The Earth’s interior is a hidden and significant water reservoir on a par with the hydrosphere. The properties and processes of the crust and the mantle are strongly modulated by the storage and transport of water. Despite significant progress made in the research of deep water cycle over the past three decades, important scientific challenges still remain. How much water is down there? How heterogeneously is water distributed on different spatial scales? Where did water originate? How has water been exchanged between external and internal reservoirs of the Earth through geological time? How significant, quantitatively, is the role of water in facilitating mantle convection and melting? What is the function of water in ore formation, deep earthquakes, and volcanic eruptions? We invite contributions from experimental, computational, analytical, petrological-geochemical and geophysical studies that progress on all aspects of water as a vital element of global geodynamics.

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.

Subduction zones are arguably the most important geological features of our planet, where plates plunge into the deep, metamorphic reactions take place, large earthquakes happen and melting induces volcanism and creation of continental crust. None of these processes would be possible without the cycling of volatiles, and this session aims to explore their role in convergent margins. Questions to address include the following. Do Atlantic and Pacific subduction zones cycle volatiles in different ways? What dynamic or chemical roles are played by subducted fracture zones and plate bending faults? How do fluids and melts interact with the mantle wedge and overlying lithosphere? Why do some of the Earth’s largest mineral resources form in subduction settings? We aim to bring together geodynamicists, geochemists, petrologists, seismologists, mineral and rock physicists, and structural geologists to understand how plate hydration/slab dynamics/dehydration, and subsequent mantle wedge melting/fluid percolation, and ultimately melt segregation/accumulation lead to the diverse range of phenomena observed at convergence zones around the globe.

Includes Augustus Love Medal by Harro Schmeling
Invited Speaker: Nestor Cerpa (University of Montpellier, France)

Subduction drives plate tectonics, generating the major proportion of subaerial volcanism, releasing >90% seismic moment magnitude, forming continents, and recycling lithosphere. Therefore, it is the most important geodynamical phenomenon on Earth and the major driver of global geochemical cycles. Seismological data show a fascinating range in shapes of subducting slabs. Arc volcanism illustrates the complexity of geochemical and petrological phenomena associated with subduction.

Numerical and laboratory modelling studies have successfully built our understanding of many aspects of the geodynamics of subduction zones. Detailed geochemical studies, investigating compositional variation within and between volcanic arcs, provide further insights into systematic chemical processes at the slab surface and within the mantle wedge, providing constraints on thermal structures and material transport within subduction zones. However, with different technical and methodological approaches, model set-ups, inputs and material properties, and in some cases conflicting conclusions between chemical and physical models, a consistent picture of the controlling parameters of subduction-zone processes has so far not emerged.

This session aims to follow subducting lithosphere on its journey from the surface down into the Earth's mantle, and to understand the driving processes for deformation and magmatism in the over-riding plate. We aim to address topics such as: subduction initiation and dynamics; changes in mineral breakdown processes at the slab surface; the formation and migration of fluids and melts at the slab surface; primary melt generation in the wedge; subduction-related magmatism; controls on the position and width of the volcanic arc; subduction-induced seismicity; mantle wedge processes; the fate of subducted crust, sediments and volatiles; the importance of subducting seamounts, LIPs, and ridges; links between near-surface processes and slab dynamics and with regional tectonic evolution; slab delamination and break-off; the effect of subduction on mantle flow; and imaging subduction zone processes.

With this session, we aim to form an integrated picture of the subduction process, and invite contributions from a wide range of disciplines, such as geodynamics, modelling, geochemistry, petrology, volcanology and seismology, to discuss subduction zone dynamics at all scales from the surface to the lower mantle, or in applications to natural laboratories.

Continental rifting is a complex process spanning from the inception of extension to continental rupture or the formation of a failed rift. This session aims at combining new data, concepts and techniques elucidating the structure and dynamics of rifts and rifted margins. We invite submissions highlighting the time-dependent evolution of processes such as: initiation and growth of faults and ductile shear zones, tectonic and sedimentary history, magma migration, storage and volcanism, lithospheric necking and rift strength loss, influence of the pre-rift lithospheric structure, rift kinematics and plate motion, mantle flow and dynamic topography, as well as break-up and the transition to sea-floor spreading. We encourage contributions using multi-disciplinary and innovative methods from field geology, geochronology, geochemistry, petrology, seismology, geodesy, marine geophysics, plate reconstruction, or numerical or analogue modelling. Special emphasis will be given to presentations that provide an integrated picture by combining results from active rifts, passive margins, failed rift arms or by bridging the temporal and spatial scales associated with rifting.

Public information:
Dear participants of EGU session GD6.3 on rifting

We will start the discussion at 10:45 CET on Friday 8 May, and it will last until 12:30 CET, although the chat will remain active for 30 min more.

This is how we plan to carry on the session:

· Every contribution will get about 5 minutes of discussion
· The conveners will introduce the contribution (title, authors,..)
· The presenting authors will give a short summary/introduction (2-3 sentences) of their work and contact details for potential further discussion (@ authors, please prepare these in advance to ensure a smooth transition).
· Discussion with participants

If time permits, we will have a more general discussion after all contributions have been presented.

Here’s the order of the presentations:

· Tortelli et al.
· Welford & Geng
· Phillips & McCaffrey
· Pan et al.
· Glerum & Brune
· Braschi et al.
· Bauer et al.
· Pagli et al.
· La Rosa et al.
· Keir et al.
· King et al.
· Lymer et al.
· Yang & Welford
· Chenin et al.
· Forzese et al.
· Frasca et al.