The origin and behaviour of carbonate minerals in diverse environments: from subduction zones to asteroids
Carbonate minerals are some of the most important carbon storage materials in both terrestrial and asteroidal settings. Understanding the origin and behaviour of carbonates as a function of pressure, temperature, and composition of coexisting phases is therefore crucial for modelling carbon fluxes. This work focuses on carbonate formation and behaviour in three distinct environments: subduction zones in Earth’s mantle, a clay- rich near-surface terrestrial environment, and the CM parent asteroid(s). Subduction zones play an important role in the deep carbon cycle that includes the transport of carbon-bearing phases in subducting slabs to deep Earth, their devolatilization, melting and dissolution in slab fluids, the transport of liberated carbon dioxide (CO2) in fluids and melts, followed by volcanic outgassing. Here, the anharmonicity and solubility of carbonates and associated metal speciation was assessed under subduction zone conditions by different in situ methods. In order to understand the anharmonicity of carbonates, the high-pressure and high-temperature vibrational properties of all naturally occurring aragonite- and calcite-group carbonates were measured by Raman spectroscopy experiments. The effects of fluid salinity, pressure, and temperature on the aqueous solubility of rhodochrosite (MnCO3) and smithsonite (ZnCO3) and Zn complexation were unravelled using the combination of synchrotron X-ray fluorescence spectroscopy and X-ray absorption spectroscopy in the diamond anvil cell (DAC). The aqueous solubility of dolomite [CaMg(CO3)2] and magnesite (MgCO3) was investigated using optical solubility experiments in the DAC. Following the experimental chapters, the role of clays in the formation of an iron oxide-bearing calcite phantom crystal is discussed and the potential of this natural composite as mineral mimetic material explored using the combination of Raman spectroscopy, scanning and transmission electron microscopy, and X-ray powder diffraction, and isotope analysis. Finally, the detailed paragenetic sequence of the CM parent asteroid(s), including multiple carbonate formation events was explored using the combination of Raman spectroscopy, electron probe microanalysis, and nanoscale secondary ion mass spectroscopy.
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