Third party funded individual grant
Start date : 15.08.2021
End date : 14.08.2024
Immiscible suphide liquids preserved as magmatic sulphide globules in the oceanic crust record the S and chalcophile element evolution of their host magmatic systems. Recent results report systematic variations in the mineralogy and chemistry of magmatic sulphide globules from convergent and divergent plate margins, but the origin of these differences, and the implications for the chalcophile element cycle in the oceanic crust, are unknown. Parameters that control the solubility of S in silicate melts include: (1) temperature, (2) pressure, (3) oxygen fugacity and (4) the degree of fractionation. Although upper mantle melting conditions and magma differentiation in the crust differ between mid-ocean ridges and subduction zones, the effects of these processes on the S saturation limit of a silicate melt and its chalcophile element budget are still poorly understood. Better constraints on the S and chalcophile element evolution of magmatic systems are critical for understanding the chalcophile element cycle in the oceanic lithosphere, the composition of seafloor hydrothermal sulphides, the formation of the continental crust, the composition of volcanic gas and possibly the metal and metalloid budget of some subaerial epithermal-porphyry deposits.
The project aims to address these questions by investigating the magmatic trace metal and metalloid flux (e.g., Co, Ni, Cu, Se, Ag, Te, PGE, Au, Bi) through the oceanic lithosphere at mid-ocean ridges and at oceanic subduction zones. State-of-the-art analytical techniques will be used to present the first global trace element data set of magmatic sulphide globules from all sections of the oceanic lithosphere, with respect to the plate-tectonic setting and the temporal evolution of the magmatic system. Samples reflecting the initiation of ocean spreading during continental break-up and recent on-axis volcanic activity at mid-ocean ridges together with a full succession of the lava pile from the youngest at the seafloor to the oldest at the lava/dyke transition record the evolution of the magmatic chalcophile trace element cycle at high temporal resolution. In order to address these objectives, a continuous sample spectrum from the upper lithospheric mantle to the uppermost crust is required, which can only be provided by drill cores, such as those recovered during DSDP, ODP and IODP expeditions. We have identified suitable cores, which together with samples from the modern seafloor and from ancient oceanic lithosphere (e.g., Troodos ophiolite) provide a comprehensive sample set including upper mantle peridotites, lower crustal gabbros, sheeted dykes and lavas from basaltic to rhyolitic composition. Magmatic sulphide globules have already been identified in many of these samples. The proposed project will allow us to develop the first models of the magmatic chalcophile trace element cycle through the entire oceanic lithosphere at both convergent and divergent plate margins.