Metals and sulphur in deep magma reservoirs may float towards Earth’s surface by hitching a ride on vapour bubbles, reports a study published online this week in Nature Geoscience. The mechanism identified in the study could explain the massive transfer of nickel from magmas to the atmosphere during the largest mass extinction in Earth’s history, the Permian/Triassic extinction event.
Magmas deep within Earth’s crust are often partly composed of sulphide melts that contain metals and sulphur. The metals, such as copper and gold, can accumulate in the shallow crust to form rich ore deposits, and the sulphur - when emitted during volcanic eruptions - can affect climate. However, sulphide melts are dense, so would be expected to sink to the bottom of the magma reservoir, making it unclear how the metals and sulphur migrate to shallower depths.
James Mungall and colleagues use laboratory experiments and theoretical models to analyse the behaviour of sulphide melts in magma rich with vapour bubbles. They find that small droplets of the sulphide melt can attach to the vapour bubbles and use the buoyancy of the bubbles to float upwards. This mechanism explains a possible route for the transfer of metals into the shallow crust to form ore deposits, as well as a process for the release of large amounts of sulphur into the atmosphere.