<nowiki>Insert non-formatted text here</nowiki>This page contains the work-in-progress proposal for the Research Coordination Network, and the different sections written by the committee. As more changes are made and sections are added, the individual sections will be broken off into their own linked pages to reduce overall chaos, clutter, and confusion.
DRAFT Outline of RCN Proposal:
Potential Proposal Titles and Key Words:
Provisional Proposal Title:
Research Coordination Network for In-situ Studies of Rock Deformation
Evolving deformation properties
In - situ Revolutions in Rock Deformation studies
"Community to advance In Operando observations of experimental rock deformation experiments" ]
VISION STATEMENT [This would go into the Intellectual Merit part of the Project Summary and perhaps again in introductory part of proposal]:
ORIGINAL COPY: The eventual scientific outcome of this RCN will be a new research direction that will make dramatic advances in our understanding of the mechanical behavior of rocks through the use of next generation synchrotron imaging and characterization technologies. These technologies will allow direct observation of processes occurring during rock deformation by examining samples in operando; while they are deforming. , These new data streams will shed light on underlying physical mechanisms allowing for superior extrapolation to Earth conditions.
The RCN will bring together several groups. It will involve primarily those who conduct laboratory rock deformation experiments and those who use synchrotron radiation to characterize the 3D distribution of phases, stress states, and grain orientation during dynamic processes such as deformation or phase transformation. The network will also include those who depend on understanding deformation process that are studied in lab experiments. These include field structural geologists, earthquake scientists, and geodynamicists. As an eventual result of the collaborations developed via this RCN, new generations of deformation equipment suitable for operation on beam lines will be designed and built and new 3D characterization techniques will be adapted for working on rocks. These technological advances and the existence of a community of scientists to use them will lead to significant scientific advances.
GROUP COPY TO EDIT: The eventual scientific outcome of this RCN will be a new research direction that advances our understanding of the mechanical behavior of rocks through the use of next-generation synchrotron imaging and characterization technologies. These technologies will allow direct observation of processes occurring during rock deformation by examining samples in operando; while they are deforming. These new data streams will elucidate the underlying physical mechanisms allowing for superior extrapolation to Earth conditions.
The RCN will bring together several groups. It will involve primarily those who conduct laboratory rock deformation experiments and those who use synchrotron radiation to characterize the 3D distribution of phases, stress states, and grain orientation during dynamic processes such as deformation or phase transformation. The network will also include those who depend on understanding deformation process that are studied in lab experiments. These include field structural geologists, earthquake scientists, and geodynamicists. As an eventual result of the collaborations developed via this RCN, new generations of deformation equipment suitable for operation on beam lines will be designed and built and new 3D characterization techniques will be adapted to the study of deforming rocks. These technological advances and the existence of a community of scientists to use them will lead to significant advances in understanding evolving mechanical properties, developing deformation textures, and changing deformation mechanisms.
[ Some Action Items: I think we need to see if we can identify signficant interest of "structural geologists, earthquake scientists, and geodynamicists". I can see that this is possible but I don't think we managed to attract them to the workshop, so we need to advertize and build community here.]
COMMENT FROM Franocois Renard: My suggestion would be to add a paragraph that describes which new scientific questions this apparatus would solve that existing rigs cannot do, such as: - partition between seismic and aseismic deformation in the upper crust - development of damage zones around faults - dynamic evolution of porosity and rock microstructure
SENTENCES TO CONSIDER FOR CREATING A PITHY MISSION STATEMENT:
Bill D.: We seek to support collaborative efforts in next-generation experimental rock mechanics that exploit the unique in operando observational capabilities of synchrotron X rays and that promote the evolution of rock deformation testing methods and hardware to keep apace of the significant advances to those capabilities anticipated in the near future. (…and to articulate that desire using far fewer pronouns.)
Lars (I went at this considering what I might write at the beginning of a proposal. Probably too long, and not sure it is the right tone): Predictions and inferences of large-scale, dynamic processes in the solid Earth, in the past, present, and future, are currently subject to severe uncertainty. We currently rely on extrapolating models of rock deformation calibrated in the laboratory to geological time and spatial scales. Unfortunately, many different models and their extrapolations are currently in competition, each with different assumptions about the underlying physics and with different implications when extrapolated to geological processes. With emerging capabilities in beamline science, we are poised for a step change in our ability to test and calibrate these models through direct observation of the underlying physics of rock deformation. However, a transformative move forward in this field requires the theoretical and technological innovation and development that can only be acheived by bringing together researchers and technicians from a broad range of backgrounds, with a new common goal of unpicking the physics of rock deformation that control the dynamics of the solid Earth.
Caleb: Goals of the RCN: To gather experimentalists, beam line scientists, structural geologists and geophysicists at hands-on workshops at synchrotron beamlines or discussion-based workshops to identify the salient questions and develop rock deformation/imaging technologies necessary to fully utilize the next generation of synchrotron light sources.
Question: How can the community of experimental geologists best utilize the coming advances in synchrotron beamline capabilities to understand the dynamic processes that control plate tectonics and affect society via natural disasters such as earthquakes and volcanic eruptions?
- Communities (PPEM email list, MSA list, and COMPRES list)
Need to identify research communities we're bringing together. PPEM is a easy coherent description of rock squeezers interested in in-situ observations of rock deformation. However, we need a better description of beamline scientists (scientific interests and self-identification).
- Research Opportunities
Somewhere in this section say that this is a propitious time to be doing this, because of the interesting new capabilities of the beam lines (or something to that effect that Don and Bill can say better).
- Science Questions that In Situ Observations Could Help Resolve
We want an overall initial paragraph introducing this section, showing how the various subjects in the following subsections to follow are of broad general interest to many geoscientists.
So far the subsections we have thought of are:
The process of localization in a fault or shear zone involves the shear displacement becoming progressively concentrated into a thinner and thinner zone. The details of how and why localization occurs depends on the deformation process and these depend on the depth in the Earth, namely upon the pressure and temperature. Examining the end product of shear deformation experiments demonstrate that in both the brittle and ductile fields sometimes localization occurs and sometimes it does not. However, by only examining the end product of such experiments it is often not possible to understand the processes that led to the localization or lack thereof, and it is typically impossible to know how the degree of localization progressed with overall displacement. Performing experiments with varying amounts of total displacement can allow some understanding of how localization progresses and the processes involved. However, there is no substitute for observing the sample as it deforms. In principle this could be done by imaging the sample with synchrotron radiation during a high-strain experiment.
[This next paragraph could be removed from here and put in somewhere else so it would apply to more than just localization.] Arranging an experimental configuration to allow this imaging is currently beyond the capability of the experimental rock deformation community. This RCN hopes to combine the apparatus-design abilities of this community with the knowledge and experience of beam-line scientists who know how to work with synchrotron radiation. Developing this network should allow the scientifically relevant experiments to be done.
Due to energy considerations, a shearing zone driven by a constant displacement rate will progress, if a viable path is available, to a shearing thickness in which the shear stress is a minimum. The change in thickness over which shear deformation occurs in both the brittle and ductile fields depends on the dependence of shear strength on both strain and strain rate. If both the strain and strain-rate dependence of the shear strength is negative then the shearing thickness will get smaller to reduce the shear stress; if both are positive then the shearing thickness will get larger to reduce the shear stress. If the strain and strain-rate dependencies are of opposite sign, then their tendencies cause changes in shear stress of opposite sign; whether the shearing thickness will increase or decrease depends on the magnitude of the contributions of each, and the result will depend on the overall displacement rate.
Brittle field. Sliding on faults at modest temperatures, pressures, and rates is well-described by rate and state friction. As expected from the arguments in the above paragraph, rate weakening friction often causes localization to occur, although the opposing tendency of strain hardening to cause delocalization can also take over as shown by Beeler et al.  for granite. The processes responsible for the transition from the dominance of rate weakening early in these experiments to the dominance of strain hardening are not clear. It may involve the reduction in particle size by comminution where the strain is higher and an associated local densification due to a local broadening of the particle size distribution. However, experiments in which changes in the particle-size distribution can be observed as it deforms would be very useful to understand the process. From experiments to differing displacements on feldspar gouges with an olivine marker-layer we know that broadly distributed shearing dominates the deformation at lower displacements and it switches to primarily localized deformation at larger displacements Scruggs and Tullis . However, why this sequence occurs is unclear and could be studied by observing the interior of the samples as they deform.
Ductile field. [I, Terry Tullis, wrote this BS and if anyone else has written something, just throw this out or use any of it that makes any sense!] A variety of mechanisms have been proposed to promote localization in the ductile field. They all involve mechanisms that make the rock weaker where where strain is higher, and so positive feedback occurs that promotes higher and higher strain regions where strain is already high. One such mechanism involves grain-size reduction which can involve a change in deformation mechanism and that can involve a lower stress, for example a change from dislocation creep to diffusion creep. Similarly reactions that involve phase changes can be promoted by deformation in shear zones and the reaction products can be weaker than the original rock. This mechanism is not able to promote progressive narrower and narrower localization, but can result in strain concentration in the part of a shear zone that reacts. Observing the progressive development of a ductile shear zone in experiments can help understand how these various processes work and help identify other possible weakening mechanisms.
Localization (AKK, wow, did we have multiple people write sections on localization?):
Tectonic plates of the Earth are defined by high strengths of crust and uppermost mantle rocks that deform by friction, crystal plasticity and viscous flow as functions of pressure and temperature that increase with depth (Schubert et al., 1976; Brace and Kohlstedt, 1980; Kohlstedt et al., 1995), and by anomalous, low strengths at plate boundaries (Zoback, 1991; Fulton et al., 2013). However, mechanical properties of the plates are not uniform, with heterogeneities and softening processes that lead to strain localization at all scales of observations, from minor shear bands (Mancktelow and Pennacchioni, 2005) that may develop by brittle and ductile mechanisms to major faults and shear zones (Chester et al., 1993; Law et al. 2013) that form the boundaries of plates themselves.
Processes that lead to localized faults and shear zones include interactions between cracks, frictional sliding, fluid-rock interaction and reaction softening, dynamic recrystallization and transitions from dislocation creep to diffusion creep, sliding and diffusion at multiple-phase grain boundaries, and water weakening (Rudnicki and Rice, 1975; Poirier, 1980). Laboratory experiments have explored many of these processes (Blacic, 1972; Tullis and Yund, 1987; Barnhoorn et al., 2005; Hansen et al., 2012; Holyoke et al., 2014). Observational and modeling studies show that strain softening and localization operate over a continuum of scales (Christiansen and Pollard, 1997; Ben-Zion and Sammis, 2003; Regenauer-Lieb and Yuen, 2004; Oliot et al., 2010). Thus, the plates themselves are more complicated rheologically than the rigid blocks of conventional plate tectonics, giving rise to broadly distributed deformation and intraplate earthquakes (Chen and Molnar, 1983; Zoback, 1992). Geodynamic models are quickly evolving to investigate strain localization [Kelemen and Hirth, 2007; John et al., 2009] but they require inputs from laboratory experiments that describe the nucleation and evolution of faults and shear zones.
Deformation experiments have helped us understand the conditions and weakening processes that lead to strain localization. However, conventional high-pressure, high-temperature laboratory methods do not lend themselves to study the nucleation or evolution of shear zones. Microstructural observations and analytical measurements are restricted to specimens before and after an experiment, and we cannot readily track evolving patterns of strain or strain rate. Deformation experiments can be interrupted at varying stages of deformation, but this approach offers only a few intermediate observations and requires many time-consuming experiments. Significant insights have been gained in understanding the nucleation and propagation of brittle shear faults during deformation by locating and mapping acoustic emissions during individual experiments (Lockner, 1993; Thompson et al., 2006). More recently, Fusseis et al. (2014) have developed a triaxial deformation apparatus that is sufficiently transparent to bright synchrotron X-rays that shear failure at lithospheric pressures can be studied by in-situ X-ray imaging. In-situ X-ray imaging during deformation offers advantages over monitoring acoustic emissions given that crack opening and porosity changes can be observed directly. Moreover, strain patterns can be imaged for samples deformed by crystal plastic and viscous processes as well, as long as minerals show sufficient density contrast to map strain spatially during experiments. In-situ X-ray diffraction during deformation experiments performed at a synchrotron beamline can supplement X-ray imaging of evolving shear zones by providing information on localized grain-scale stresses and changing crystallographic fabrics.
Real-time X-ray imaging and diffraction measurements for samples deformed at high pressures and temperatures at synchrotron beamlines will revolutionize our ability to study shear zone nucleation and development. These methods have been proven for smaller samples deformed at higher pressures (Wang et al., 2003; Durham et al., 2009; Weidner et al., 2010) owing to the concentrated efforts of mineral physicists and beamline scientists. However, significant innovations will be required to apply these methods to larger samples necessary to study strain localization within multiple-phase rocks. These developments require significant multi-disciplinary collaborations between rock mechanics specialists, rock physicists, and beamline scientists that will be facilitated by RCN funding.
nick: speaking of localization experiments, how far are we away from doing a 'lockner-style' experiment with x-ray imaging where strain rate is controlled by feedback from the imaging (stress,degree of preferred orientation, degree of phase transformation, whatever) and does it make any sense to include something like that in this rcn?
Measurement of the anisotropic properties of rocks also requires new technological advances for key advances to be made. Anisotropy in seismic velocity has been one of the primary geophysical observations used to infer the kinematics of flow in Earth’s interior (e.g., Hess 1965, Tanimoto and Anderson, 1984, Long and Becker 2010). Much progress has been made linking seismic anisotropy to the microscopic rotation of crystals in mantle rocks during deformation (e.g., Zhang and Karato, 1995; Hansen et al., 2014), leading to calibration of numerical models for predicting the evolution of anisotropy in an imposed flow (e.g., Tommasi et al., 2000, Kaminski and Ribe, 2001).
Although these models do well at predicting long-term, steady-state anisotropy, they unfortunately, struggle to explain the evolution of anisotropy in Earth, especially when the deformation paths are complex (e.g., Becker et al., EPSL, 2014). Furthermore, the dramatic changes in anisotropy with variations in chemical environment, thermomechanical conditions, and deformation mechanism are not yet well mapped out, making it difficult to interpret large-scale, spatial variations in anisotropy (for example, compare interpretations of the lithosphere-asthenosphere boundary by Hansen et al., PNAS, 2016 and Hedjazian et al., EPSL, 2017).
Further elucidation of these key features of anisotropy in upper-mantle rocks requires new technological advances. Current experimental observations of anisotropy development generally occur ex situ, making it difficult to document the progressive evolution of anisotropy or to link the developed fabric to specific experimental conditions. In operando measurements of anisotropy are now a reality through synchrotron-based diffraction measurements (e.g., Ohuchi et al., PEPI, 2015), and their increased implementation will be a step-change in our understanding of the dependence of anisotropy on deformation path, chemistry, pressure, temperature, and deformation mechanism.
Aftershocks and post-seismic deformations are influenced by the rheology of the mid to lower crust and upper mantle (Owen et al., 2002; Kenner and Segall, 2003; Ryder et al., 2014). Models of post-seismic deformation are generally constructed using homogeneous viscous layers for the crust and upper mantle deforming according to a monophase power law rheology, usually quartz or feldspar and olivine, respectively (Pollitz et al., 2000; Freed and Burgmann, 2004; Hetland and Hager, 2005; Burgmann and Dresen, 2008, Barbot and Fialko, 2010; Ryder et al., 2014; Zhang and Shcherbakov, 2016). However, most rocks in the mid to lower continental crust and upper mantle are heterogeneous and contain anisotropic features such as compositional foliations, lineations and lattice preferred orientations due to previous deformations, which can affect the strength of these rocks.
Strengths of brittle rocks have been shown to vary significantly as a function of foliation orientation relative to the compression direction (Jaeger 1960; Donath, 1961; 1972; Borg and Handin, 1966; Gottschalk et al., 1990; Shea and Kronenberg, 1992; 1993; Rawling et al., 2002). Recent work by Hansen et al. (2012) has demonstrated that olivine deformed to high shear strains develops a strong lattice preferred orientation that imparts an orientation-dependent strength (viscous anisotropy), similar to that of foliated rocks in the brittle upper crust. In addition, Qi et al. (2015) observed the development of a viscous anisotropy in olivine + melt aggregates due to strain localization in melt-rich zones. These data indicate that the strengths of the Earth’s crust and mantle are likely anisotropic, yet our models of their strengths are dominantly based on flow laws derived from experiments on isotropic materials (Gleason et al., 1995; Mei and Kohlstedt, 2001; among others).
Investigations performed using synchrotron radiation are uniquely advantageous to investigate how foliations, lineations and lattice preferred orientations create viscous anisotropies in rocks with crustal or mantle compositions. Analyses of in operando stresses in individual phases in polyphase rocks are possible where the X-ray spectra do not overlap, which allow investigators to determine strain partitioning between phases. It is also possible to measure development of lattice preferred orientation development and destruction in monophase aggregates during experiments (e.g. Bollinger et al. 2013). X-radiographs allow investigators to measure different strain rates in samples with different characteristics deformed in series. These types of data will help increase the accuracy of models of deformations of the Earth’s crust and mantle during the seismic cycle.
Transformation Plasticity (NEEDS WORK-DLG)
Transformation plasticity (TSP) arises from internal stresses generated by a volume change during phase transformation, which effectively cause a material to (locally, at the grain scale) reach its yield point; the application of a small differential stress then biases the deformation in the direction of the applied stress. TSP may result in anomalous weakening at olivine-spinel and other phase boundaries in the Earth, and may be generally important for the internal dynamics and evolution of planetary bodies, including larger icy satellites. Complex bending of subducted slabs in the Earth depicted in tomographic studies might be caused by TSP-induced slab weakening (Panasyuk and Hager, 1998). TSP might also explain low viscosity layers appearing in models of the global geoid and of glacial isostatic adjustment. More broadly, TSP may be the ubiquitous consequence of the many metamorphic reactions occurring in the Earth’s lithosphere (Poirier REF).
Although TSP is potentially an important deformation mechanism in the Earth’s lithosphere and mantle, experimental evidence for this behavior in earth materials is lacking. TSP is typically studied in laboratory experiments by applying a modest differential stress to a sample whilst cycling the temperature (at constant pressure) about a phase boundary. In a rare, if not only, demonstration of pressure-induced TSP for ice, a small differential stress was applied to samples cycled in pressure about the ice I-II phase boundary at constant temperature (Dunand et al., 2000). The viscosity of the ice in the midst of the phase transformation was ~7 orders of magnitude smaller than either pure ice I or pure ice II at the same temperature. The ice experiments represent the first demonstration of pressure-induced TSP for any material.
The unique capabilities of the D-DIA apparatus make is well-suited to study TSP in earth materials. In particular, XRD can be used in operando to monitor the progress of various phase transformations, and to quantify the stress in the transforming and transformed phases. The D-DIA in its current configuration can be used to study TSP in iron-rich olivine and in various other systems, for example, albite-jadeite, low to high quartz, XXXXX, and other systems. With improvements in pressure capabilities in the D-DIA, TSP experiments could also be conducted on more Mg-rich olivine samples.
Slow buoyancy-driven creep in the Earth’s asthenosphere and steady plate motions of the lithosphere are commonly modeled using steady-state rheological laws (Williams and Richardson, 1991; England and Molnar, 1997; Zhong et al., 2000; Bercovici, 2003; Behr and Platt, 2011). These models benefit from experimental flow laws and determinations of the relationships between flow strength, strain rate, temperature, grain size and thermodynamic conditions for an extensive number of mantle and crustal silicates (Kohlstedt et al., 1995). However, most flow laws determined for rocks and minerals at high pressure and temperature apply only when deformation in the Earth has reached a steady-state in which strain rate at a given stress is constant. Transients in mechanical response due to abrupt or slow changes in loading, and the associated evolution in microstructural state remain to be explored.
Geodetic studies of deformation associated with the earthquake cycle suggest an important role of transient rheologies in postseismic response (Pollitz, 2003; Freed et al., 2007, 2012; Bürgmann and Dresen, 2008). Episodic tremors, slow earthquakes and creep in Cascadia and the central San Andreas fault system reflect intrinsically transient behavior of faults and aseismic deformations of surrounding lithosphere (Szeliga et al., 2004; Ghosh et al., 2010; Guilhem and Nadeau, 2012; Khoshmanesh and Shirzaei, 2018). Thus, transient postseismic and interseismic slip measurements require viscoelastic models that apply to changing stress states (Klein et al., 2016; Xu et al., 2018).
Similarly, mantle flow models of glacial rebound and sea level histories require rheological relations that capture transient creep and viscoelastic responses under changing stresses (Argus et al., 2014; Caron et al., 2017). At the opposite extreme of deformation rates, seismic waves may be attenuated by transient viscoelastic responses that are not given by steady-state flow laws (Cooper, 2002; Jackson and Faul, 2010; McCarthy et al., 2011).
Transient constitutive creep laws have not been reported for many rocks, owing to the difficulty of conventional experimental methods to characterize changing defect densities, microstructures and fabrics (Handin et al., 1986). Constitutive laws have been developed (Hart, 1970, 1976) that can treat transient flow of crystalline solids over a wide range of time scales. However, only few studies have attempted to relate constitutive parameters such as material hardness to microstructures (Stone et al, 2004) or the evolution of hardness to changing defect densities. Conventional high-pressure, high-temperature laboratory methods have yielded useful relationships between steady-state flow laws and resulting defect densities and microstructures (Karato, 1987; Stipp and Tullis, 2003). However, changes in defect density, microstructures, and fabrics can only be inferred by comparing samples before and after experiments, or by microstructural observations and measurements at intermediate strains that require experiments to be interrupted repeatedly (Hansen et al., 2012).
In-situ X-ray diffraction during high-pressure, high-temperature deformation will revolutionize studies of transient creep of silicates by tracking changes in defect density, deformation microstructures, and crystallographic textures. Dispersion of X-ray diffraction can be used as a proxy for internal strain and defect densities during deformation. Changes in diffraction patterns can be used to detect subgrain and recrystallized grain populations, and diffraction data can be inverted to determine changing crystallographic alignments. However, developing these promising methods will require collaborations between rock mechanics specialists, rock physicists and beamline scientists.
Transients (AKK, also looks like more than one of us has been working on transient deformation)
The transient creep of rocks at high temperatures is a central process in a variety of geodynamic processes. During transient creep, the effective viscosity of a deforming rock gradually evolves in tandem with the rock microstructure until a steady-state viscosity is reached. By far, the bulk of investigations into the rheological behavior of rocks have focused on measuring and predicting steady-state viscosities (e.g., Hirth and Kohlstedt, 2003). However, the initial viscosities at the onset of creep (or just after a change in stress) can be several orders of magnitude lower than the eventual steady-state value.
Considering that steady-state viscosities are not generally reached until strains of at least 10^-2 have been achieved, geodynamic processes in which the strains are relatively small should be better characterized by the viscosities associated with transient creep. For instance, transient creep of the upper mantle has been identified as a major contributor to geodetically observed surface deformations during post-seismic creep (Pollitz, 2005; Freed et al., JGR, 2012; Masuti et al., Nature, 2016; Qiu et al., Nature Comms., 2018), for which the strains are typically <10^-4. Because transient viscosities also continue to evolve during postseismic deformation, they likely cause the rates at which stresses rebuild on seismogenic faults (and their neighboring faults) to be time dependent. Although the most sophisticated earthquake forecast models do incorporate time-dependent loading according to average plate motion rates (Field et al., 2014, 2015, and 2017), they still do not incorporate variable loading rates that would occur due to transient creep of the lower crust and upper mantle. In addition, transient viscosities are expected to be important, although have not yet been thoroughly considered, in other small-strain processes including flexure of the lithosphere near volcanic loads (Zhong and Watts, 2013) or in subducting slabs near trenches (Hunter and Watts, 2016), at which the strain rarely exceeds 10^-2.
Unfortunately, there is a paucity of data describing the transient creep of rocks. This lack of data primarily stems from the difficulty in measuring sample strain with sufficient resolution. Often the employed deformation apparatus is sufficiently compliant that isolating the sample displacement from the measured displacement requires an unreasonably precise calibration of the apparatus compliance. Some progress has been made in measuring transient creep by calibrating the compliance of a gas-medium apparatus (Chopra, 1997), but still with difficulty measuring strains below 10^-3. Perhaps the most robust measurements have been made on single crystals deformed in apparatus with no confining pressure such that an extensometer can directly measure the sample displacement (Hanson and Spetzler, 1994; Cooper et al., 2016). Unfortunately, the lack of confinement does not allow polycrystalline samples to be investigated due to the potential for microcrack formation and limits investigations to mineral phases that are stable at room pressure.
The implementation of synchrotron-based deformation experiments presents an exciting new avenue for measurements of transient creep. The ability to capture radiographs of the sample assembly while at high temperatures and pressures allows essentially all of the above difficulties to be overcome. For example, radiographs from D-DIA experiments allow measurement of strains as small as 10^-5 (Li and Weidner, RSI, 2007), and pressures and temperatures can be elevated enough to investigate polycrystalline aggregates of a wide-variety of relevant minerals. However, there is still a need for technological development considering most transient creep experiments are conducted by holding the applied load constant, while current high-pressure apparatus installed on beamlines are designed to be driven at a constant displacement rate.
Could spike fluids so they would show up in images so as to understand the pathwyas followed. Could also do sequential injection of different fluids to look at the fluid interactions that occur (might have applications in extracting oil from sediments) Melt migration and pathways and how they develop
Flow of polyphase materials
The flow of polymineralic rocks is more complex and more relevant to geology than that of the materials we normally chose in the laboratory. With single crystals we are concerned with effects of environmental parameters (P, T, chemistry); controls on the rheological behavior of monomineralic polycrystalline materials also include flow mechanisms allowed by the presence the grain boundaries, and processes such as partial melting, and polymorphism; and LPO. A polymineralic rock requires further consideration of spatial distribution, crystallographic orientation and the behavior of polyphase grain boundaries, phase separation, chemical reaction, etc. The complex processes that can result from the numerous interactions and their evolution with time and strain make the experimental approach almost intractable, especially given that m microanalysis can be done only on single snapshot of the deformed rock sample, that at the very end of a run. Thus such research is usually directed towards narrow, end-member regimes, such as binary composites of phases with greatly contrasting strength (many refs), or t restricted o directed studies of particular effects (effect of mineral reactions on the evolution of microstructures, Herwegh 2011; effects of water, fo2, Hitchings, 1989), etc. etc. In the absence of experimental constraint, much reliance has been made on modeling, which has not proved to be very productive in the grand scheme of things (refs refs)
A path towards real-time microanalysis in 3D in the synchrotron [presumably detailed elsewhere in the proposal] will fundamentally change the scientific approach to the rheological behavior of rocks, in that the relevant physical processes open to direct study will no longer be limited to those which change little (e.g., "steady-state") or only only linearly with time and strain. (The "solution" will still prove evasive), but a larger number of investigators will be attracted to studies that are closer to realisma and hold more promise of meaningful result.
New mechanisms that happen in polyphase and not in single phase rocks
Mixing laws for polyphase flow laws and how the interactions evolve with strain and changing microstructure Reactions occurring during deformation - transformation plasticity
There are two reasons to pursue high-resolution rock rheology with synchrotron X rays. The first is to overcome what is essentially a growing pain, and the second is to pursue revelatory topics in the microphysics of deformation. Regarding the first, the means for deforming samples at mantle pressures to 20 GPa and above had existed for decades, but until the breakthrough application of penetrating synchrotron X rays to the art (Weidner refs), there had been no means for measuring stress and strain rate in the small sample volumes (~1 mm3) required by the high pressure machines. With the ability of synchrotron X rays to penetrate the confines a solid-medium high-pressure apparatus to provide imaging and diffraction of small samples significant discoveries of the nature deformation of mantle materials at high-pressure have been made. The advantages of direct in operando sample analysis with synchrotron X rays have also attracted interest of lower pressure conventional rock mechanics research as well (refs). (Witness this proposal!). However, the pendulum has now swung in the other way: rheological measurements in high-pressure apparatus are only semi-quantitative and therefore rather unattractive to low-pressure studies. The problem is largely technical: Good resolution of rheological parameters characterizing the T, P, stress, g.s. dependence, etc of flow is largely limited by sample volume. The 1 mm3 volume also limits run temperatures to those below where significant grain growth occurs (with resultant loss of resolution) and makes it difficult to control water fugacity over the duration of an experiment, difficulties that would largely vanish with sample volumes >10 mm3. Such volumes are quite ordinary (on the small side, actually) for low-pressure rock mechanics and with newer large-capacity loading frames and solid medium deformation devices such as the DDIA-30, can also serve in deformation experiments to at least 10 GPa.
The second aspect is unrelated to the first, and relates to the mapping the state of stress in a polycrystalline rock at the subgrain level. Modeling (refs) has suggested that intragrain stress gradients are often significant, not only near obvious contacting grain edges, but on larger scales that impact the deformation of the whole grain in ways that would not be predicted on the basis of, say EPSC modeling.
Experiments will be testing models and helping to develop models
Having modelers involved in the RCN what would allow the modelers to consider what they would like to see happening within experiments and so help design adn interpret the experiments
[ This is an older part of the outline, probably replaced by the above:
* Ductile Deformation * Brittle Deformation * Intact Rock * Friction ]
Ideas for Science Qs and potential approaches -
Character of crust and lithosphere, plate boundary processes, flow of asthenosphere, earthquake source physics all depend on fundamental mechanical properties of rocks that can be investigated in lab experiments. Conventional rock deformation experiments allow measurement of mechanical properties and the analysis and imaging of samples before and after deformation by a wide array of analytical and imaging instruments. However, intermediate states are not readily examined without performing large numbers of experiments to intermediate strains/states.
Mineral physics experiments have benefited from in-situ ability to image samples and measure diffraction during experiments using bright, highly focused X-ray beamlines of synchrotron facilities. With extension of these methods to larger samples during deformation, major improvements can be made to monitor and understand deformations during experiments, tracking the evolution of mechanical behavior with changes changes in strain, microstructure, and fabric.
In the following - One option is to emphasize applications of rock deformation that RCN workshops and technical developments would address - variety or selected topics in Earth geodynamics, EQ mechanics -
Q: Should we reserve details of methods and strategies to later section(s) that would focus on technical virtues of X ray imagine and diffraction ? Or Combine ? In the following, I list some topics that were brought up at the workshop and in-situ beamline capabilities that could address. But I wonder if we don’t want to just address the science questions here first, and combine the beamline methods and need for RCN workshops in later sections.
1) Scales of Deformation (Durham) Mechanical properties of Earth are scale -dependent
From defects to shear zones
Large scale deformation and contributing microscale processes
Deformation processes - atomic scale to grain scale to mesoscale folding and fracture, shear zones to plate boundaries to plumes and subducting plates - scales of flaws, all varieties of heterogeneities
Importance of in-situ imaging larger samples
2) Coupling lattice Strain measurements with modeling (Burnley) Fundamental understanding of deformation of polycrystalline solids and
applications to use of microstructural observations to large-scale deformations in the Earth’s lithosphere and asthenosphere
Macroscopic mechanical properties vs grain-scale stresses/strains - calibrating micromechanical models through mapping stress/strain heterogeneity Improved diffraction analysis, improved modeling
3) Transient Creep and non-steady state constitutive laws - importance to Earth (Karato, Hansen)
transient creep associated with changes in loading - post seismic creep or interseismic creep of the earthquake cycle. Note the increasing need for time-depenent loading in earthquake hazard modelling Glacial rebound as loads are decreased or increased
Detecting defect densities by X-ray diffraction - links to internal hardness States, defect distributions, subgrain sizes, recrystallization, developing CPO, layering, and anisotropy Evolution of mechanical properties with fabric and microstructures
4) Shear fracture propagation (Zhu) Analyses of samples before and after development of shear fractures cannot
answer many questions of their nucleation or propagation. Prior to recent synchrotron imaging of samples during failure (Zhu et al, refs), only way to do this has been to monitor and locate AE events (Lockner et al., refs). Remaining questions and what we want to learn
3-D imaging as function of time during shear fracture propagation
5) Earthquake source physics, rapid fault rupture, slow and episodic fault slip
depend on frictional properties of rocks and wear products (gouge). Quasi- static and dynamic rock friction depend on processes at points of contact, populations of contacts that we have good theories for. However, to resolve them, imaging and friction during rock friction experiments would be useful.
Rock Friction and Imaging - stresses at points of contact, X-ray imagine and diffraction - evaluation of crystalline and amorphous wear products (Tullis)
6) Rock Physics Studies (Schmitt)
Linking Macroscopic rock Properties to Microscopic properties (pores, etc) Macroscopic Damage and microscopic descriptions Sources of Anisotropy Friction
Ways that in-situ imaging and diffraction can answer important questions
7) Strain localization and formation of shear zones (Kronenberg)
Heterogeneities in rocks that originally exist and are generated during deformation exist at many scales - some that lead to fine-scale (mm) shear zones and some leading to plate boundaries (SAF). Understanding the physics of strain softening and shear zone development is critical to understanding deformation of the lithosphere. Yet, understanding their development has been frustrated by the sparse observations of samples before and after deformation.
Monitor changes in defect densities, crystallographic preferred orientations, recrystallization during deformation by Xray imaging and diffraction Map stress/strain heterogeneity and controls on localization
8) Anisotropic mechanical properties and links to fabric, layering, and crystallographic preferred orientations (Hansen) - fundamental behavior of rock deformation, beyond simplifications of steady-state isotropic mechanical behavior
Ability to measure X-ray diffraction during experiments and determine evolving crystallographic preferred orientations
Ability to link crystal orientation to stress state
9) Rheological Mixing Laws (Karato, Kronenberg)
Most experimentally measured flow laws are appropriate to single-phase (mineral) polycrystalline rocks. Most rocks (crust and mantle) consist of multiple phases and require mixing laws that allow us to express flow laws as functions of individual phase flow laws, volumetric proportions of phases, and textures of the rocks (refs, Tullis et al, etc).
Study of flow laws of 2-phase rocks will be greatly improved by direct internal stress (diffraction) and strain (imaging) measurements within the constituent minerals during deformation.
10) Transformation plasticity and reaction softening/hardening (Goldsby)
Tectonic/geodynamic examples of potential transformation plasticity and deformation during metamorphic reactions
Utility of in-situ diffraction and imaging to study transformation plasticity
11) Phase Mixing and Changes in Deformation Mechanisms at High Strains (Skemer)
Tectonic/geodynamic examples of transitions in deformation mechanisms and flow laws as phase mixing occurs
Utility of in-situ imaging and diffraction to study phase mixing during deformation
12) Melt Segregation and Deformation of partial melts (Kohlstedt, Faul)
Deformation of partial melts in the Earth, segregation of melts from solids and importance for melt migration
Utility of in-situ diffraction and imaging to study melt segregation during shear deformation
13) Transformation faulting and earthquake instabilities in subduction systems (Burnley, Durham)
Intermediate to deep focus EQ and instabilities developed during high-pressure phase transitions.
Utility of in-situ diffraction and imaging to study new/secondary phases during reaction and deformation
14) Seismic attenuation (Goldsby, Hansen?, Karato?)
- Why the timing of this project meshes well with progress in Synchrotron Development
Many of these scientific questions call for in-situ imaging of samples and measurements of internal (microscale) strains, stresses, crystallographic preferred orientations. These have been developed for small samples at high P, T in Mineral Physics studies. Need for similar in-situ imaging and diffraction studies of larger samples during deformation.
Synchrotron Timing - Perfect timing of RCN to coordinate and develop new collaborations and methods of study as new, brigher beamlines come online (Zhong Zhong et al) New, brighter Beamlines (capabilities & dates)
What are major advantages and why do we need RCN to pursue these opportunities
- Technical Developments
Technical Developments and Needs for RCN Workshops to develop scientific strategies, collaborations, and new methods at beamlines
Importance of In-situ Imaging and Diffraction
Coupling rock deformation studies with X-ray beamline science
Ultra-fast elasticity measurements (Whitaker)
Diffraction Microscopy and Tomography (Almer, Xiao) In-situ micromechanical testing (Pagan)
The past fifteen years have seen a wide proliferation of high-energy synchrotron X-ray techniques capable of non-destructively probing the microstructure and micromechanical response of polycrystalline materials. These techniques include near-field high-energy diffraction microscopy (HEDM) capable of reconstructing full 3-D orientation fields, far field HEDM capable of determining the average orientation and elastic strain states of thousands of individual grains simultaneously, transmission orientation and strain pole measurements that probe the orientation dependence of lattice strain in grain ensembles, and energy dispersive diffraction mapping used to determine 3-D elastic fields in large specimens. These techniques have proven to be extremely valuable for understanding how material microstructure can influence both plasticity and fracture processes in metallic alloys. The natural similarities of deformation mechanisms in both metallic alloys and geological materials point to the opportunities for applying these X-ray techniques to study geological deformation processes. To make these new studies possible, geophysics researchers must make connections with the appropriate beamline staff and be trained in both the experimental techniques and data processing methods. This proposal aims to make this possible and work to create a new field of synchrotron users.
Broad X-ray beams (Rivers et al)
- What Workshops are needed?
- Beamline visits
- What science can be done with what Technology
- Steering Committee
Year 1 - Bring the newbies and teach them beamline experiments: Hands On 1
Year 2 - What we can do now is nice, but can we do this? - Big Group 1
Year 3 - Modifications of existing techniques and capabilities to new science: Hands On 2
Year 4 - We need new technology. Let's develop it. - Big Group 2
Year 5 - Hands On 3
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RCN Workshop Ideas – Terry Tullis NOTE: This has a lot more detail than the list originally in the Wiki. Sorry ‘bout that!
1. This workshop need not be held at a beam line. The focus would be on listing all the scientific problems that the community hopes might be answered by in situ observations on a beam line. The intent is to describe them in enough detail that the type of observations and experimental geometry, sample size, etc. that are needed to help answer them could be discussed in some depth. The overall aim of the workshop would be to determine 1) the range of experimental needs for all the scientific problems we can think of at the outset, and 2) to try to group them into categories of experimental setups that might allow their study. If only a few types of experimental setups could solve several problems, these could be prioritized in order to determine where subsequent design efforts for experimental setups should focus. Prioritization would be based on both the number of scientific problems that each setup could be used for as well as how easy it would be to move from existing technology to what is needed. Possible examples, just to get us thinking, of such categories of experimental setups are standard triaxial sample at pressures up to 100 MPa, sample dimensions of 1-3 cm; ring-shear samples at pressures up to 25 MPa, sample rings 4-5 cm in diameter, axis of shear-rotation rotatable from parallel to perpendicular to beam line and translatable in the direction that is both perpendicular to the beam line and to the rotation axis of the shear-rotation axis; IR spectroscopy, as a function of time and normal stress, of an internally reflected, synchrotron-generated IR beam traveling along a smooth interface between two oxidized silicon pieces pressed together; imaging, as a function of time and normal stress, of the sizes of contacts between two rough surfaces pressed together.
2. This would be held at some beam line and subsequent workshops would be held at other beam-lines. Among the beam lines to be considered are Brookhaven, Argonne, and Rochester (more?). For each of the workshops held at a beam-line, one element of the workshop would be to have presentations of the strengths and weaknesses of this particular beam-line. Possibly could include hands-on work of some participants using the beam-line prior to the actual workshop, followed by brief presentations of what was done. The other element would be to hear presentations and to discuss the progress made in designing the various experimental setups that were prioritizes in the first workshop. The primary focus would be on the highest priority setup identified in the first workshop, with less time spent on the lower priority setups. Groups of people interested in each setup would have been meeting either in person or virtually during the intervening year to make as much progress as possible on each setup. If any of the experimental designs reach the stage that they are ready for submission as a research proposal to the IF program at NSF, then the group responsible would submit such a proposal.
3. Similar to 2, except that the workshop would be held at a different beam line and that the number 2 priority would be the primary focus of the discussion on progress on experimental setups.
4. Similar to 2, except that the workshop would be held at a different beam line and that the number 3 priority would be the primary focus of the discussion on progress on experimental setups. More time than in other workshops would be spent also discussing progress on some of the lower priority setups.
5. Might or might not be held at a beam line (a fourth one or a repeat visit). Focus would be on summary presentations of all the progress made during the course of the RCN and in planning on how the community that has been formed through the RCN can continue to work together productively following the termination of the RCN grant.
EXAMPLE WORKSHOP - DCP
GEOPHYSICS HEDM WORKSHOP
A student geophysics-orientated high energy diffraction microscopy (HEDM) workshop would consist of a series of lectures giving an overview of the technique along with hands-on training collecting and processing diffraction data using the HEXRD software package. Students will be given the opportunity to collect data from their own samples (specifically geological materials) each afternoon/evening. To make data collection possible, the workshop will be limited to 10-15 students. Objectives: The workshop will be 2.5 days with the goal outcome of having students introduced to taking data at a synchrotron X-ray beamline and understand how these techniques can be applied to their own research for the purpose of future experiment design.
Day 1, AM (Lectures):
• Technique Overview
• Experiment Preparation / Sample requirements
• Microstructural and Micromechanical Response from HEDM Data
Day 1, PM (Data Collection):
• Group Near Field-HEDM Measurement
• Individual Far Field-HEDM Measurements
Day 2, AM (Lectures + Data Processing):
• Assessing Data Quality
• HEXRD Software Introduction
• Being processing data collected previous night
Day 2, PM: (Data collection 2):
• Continued Individual Far Field-HEDM Measurements (apply lessons learned from previous afternoon/morning)
Day 3 AM (Data Processing 2):
• Continued processing of data collected throughout workshop with help from workshop organizers
• Student Registration $250, goes towards incidentals and speaker travel
• Lodging $100/night
Slightly different version of workshop (Holyoke)
The workshops are broken into two large workshops and five smaller, hands-on workshops, if the budget permits.
First large workshop (similar to APS workshop size), Year 1: This two day workshop is focused on selling the idea of working at the beamlines to people who do not currently use synchrotron-based techniques, but are interested in the broad science questions above. The first day would be a series of talks demonstrating the capabilities of the various beamlines, but focused on imaging techniques to engage both field-based, theoretical and experimental investigators. A mix of beamline scientists and current users would present the technical capabilities and applications, respectively, of each beamline (NSLS-II, 6-BM-B, GSE-CARS, CHESS, and Lawrence Berkeley for high resolution FTIR mapping). Describing the increases in image/analytical resolution or experimental capabilities coming in the future should be part of each beamline scientist or user’s presentation. The second day can be broken into smaller groups of beamline scientists and current users to discuss the entire process of how a new user who has no experience with this type of work can come to the lab for the first time and leave with useful data. The beamline scientists and users can also work with the attendees to develop proposals for beam time at the various beamlines.
Second large workshop Year 2 or 3: Two day workshop focused on developing groups to write proposals for new experimental technology development. The general areas of development would likely be: 1) large shear displacement apparatus (lower P and larger samples than the Drickamer apparatus) to address questions related to polyphase textural evolution/viscous anisotropy, melt interconnectivity/transport, reaction-induced superplasticity and friction processes, 2) lower pressure, larger sample axial compression devices for axial compression to address problems related to fluid rock interaction, reaction-induced superplasticity and fracture development and 3) improving current technologies, such as the D-DIA, which can be used to address similar questions.
Can these workshops be scheduled before AGU or is a two day workshop and AGU too much time? They may be cheaper to run at APS, but that involves extra travel time.
Five hands-on workshops (smaller participant groups): The format of each of these workshops can be identical to the one posted by Darren. One day of how-to, one really long day of work on beamline, one for learning to process data. Volunteers from the steering committee who have experience at the beamline could help beamline scientists with operation. Years 1-5: APS, CHESS, NSLS-II, APS (if upgrades finished), LBL.
In addition to these workshops, it wouldn’t cost anything extra to propose synchrotron-work focused sessions at AGU in years 2-5, which the steering committee can chair and encourage the attendees (beneficiaries) of the both types of workshops to showcase their results.
Workshop for stress – strain – time at APS 6BMB with the DDIA This is a hands-on workshop illustrating the capabilities of the DDIA at 6BMB at APS. It uses the DDIA and is illustrated to fit into 5 days with possible extension to study samples brought by participants.
Max: 10 students
Day 1: Lectures on the fundamentals: what is it, how do we measure it?
Day 2: Lectures and preparing samples. Introduction to equipment, control system, etc. End day with loaded sample assemblies.
Day 3: Experiment by all, millihertz and megahertz elastic/anelastic properties. Look at ringwoodite to olivine sample as pressure is decreased at high temperature for Fa70.
Day 4: Experiment by all, plastic properties of sample. Look at olivine (again).
Day 5: Analyze data. Divide it up among individuals/groups. After dinner summarize results.
Day 6 and 7: Experiments for students that brought their own samples and are pre-approved. Samples can be prepared during day 5 as others reduce data…
THOUGHTS ON WORKSHOPS (Goldsby)
I liked the second of Wenlu's ideas about workshops – with each centered around capabilities or methods (imaging, deformation, large volume, etc.), to which people bring their favorite scientific problem. That seems better than organizing around scientific topics (there are more topics than available workshops), and dovetails better with the overall goal of the RCN – to integrate existing and emerging technology with new science. Each workshop on a given method would be tasked with describing the state of the art, what the coming beam line advances will bring and make possible, and how these existing and new techniques can be applied to specific geophysical problems. The workshops would involve beam line scientists, materials scientists (who are likely further along than earth scientists in using various methods), and geophysicists/rock mechanicians.
I think the hands-on workshops should be attached to and topically appropriate for each of the Methods workshops. It seems unlikely that we will make a major innovation, though, or be able to look at multiple samples that people bring to the workshop, in the limited time available, depending on the kind of experiments that are being done. A better model for the hands-on component might be to identify ahead of time some unique experiment that could be done that demonstrates possibilities. In the Imaging workshop, for example, it might be cool to look at a sample from a friction experiment on gouge (with the experimental fault not separated) to look for localized slip surfaces within the sample. In the D-DIA workshop, we could do a transformation plasticity experiment, a cyclic (tension/compression) experiment like Lars Hansen has developed, or some other whiz-bang experiment. In the large volume workshop, we could do something novel that can’t be done with a smaller sample (attenuation?, others). These demos ideally would be bench-tested ahead of time by beamline scientists and/or practitioners to see how well they work. Students would be encouraged to operate the experiments, with a lot of help from a beam line scientist or practitioner. With time permitting, people might try to study samples they bring, depending on the topic, but there will likely not be enough time.
Could have a first overarching meeting, but we just did that. A possible schedule might be:
Workshop 1 - Imaging - What is possible generally with existing and emerging technology? Scientific topics: localized frictional slip, the permeability structure of rocks, etc.
Workshop 2 - Deformation - What is possible generally with existing and emerging technology? Topics: transient creep, attenuation, transformation plasticity, evolution of CPO with strain, etc.)
Workshop 3 - Diffraction
Workshop 4 - Large volume capabilities - What new or existing problems can be addressed or better addressed with larger sample volumes? Topics: attenuation, others
Workshop 5 - What progress have we made? What are the next steps?
If we wanted a first meeting to set the stage overall:
Workshop 1 - Overview
Workshop 2 - Imaging - What is possible generally with existing and emerging technology? Scientific topics: localized frictional slip, the permeability structure of rocks, etc.
Workshop 3 - Deformation - What is possible generally with existing and emerging technology? Topics: transient creep, attenuation, transformation plasticity, evolution of CPO with strain, etc.)
Workshop 4 - Large volume capabilities - What new or existing problems can be addressed or better addressed with larger sample volumes? Topics: attenuation, others
Workshop 5 - Diffraction?
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Why synchrotron-based mineral-rock physics?
Composition and structure of Earth (and other planets) can be studied based on the combination of various observations (gravity, composition of various planetary materials (e.g., mantle rocks, meteorites), seismic velocities, etc.) and the results of studies on materials properties under extreme conditions. There have been major progress in both fields, and we now have a good model of composition of Earth and other planets.
However, Earth and other planets are not static bodies but they are dynamic and evolving. Presence of earthquakes (on Earth) and volcanism and geochemical observations on some isotopes demonstrate this for a broad range of time scales. Consequently, many key questions on Earth (and other planets) can be addressed only through the studies on the dynamics and evolution of these planets. For example, one may ask how has Earth maintained temperate climate for billions of year that allowed life to emerge and evolve. One may also ask why plate tectonics operates on Earth but not on Venus. From more societal point of view, one may ask why fault motion is unstable causing earthquakes in some cases, while it is stable or nearly stable in other cases (slow earthquakes versus “normal” earthquakes). And as we will show later, when properties or processes related to the dynamics and evolution of Earth are to be studied, one will need to characterize heterogeneous and evolving properties that requires a use of a large volume apparatus combined with high resolution probes such as high intensity x-ray provided by a synchrotron facility.
A wide range of geological, geophysical and geochemical observations provides hints (constraints) on how these dynamic and processes might occur or have been occurring on Earth and on other planets. They include the distribution and frequency of earthquakes, the distribution of seismic wave velocities, attenuation and electrical conductivity, and the chemical composition of various materials including basaltic rocks and mantle rocks. In addition, geodetic measurements of crustal motion after the melting of ice sheets or after an earthquake provide constraints on rheological properties of Earth’s interior that control the nature of materials circulation.
However, understanding the evolution and dynamics of Earth and other planets through these observations is not straightforward. For example, deformation of rocks is often time-dependent and non-uniform. Strength of rocks at short time scales (e.g., deformation after the melting of ice sheets) and that at longer time scales (e.g., deformation associated with plate motion) can be largely different. Localized deformation is often found and plays a critical role in various geological processes, but charactering the processes of localization from these observations is difficult. In addition, chemical reactions or phase transformations may influence the nature of deformation potentially leads to localized unstable deformation. But a laboratory study of such a process is challenging for the same reasons. Furthermore, most of geodetic observations involve small strain (comparable to or less than elastic strain) and the connection of these observations to the flow properties in geological time scale (i.e., large strain deformation) is unclear.
The richness of mechanical behavior is caused by the complexities in rock structure that leads to evolving heterogeneous stress-strain inside of a deforming rock. Studying the role of evolving structure and evolving internal stress-strain is difficult if one uses a conventional method where only macroscopic stress-strain relationship is measured and the microstructure was studied only after an experiment (post mortem observations).
Similarly, constraining the processes of melt generation and migration from geochemical observations is difficult because the relation between these observations and the processes of melt generation and transport is non-unique. In addition, experimental studies on melt generation and transport is challenging because these processes are controlled by the geometry of melt and internal stress at the melt-mineral boundaries both of which evolve and most likely they depend on the stress level (or the time scale in which these processes occur) that differ substantially between the lab and Earth.
Common to these processes is the fact that they are affected largely by the microstructures and by the internal stress-strain in a rock with a variety of scales that evolve with time (strain). Synchrotron facilities provide an excellent opportunity to study these properties by providing the key information on microstructural and internal stress-strain evolution during an experiment (i.e., in-situ observations). Synchrotron produces high intensity and highly collimated x-rays. Consequently, one can investigate various properties with high spatial resolution. When combined with a theoretical model, one can also investigate the distribution of internal stress (and strain) including the variation of stress among crystals with different orientations from diffracted x-rays. Since the x-ray intensity is strong, most of these measurements can be done in a short period, and therefore in many cases, one can trace the evolution of properties of a sample during an experiment.
We note that most of these properties are highly sensitive to temperature and to chemical environment including water and oxygen fugacity. Also many of these properties or processes involve a variety of space scale from crystal dislocations to grain-boundaries, cracks and boundaries of different phases. For these reasons, a relatively large volume apparatus will be best suited to conduct these experimental studies combined with a synchrotron facility.
In the following, we will --------.
-- Shun-ichiro Karato; updated 12pm, 03 October, 2018