peridotite from volume strain measurements

“…Longer time will promote both chemical and textural equilibrium. Studies of melt-solid texture suggests that liquids tend to stabilize at triple junctions (Bussod and Christie, 1991;Faul et al, 2004;Jackson et al, 2006;von Bargen and Waff, 1986;Zhu et al, 2011) with some melt at grain interfaces. We have reported the evolution of the texture in (Du et al, 2014).…”