Periodic Reporting for period 2 - EarthMelt (Melting the Earth: The role of magma oceans in defining the Earth’s physical and chemical evolution)
Reporting period: 2023-05-01 to 2024-10-31
The challenge: Catastrophic planetary collisions impacts during the Earth’s first 500 million years in the aftermath of the planetary collision that formed the Moon provided enough energy to melt the planet’s interior, creating planetary-scale volumes of liquid molten rock, or “magma oceans”. The subsequent cooling and crystallisation of these vast volumes of liquid rock determined the physical and chemical properties of the Earth's interior, which governs the structure and compostion of our planet today. However, we do not know exactly where and how the Earth’s magma oceans crystallised, and whether remnants of early magma ocean material, or the sulfur-rich melt that may have separated from it, are still preserved at the base of the Earth’s mantle today, where they may act as reservoirs for volatiles and rare metals. We also do not know if this residual material has remained inert throughout the course of Earth history or whether it has been sampled by mantle melting events, potentially transferring its precious cargo of volatiles and metals to the planet’s surface. A major issue is that the evidence for early magma ocean processes on Earth has been largely erased by the tectonic mixing processes that have operated over the past ~3 billion years. This lack of physical evidence limits our ability to test and refine planetary magma ocean models and we need geochemical tracing tools to unravel these processes.
Societal importance: The chemistry of the Earth's interior and surface are fundamentally linked via the processes of volatile gases being released from the interior such that understanding the chemical evolution of the Earth's interior is fundamental to understanding our planet's future long-term habitability. Understanding the chemistry of our planet's interior, particularly of metals closely associated with sulfur, is profoundly important to to understanding whether there is the potential for spatial-temporal controls on the distribution of precious metals (like platinum, gold and copper) in the Earth's interior and hence in deposits close to the surface.
Overall objectives: To develop a series of novel and robust stable isotope tracers that can be used to probe early differentiation and magma ocean events. To calibrate the behaviour of these systems experimentally and to apply these data to natural samples where we will develop internally-consistent thermodynamic equilibria models of stable isotope fractionation to help us to interpret the data and hence constrain the record of magma ocean crystallisation on Earth.
Societal importance: The chemistry of the Earth's interior and surface are fundamentally linked via the processes of volatile gases being released from the interior such that understanding the chemical evolution of the Earth's interior is fundamental to understanding our planet's future long-term habitability. Understanding the chemistry of our planet's interior, particularly of metals closely associated with sulfur, is profoundly important to to understanding whether there is the potential for spatial-temporal controls on the distribution of precious metals (like platinum, gold and copper) in the Earth's interior and hence in deposits close to the surface.
Overall objectives: To develop a series of novel and robust stable isotope tracers that can be used to probe early differentiation and magma ocean events. To calibrate the behaviour of these systems experimentally and to apply these data to natural samples where we will develop internally-consistent thermodynamic equilibria models of stable isotope fractionation to help us to interpret the data and hence constrain the record of magma ocean crystallisation on Earth.
The project has involved the installation and delivery of a new type of mass spectrometer that is capable of making the highly precise isotope ratio measurements needed for this project. This instrument is a MS/MS collision reaction cell (CRC) multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS): ThermoFisher Neoma. The instrument was delivered in April 2023 and installed in June 2023 and since then we have been testing it and pushing its capabilities to make novel measurements of elements that are not normally studied for their stable isotope compositions (like Pt and the REE).
A major goal of this project was to experimentally calibrate isotope tracer behaviour at conditions relevant to planetary processes. To this end, we designed a new type of experiment that allowed us to study isotope partitioning between solid metal (Ni or Pt) and iron-sulfide alloy, effectively allowing us to simulate reactions taking place in planetary cores, albeit at much lower temperatures (1150C-1400C) and at surface pressures. We then carried out experiments under different conditions where we varied key parameters, including temperature and oxidation state, in order to evaluate their effects of isotope partitioning.
We have also analysed ancient rocks (over 2 billion years old) that were formed by melting of the Earth's interior before extensive tectonic mixing had erased any signatures of magma ocean processes. Our results point to chemical and mineralogical heterogeneities in the Earth's interior that had been established ~ 2.7 billion years ago and we are now evaluating these results in the light of our isotope partitioning models to determine whether these chemical signals reflect early tectonic processes or are inherited from deep magma ocean events.
We have carried out several detailed studies of rocks erupted from modern 'hot spots', which are the volcanic surface expressions of mantle plumes. We have interpreted our data for natural rocks in the light of unique thermodynamic models we have built and our results are disseminated in the high-profile journals Science Advances, Earth and Planetary Science Letters and Geochimica et Cosmochimica Acta. Our results show that novel stable isotope tracers can indeed be used to trace variations in the mineralogy of the regions of the Earth's interior from which plumes originate and the quest to find ancient magma ocean material in these deep regions of the Earth continues.
We have carried out Fe several suites of Archean melts, including Archean ferropicrites that may represent ancient magma ocean melts and thermodynamic modelling of this dataset is underway. Ca isotope development is currently underway but delays to instrument delivery and installation mean that this component of the project has also been delayed. We have also carried out Zn isotopes of the same Archean samples and have exciting results, so we may refocus research in this direction, depending on further tests and results. We are also developing new stable isotope systems that may be highly sensitive to the crystallisation of high-pressure magma ocean phases including U and Ce (tracing calcium perovskite), Hf (tracing bridgmanite) as well as other systems that may be sensitive to sulfide partitioning (Cu) and the late addition of meteorite material to the Earth in its magma ocean state (Ge; tracing volatile-rich meteorite material).
A major goal of this project was to experimentally calibrate isotope tracer behaviour at conditions relevant to planetary processes. To this end, we designed a new type of experiment that allowed us to study isotope partitioning between solid metal (Ni or Pt) and iron-sulfide alloy, effectively allowing us to simulate reactions taking place in planetary cores, albeit at much lower temperatures (1150C-1400C) and at surface pressures. We then carried out experiments under different conditions where we varied key parameters, including temperature and oxidation state, in order to evaluate their effects of isotope partitioning.
We have also analysed ancient rocks (over 2 billion years old) that were formed by melting of the Earth's interior before extensive tectonic mixing had erased any signatures of magma ocean processes. Our results point to chemical and mineralogical heterogeneities in the Earth's interior that had been established ~ 2.7 billion years ago and we are now evaluating these results in the light of our isotope partitioning models to determine whether these chemical signals reflect early tectonic processes or are inherited from deep magma ocean events.
We have carried out several detailed studies of rocks erupted from modern 'hot spots', which are the volcanic surface expressions of mantle plumes. We have interpreted our data for natural rocks in the light of unique thermodynamic models we have built and our results are disseminated in the high-profile journals Science Advances, Earth and Planetary Science Letters and Geochimica et Cosmochimica Acta. Our results show that novel stable isotope tracers can indeed be used to trace variations in the mineralogy of the regions of the Earth's interior from which plumes originate and the quest to find ancient magma ocean material in these deep regions of the Earth continues.
We have carried out Fe several suites of Archean melts, including Archean ferropicrites that may represent ancient magma ocean melts and thermodynamic modelling of this dataset is underway. Ca isotope development is currently underway but delays to instrument delivery and installation mean that this component of the project has also been delayed. We have also carried out Zn isotopes of the same Archean samples and have exciting results, so we may refocus research in this direction, depending on further tests and results. We are also developing new stable isotope systems that may be highly sensitive to the crystallisation of high-pressure magma ocean phases including U and Ce (tracing calcium perovskite), Hf (tracing bridgmanite) as well as other systems that may be sensitive to sulfide partitioning (Cu) and the late addition of meteorite material to the Earth in its magma ocean state (Ge; tracing volatile-rich meteorite material).
Our new experimental studies of Ni and Pt isotope partitioning between solid metal and sulphide are the first such experiments of their type for these isotope systems and in the case of Pt, the first experiments at all for this isotope system.
The results, which are surprising and exciting, reveal that (i) Ni isotope fractionation is highly dependent on oxidation state and (ii) that there is significant and large Pt isotope fractionation between metal and sulphide alloy.
The new systems we are developing will involve measurements that will be some of the first of their kind in the world (e.g. Hf and Ge). While these new stable isotope systems have been selected to achieve the EarthMelt objectives as they are likely to be highly sensitive to the crystallisation of high-pressure magma ocean phases, sulfide partitioning and the late addition of meteorite material to the Earth they are also likely to have many other applications, e.g. to the search for sustainable supplies of critical metals to Europe.
The results, which are surprising and exciting, reveal that (i) Ni isotope fractionation is highly dependent on oxidation state and (ii) that there is significant and large Pt isotope fractionation between metal and sulphide alloy.
The new systems we are developing will involve measurements that will be some of the first of their kind in the world (e.g. Hf and Ge). While these new stable isotope systems have been selected to achieve the EarthMelt objectives as they are likely to be highly sensitive to the crystallisation of high-pressure magma ocean phases, sulfide partitioning and the late addition of meteorite material to the Earth they are also likely to have many other applications, e.g. to the search for sustainable supplies of critical metals to Europe.