Magmatic Pathways in Large Igneous Provinces

Friday, 19 December 2014: 4:15 PM
Richard E Ernst, Carleton University, Earth Sciences, Ottawa, ON, Canada
Large Igneous Provinces (LIPs) provide a context for studying a range of magma ascent, emplacement and extrusion scenarios. LIPs are intraplate magmatic events, of mainly mafic magma, > 0.1 Mkm3, and often above 1 Mkm3, in both continental and oceanic settings, and are typically characterized by a short duration magmatic pulse or multiple short pulses over a maximum of a few 10s of Ma. Continental LIPs can have significant volumes of associated silicic magmatism and also carbonatites and kimberlites.

Aspects to consider are how LIP magma ascends into the lithosphere from an underlying asthenospheric source(s) (e.g. mantle plume), the patterns for the subsequent distribution of magma within the lithosphere (mantle and crust), and links to surface volcanism. Lithosphere-entry scenarios include ascent: (a) from a widely distributed asthenospheric source; (b) from a localized source region, e.g. above the plume center; (c) along zones of triple-junction rifting; (d) along translithospheric fracture zones, and (d) from buoyant plume material that has moved sideways along the base of the lithosphere (e.g. sublithospheric channelling).

Upon ascent, magma is distributed vertically and laterally within the crust as dykes and sills, with the involvement of staging magma chambers. Most dramatically, giant radiating and circumferential dyke swarms can have a radii of >1000 km and >250 km, respectively, centered on the plume. Extrusive magmatism can be fissure- or edifice-fed, and individual flows can extend for 100s to perhaps even a 1000 km. As a consequence of lateral flow in dykes, lava flows and sills can be emplaced at great distances from the plume center; laterally propagating dykes that intersect a sedimentary basin can continue into the basin as sills, and local lava flows can be formed when the upper edge of a dyke intersects the paleosurface. The main locus of magmatism can shift during a LIP event, due to plate movement over an underlying plume. Picrites and high-Mg magmas are preferentially concentrated above the plume-center region.