The Brittle‐Ductile Transition Predicted by a Physics‐Based Friction Law

A theory of the brittle‐ductile transition (BDT) is shown to be a direct consequence of a recently developed physics‐based constitutive law for rock friction (Aharonov & Scholz, 2018, https://doi.org/10.1002/2016JB013829), which assumes exponential creep on contacts. The theory was previously tested against experimental data for sliding at low ambient temperature and stress. Here, theoretical interpretation of experimental data at high temperature and stress shows that at some point the real area of contact reaches a maximum value beyond which it becomes fixed. The constitutive law shows that this marks the onset of the BDT, beyond which sliding changes from frictional to an exponential flow law for low‐temperature plasticity. Application to the Earth's crust shows that beyond this point, strength fall linearly with depth until it intersects the power law for bulk flow of the country rock, which marks the lower boundary of the BDT. Modeling, constrained by experimental data for granite, predicts that the BDT starts at a temperature of about 300°C, at a depth of 11–13 km in the continental crust, depending on fault slip rate and temperature gradient. The completion of the BDT is similarly calculated to occur around 475°, at 16–18 km, in agreement with laboratory and field observations. The BDT is thus found to be a region spanning about 175°C with a width of several kilometers.Within the exponential flow region, the structural outcome would be a relatively narrow mylonitized fault zone, which widens into a broader region of shear at the base of the BDT

Solid-fluid interactions in porous media : processes that form rocks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.Includes bibliographical references (p. 135-143).by Einat Aharonov.Ph.D

Fingerprinting stress: stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding-the case of the Monte Nero anticline in the Apennines, Italy

In this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold-and-thrust belt. First, we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion. Second, we use our new approach to present a high-resolution deformation and stress history that affected Meso-Cenozoic limestone strata in the Monte Nero Anticline during its late Miocene-Pliocene growth in the Umbria-Marche Arcuate Ridge (northern Apennines, Italy). In this area an extensive stylolite-joint/vein network developed during layer-parallel shortening (LPS), as well as during and after folding. Stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during LPS. The stress regime oscillated between strike slip and compressional during LPS before ultimately becoming strike slip again during late stage fold tightening. Our case study shows that high-resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses. Beyond regional implications, this study validates our approach as a new powerful toolbox to high-resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

Editorial: Flow and Transformation in Porous Media

Editoria

Sedimentary stylolite networks and connectivity in Limestone: Large-scale field observations and implications for structure evolution

International audienceStylolites are rough surfaces, formed by localized rock dissolution, and prevalent in carbonates and other sedimentary rocks. Their impact on porosity and permeability, and capacity to accommodate compactive strain, are well documented. This paper presents a meso-scale field study on sedimentary stylolites in carbonates, characterizing large-scale distributions of stylolites, including measurements conducted on longer than kilometer-long stylolites. Our field study suggests that on large-scales connections between stylolites become important. Since connectivity, and also lack of connectivity, are expected to play a significant role in strain accommodation and hydraulic rock properties, we suggest that large-scale analysis may require a new characterization scheme for "stylolites populations", based on their connectivity. We therefore divide sedimentary stylolite populations into three end-member types, which are correlated with the three possibilities for percolation of such systems: isolated stylolites (with zero percolation/connectivity), long-parallel stylolites (with 2-dimensional percolation/connectivity), and interconnected stylolite networks (with 3-dimensional percolation/connectivity). New statistical parameters and measures are devised and used to quantitatively characterize the different population types. Schematic mechanistic models are then offered to explain the evolution of the three end-member connectivity-classes. In addition we discuss the effect on fluid flow of the different population types

The Life and Death of Stylolites: stylolite roughness as indicator for the duration and amount of dissolution

International audienceStylolites are rough surfaces formed by localized dissolution, mostly in carbonates and sandstones. They often account for a large degree of dissolution, and their impact on porosity and permeability is well recognized. Understanding their formation mechanism can advance our ability to predict their occurrence and effect on flow, which has appreciable geological and economical implications. Still, many fundamental issues concerning their structure and evolution are still unresolved. This manuscript studies the roughening of long parallel stylolites, which are one of three types of stylolite populations identified by us in a separate paper. Here we report measurements of stylolite surface roughness at a scale larger than ever measured before (10-2-101m). Measurements were performed using ground-based-LIDAR on 6 naturally-exposed surfaces of >km long stylolites in Northern Israel. The outcome of these measurements is a topography model of the surfaces, on which different techniques for calculating their roughness characteristics were used. Our results show that up to scales of ~10cm, the average deviation of the surfaces from a planar surface is related to the scale by a power-law with an exponent H. The surfaces are thus defined as self-affine only up to ~10cm with H~0.7. Above this scale H decreases almost to zero. This observed upper-bound of self-affine roughness measured here for the first time has been predicted by theory [1, 2, 2bis]. Our measurements support these theoretical models and together with them present a scenario in which stylolites evolve from preferential dissolution along an existing surface that was initially smooth and progressively roughened with time. Such a mechanism of stylolites growth is different from previously suggested mechanisms for other classes of stylolite which might propagate sideways from an initial defect. Based on the theoretical roughening model that we adopted, the upper limit to fractality for this class of stylolites may be used as a measure of the amount of dissolution on stylolites. Indeed, the amount of dissolution of the stylolites in our field site which we calculated from the upper limit to fractality is comparable to our estimates of dissolution from two additional independent techniques

Unsteady granular flows down an inclined plane

International audienceThe continuum description of granular flows is still a challenge despite their importance in many geophysical and industrial applications. We extend previous works, which have explored steady flow properties, by focusing on unsteady flows accelerating or decelerating down an inclined plane in the simple shear configuration. We solve the flow kinematics analytically, including predictions of evolving velocity and stress profiles and the duration of the transient stage. The solution shows why and how granular materials reach steady flow on slopes steeper than the angle of repose and how they decelerate on shallower slopes. The model might facilitate development of natural hazard assessment and may be modified in the future to explore unsteady granular flows in different configurations