Viscous energy dissipation and strain partitioning in partially molten rocks

Publication Type  Journal Article
Year of Publication  2005
Authors  Holtzman, B. K.; Kohlstedt, D. L.; Morgan, J. P.
Journal Title  Journal of Petrology
Volume  46
Issue  12
Pages  2569-2592
Journal Date  Dec
ISBN Number  0022-3530
Accession Number  ISI:000233414600006
Key Words  melt transport; rheology; self-organization; strain localization; strain partitioning; melt segregation; upwelling mantle; flow; migration; compaction; viscosity; localization; lithosphere; extraction; generation

We develop a steady-state fluid-mechanical analysis describing the effect of strain partitioning on viscous energy dissipation. As observed in experimental studies of shear deformation of partially molten rocks, strain partitions when melt segregates because viscosity is reduced in regions of elevated melt fraction. The equations derived here are based on parameters measured in experiments, describing the evolution of melt distribution and rheological properties. We find that the dissipation depends strongly on the configuration of the melt-rich network of shear zones, including the average angle, volume fraction of melt and amplification of strain rate in the melt-rich bands. Minima in energy dissipation as a function of band angle develop, corresponding to configurations of melt networks that minimize the difference in mean stress between the band and the non-band regions. We propose that the organization of band networks occurs by the interplay between strain localization and viscosity variations associated with melt segregation. The band networks maintain a steady-state angle during shear by continuously pumping melt through the network. The development of strain partitioning in melt-rich networks will modify the energetics of melting and melt transport by efficiently extracting melt and reducing effective viscosity.


985YKTimes Cited:3Cited References Count:36

URL  <Go to ISI>://000233414600006
DOI  DOI 10.1093/petrology/egi065