Lateral magma flow in sill-complexes: towards a paradigm shift in volcanology
Craig Magee1, James D Muirhead2, Alex Karvelas3, Christopher A-L Jackson1, Ian Bastow1, Simon P Holford4, Nick Schofield5, Carl TE Stevenson6, Charlotte McLean7, William McCarthy8, Olga Shtukert3
1Basins Research Group, Department of Earth Science and Engineering, Imperial College, London, SW7 2BP, UK
2Department of Geological Sciences, University of Idaho, Moscow, Idaho 83844, USA
3Schlumberger Multiclient, Schlumberger House, Buckingham Gate, West Sussex, RH6 0NZ, UK
4Australian School of Petroleum, University of Adelaide, Adelaide, SA 5005, Australia
5Geology & Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen, AB24 3UE, UK
6School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK
7School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
8Department of Earth Sciences, University of St Andrews, St Andrews, KY16 9AL, UK
Abstract
The structure of magma plumbing systemscontrolsthe distribution of volcanism,thereby influencingcontinental break-upand passive margin evolution. However, delimiting the structure of entire plumbing systems isdifficult because: (1) intrusion networks cannot be directly accessed at active volcanoes; (2) field outcrops are limited by exposure; and (3) the resolution of geophysical data imaging the sub-surface is restricted. As a result, models involving the vertical transfer of magma in dikes,which extend from a melt source to overlying reservoirs and eruption sites,dominate the volcanic literature. Whilst there is evidence supporting the existence ofvertically stacked plumbing systems, we compile a series of field- and seismic reflection-based case studies documenting the importance of extensive lateral magma transport (up to 4100 km) within sill-complexes. Most of these sill-complexes are emplaced into sediment-filled rift basins (e.g., Rockall Basin, NE Atlantic; Ceduna Sub-basin, offshore southern Australia; Karoo Basin, South Africa). There is also evidence that some sill-complexesoccur within crystalline, continental crust (e.g., in the YilgarnCraton, Australia). The case studies presented demonstrate that sill-complex emplacement is largely controlled by host rock lithology and structure. Sill intrusion is accommodated through roof uplift or, alternatively, via non-brittle processes (e.g., porosity reduction induced by host rock fluidization) that may not deform the overburden.The full or partial accommodation of magma by space-making mechanisms other than roof uplift means that intruding magma volumes may be underestimated by orcompletely hidden from ground deformation analyses. We show that plumbing systems need not be vertically stacked.Magma can instead be transported within laterally extensive (up to 3 × 106 km2) sill-complexes,promoting the development of volcanoes that do not overlie the melt source.