Diamonds as a tracer for volatiles

By James Crosby, University of Cambridge

A key aspect of igneous petrogenesis is the source of magma accumulating in a plumbing system. Many of these systems show evidence of magma mixing from distinct geological reservoirs and this therefore raises important questions about geodynamic processes. To further understand these processes I investigated He-C-N isotopic systematics of polycrystalline diamonds to trace the source of volatiles in the mantle. My findings indicate that volatiles sourced from crustal and mantle reservoirs can mix at great depths under diamond-forming conditions. In addition to further constraining diamond petrogenesis and these implications on long-term volatile cycling, these observations highlights how magmas can mix at great depths from distinct sources before becoming emplaced at shallower levels.

James carried out this work as part of his MSc at the University of St Andrews, under the supervision of Sami Mikhail and Fin Stuart. He is now a PhD student at the University of Cambridge, supervised by Sally Gibson, continuing to focus on volatile behaviour. James’ current research involves the novel analysis of volatile elements and noble gas isotopic ratios in both nominally volatile-free minerals and volatile phases present in mantle xenoliths in order to constrain the volatile flux in the mantle. To find out more about his research visit James’ website and blog- http://james-crosby.com and follow him @GeochemJC.