Building a tectonic plate: Magma, water and faults in the oceanic lithosphere
At mid-ocean ridges, tectonic plates are pulled apart and the Earth's mantle slowly rises and is partially molten, producing magma that rises and solidifies to form new crust, the outer low-density layer of the Earth. However, on some ridge sections where magma supply is low, the production of magma by mantle melting is less efficient and creation of new crust cannot keep up with the stretching of the tectonic plates. Here faulting brings mantle rocks to the surface and produces anomalous "non-volcanic" seabed, containing rocks from the Earth's mantle. These mantle rocks are chemically modified by contact with sea water penetrating cracks and fractures. Circulating water becomes assimilated in the structure of the rocks, modifying the minerals that compose it. This process often produces a family of minerals called serpentinites and is thus called serpentinization. At the same time the mantle rocks transfer heat and chemicals to the hydrothermal fluids, which are transported to the seabed and escape into the ocean at hydrothermal vent sites.
The chemicals released near the vents can include precious metals and trace elements and give rise to valuable mineral deposits. The extreme physical conditions of high pressure, high temperature and high acidity, sustain unique biological communities that are thought to represent the closest present day analogue of the conditions that led to the development of early life on Earth. Hydrothermal processes in non-volcanic crust represent an important gateway for energy and chemical exchange between the solid Earth and the oceans, but its deep structure and formation mechanisms are still poorly understood. What is the composition of non-volcanic crust? How widespread is it in the World's oceans? How much water does it assimilate?
I aim produce an integrated model of accretion and hydration of the oceanic lithosphere at slow-spreading ridges and to characterize the interaction between magma, faults, and hydrothermal fluids. My study focuses on the Rainbow area of the Mid-Atlantic Ridge, a ridge section where the tectonic stretching and magmatic input vary rapidly in space, providing a complete picture of the different conditions encountered along the global mid-ocean ridge system. I use full-waveform seismic tomography, a geophysical imaging technique which uses the entire record of the seismic oscillations, and joint geophysical inversion, to reconstruct a detailed and complete representation of the rock properties beneath the seabed. I will combine these constraints with rock physics and automated rock classification aided by machine learning to estimate composition, porosity, melt content and hydration. My work will have implications for the energy and chemical exchange between the solid Earth and the oceans, and for the recycling of chemicals in the deep Earth.
Water in subducting slabs
Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Seismological imaging methods can be used to constrain slab fluid transport and release and their effects on subduction zone seismogenesis. I used joint active source/local earthquake tomography to constrain the properties of the subducting slab and the megathrust fault in the Central Lesser Antilles. This project was funded by an AXA Research Grant Postdoctoral Fellowship.
More about the rationale and results: https://www.axa-research.org/en/projects/michele-paulatto
I worked with Joanna Morgan to apply 3D full-waveform inversion (FWI) to obtain a high-fidelity, high-resolution image of magma distribution beneath Santorini, the volcano linked to the demise of the Minoan civilisation in ~1650 BC. Santorini has recently experienced significant activity, suggesting that large eruptible volumes of magma are again accumulating close to the surface. We are using 3D FWI to determine the detailed distribution of melt beneath the volcano, and track magma pathways throughout the crust, at unprecedented resolution.
Learn more about the Santorini Tomography project: http://santorini.uoregon.edu/
More information on the field expedition on the RV M. G. Langseth: http://www.obsip.org/experime...
This project is funded by a Leverhulme Trust Research Project Grant
The focus of my PhD project was the application of seismic tomography to study the plumbing system of an active volcano. My work has involved the integration of seismic tomography with numerical models of magma chamber growth to study the magma chamber feeding the current eruption at the Soufriere Hills Volcano, Monterrat. Constraints on the geometry, volume and other characteristics of magma chambers are particularly valuable as they are important parameters for the modelling of eruption processes which in turn are key to eruption forecasting and the mapping of hazard.
Results of the seismic tomography. Three-dimensional view of the island of Montserrat and the seismic velocity model with tomographic slices at 3 and 7 km depth. Notice the low-seismic-velocity region beneath Soufrière Hills Volcano.
Learn more about my tomography model of the Soufriére Hills Volcano by reading my research paper on G-cubed: doi:10.1029/2011GC003892
The 3D P-wave velocity model can be downloaded freely from my ResearchGate pages: Montserrat_3D_Vp_model