| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Journal of Petrology | Volume 45 | Number 2 | Pages 275-298 | 2004
© Oxford University Press 2004; all rights reserved
Rheological Properties of Partially Molten Lherzolite
DEPARTMENT OF GEOLOGY AND GEOPHYSICS, PILLSBURY HALL, UNIVERSITY OF MINNESOTA, MINNEAPOLIS, MN 55455, USA
* Corresponding author. Telephone: 612-626-0572. Fax: 612-625-3819. E-mail: zimme030{at}umn.edu
Lherzolite samples synthesized from fine-grained powders prepared from a natural xenolith were deformed at P = 300 MPa and 1373 
T 1573 K in a high-resolution gas-medium deformation apparatus. Below and above the solidus of Ts 
1433 K, fine-grained lherzolite exhibits a transition from diffusional creep at low stress to dislocation creep at high stress. The transition occurs at a differential stress 
100 MPa in samples with a grain size d 20 µm and a melt fraction 
0·03. Extrapolation to upper-mantle conditions suggests that a similar transition will occur in the mantle for d = 2 mm at 0·5 MPa. Therefore, both creep mechanisms are likely to contribute to deformation of partially molten regions of the mantle. We determined an empirical relationship for the dependence of strain rate 
on using data for melt-free olivine, analysis of the subsolidus and hypersolidus creep behavior of lherzolite and constraints on (T) from our experimentally determined melting curve. We find that increases approximately exponentially with increasing in both the diffusional and dislocation creep regimes. The observed enhancement in as a result of melt is much larger than anticipated based on deformation models that consider only an isotropic distribution of melt in triple junctions and do not incorporate the presence of melt along some grain boundaries and the melt preferred orientation that develops during deformation. The results for lherzolite are similar to results reported previously for olivine plus basaltic melt samples, indicating a minor effect of pyroxene content for deformation of partially molten peridotites. Our constitutive equation provides a basis for modeling geodynamic processes in the partially molten mantle beneath mid-ocean ridges and in the mantle wedge above subducting slabs.
KEY WORDS: ophiolite; peridotite; upper mantle; mid-ocean ridge; partial melt; deformation mechanism; diffusional creep; dislocation creep; grain boundary sliding; experimental studies; fine-grained materials
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  D. L. Kohlstedt, M. E. Zimmerman, and S. J. Mackwell Stress-driven Melt Segregation in Partially Molten Feldspathic Rocks J. Petrology, July 22, 2009; (2009) egp043v1. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Rabinowicz and M. J. Toplis Melt Segregation in the Lower Part of the Partially Molten Mantle Zone beneath an Oceanic Spreading Centre: Numerical Modelling of the Combined Effects of Shear Segregation and Compaction J. Petrology, June 1, 2009; 50(6): 1071 - 1106. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. K. Holtzman and D. L. Kohlstedt Stress-driven Melt Segregation and Strain Partitioning in Partially Molten Rocks: Effects of Stress and Strain J. Petrology, December 1, 2007; 48(12): 2379 - 2406. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Scoppola, D. Boccaletti, M. Bevis, E. Carminati, and C. Doglioni The westward drift of the lithosphere: A rotational drag? Geological Society of America Bulletin, January 1, 2006; 118(1-2): 199 - 209. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. K. HOLTZMAN, D. L. KOHLSTEDT, and J. P. MORGAN Viscous Energy Dissipation and Strain Partitioning in Partially Molten Rocks J. Petrology, December 1, 2005; 46(12): 2569 - 2592. [Abstract] [Full Text] [PDF]
|
|