Rheological weakening due to phase mixing in olivine + orthopyroxene rocks

2017 Fiscal Year Final Research Report

• Project/Area Number: 16K17832
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Shimane University
• Principal Investigator: Tasaka Miki 島根大学, 総合理工学研究科, 特任講師 (80772243)
• Research Collaborator: Kohlstedt David L. University of Minnesota, Department of Earth Science ; Zimmerman Mark E. University of Minnesota, Department of Earth Science ; Stünitz Holger University of Tromsø, Department of Geology ; Heilbronner Renée Basel University, Geological Institute
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: かんらん石 / 輝石 / 鉱物混合層 / 歪み弱化 / 拡散速度

Outline of Final Research Achievements

To understand the processes involved in rheological weakening due to phase mixing, we conducted high-strain torsion experiments.
Samples composed of olivine plus 26% orthopyroxene were deformed to outer radius shear strains of up to γ <= 26. Microstructural observations demonstrate that, with increasing shear strain, grain size decreased and mixtures of small, equant grains developed. The mechanical data with associated changes in microstructure demonstrated that our samples deformed (i) by dislocation-accommodated grain-boundary sliding (disGBS) with subgrains present at lower strains and (ii) by disGBS with subgrains absent at higher strains. The evolution of both the mechanical and the microstructural properties observed in this study provide insights into the dynamic processes associated with rheological weakening and strain localization in the plastically deforming portion of the lithosphere.

Free Research Field

実験岩石学