Shear Deformation of Upper Mantle Mineral Analogues: Test to 55kb at 27c

摘要

Shear deformation of upper mantle mineral analogues forsterite, enstatite, diopside and labradorite at 27C temperature, 5 to 55 kb average pressure, and at strain rates from 1/sec to .003/sec indicates that all minerals have high average shear strengths. Shear strength for North Carolina and Hawaiian olivine is 15.17 kb at 50 kb average pressure. Average shear strength for Madagascar diopside and Labrador labradorite are 14.90 kb to 14.03 kb and 13.15 kb, respectively, at 50 kb average pressure. Each shear stress-normal pressure curve is resolvable into two regions of constant but different slopes separated by a broad transitional knee. These represent separate and distinguishable behavior. The predominant behavior at all pressures is cataclastic; intragranular flow becomes significant only at high pressures. Violent snapping accompanies rotation at 27C and relates to surficial stick-slip between sample and pistons. All snapping ceases at 300C. Enstatite inverts to clinoenstatite at 35 = 1 kb mean pressure under the influence of shear stress at 27C. (Author)