Experimental observation of a new attenuation mechanism in hcp-metals that may operate in the Earth's inner core

DOI: 10.1029/2023GC011386

Authors: Simon A. Hunt (University of Manchester) , Andrew M. Walker (University of Leeds; University of Oxford) , Oliver T. Lord (University of Bristol) , Stephen Stackhouse (University of Leeds) , Lewis Schardong (The Geological Survey of Israel) , Lora S. Armstrong (TU Delft) , Andrew J. Parsons (University of Plymouth) , Geoffrey E. Lloyd (University of Leeds) , John Wheeler (University of Liverpool) , Danielle M. Fenech (University of Cambridge) , Stefan Michalik (Diamond Light Source) , Matthew L. Whitaker (Stony Brook University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Geochemistry, Geophysics, Geosystems , VOL 25

State: Published (Approved)
Published: June 2024
Diamond Proposal Number(s): 23970

Abstract: Seismic observations show the Earth's inner core has significant and unexplained variation in seismic attenuation with position, depth and direction. Interpreting these observations is difficult without knowledge of the visco- or anelastic dissipation processes active in iron under inner core conditions. Here, a previously unconsidered attenuation mechanism is observed in zinc, a low pressure analog of hcp-iron, during small strain sinusoidal deformation experiments. The experiments were performed in a deformation-DIA combined with X-radiography, at seismic frequencies (∼0.003–0.1 Hz), high pressure and temperatures up to ∼80% of melting temperature. Significant dissipation (0.077 ≤ Q−1(ω) ≤ 0.488) is observed along with frequency dependent softening of zinc's Young's modulus and an extremely small activation energy for creep (⩽7 kJ mol−1). In addition, during sinusoidal deformation the original microstructure is replaced by one with a reduced dislocation density and small, uniform, grain size. This combination of behavior collectively reflects a mode of deformation called “internal stress superplasticity”; this deformation mechanism is unique to anisotropic materials and activated by cyclic loading generating large internal stresses. Here we observe a new form of internal stress superplasticity, which we name as “elastic strain mismatch superplasticity.” In it the large stresses are caused by the compressional anisotropy. If this mechanism is also active in hcp-iron and the Earth's inner-core it will be a contributor to inner-core observed seismic attenuation and constrain the maximum inner-core grain-size to ≲10 km.

Subject Areas: Earth Science


Instruments: I12-JEEP: Joint Engineering, Environmental and Processing

Other Facilities: X17B2 at NSLS

Added On: 24/06/2024 08:39

Documents:
Geochem Geophys Geosyst - 2024 - Hunt - Experimental Observation of a New Attenuation Mechanism in hcp%E2%80%90Metals That May.pdf

Discipline Tags:

Earth Sciences & Environment Geology Geophysics

Technical Tags:

Diffraction