Subduction drives plate tectonics, generates the major proportion of subaerial volcanism, forms continents, and entrains surface material back to the deep Earth. Therefore, it is arguably 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. Surface topography provides insight in the orogenic processes related to subduction and continental collision.
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.
From Oceanic to Continental Subductions: tectonics and earthquakes
Many new high quality and high resolution geophysical and geological data had been acquired in the past years that need to be updated, re-analysed and re-interpreted in the light of our present knowledge in subductions processes. Moreover it is needed to better clarify the temporal and spatial evolution of those processes in order to much precise our geodynamic ideas of mountain building, subduction, transition of collision to subduction, or transition of subduction to collision.
Among other global places, the zone from Japan, Taiwan to the Philippines is a key area to study such subduction/collision transition due to the rapid convergence between Eurasian and Philippine Sea plates. There are geodynamic inversion of the east dipping Manila oceanic subduction, that evolves northward, first, into a Continental Subduction (also called Collision) onshore Taiwan, then secondly, east of Taiwan, into the north dipping Ryukyu arc/continent subduction. Due to the so rapid Plates shortening rate (10cm.y-1), those active Oceanic to Continental Subductions processes in Taiwan creates 1/8 of the annual seismicity in the World !
There are other places in the World active or not, that should also be taken into careful consideration in order to reveal and lead us to better understand new tectonic processes (e.g.: Alpes, Pyrénées, Cascades and so on).
To conclude in this EGU session, we aim to update the existing geodynamic state of the art of the oceanic to continental subductions processes after so numerous data that had been collected recently and all the works that had been done on this subject. Therefore this EGU Session should help us to much better understand the tectonics related to plate, plate collision and the transition between the subduction and collision.
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.
Lena Melekhova (Bristol University)
Ingo Grevemeyer (GEOMAR)
Lithosphere and Upper Mantle Heterogeneities Shaping Surface Deformation and Subduction Dynamics.
The lithosphere, the outermost shell of the Earth, constitutes the upper thermal boundary layer of mantle convection. It is well established that its properties play a central role in the development of solid Earth dynamics. Through its properties the lithosphere also provides a primary source of thermal and chemical anomalies for mantle convection when it is injected in the mantle as subducting slabs. Here, the subduction of cold and dense oceanic lithosphere into the underlying mantle acts as the major driving force of plate motion, and as a key component of the water and carbon cycles throughout the Earth. At the global scale, some of these lithosphere heterogeneities include rheological stratifications, sutures, fracture zones, and lateral and vertical variations in temperature and composition. These exist at various scales and play a major role in determining subduction dynamics and the degree of lithosphere-mantle decoupling. Deciphering the interaction of the lithosphere with the underlying asthenosphere and deeper mantle is critical to understanding the secular evolution of the Earth system and to reconcile models with natural observations. This session aims to highlight recent advances in constraining the scales and amplitudes of heterogeneities in the lithosphere as well as their dynamic role. We welcome multidisciplinary contributions. Some key areas of interest are lithospheric structure and morphology, subduction kinematics and dynamics, slab-mantle interaction and slab deformation, active margin tectonics and subduction-induced seismicity.
Continental rifting is a multi-facetted process spanning from the inception of extension to continental rupture or the formation of a failed rift. This session aims at combining new data sets, 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 of faults and ductile shear zones, tectono-magmatic and sedimentary history, lithospheric necking and rift strength loss, influence of the pre-rift lithospheric structure, mantle dynamics and associated effects on rifting processes, as well as continental break-up and the transition to sea-floor spreading. We encourage contributions using multi-disciplinary and innovative methods from field geology, geochronology, seismology, geodesy, marine geophysics, plate reconstruction, or modeling. Focus regions may include but are not limited to the Atlantic, Indian Ocean, Mediterranean and South China Sea (e.g. IODP 367/368 area) rifted margins, or the East African, Eger, Baikal and Gulf of California rift systems. 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.
Cross-disciplinary investigations of extensional systems
What controls lithosphere evolution during extension? The aim of this session is to investigate diverging systems over a wide range of spatial and temporal scales, and at all stages in the life cycle of divergent plate boundaries including continental rifting, mantle exhumation and seafloor spreading.
A special emphasis will be given to
(1) studies that couple lithospheric deformation models to plate kinematics, and that integrate possibly the role of serpentinisation and/or magmatism in the models.
(2) works that analyse subsidence and thermal effect of rifting and break-up.
(3) paleogeographic reconstructions revealing the influence of sedimentation and lithosphere structure evolution on biogeochemical cycles and oceanographic circulation.
(4) contributions that elucidate extensional modes through the interplay between tectonic structures, magmatism and the stratigraphic record using field, petrological and seismic data.
Volcanic versus non-volcanic rifts and passive margins, from rift to ridge
New observations and modeling allow us to investigate the underlying processes responsible for volcanic and non-volcanic rift and passive margin formation. Key questions to be resolved include 1) what controls the amount and distribution of magmatism during volcanic to non-volcanic rift and passive margin formation. 2) How does magmatism impact the tectonic evolution of these systems and what are the structural and rheological controls of magmatism and feedbacks on tectonic deformation. 3) How are structural style of passive margin formation and magmatism linked? 4) What are the consequences of magmatic versus a-magmatic systems for the associated sedimentary basins? 5) What is the depositional environment for formation of seaward dipping reflector sequences and which processes control anomalous vertical motions during basin evolution? We encourage abstracts that offer new insights into processes underlying volcanic and non volcanic rift-passive margin formation from rift to ridge, using constraints from observations and modeling.
Rifted margins: Geological and geophysical observations, interpretations and their uncertainty with respect to the understanding of their evolutions and architectures
The integrated study of field (young, and ancient analogues preserved in orogenic systems), seismic reflection/refraction, gravity/magnetics, well data (exploration and IODP), analogue and thermo-mechanical modelling approaches have greatly improved our understanding of the processes that influence and modify the architecture (crustal, magmatic, sedimentary, structural and thermal) of the distal domain of rifted margins. As more data becomes available our appreciation of the 3D and ultimately 4D geodynamic processes that influence the formation and present day structure of distal margins is evolving. Although all rifted margins are somewhat unique, similar genetic processes are often proposed despite the underlying interpretational uncertainties. These uncertainties can impact the resulting interpretations relating to the tectono-magmatic and crustal models. Therefore, despite many models the process often remains controversial and/or far for being well constrained.
This session would like to explore and discuss the observations and interpretations derived from geological and geophysical datasets across rifted margins and distal margins. Importantly, uncertainties should be addressed with respect to our current understanding of the genetic rift-domain evolution. Observations should focus on the evidences for processes that impact the final architecture, rock content and thermal imprint of conjugate margins. This relates to the observed style of extension and thinning (high vs low angle faulting and static vs dynamic interpretations and their evidence), vertical motions (e.g. uplift and subsidence), the isostatic impacts of the tectonic, magmatic and stratigraphic history relating to the genetic-rift domains.
Geodynamics of continent collisions: subduction, collision and exhumation processes (including TS Division Outstanding ECS Lecture by Daniel Pastor-Galán)
This session focuses on continental collision, with an aim to understand the geodynamic processes of the subduction of rocks, continent collision and exhumation of the metamorphic core of the orogen including the subduction channel. Numerous studies of colliding continental plates show the complex interaction and feedback of processes related to the thermo-mechanical history recorded in pressure-temperature-deformation-time paths of the subducted and exhumed rocks. With modern analytical techniques, important parameters such as differential stress, strain rates, exhumation rates, kinematics, rheology, temperature and pressure can be revealed from selected rock samples from ancient and modern collision orogens such as the Alpine-Zagros-Himalayan chain, Caledonides, Variscides, or Grenville. In this session, we anticipate contributions from a broad spectrum of geoscientists, which focus on geodynamics of continent collision of ancient and recent collisional orogens.
Accretion, collision and oroclinal bending in the Late Paleozoic: linking with the supercontinental evolution
The supercontinental cycle has profound influences on the evolution of the solid Earth, climate, and life at least since the Paleoproterozoic. Our understanding on the geodynamics of the supercontinental assembly and its link with global accretional and collisional events as well as large-scale orogenic curvatures (oroclines) remains incomplete. Here we focus on the Late Paleozoic evolution of the Pangea supercontinent, which was accompanied by a series of accretionary, collisional and orocline bending events within its core (Appalachian-Variscan-Alleghanian) and along its external boundaries (Terra Australis, Central Asian Orogenic Belt and Western Americas belts). We hope to bring new data and fresh ideas together to further understand the geodynamic link of the global orogenic evolution with the supercontinent assembly. We welcome all contributions on Late Paleozoic geology, paleomagnetism, tectonics and geodynamics.
Invited Speaker: Professor William (Bill) Collins (Curtin University)
Presentation Title: Billion year cyclicity through Earth history: causes and consequences
The session is organized in cooperation with IGCP Project 662: “Orogenic architecture and crustal growth from accretion to collision: examples from the Central Asian Orogenic Belt and Tethyan orogen”, which is supported by UNESCO-IUGS. For more information, please refer to the weblink of IGCP 662: http://igcp662.org.cn/
Oceanic and continental transform faults: towards a multi-disciplinary approach
Transform faults form major active plate boundaries and are intrinsic features of plate tectonics and plate accretion. Submarine transforms are likely to be fundamental pathways for fluid circulation in depth, thus significantly contributing to the exchange between the lithosphere and the hydrosphere. This implies serpentinization and weathering that affect the mechanical properties in the deformation zone. An open question is the influence of the elemental exchange between the crust and ocean water on these processes, as well as the interactions with the biosphere, both at the surface and at depth. Continental transforms and strike-slip faults are often a site of major earthquakes, representing major hazards for the population. Here too, the role of weathering in the deformation zone is still unconstrained. Both types of faults are still poorly known in terms of structure, rheology and deformation. These features are seismically active zones, with large earthquakes often being recorded on the largest faults. Yet, little is known about the rupture process, seismic cyclicity and active deformation of transform faults. Recent works have shown that fracture zones, supposedly inactive features, can be reactivated and be the site of large earthquakes and deformation. Additional open questions are the way transform faults deform under far-field stresses, such as plate kinematic changes, and under more local stresses, what are the time constants of the processes and what are the primary controls of the tectonic and magmatic styles of the response. The tectonic and magmatic response of large offset transforms, particularly, is still largely unknown.
This session aims to present recent results on studies of these large features, especially on the rheology, deformation patterns, rupture processes, fluid circulation and physical properties of transform faults. We welcome observational studies on strike-slip and transform faults, both continental and oceanic, on fracture zones and on transform continental margins (structural geology and tectonics, geophysical imaging of the crust and lithosphere, petrology and geochemistry, seismology, fluid circulation and rock alteration, geodesy) as well as modelling studies, both analogue and numerical. Cross-disciplinary approaches are encouraged. The submission of abstracts divulging on-going international projects (drilling sites, seismic reflection imaging along strike-slip faults) are also welcome. This session is promoted by the Oceanic Transform Faults working group of InterRidge.
The impact of mantle serpentinization on the evolution of rifted margins, oceanic ridges & subduction zones: new insights from geophysical & petrological observations, & numerical/analogue modelling (incl. Stephan Mueller Medal Lecture by Serge Lallemand)
Serpentinization is a mantle hydration reaction of major interest because of its implication in the evolution of rifted margins, mid-ocean ridges, and subduction zones. Serpentinization leads to weak hydrous minerals crystallization that yields to a reduction in the friction coefficient and an increase in the volume of mantle rock.
In rifted margins and mid-ocean ridges, weak serpentinized peridotite and serpentinization-driven fluid overpressure are known to have a critical role in the kinematics of low-angle detachment faulting that exposes mantle lithology to the seafloor. At mid-ocean ridges, these low-angle structures control the formation of oceanic core complexes, while at rifted margins control the exhumation of large portions of sub-continental mantle. Serpentinization is also an exothermic reaction that can produce significant heat and derive serpentinite hosted hydrothermal systems, and thus impact the submarine ecosystems.
In subduction zones, crustal-scale normal faulting associated with the bending of the incoming oceanic plate at the outer rise enables water percolation to the oceanic mantle, triggering serpentinization. Multi-stage fluid release from the subducting slab caused by the breakdown of hydrated mantle minerals triggers the production of flush melting and consequently the arc volcanism. The heterogeneous water release controls also the depth of earthquake generation and therefore the size of the seismogenic zone.
Overall, understanding mantle serpentinization is critical to understand the dynamics of plate tectonics. To this end, this session aims at bringing together researchers of divergent and convergent settings to enhance our understanding of the kinematics of mantle serpentinization and its geodynamic implications. We encourage all related contributions, from geophysical and/or petrological studies to numerical/analogue modelling that provide temporal and spatial constraints of the process of serpentinization, as well as insights into its role during the evolution of rifted margins, oceanic ridges, and subduction zones. We strongly encourage the contribution of young researchers.