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Exploration of melt inclusion geometry, entrapment and post-entrapment processes in 3D using X-Ray and diffraction computed tomography

Bridie V. Davies1, Roxane Buso1, Elizabeth Evans2, David A. Neave1, Matthew Pankhurst3, Lucia Pappalardo4, Margherita Polacci1, Alberto Leonardi5, Margaret Hartley1.

  • Affiliations:  1Department of Earth and Environmental Sciences, University of Manchester, Oxford Rd, Manchester M13 9PL, UK; 2National Facility for X-ray Computed Tomography, Henry Royce Institute Hub Building M13 9PL, UK; 3 Gaiaxiom Pty Ltd, Denmark; 4Istituto Nazionale di Geofisica e Vulcanologia, Naples, Italy; 5Physical Sciences, Diamond Light Source (United Kingdom), Diamond House - Harwell Science & Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom 

  • Presentation type: Talk

  • Presentation time: Thursday 09:00 - 09:15, Room S150

  • Programme No: 1.1.3

  • Theme 1 > Session 1

Abstract

Understanding the origins and fidelity of geochemical signatures recorded in melt inclusions (MI) - and associated vapour bubbles - is essential for accurate reconstructions of magmatic plumbing systems. However, inaccuracies in 2D-to-3D conversion methods lead to over- and underestimation of glass inclusion and bubble volumes. These volumetric uncertainties propagate into reconstructions of MI volatile contents and inclusion-to--bubble volume ratios, and MIs may be incorrectly inferred to cross the defined boundary for heterogeneous entrapment. Further, entrapment and post-entrapment processes aren't always evident in 2D images, resolvable using optical microscopes, or preserved during destructive sample preparation. Acquiring 3D MI and bubble volumes offers an enticing prospect towards accurate interpretation of geochemical data and preservation of key textural indicators of crystallization and post-entrapment processes. We present 3D olivine-MI-vapour bubble morphologies and their geometric and structural relationships for primitive olivine crystals from three case study eruptions from Iceland (Stapafell and Borgarhraun) and the Canary Islands (El Hierro), acquired via X-ray diffraction and computed tomography. Our 3D data reveal several MI morphologies present across olivine hosts representative of a range of growth mechanisms. Reconstructions of complex vapour bubble-MI geometries linked to microscopic fractures provide evidence of post-entrapment processes not visible via optical microscopy. Our findings demonstrate the importance of exploring MI-host morphologies and relationships in 3D to gain insights into crystallisation, MI entrapment and post-entrapment processes and ensure reliable interpretation of geochemical datasets.