Textures in deforming forsterite aggregates up to 8 GPa and 1673 K
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We report results from axisymmetric deformation experiments carried out on forsterite aggregates in the deformation-DIA apparatus, at upper mantle pressures and temperatures (3.1–8.1 GPa, 1373–1673 K). We quantified the resulting lattice preferred orientations (LPO) and compare experimental observations with results from micromechanical modeling (viscoplastic second-order self-consistent model—SO). Up to 6 GPa (~185-km depth in the Earth), we observe a marked LPO consistent with a dominant slip in the (010) plane with one observation of a dominant  direction, suggesting that (010) slip system was strongly activated. At higher pressures (deeper depth), the LPO becomes less marked and more complex with no evidence of a dominant slip system, which we attribute to the activation of several concurrent slip systems. These results are consistent with the pressure-induced transition in the dominant slip system previously reported for olivine and forsterite. They are also consistent with the decrease in the seismic anisotropy amplitude observed in the Earth’s mantle at depth greater than ~200 km.
KeywordsForsterite Deformation High pressure D-DIA Lattice preferred orientation Micromechanical modeling
The authors thank Hayian Chen (Stony Brook University), Jennifer Girard (Florida International University, now at Yale University) and Caleb Holyoke (Texas A&M University, now at the University of Akron), for their assistance at the NSLS X17B2 beamline, K. Yuan (Univ. California Berkeley) for assistance in the anisotropy plot of Fig. 3b, N. Hilairet for useful discussions and the two anonymous reviewers for their comments. This research was supported by the Consortium for Materials Properties Research in Earth Sciences (COMPRES) under NSF Cooperative Agreement EAR 06-49658, as well as the Agence Nationale de la Recherche (ANR) Grant BLAN08-2_343541 “Mantle Rheology.” Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.
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