Magma Transport Pathways in Large Igneous Provinces: Lessons from Combining Field Observations and Seismic Reflection Data

Abstract

Large Igneous Province (LIP) formation involves the generation, intrusion, and extrusion of significant volumes (typically >1 Mkm 3) of mainly mafic magma and is commonly associated with episodes of mantle plume activity and major plate reconfiguration. Within LIPs, magma transport through Earth's crust over significant vertical (up to tens of kilometres) and lateral (up to thousands of kilometres) distances is facilitated by dyke swarms and sill-complexes. Unravelling how these dyke swarms and sill-complexes develop is critical to: (i) evaluating the spatial and temporal distribution of contemporaneous volcanism and hydrothermal venting, which can drive climate change; (ii) determining melt source regions and volume estimates, which shed light on the mantle processes driving LIP formation; and (iii) assessing the location and form of associated economic ore deposits. Here, we review how seismic reflection data can be used to study the structure and emplacement of sill-complexes and dyke swarms. We particularly show that seismic reflection data can reveal: (i) the connectivity of and magma flow pathways within extensive sill-complexes; (ii) how sill-complexes are spatially accommodated; (iii) changes in the vertical structure of dyke swarms; and (iv) how dyke-induced normal faults and pit chain craters can be used to locate sub-vertical dykes offshore. the most important component of LIP magma plumbing systems and typically form impressive swarms that can extend laterally for >2000 km (Fig. 1) (e.g. Ernst 2014; Ernst and Baragar 1992; Ernst et al. 2001; Ernst et al. 1995; Halls 1982). Giant circumferential (subcircular to elliptical) swarms up to 2000 km in diameter have also been recently recognized (e.g. Buchan and Ernst, 2018a, b). However, field observations reveal that sill-complexes, i.e. extensive interconnected networks of sills and inclined sheets (e.g. the Siberian Trap sillcomplex is exposed over >1.5 × 10 6 km 2), form the primary volumetric elements of many LIP plumbing systems (Fig. 1) (e.g.

Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

“…Advancing our understanding of dyke swarm emplacement thus requires a method for imaging their 3D structure in detail (e.g. Magee et al, 2018Magee et al, , 2019Phillips et al, 2018).…”

Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

“…Giant dyke swarms are recognised worldwide onshore (e.g., Ernst and Youbi, 2017;Ernst, 2014;Bryan and Ernst, 2008;Coffin and Eldholm, 2005;Coffin and Eldholm, 1994;Bryan et al, 2010;Hou et al, 2010;Halls and Fahrig, 1987;Halls, 1982;Ernst and Baragar, 1992). Projection of these onshore dyke swarms and the known importance of dyking to break-up and formation of magma-rich margins suggests dyke swarms should also be prevalent on offshore continental shelves (see Magee et al, 2019 and references therein). Our work extends a growing consensus that vertical dykes can be recognised in seismic reflection data imaging continental margins (e.g., Wall et al, 2010;Bosworth et al, 2015;Malehmir et al, 2018;Holford et al, 2017;Kirton and Donato, 1985;Ardakani et al, 2017;Jaunich, 1983;Plazibat et al, 2019).…”

“…In particular, Phillips et al (2018) demonstrated the width of a dyke swarm imaged offshore southern Norway increased with depth, implying the plan-view morphology of a dyke swarm may not be a proxy for its 3D geometry (or total volume); i.e. the plan-view morphology of a dyke swarm is a function of its attitude relative to the present topography (see also Magee et al, 2019). We can use different physical, analytical, and numerical modelling approaches to evaluate the 3D geometry of dyke swarms, and to establish how their structure can be inferred from principally 2D, surfacebased analyses.…”

“…However, these model predictions are difficult to validate without constraints on the true 3D form of natural dyke swarms (e.g., Paquet et al, 2007;Bunger et al, 2013;Jolly and Sanderson, 1995;Macdonald et al, 1988). Advancing our understanding of dyke swarm emplacement thus requires a method for imaging their 3D structure in detail (e.g., Magee et al, 2019;Magee et al, 2018;Phillips et al, 2018).…”

Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

“…(e.g., Macdonald et al, 1988;Jolly and Sanderson, 1995;Paquet et al, 2007;Bunger et al, 2013). Advancing our understanding of dyke swarm emplacement thus requires a method for imaging their 3D structure in detail (e.g., Magee et al, 2018;Phillips et al, 2018;Magee et al, 2019).…”