Experimental constraints on the strength of the lithospheric mantle

Abstract

[1] To provide a better understanding of rheological properties of mantle rocks under lithospheric conditions, we carried out a series of experiments on the creep behavior of polycrystalline olivine at high pressures (∼4-9 GPa), relatively low temperatures (673 ≤ T ≤ 1273 K), and anhydrous conditions, using a deformation-DIA. Differential stress and sample displacement were monitored in situ using synchrotron X-ray diffraction and radiography, respectively. Experimental results were fit to the low-temperature. On the basis of this analysis, the low-temperature plasticity of olivine deformed under anhydrous conditions is well constrained by our data with a Peierls stress of s P = 5.9 ± 0.2 GPa, a zero-stress activation energy of E k (0) = 320 ± 50 kJ mol, and A P = 1.4 × 10. Compared with published results for high-temperature creep of olivine, a transition from low-temperature plasticity to high-temperature creep occurs at ∼1300 K for a strain rate of ∼10 −5 s −1 . For a geological strain rate of 10 −14 s −1 , extrapolation of our low-temperature flow law to 873 K, the cutoff temperature for earthquakes in the mantle, yields a strength of ∼600 MPa. The low-temperature, high-stress flow law for olivine in this study provides a solid basis for modeling tectonic processes occurring within Earth's lithosphere.

Stress evolution and associated microstructure during transient creep of olivine at 1000–1200 °C

“…Experiments performed at temperatures relevant to the uppermost lithospheric mantle (≤ 1000 °C, e.g. Raterron et al, 2004;Demouchy et al 2009Demouchy et al , 2013Demouchy et al , 2014Mei et al, 2010;Idrissi et al, 2016;Tielke et al, 2016) report a lower strength of olivine than was expected from extrapolation of high-temperature flow laws. The low temperature plasticity is a key to understanding deformation of the shallow upper mantle (Hirth & Kohlstedt, 1995) but also in subducting slabs Kirby, 1980;, where it governs the stress storage capacity and therefore the maximal stress release of deep earthquakes (e.g., Proietti, 2016).…”

Experimental investigation of the creep behavior of garnet at high temperatures and pressures

“…The starting garnet grains contain <10 ppm wt.% of dissolved hydroxyl as detected using Fourier transform infrared (FTIR) techniques (Jin et al, 2001). In preparing a sample assembly for deformation, a deformation cell was made of bone-dry mullite, which was previously demonstrated to provide anhydrous deformation conditions (Mei et al, 2010;Durham et al, 2009). Before each run, a sample assembly was dried in a vacuum oven at T=420 K for more than 10 h to remove surface moisture incurred during the preparation processes.…”

The thermal state and strength of the lithosphere in the Spanish Central System and Tajo Basin from crustal heat production and thermal isostasy

“…The behavior of the upper lithospheric man tle is in turn largely controlled by low-temperature plasticity of olivine-rich rocks (Mei et al, 2010), resulting in a rheology signif icantly weaker than that usually used for the lithosphere mantle. Under anhydrous conditions, Mei et al (2010) define a flow law for a quasi steady state deformation of olivine under low-temperature and high-stress, which can be written in terms of differential stress as…”

“…Thus, the mechanical behavior and rheo logical stratification of the lithosphere in continental areas are largely a consequence of local conditions (e.g., Afonso and Ranalli, 2004;Furlong and Chapman, 1987;Ruiz et al, 2006;Wa tts and Burov, 2003). On the other hand, recent laboratory experiments conducted under controlled microstructural and chemical condi tions have shown a significant effect of important parameters on the rheological properties of major silicate rocks (BOrgmann and Dresen, 2008), and have yielded new rheological laws describing the first-order mechanical behavior of the lithospheric materials (e.g., Katayama and Karato, 2008;Keefner et al, 2011 ;Mei et al, 2010).…”

“…Finally, we have used our result for the thermal structure in order to analyze the strength of the lithosphere in the study area. To make this, we have implemented a new rheo logical law for the upper lithospheric mantle, largely controlled by low-temperature plasticity of olivine-rich rocks (Mei et al, 2010). All of this provides an opportunity to refine existing thermal and rheological models and litho spheric strength determinations of the study area.…”