The Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS): Background
Delivering the fundamental science
needed to sustain Australia’s resource base
Water is essential for human existence, indeed for life’s beginning. The circulation of water and other fluids lubricates the deep-seated dynamics that keep Earth geologically alive, and its surface habitable. Several oceans worth of water may be present inside Earth, and the exchange of water and other fluids between the surface and the deep interior plays a crucial role in most Earth systems, including the evolution of the surface, the hydrosphere, the atmosphere, the biosphere, and the development of giant ore deposits.
Subduction - the descent of oceanic plates into the mantle - carries water down into Earth’s interior; dehydration of the subducting crustal slabs at high pressure and temperature releases these fluids into the mantle, causing melting and controlling the strength, viscosity, melting temperature and density of rocks in the deep Earth, as well as the structure of major seismic discontinuities at 410 and 660 km depth. The partial return of some of these materials to the surface through mantle-plume activity provides a mechanism for tectonic cyclicity, which may have varied over geological time. These effects dominate solid-Earth dynamics and make plate tectonics possible, but the origin, abundance, speciation and movements of fluids in the deep interior are largely unknown, and represent key issues in modern geoscience.
Until recently, a real understanding of the workings of Earth’s deep plumbing system has been tantalisingly out of our reach. Now, rapid advances in geophysics are producing stunning new images of variations in physical properties such as seismic velocity and electrical conductivity in the deep Earth, but interpretation of these images in terms of processes and Earth’s evolution is only in its developmental stages. It requires new kinds of data on deep-Earth materials, and especially on the effects of deep fluids and their circulation.
To provide the knowledge needed to reach a new level of understanding of Earth’s evolution, dynamics and fluid cycle(s) through time, CCFS integrates information across geology, tectonics, experimental and analytical geochemistry, petrophysics, geophysics, and petrophysical and dynamical modelling. These disciplines have traditionally represented ‘research silos’, but CCFS has brought them together to provide a significant increase in our national research capability.
Research programs within the Centre are focused to provide maximum synergy for the scope enabled by the resource base. As it is not possible to encompass the full range of research about the Earth’s fluid cycle and deep Earth dynamics, all applied and mature strategic research is carried out in parallel, supported by other funding sources. The Research Program structure was revised in 2014 to ensure the overarching goals were being fulfilled. The resulting Flagship Programs were put in place as cross-node streams contributing to the three global Themes (Early Earth, Earth Evolution and Earth Today).
These are structured to capitalise on the people and resource context of the Centre in a way not possible with a shorter timeframe, or without the critical mass of research expertise, depth and breadth. More detailed information is given in “The CCFS Research Program” and “Research Highlights”.
In order to track the input of coalescing strands, the concept of programs contributing to understanding Earth Architecture and/or Fluid Fluxes helps track the pieces of the giant 4-dimensional Earth puzzle being solved by CCFS and encapsulates the relationship of all the CCFS programs to Earth ‘fluids’.
“Architecture” is the ‘roadmap’ for fluids
“Fluid Fluxes” represents the ‘traffic report’
All Research highlights and Projects are now keyed to this framework shown diagrammatically below:
Theme 1: Early Earth
The Early Earth - Its formation and fluid budget. This theme focuses on the nature of Earth’s early differentiation and the role of fluids. Ancient (>3 Ga) rocks may yield evidence for early life, and analysing the mass-independent fractionation of Fe and S isotopes allows us to test the involvement of biological processes in ancient deposits.
The earliest record of Earth’s magnetic field provides new information on when the core’s geodynamo formed and the geometry and intensity of its field and is used to track the movement of Archean tectonic plates. The geochemical nature and dynamic behaviour of the mantle in the early Earth continues to be assessed using in situ analysis of targeted minerals from a variety of mantle rock types and tectonic environments, coupled with dynamic modelling.
Theme 2: Earth’s Evolution
Earth’s Evolution - Fluids in crustal and mantle tectonics; recycling of fluids into the deep mantle; hydrosphere, atmosphere and the deep Earth. Earth has evolved through cycles of crustal formation and destruction, punctuated by ‘tipping points’, when rapid cascades of interlinked events produced dramatic changes in the composition of the oceans, the oxygen levels of the atmosphere, the tectonic behaviour of the crust and mantle, and the distribution of mineral and energy resources. These events changed the distribution and behaviour of fluids in the deep Earth, and each altered Earth’s evolution irreversibly.
Key issues are: when did subduction start; how did it contribute to the Earth’s cooling; how has this process evolved through time? Isotopic studies define the rates of continental growth vs recycling through time and test linkages between crust and mantle events. Geophysical imaging and dynamic modelling have been used to build 3D models of subduction dynamics, thermal evolution and geodynamic cycles. Stable-isotope studies track water and other fluids in their cycles through the Earth and the hydrosphere.
Theme 3: Earth Today
Earth Today - Dynamics, decoding geophysical imaging, and Earth resources. Geophysical imagery gives us a snapshot of the current status of the deep Earth but also carries the imprints of past processes. Realistic interpretation of these data provide us with new insights into Earth’s internal dynamics and has practical consequences, e.g. for resource exploration. We are developing thermodynamically and physically self-consistent dynamic codes to model complex processes and their expression in geophysical and geochemical observables. These codes are used to identify the processes that have controlled the fluid cycle through Earth’s history.
Measurements of the physical properties of potential deep Earth materials at extreme conditions feed into petrophysical modelling of seismic data in terms of composition, temperature and anisotropy. Measurements of metal complexing at realistic conditions that mimic real ore-system fluids/melts provides new ways to interpret observations on fluid/melt inclusions in minerals. CCFS is investigating the role of organo-metallic compounds in metal transport, using the capabilities of the Australian Synchrotron, to understand the role of such compounds in the formation of large mineral systems.