NSFGEO-NERC: Magnetotelluric imaging and geodynamical/geochemical investigations of plume-ridge interaction in the Galapagos
Lead Research Organisation:
University of Cambridge
Department Name: Earth Sciences
Abstract
Understanding how melt aggregates in our planet's deep interior, i.e. its mantle, during melting remains a critical and fundamental open question in the Earth Sciences. This has important impliactions for topics as diverse as geodynamics and volcano science. Although the transport of melt in the mantle has been typically modelled as being a diffuse process, a variety of geological, geochemical, experimental and theoretical results suggest that this might occur via a network of channels that are 10s of m to km in width during long-distance (100s of km) lateral melt transport. However, it has been challenging to validate these theoretical models via natural observations and assess the importance of melt channelisation in the mantle across different tectonic settings.
One geodynamic setting that provides an ideal natural laboratory to understand this channelised transport of melt is the interaction of mantle plumes with nearby mid-ocean ridges (< 1000 km distance). This is because melts derived from a mantle plume provide a distinct geochemical tracer for tracking melt transport processes. The key observed characteristic of this type of interaction is the presence of linear chains of volcanoes (volcanic lineaments). A classic example is the Wolf-Darwin Lineament in Galápagos, a ~ 200 km long volcanic feature extending from above a region where there is currently melting taking place within a mantle plume located ~ 250 km south of the Galápagos Spreading Centre. In our previous work we find that a variety of geophysical and geochemical observations for the Galápagos lineaments are naturally explained in a model where they overlie a network of volatile- and melt-rich channels connecting the Galápagos plume to the Galápagos Spreading Centre. Such volcanic lineaments are found in other plume-ridge interaction settings worldwide (e.g. Reunion, Easter, and Discovery).
We propose to use a combination of newly collected geophysical data and novel geochemical observations of the Galápagos lineaments and the Galápagos Spreading Centre. Specifically, we propose to use an array of ~ 60 state-of-the-art broadband marine instruments, dropped overboard from the research ship, to measure electrical conductivity in sections at depths of ~60 to 100 km along and across the volcanic lineaments and the plume-affected ridge segments. Synthetic modelling demonstrates that the conductivity signals associated with the melt channels that we hypothesize are very likely to be detectable. We will couple the results from the geophysical survey with geodynamical models for Galápagos plume flow towards the ridge in order to test our findings and discern among the different possible melt channelisation mechanisms. Finally, while the geophysical instruments are recording data, we propose to dredge samples of igneous rocks along both the northern Galápagos volcanic lineaments and the lineament-spreading ridge intersections. We will analyse these for their geochemistry in order to constrain the contribution of melts from the mantle plume. This work will lead to significant, if not transformative, advances in our understanding of how mantle plumes generated near Earth's core-mantle boundary interact with 'shallow' tectonic features (mid-ocean ridges), and mantle melt transport processes in general.
Furthermore, our work will shed important light on the interaction of deep Earth processes on surface systems. This is because the volcanic lineaments that we believe represent the surface expressions of melt transport in the mantle in the Galapagos are fundamental to the migration of marine species in the eastern Pacific (e.g. whale sharks). Our study will provide important constraints on how these topographic features form on the ocean floor and also their potential long-term influence on marine ecosystems.
One geodynamic setting that provides an ideal natural laboratory to understand this channelised transport of melt is the interaction of mantle plumes with nearby mid-ocean ridges (< 1000 km distance). This is because melts derived from a mantle plume provide a distinct geochemical tracer for tracking melt transport processes. The key observed characteristic of this type of interaction is the presence of linear chains of volcanoes (volcanic lineaments). A classic example is the Wolf-Darwin Lineament in Galápagos, a ~ 200 km long volcanic feature extending from above a region where there is currently melting taking place within a mantle plume located ~ 250 km south of the Galápagos Spreading Centre. In our previous work we find that a variety of geophysical and geochemical observations for the Galápagos lineaments are naturally explained in a model where they overlie a network of volatile- and melt-rich channels connecting the Galápagos plume to the Galápagos Spreading Centre. Such volcanic lineaments are found in other plume-ridge interaction settings worldwide (e.g. Reunion, Easter, and Discovery).
We propose to use a combination of newly collected geophysical data and novel geochemical observations of the Galápagos lineaments and the Galápagos Spreading Centre. Specifically, we propose to use an array of ~ 60 state-of-the-art broadband marine instruments, dropped overboard from the research ship, to measure electrical conductivity in sections at depths of ~60 to 100 km along and across the volcanic lineaments and the plume-affected ridge segments. Synthetic modelling demonstrates that the conductivity signals associated with the melt channels that we hypothesize are very likely to be detectable. We will couple the results from the geophysical survey with geodynamical models for Galápagos plume flow towards the ridge in order to test our findings and discern among the different possible melt channelisation mechanisms. Finally, while the geophysical instruments are recording data, we propose to dredge samples of igneous rocks along both the northern Galápagos volcanic lineaments and the lineament-spreading ridge intersections. We will analyse these for their geochemistry in order to constrain the contribution of melts from the mantle plume. This work will lead to significant, if not transformative, advances in our understanding of how mantle plumes generated near Earth's core-mantle boundary interact with 'shallow' tectonic features (mid-ocean ridges), and mantle melt transport processes in general.
Furthermore, our work will shed important light on the interaction of deep Earth processes on surface systems. This is because the volcanic lineaments that we believe represent the surface expressions of melt transport in the mantle in the Galapagos are fundamental to the migration of marine species in the eastern Pacific (e.g. whale sharks). Our study will provide important constraints on how these topographic features form on the ocean floor and also their potential long-term influence on marine ecosystems.
