Nature of Project

Computational (interfacing with observational data from a range of fields).

Essential Background

• PHYS 3070 (Physics of the Earth)
• EMSC 8023 (Advanced Data Sciences)
• EMSC 80XX (Computational Geosciences)

Background

Geodynamics occupies a unique position in the solid Earth Sciences. It is primarily concerned with the dynamical processes affecting the Earth, both within its interior and at its surface, although it can also be applied to the interiors and surfaces of other terrestrial planets and their moons. Primarily, geodynamics exploits fundamental physical principles and wide-ranging observational datasets to interpret and predict Earth’s behaviour. It relies heavily on observational data from a range of fields (e.g. geology, geochemistry, geophysics, geochronology, some of which is acquired remotely and over long periods of time), in addition to laboratory data, and deals with Earth’s complex material properties. Indeed, many important geodynamical processes owe their existence to the interplay between complex material behaviour, dynamics, Earth’s structure and its thermo-chemical evolution.

The major paradigms shaping the solid Earth Sciences over recent decades are essentially geodynamical concepts. Perhaps the best known of these is plate tectonics and continental drift. These have stood the test of time, have been supported by observations from a range of disciplines, and are now widely-acknowledged as the basic phenomena governing the long-term evolution of Earth’s surface. Another fundamental paradigm is mantle convection: the basic engine for plate tectonics and the most important process controlling the structure and long-term evolution of our planet’s interior, including its temperature and composition.

Through their overall success in explaining diverse observations, these geodynamical concepts provide a foundation for much of the Earth Sciences, yet they raise fundamental questions that remain unanswered. These grand challenges fit within the broader context of the Earth System, for which an inter-disciplinary perspective will be vital for progress.

Possible Future Research Avenues

1. The Thermo-Chemical Evolution and Surface Expression of Mantle Dynamics: mantle convection is the engine driving our dynamic Earth. It transports Earth’s internal heat to its surface, generating continental and oceanic crust in the process, which are subsequently consumed through subduction. Mantle convection is reflected in near-surface phenomena such as continental deformation and mountain building, sea level changes, earthquakes and volcanism, as well as the activity of Earth’s magnetic field. The grand challenge is to understand the operation of this giant heat engine over geologic time, and how it has controlled Earth’s evolution, its present-day structure and its composition. Fundamental outstanding research directions include:
   • Reconstructing mantle flow: how can we combine diverse observational datasets from geology, geochemistry, geochronology and geophysics, with novel inverse modelling techniques, to reconstruct mantle structure, mantle flow, its expression at Earth’s surface and its evolution towards the present-day?
   • Linking Earth’s surface to its deep interior: understanding the diverse surface expressions of mantle convection, represented by mid-ocean ridges, subduction zones, intra-plate volcanism and seismicity remains at the centre of global geodynamics. Dynamic topography, defined as the transient topographic response of Earth’s surface to underlying mantle flow, provides a direct link between Earth’s deep interior and surface processes, including global ocean circulation and climate change, although the nature of this link remains poorly understood. The significance of dynamic topography in controlling Earth’s past and present surface environment, therefore, remains unclear and is a possible avenue for future research.
2. Intra-plate Volcanism - Causes and Consequences: most of Earth’s volcanism is concentrated at tectonic plate boundaries, where plates move away from one another to create mid-ocean ridges, or where one plate slides beneath another to form a subduction zone. However, an important and widespread class of volcanism occurs within plates, or across plate boundaries. The origin of these so-called intra-plate volcanic provinces, which include the most rapid and voluminous volcanic episodes recorded in Earth’s history, remain enigmatic, even though they are associated with global mass extinction events, initiating the seafloor spreading that produced many of the world’s oil and gas basins, and the genesis of many of Earth’s natural resource. The outstanding challenge here is to understand the nature of mantle flow and the anomalies that produce this intra-plate melting, their associated volcanic hazard, and the potential role for mantle plumes, upwellings of abnormally hot rock that rise to Earth’s surface from the CMB, in dictating larger-scale tectonics, global mass extinction events, continental-breakup and mineralization. The Australian continent, which hosts one of the world’s largest intra-plate volcanic provinces, provides the natural laboratory that will underpin progress in this area, with specific future research directions including:
   • Mechanisms and associated hazard: what are the dynamical mechanisms underpinning intra-plate volcanism? How much intra-plate volcanism is related to mantle plumes? Constraints on the mechanisms underpinning volcanism bear strongly on the associated volcanic hazard and are vital if we are to understand their future eruptive potential.
   • Melting and melt-transport: how do changes in lithospheric thickness affect mantle melting and the associated volcanism? How do these melts rise through the mantle and crust? Can we invert melt geochemistry for mantle temperature, pressure and composition?
   • Influence on tectonics and continental breakup: is there a plume contribution to the asthenosphere? If so, how does it influence tectonics? Why does the arrival of a plume head at Earth’s surface often initiate continental breakup? Do plumes play a role in the force-balance governing plate motions?
   • how does intra-plate volcanism influence the generation, preservation and destruction of diamonds?  Can we better understand the formation and distribution of high-temperature komatiites and picrites, which are key hosts for nickel and platinum group element deposits? Can we isolate the role of mantle plumes in the generation (or destruction) of hydrocarbon resources?
3. The Generation of Plate Tectonics from Mantle Convection and the Force-Balance Governing Plate Motions: understanding how plates self-consistently arise from planetary convection has long been a major goal in geodynamics. It was traditionally believed that since plate-like motion is discontinuous, it could not be predicted or reproduced by viscous mantle convection. However, over recent decades there has been major progress with models of mantle dynamics yielding plate like surface motions, through the incorporation of more sophisticated rheological weakening mechanisms, such as brittle/plastic yielding or damage mechanics. Nonetheless, there is no accepted geodynamical theory that can accurately and quantitatively predict how most plate tectonic motions (ridges, subduction zones, strike slip faults) arise or initiate from the convecting mantle, how plates have formed and evolved through time, when plate tectonics initiated on Earth, why Earth is the only terrestrial planet with plate tectonics, and whether Earth’s other unique features (liquid water, a stable temperate climate, and life) are causes or effects of plate tectonics. These are the major questions and challenges of the plate generation problem. They will remain the focus of a broad and active area of research for years to come. Some specific future research directions for geodynamics centre around:
   • The physics of plate generation: how does mantle convection give rise to plate-like motions? What are the relevant rheological feedbacks controlling the generation of plate tectonics?
   • Subduction initiation: how does cold still lithosphere become unstable and sink? How do pre-existing weak zones evolve into subduction zones?
   • Tectonic evolution: how do plates grow and reorganize? How do plate boundaries evolve, die, and reactivate?
   • Onset: when was the onset of plate tectonics? What are the conditions for this onset? Was the early pre-plate-tectonic Earth (if it existed) similar to a non-plate-tectonic planet like Venus?