Leif Tokle

Leif Tokle
ETH Zurich | ETH Zürich · Department of Earth Sciences

PhD

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23
Publications
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Publications

Publications (23)
Article
Full-text available
Variation in the effective strength of the lithosphere allows for active plate tectonics and is permitted by different deformation mechanisms operating in the crust and upper mantle. The dominant mechanisms are debated, but geodynamic models often employ grain-size-independent mechanisms or evaluate a single grain size. However, observations from n...
Conference Paper
Full-text available
We investigate the rheological and microstructural properties of aggregates of ilmenite and olivine deformed in shear in a Griggs apparatus. The experiments constrain the effective viscosity of an ilmenite-bearing lunar mantle as a function of ilmenite content and shear strain. Ilmenite exhibits viscous anisotropy, deforming by basal slip in shear,...
Article
The primary objective of this work is to constrain the physical and chemical effects of ilmenite on the spectral properties of high‑titanium lunar basalts. Here we use a combination of electron probe microanalysis, x-ray diffraction and VIS-NIR spectroscopy to characterize a suite of Apollo 17 High-Ti lunar basalts and a suite of synthetic laborato...
Article
Full-text available
Differential stress magnitude is a fundamental parameter in the study of geodynamic processes in the continental lithosphere, and is typically estimated in quartz- and olivine-dominated lithologies using recrystallized grain size piezometers. Here we evaluate the piezometric relationships in natural mylonites with mineral pairs of quartz–feldspar a...
Article
Full-text available
Relationships between the recrystallized grain size and stress are investigated for experimentally deformed water‐added quartz aggregates. For stresses ≥100 MPa there is a variation in the measured recrystallized grain size for a given stress. This variation correlates with a change in the c‐axis fabric in general shear experiments, where samples w...
Preprint
Full-text available
Geodynamic numerical models often employ solely grain-size-independent dislocation creep to describe upper mantle dynamics. However, observations from nature and rock deformation experiments suggest that shear zones can transition to a grain-size-dependent creep mechanism due to dynamic grain size evolution, with important implications for the over...
Article
Full-text available
The viscosity of ilmenite is an important parameter that is thought to have influenced the thermal and chemical evolution of the lunar cumulate mantle. We conduct deformation experiments on two different ilmenite compositions, ilmenite100 (FeTiO3) and ilmenite40 ((Fe0.4Mg0.6)TiO3), to investigate the influence of pressure and Mg‐content on the rheo...
Article
Full-text available
We performed deformation and grain growth experiments on natural olivine aggregates with olivine water contents (COH = 600 ± 300 H/106 Si) similar to upper mantle olivine, at 1000–1200°C and 1,400 ± 100 MPa confining pressure. Our experiments differ from published grain growth studies in that most were (1) conducted on natural olivine cores rather...
Conference Paper
Full-text available
During the early evolution of the Moon, the lunar mantle is proposed to have undergone an event known as cumulate mantle overturn, where an initially shallow layer of ilmenite sank into an underlying olivine cumulate layer due to a large density and viscosity contrast [1]. It is unclear how the addition of low viscosity ilmenite to the lunar mantle...
Preprint
Full-text available
We performed deformation and grain growth experiments on natural olivine aggregates with moderate olivine water contents (COH = 600±300 ppm H/Si) at 1000-1200°C and a confining pressure of 1400±100 MPa. Our experiments differ from published grain growth studies in that most were: 1) conducted on natural olivine cores rather than hot-pressed aggrega...
Article
Full-text available
We determined the activation volumes (V*) for polycrystalline magnesite with grain sizes of 2 and 80 µm deforming by low temperature plasticity (LTP) mechanisms (kinking and dislocation glide), diffusion creep, and dislocation creep at temperatures of 500, 750, and 900 °C, respectively, and a strain rate of 1–2 × 10−5 s−1 at effective pressures of...
Article
We investigated quartzite flow laws based on data from 21 different experimental studies on samples deformed with added water at temperatures from 700 to 1200C. Two clear trends emerge: one with a power-law stress exponent of n = 4 +/- 0.3 and the other, at higher stresses and lower temperatures, with a stress exponent of n = 2.7 +/- 0.3. The chang...
Conference Paper
We conducted general shear experiments to investigate the role of mica content on the microstructural evolution and rheological properties of quartz aggregates. In previous studies, axial compression experiments were conducted on quartz aggregates to develop a better understanding of the relationship between flow strength and lattice preferred orie...
Article
The Pioneer migmatite-cored metamorphic core complex in south-central Idaho is bounded by the N-dipping Wildhorse Detachment fault, a low-angle normal fault that separates low-grade metasediments and volcanics from amphibolite facies metasediments, migmatites, and granites. The complex developed during the Eocene owing to extensional deformation an...

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Project (1)
Project
Experimentally determine rheological properties of lunar mantle-relevant minerals and multiphase aggregates (ilmenite; ilmenite-olivine). Using the experiments and present-day lunar surface and interior features as constraints, develop new models exploring lunar differentiation, with a focus on cumulate mantle overturn.