Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist

Abstract

The origin of intermediate-depth seismicity has been debated for decades. A substantial fraction of these events occurs within the upper plane of Wadati-Benioff double seismic zones believed to represent subducting oceanic crust. We deformed natural lawsonite-rich blueschist samples under eclogite-facies conditions (1.5 < P < 3.5 GPa; 583 K < T < 1121 K), using a D-DIA apparatus installed at a synchrotron beamline continuously monitoring stress, strain, phase changes, and acoustic emissions (AEs). Two distinct paths were investigated: i) heating during deformation at pressures > 2.5 GPa to maximum temperatures ranging from 762-1073 K, during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite-eclogite and the breakdown reaction of lawsonite was

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

“…Since the latter reaction is predicted to occur across a very restricted P–T range (Figure c), it is likely to have produced a fluid pulse and may conceivably have induced brecciation by dehydration embrittlement. This would be consistent with the record of acoustic emissions spatially correlated to crack formation during the crossing of the glaucophane‐out reaction in experiments studying the eclogitization of lawsonite‐blueschists (at confining pressure of 2.5 GPa; Incel et al, ). But the authors, based on the presence of nanometric, newly formed omphacite grains on fracture and shear band walls, argued for a process of transformational faulting rather than dehydration embrittlement.…”

“…For example, it is the presence of fluids triggering or resulting from brittle deformation (e.g., Hertgen et al, 2017;Locatelli et al, 2018;Pennacchioni & Cesare, 1997). If dehydration reactions with positive reaction volumes are considered as a potential trigger for brittle deformation associated to earthquake nucleation at the scale of subduction zones (e.g., Abers et al, 2013;Lund & Austrheim, 2003;Spinelli & Wang, 2009;Wong et al, 1997), small scale evidence is still debated, as shown by experimental data (i.e., dehydration embrittlement vs. transformational faulting; e.g., Incel et al, 2019Incel et al, , 2017Okazaki & Hirth, 2016). Brittle precursors are likely erased by subsequent reworking, and examples of eclogite-facies brittle structures, such as high-pressure veins (Gao et al, 2007;John & Schenk, 2006;Philippot, 1987;Philippot & Kienast, 1989a;Widmer & Thompson, 2001) and eclogite-facies breccias (Angiboust, Langdon, et al, 2012;Locatelli et al, 2018), are scarce.…”

Energy Balance From a Mantle Pseudotachylyte, Balmuccia, Italy

“…The relationship between intermediate‐depth seismicity and hydrous minerals is still a matter of debate (Deseta, Ashwal, & Andersen, ; Hacker et al, ; Incel et al, ; Gasc et al, ; Okazaki & Hirth, ; Peacock, ). Recent experimental results show that the dehydration of antigorite even in small amounts can induce the formation of micropseudotachylytes in olivine aggregates (Ferrand et al, ), associated with stress drops on the order of 100 MPa and water‐bearing glass in fractured olivine.…”

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

“…Based on recorded acoustic emissions and microstructural observations of the recovered samples, faulting was demonstrated to occur at a differential stress of ~3 GPa, in a temperature range of ~370–450 °C, and an axial strain of 5–19%. Seismic slip was interpreted to occur during the transition from lawsonite‐blueschist to lawsonite‐eclogite (Incel et al, ).…”

“…(a) BSE image of blueschist sample deformed at 3 GPa confining pressure in the temperature range 310–800 °C (Incel et al, ). The sample is cross cut by conjugated faults.…”