Geophysical data demonstrate elevated seismic activity in subduction zones. Here dehydration and fluid pressure cycling as a function of increasing compaction and metamorphic grade are closely linked to deformation over a multitude of spatial and time scales. The highly anisotropic and initially fluid saturated marine sediments and altered oceanic crust dehydrate, while being incorporated into the accretionary wedge and subducted under the upper plate. Under high tectonic stresses, fluid overpressure eventually results in mechanical instabilities, promoting either hydrofracturing or ductile failure giving way for fluids to circulate. Collection of these fluids at the micron-scale and propagation along pathways up to the deca-kilometre scale are probably in charge for phenomena such as episodic tremor and slow slip. Increasing evidence from geophysical and seismic studies suggest that accumulation of slow slip events and fluids may even trigger devastating high-energy megathrust earthquakes. Quantitative understanding about (i) the release of fluids from their host rocks, (ii) the effect of localisation of both fluid flow and deformation and (iii) their effect on seismic activity are therefore crucial to understand the complex feedback processes. This system can only be fully understood by a close collaboration between experts from structural geology, metamorphic petrology and geophysics. In this interdisciplinary session, we therefore invite contributions from natural, experimental- and numerical modelling-based studies focussing on both exhumed (paleo) and active subduction zones.

Fractures and faults are common tectonic features within shallowly deformed rocks. Fracture networks play a fundamental role in fluid migration. Understanding the mechanical and chronological development of fracture networks is therefore key for tectonic studies as well as for resources exploration and waste repositories studies.
Fractures and faults are witnesses of the medium history, resulting from processes controlled by physical forces and/or chemical potential. A better understanding of the parameters that control fracture complexity in rocks will lead to new tools for reconstructing crustal-scale processes such as fluid flow and fluid-rock interactions, paleostress evolution and earthquake tectonics. However, the great challenge is the understanding of dynamic feedbacks between fluid flow, permeability rise/fall, chemical reactions and rock failure. Fluid sources, fluid flow and fluid-rock interactions vary spatially and temporally as a function of basin and reservoir structural evolution, altering the physical/mechanical properties of fractures and host rocks.
Fractures form at all stages of rock history, from early diagenesis/burial to major deformation events. Building realistic conceptual and predictive models of fracture types and occurrence therefore requires recognition of fractures formed prior to, and during deformation events. A blind spot in fracture analysis has been for long the lack of constraints on the absolute timing of brittle failure and structural diagenesis. Recent progress in absolute dating of calcite cements/coatings of veins/faults has proven the relevance of meso-structures to regional structural evolution, allowing for a refined tectonic history. New steps forward include a better appraisal of the rate of development and lifetime of individual fracture and fracture sets, and of the timing and rate of fluid flow in fractured rocks.
This session aims at bringing together scientists working in the field, in the lab, and on simulations to foster discussion towards improving our understanding of (1) the mechanics, occurrence, timing and stress history of fractures in upper crustal rocks, and (2) the role fracture networks play on subsurface fluid flow. We welcome contributions from all fields, including structural geology, mechanics, isotope geochemistry, and hydrogeology that aim at comprehending the development of fracture systems in time and space and their co-evolution with fluid flow in a variety of geological settings.

Fractures are discontinuities in rocks that are present in almost all geological settings and at any scale. They may represent small-scale fissures or build up large scale faults. Fractures are extreme forms of heterogeneities, often with a small extension but huge impact.
The presence of fractures modifies the bulk physical properties of the original media by many orders of magnitudes, and they often introduce a strongly nonlinear behavior. This refers in particular to the mechanical properties via reduction of strength and stiffness. Fractures also provide the main flow and transport pathways in hard rock aquifers, dominating over the permeability of the rock matrix, as well as creating anisotropic flow fields and transport. Understanding their hydraulic and mechanical properties of fractures and fracture networks thus are crucial for predicting the movement of any fluid such as of water, air, hydrocarbons, or CO2. Consequently, fractures are of great importance in various disciplines such as hydrogeology, hydrocarbon reservoir management, and geothermal reservoir engineering.
The geologist toolbox to explore and model fractured rocks is getting more and more extended. This session is dedicated to novel ideas and concepts on treating the challenges related to the generic understanding, the characterization and the modelling of fractured geological media.
Contributions are welcome from the following topics
• Exploration methods for mechanical and/or hydraulic characterization of fractured media
• Structural construction of fractured media by deterministic or stochastic approaches,
• Representation of static hydraulic and/or mechanical characteristics of fractured media involving continuous or discontinuous methods,
• Simulation of dynamic processes and the hydraulic and/or mechanical behavior of fractured media,
• Theoretical studies and field applications in fractured geological formations,
• Concepts of accounting for fractured properties specifically in groundwater, petroleum or geothermal management applications.

The goal of this session is to reconcile short-time/small-scale and long-time/large-scale observations, including geodynamic processes such as subduction, collision, rifting or mantle lithosphere interactions. Despite the remarkable advances in experimental rock mechanics, the implications of rock-mechanics data for large temporal and spatial scale tectonic processes are still not straightforward, since the latter are strongly controlled by local lithological stratification of the lithosphere, its thermal structure, fluid content, tectonic heritage, metamorphic reactions and deformation rates.

Mineral reactions have mechanical effects that may result in the development of pressure variations and thus are critical for interpreting microstructural and mineral composition observations. Such effects may fundamentally influence element transport properties and rheological behavior.
Here, we encourage presentations focused on the interplay between metamorphic processes and deformation on all scales, on the rheological behavior of crustal and mantle rocks and time scales of metamorphic reactions in order to discuss
(1) how and when up to GPa-level differential stress and pressure variations can be built and maintained at geological timescales and modelling of such systems,
(2) deviations from lithostatic pressure during metamorphism: fact or fiction?,
(3) the impact of deviations from lithostatic pressure on geodynamic reconstructions.
(4) the effect of porous fluid and partial melting on the long-term strength.
We therefore invite the researchers from different domains (rock mechanics, petrographic observations, geodynamic and thermo-mechanical modelling) to share their views on the way forward for improving our knowledge of the long-term rheology and chemo-thermo-mechanical behavior of the lithosphere and mantle.