How can miniature magnets reveal secrets about how magma travels to the surface?

Simon Martin – University of Liverpool, UK

A key aspect with how magma travels to the surface is to understand how it flows through intrusions. Understanding magma transport and emplacement within the Earth’s crust can give us valuable insights into the processes occurring in active volcanic complexes. A commonly used method to determine the direction of magma flow is anisotropy of magnetic susceptibility (AMS) analysis, where the orientation of the long axis of larger magnetic crystals (>0.05 mm) is being inferred as the direction of flow. However, anisotropy of anhysteretic remanent magnetisation (AARM) can also be used, and it focuses on the fabric exhibited by the orientation of the finer grained magnetic particles (<0.05 mm). Detailed sampling across the breadth of a sill from the Isle of Skye, Scotland, has identified changes in flow direction which may be linked to different processes occurring during emplacement and solidification.

In our study we found that the AMS fabrics preserved an initial flow direction at the sill margins, which then reoriented through time as shown by a change in orientation with increased distance from the margins (Figure A, left). The AARM fabrics represented melt-percolation flow of the interstitial fluid through a crystal framework that formed during solidification (Figure A, right; Figure B). You can read more about this research in our recently published paper: “The Origin and Evolution of Magnetic Fabrics in Mafic Sills” (https://doi.org/10.3389/feart.2019.00064)

Simon Martin is currently undertaking his PhD research as part of the MAGMA lab at the University of Liverpool, UK, supervised by Janine Kavanagh and Andy Biggin, whilst teaching as a Graduate Teaching Assistant for several undergraduate classes in petrology, sedimentology, volcanology, and physical geography. He is interested in the laboratory modelling of natural processes, i.e. intrusions and lava flows, using analogue materials, and ground-truthing these models using field and petrological studies of natural rock fabrics.