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Frictional properties of basalt experimental faults and implications for volcano-tectonic settings and geo-energy sites
Tectonophysics ( IF 2.9 ) Pub Date : 2021-04-23 , DOI: 10.1016/j.tecto.2021.228883
Piercarlo Giacomel , Roberta Ruggieri , Marco M. Scuderi , Elena Spagnuolo , Giulio Di Toro , Cristiano Collettini

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.



中文翻译:

玄武岩实验断层的摩擦学性质及其对火山构造环境和地能站点的影响

我们进行了一系列实验,目的是检验在火山构造环境和原位地能玄武岩位置中,未改变的玄武岩在被认为是浅层滑动的代表条件下的摩擦特性。对发掘出的地下断层和裂缝类似物的科学钻探和现场研究表明,玄武岩中的摩擦滑动可能发生在一定数量的磨损碎屑内的剪切带中或沿局部接合面发生。为了阐明微观结构的非均质性如何影响玄武岩滑移不稳定性的成核作用,我们在室温,干燥和潮湿条件下,在低法向应力(4–30 MPa)下,对模拟断层泥和裸露的岩石表面进行了剪切。我们执行了速度步进(0。1–300μm/ s)和滑动保持滑动(保持30–3000 s)来确定玄武岩的摩擦稳定性和愈合特性。在所有测试中,我们观察到与重要的摩擦再磨合相关的高摩擦系数。总体而言,我们的结果表明,微观结构的异质性极大地影响了玄武岩的摩擦速度依赖性:而对于正应力≥10MPa,在裸露的表面切屑生产中,剪切局部化伴随着催化作用和晶粒尺寸减小有利于粉末状样品向速度弱化行为的转变在剪切过程中,促进了向速度强化行为的转变。我们的结果表明,在经过测试的条件下,摩擦不稳定性可能会在剪切区域中迅速成核,在这些区域中(未改变的)玄武质凿岩层中的变形是局部的,

更新日期:2021-04-29
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