Grain scale deformation in ultra-high-pressure metamorphic rocks—an indicator of rapid phase transformation

Abstract

Abstract. An important question in geophysics is whether earthquakes (EQs) can be anticipated prior to their occurrence. Pre-seismic electromagnetic (EM) emissions provide a promising window through which the dynamics of EQ preparation can be investigated. However, the existence of precursory features in pre-seismic EM emissions is still debatable: in principle, it is difficult to prove associations between events separated in time, such as EQs and their EM precursors. The scope of this paper is the investigation of the pre-seismic EM activity in terms of complexity. A basic reason for our interest in complexity is the striking similarity in behavior close to irreversible phase transitions among systems that are otherwise quite different in nature. Interestingly, theoretical studies (Hopfield, 1994;Herz and Hopfield 1995;Rundle et al., 1995;Corral et al., 1997) suggest that the EQ dynamics at the final stage and neural seizure dynamics should have many similar features and can be analyzed within similar mathematical frameworks. Motivated by this hypothesis, we evaluate the capability of linear and non-linear techniques to extract common features from brain electrical activities and pre-seismic EM emissions predictive of epileptic seizures and EQs respectively. The results suggest that a unified theory may exist for the ways in which firing neurons and opening cracks organize themselves to produce a large crisis, while the preparation of an epileptic shock or a large EQ can be studied in terms of "Intermittent Criticality".

Intergranular coesite and coesite inclusions in dolomite from the Dabie Shan: Constraints on the preservation of coesite in UHP rocks

“…It is noteworthy that the coesite inclusions rarely show an ideal spherical morphology and that both the fractures and the healed microstructural defects are often concentrated at the “corners” of the inclusions (Figures c,d and ). Some dolomite grains exhibit undulose extinction resulting from the coesite–quartz transition (Figure e); similar plastic deformation has been rarely reported in UHP rocks (Lenze, Stöckhert, & Wirth, ).…”

The deformation record of olivine in mylonitic peridotites from the Finero Complex, Ivrea Zone: Separate deformation cycles during exhumation

“…[] at temperatures above 1000°C, high strain rates (>10 −5 s −1 ) and high differential stress of 500 MPa. Generally, the simultaneous activation of both glide systems requires high differential stresses to reach the critical shear stress for both glide system at the same conditions. The formation of kink bands is known for instance from micas [ Bell et al ., ; Mares and Kronenberg , ], pyroxenes [ McLaren and Etheridge , ], kyanite [ Lenze et al ., ] and also for hexagonal Ti 3 SiC 2 [ Barsoum et al ., ]. Kink bands in single crystals can be described as a pair of kink band boundaries, across which there is a change in orientation of the active glide plane [e.g., Nicolas and Poirier , ; Barsoum et al ., ].…”

Exhumation of (ultra-)high-pressure terranes: concepts and mechanisms

“…Microstructural evidence from quartz suggests that it transformed into coesite and back into quartz during subduction and exhumation. Laboratory experiments suggest that this transition takes place within hours (Lenze et al, 2005). Randomly oriented twins in jadeite and kinbands in kyanite suggest that deformation at UHP conditions was driven by the volumetric change from coesite to quartz rather than any far-field tectonic stress (Lenze and Stockhert, 2007).…”