Publication Date:
2021-12-22
Description:
We performed a suite of experiments aimed at examining the frictional properties of unaltered basalts at conditions considered to be representative of slip at shallow depths in volcano-tectonic environments and in-situ geo-energy basaltic sites. Scientific drilling and field studies on exhumed subsurface faults and fractures analogues suggest that, frictional sliding in basalts can occur in shear zones within a volume of wear debris or along localized joint surfaces. To illuminate how microstructural heterogeneities affect the nucleation of slip instabilities in basalts, we sheared simulated fault gouge and bare rock surfaces at low normal stresses (4–30 MPa) at ambient temperature, under room-dry and wet conditions. We performed velocity steps (0.1–300 μm/s) and slide-hold-slides (30–3000 s holds) to determine the frictional stability and healing properties of basalts. In all the tests, we observed high friction coefficient associated with important frictional restrengthening. Overall, our results show that microstructural heterogeneities strongly affect the friction velocity dependence of basalts: while for normal stresses ≥10 MPa, shear localization accompanied by cataclasis and grain size reduction favors the transition to velocity weakening behavior of powdered samples, on bare surfaces gouge production during shearing promotes a transition to a velocity strengthening behavior. Our results imply that at the tested conditions, friction instabilities may promptly nucleate in shear zones where deformation within (unaltered) basaltic gouge layers is localized, such as those located along volcanic flanks, while joint surfaces characterized by rough rock-on-rock contacts are less prone to unstable slip, which is suppressed at velocities ≥10 μm/s.
Description:
This work has benefited from the European Research Council project 614705 NOFEAR and Progetti di Ateneo La Sapienza Collettini 2018 grants. We are grateful to F.lli LIZZIO S.r.l. for providing Etnean basalt samples. We acknowledge D. “Mimmo” Mannetta, L. Tauro, and E. Masiero for thin section preparations and sample saw-cut, F. Zorzi for XRF and XRPD analyses, M. Nazzari for providing assistance with the SEM, and S. Mollo and E. Del Bello for technical support for the use of the He-pycnometer and the Separation Analyzer LUMiReader. We thank C. Marone for the XLook program for obtaining RSF parameters. CWA Harbord and S. Aretusini are acknowledged for technical support in the HP-HT laboratory and during SHIVA experiments. Telemaco Tesei is thanked for insightful discussion regarding this study. Carolina Giorgetti is thanked for her precious and constructive comments that helped to improve the quality of this study.
Description:
Published
Description:
228883
Description:
3T. Fisica dei terremoti e Sorgente Sismica
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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