Subduction zones represent a tectonic environment where the Earth's crust is subducted into the mantle, but several components are returned to the surface via arc magmatism. These include Cu and S, which form Porphyry Copper Deposits (PCD). It has been suggested these 'hot spots' of Cu represent local oxygen fugacity (fO2) anomalies resulting from strongly oxidized conditions in the magma at some stage on the journey from slab to near-surface. One obstacle to our understanding of this journey is the difficulty in controlling fO2 in high-pressure experiments representing the mid- to lower-crust. A major part of this thesis was spent wrestling with experimental problems related to 102 control in the high-pressure piston-cylinder apparatus. This led to a new capsule design, which was used subsequently to study the evolution and speciation of sulphur at mid- to deep-crustal magmatic conditions. Results confirm that oxidized conditions leading to suppression of sulphide phases is an important process in the formation of PCDs but this is important even in the deep crust. fO2 plays an important role in controlling the volatile species, but also S speciation and solubility in the melt, across the 'sulphide (S2-) to sulphate (S6+)' transition. Experiments show a strong shift of this transition to more oxidized conditions with the increasing depth, expanding sulphide stability. Sulphide saturation can still be avoided by deep S-degassing but requires exceptionally large amounts of COH-fluid, rare even for arc magmas. The transition also appears to involve a species that causes a solubility minimum as 'well as enhancing Au solubility. Samples from the high 102 , 1815 eruption of Tambora were found to have sulphide but these were found to be subject to desulphurisation, allowing to examine the release of Cu with the S, but also the role of sulphide in the subsequent global climate change in 1816.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:702164 |
| Date | January 2016 |
| Creators | Matjuschkin, Vladimir |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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