WP1: How to create new plate boundaries - Coordinators: A. Davaille (CNRS-FAST) & J.L. Bodinier (UM2)
The research projects in this work package aim to gain understanding the processes leading to the creation of a new plate boundary by answering the following questions: Which processes produce localized deformation within a plate leading to formation of new plate boundaries? What is the effective plate rheology? How does it evolve? Which is the role of the lithosphere structure and of the external forcing on subduction initiation/jumps and on rifting? How does partial melting and melt transport affect the deformation of the lithosphere and favour continental break up?
ESR1. Thermo-mechanical laboratory models of subduction. Supervisors: C. Faccenna/F.Funiciello (Roma TRE) & A. Davaille (FAST), Coll.: J. Wookey (UNIVBRIS), G. Barruol (UM2), H. Paulssen (UU), N. Ribe (FAST)
The aim of this project is to find and test new T-dependent materials displaying localized deformation to investigate the kinematics and dynamics of the subduction process from its initiation to maturity. Results of these models will be compared to seismological observations (ESR8, ER1), to models and observations of subduction reorganization (ESR2) and to analytical and numerical models of buoyancy-driven subduction (ER2).
ESR2. influence of the lithospheric heterogeneity on global plate tectonics and mantle convection. Supervisors : P. Tackley (ETH ZURICH) & A. Davaille (FAST); Coll.: N. Coltice (Lyon)
This project will associate numerical models of global plate tectonics – mantle convection and observations of natural systems to investigate the relative roles of the structure of the lithospheric plates on mantle convection and plate tectonics cycles. .
ESR3. Feedbacks between reactive melt transport, melt segregation, and deformation in the mantle . Supervisors: J.L. Bodinier /A. Tommasi (UM2) & J. Connolly (ETH ZURICH); Coll. T. Gerya (ETH ZURICH); C. Garrido (CSIC)
This project will couple a petro-structural and geochemical study of mantle rocks (in the field and in the lab) to numerical modeling to constrain the relations between melt transport/segregation and deformation in the mantle. We will test, for instance, if the observed gap between ultramafic (olivine-rich) and mafic (pyroxene-rich) compositions does mark a threshold for melt segregation during porous transport in the mantle by coupling a systematic analysis of compositions and microstructures of fertile lherzolites, layered pyroxenites, and websterites in peridotite massifs to theoretical models of melt transport and segregation in the mantle. Fine analysis of the microstructures in natural systems with variable melt-rock interactions will be used to constrain the feedbacks between deformation and melt segregation. The results of these studies will be implemented in geodynamic models to investigate the consequences of this process to the erosion of the subcontinental mantle lithosphere and to the dynamics of subduction and ridge systems.
ESR4. The evolution of the subcontinental mantle lithosphere: petro-structural study of the Beni Boussera peridotite massif, Morocco. Supervisors: C. Garrido (CSIC) & A. Tommasi/J.L. Bodinier (UM2) Coll. T. Gerya (ETH ZURICH); C. Faccenna (Uniroma TRE); M. Kendall (UNIVBRIS)
This project will associate petrological, structural and geochemical observations in the Beni Boussera peridotite massif in the Alboran region (Morocco) to coupled geochemical-petrological and thermo-mechanical numerical models to investigate the interactions between deformation and melt transport and the role of magmas in the thinning of the lithospheric mantle in extensional environments.
ESR5. Processes and properties controlling the formation of lithosphere-scale shear zones. Supervisors: B. Kaus/T. Gerya (ETH ZURICH) & A. Tommasi /A. Vauchez/S. Demouchy (UM2)
To investigate the processes involved in the development of lithospheric-scale shear zones, this project will associate analysis of mantle rocks deformed under lithospheric conditions, experimental data on low-temperature deformation of olivine, numerical modelling of the deformation and anisotropy, and seismic anisotropy observations.
WP 2: Plates and convective patterns in subduction settings - Coord.: M.Kendall (UNIVBRIS) & T. Gerya (ETH Zurich)
This WP focuses on the interactions between chemical and physical processes in subduction zones. The main questions are: How does water release and partial melting affect flow in the mantle wedge, its thermal structure, and the plates’ deformation? Which are the major fluid transport mechanisms in the upper mantle? How do they interact with the deformation?
ESR6. Observations and models of the interactions between fluids and deformation above a subduction zone. Supervisors: T. Gerya/J. Connolly (ETH ZURICH) & A. Tommasi (UM2), Collaborations: J. Wookey (UNIVBRIS), G. Barruol & S. Demouchy (UM2), H. Paulssen (UU), C. Garrido (CSIC)
To unravel the effect of hydrated fluids and partial melting on the deformation, we will associate: (1) the analysis of the microstructures, mineralogy and chemistry of subduction-derived mantle xenoliths to characterize the fluid-rock interactions and their effect on the deformation in the mantle wedge and (2) coupled geochemical-petrological and thermo-mechanical numerical models of the lithosphere and mantle with an explicit description of fluid transport processes and chemical exchanges.
ESR7. Imaging the distribution of fluids and of the deformation above the active Indonesian subduction zone. Supervisors: J. Wookey (UNIVBRIS) & G. Barruol/A. Tommasi (UM2), Collaborations: C. Faccenna (Uniroma TRE), T. Gerya (ETH ZURICH), N. Ribe (FAST)
The ESR will associate seismological observations (seismic tomography, shear wave splitting, and receiver functions) on data from broadband seismic stations in Indonesia with multi-scale numerical models of deformation and anisotropy in a subduction setting to investigate the deformation and fluid distribution beneath this active subduction.
ER1. Upper mantle heterogeneity and depth-dependent anisotropy in the western Mediterranean and the Gulf of California subduction zones. Supervisors: H. Paulssen (UU) & G. Bokelmann (UM2), Collaborations: C. Faccenna (Uniroma TRE), T. Gerya (ETH ZURICH), N. Ribe (FAST)
The ER will use surface wave waveform modelling techniques, receiver functions, and anisotropy measurements to image the upper mantle seismic heterogeneity and depth-dependent anisotropy in two subduction zone settings: the western/central Mediterranean, using the existent dense network of temporary and permanent stations, and the Gulf of California, where the NARS-Baja experiment runs since 2002. These observations will be compared to numerical and laboratory models of subduction (ESR1 & ESR6).
WP3. Plates in mantle convection: the global story - Coord.: P. Tackley (ETH Zurich) & N. Ribe (CNRS-FAST)
This WP focuses on the large-scale properties of mantle convection and plate tectonics. The main questions are: How do plates influence the convective pattern? Can mantle plumes weaken cold lithospheric plates? Can we trace their whereabouts in the mantle using geochemical and seismological data?
ESR8. Thermal convection with plate tectonics in the laboratory. Supervisors: A Davaille (FAST), C. Faccenna (Uniroma TRE), Collaboration: P.Tackley (ETH ZURICH)
This project aims at producing in the laboratory thermal convection and plate tectonics in a self-consistent manner by using complex rheology fluids. The ESR will characterize systematically the different regimes of thermal convection (existence of plates and/or plumes, the temperature and velocity structures, time evolution) by varying the rheological properties of the fluids and boundary conditions. Numerical models will allow extending the investigation to a larger range of conditions.
ESR9. How do mantle plumes help to thin and break up the lithosphere? Supervisors: A. Tommasi/D. Arcay (UM2) and G. Hellfrich (UNIVBRIS), Coll.: A. Davaille (FAST), G. Barruol (UM2), C. Garrido (CSIC)
This project will associate coupled geochemical-petrological and thermo-mechanical numerical models and seismological observations in Cape Verde and Polynesia to study the role of mantle plumes in the erosion of the lithosphere. The dynamics of plumes in the convective mantle will be constrained by comparison to laboratory models of mantle plumes developed at the FAST.
ESR 10. Geochemical probing of mantle plume dynamics. Supervisors: T. Elliott (UNIVBRIS), P. Tackley (ETH ZURICH), O. Alard (UM2)
This project will analyse a range of geochemical tracers (from novel stable isotope measurements to in-situ elemental analysis) in lavas from the Cape Verde islands to investigate the importance of compositional heterogeneity in plume melt compositions. These data will be used as inputs to geodynamic modelling of the Cape Verde swell and uplift of the individual islands.
ER2. Analytical and numerical models of buoyancy-driven subduction. Supervisors: N. Ribe (FAST), C. Faccenna (Uniroma TRE), Coll.: P. Tackley (ETH ZURICH), J. Wookey (UNIVBRIS), H. Paulssen (UU)
The fellow will carry out a combined analytical and numerical study of free (buoyancy-driven) subduction using a boundary-integral formulation to reduce the dimensionality of the problem, eliminate wall effects, and accurately track the slab-mantle interface. The work will lead to quantitative scaling laws for the time-dependence of key geophysical parameters (plate speed, trench rollback speed, slab deformation style, seismic anisotropy), which will allow to understand the physical mechanisms responsible for the different subduction modes observed in the laboratory experiments (ESR1) and inferred from seismological data (ESR7, ER1).