Sulfur is one of the quintessential volatile elements associated with volcanoes. It makes nasty volcanic gases and may even erupt in its molten form. It comes in (at least) four common oxidation states (S^2-, S⁰, S⁴⁺, S⁶⁺) and has four stable isotopes (³²S, ³³S, ³⁴S, ³⁶S), and why not. With sulfur, more is more. Which makes it difficult to understand. And therefore, fun.

Sulfur isotope studies in basalts have had something of a new coming in recent years. Improved extraction protocols and analytical techniques now make it possible to resolve small variations in mantle derived basalts in triple isotope space, with even the least abundant isotope ³⁶S just about within reach. This has lead to two major breakthroughs in the last decade: (1) Demonstration that the mantle has a non-chondritic S isotope signature, most likely resulting from the separation of the core from the mantle soon after Earth's accretion [Labidi et al. 2013, Nature, 501], and (2) the discoveries of mass-independent S isotope signals in ocean island basalts at Mangaia [Cabral et al., 2013, Nature, 496] and Pitcairn [Delavault et al. 2016, PNAS, 113], that provide remarkable evidence for deep recycling of Archaean sediments and their re-emergence in mantle plumes.

The Iceland mantle plume samples perhaps the most ancient material on the planet, hidden away from sight and kept safe for > 4.45 Ga in the lower mantle (geochemical evidence for this comes from primordial ratios of noble gases like He and Xe as well as W isotope anomalies measured in Icelandic basalts). Icelandic basalts also show a geochemical whiff of recycled material of poorly known origin. The aim of this project is to investigate the multiple sulfur isotopic composition in Icelandic basalts and see what they may have to say about the origin of sulfur in the Iceland mantle, and by extension, the young Earth. To this end, we analyzed quadruple sulfur isotopic compositions of 59 subglacial glasses across all active volcanic zones in Iceland.