For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine-orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere.rheology | two-phase | Zener pinning | deformation mechanisms | electron probe microanalysis P late tectonic style of convection is characterized by regions of localized deformation, such as subduction zones, and the origin of these regions needs to be investigated to understand why plate tectonics operates on Earth. Localized deformation at plate boundaries involves not only brittle fracture at shallow portions but also localized deformation in the ductile shear zones (1-4). Although the basic processes of localized deformation in the brittle regime are well understood (5, 6), mechanisms of localized deformation in the ductile regime remain elusive. The strength profile of the lithosphere in a standard model (7) predicts stresses that are much higher than the critical strength below which plate tectonic style of convection would occur (8,9).Among the possible mechanisms of shear localization (10), grain size reduction is most often recognized in ductile shear zones and has been given particular attention in previous studies (11)(12)(13)(14)(15). Grain size reduction can occur during high-temperature deformation by dynamic recrystallization during dislocation creep (16,17). In many cases, small grains are formed along preexisting grain boundaries (18). If the degree of grain-size reduction is large enough and these fine-grained regions are connected, then regions of small grain size will be deformed by grain-size-sensitive creep processes-diffusion creep or dislocation creep accommodated by grain-boundary sliding (Dis-GBS) introduced by Hirth and Kohlstedt (1995) (19). Deformation in both regimes results in the weakening of a rock, although less so in the Dis-GBS regime. In addition, for this weakening to cause substantial shear localization, the ...

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Summary Using palmitic acid (PA) as an organic phase change material (PCM), a series of PA/diatomite composite PCMs (CPCMs) composed of PA absorbed into diatomite mesopores with different mass contents were made through direct impregnation method. Nitrogen adsorption‐desorption curves indicated the porous structure of diatomite with the specific surface area and the mesopore peak at 40 m2/g and 3 to 5 nm, respectively. The form‐stability measurement indicated that the maximum mass loading capacity of PA was 55 wt%. The melting temperature and fusion enthalpy of the PA/diatomite CPCM (55 wt%) were calculated from DSC at 63°C and 88 J/g, respectively. The thermal cycle test implied that the PA/diatomite CPCM with 55‐wt% PA loading showed excellent thermal reliability after 1000 thermal cycles. Moreover, the composite has thermal conductivity at 0.5810 W/m·K and enhanced thermal storage/release rate. PA/diatomite CPCM (55 wt% PA) was a suitable candidate for modern building energy saving and industrial solar energy.

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