Physical volcanology of continental large igneous provinces: update and review

Abstract

Large igneous provinces (LIPs) form in both oceanic and continental settings by the emplacement and eruption of voluminous magmas ranging from basalt to rhyolite in composition. Continental flood basalt provinces are the best studied LIPs and consist of crustal intrusive systems, extensive flood lavas and ignimbrites, and mafic volcaniclastic deposits in varying proportions. Intrusive rocks are inferred to represent the solidified remnants of a plumbing system that fed eruptions at the surface, as well as themselves representing substantial accumulations of magma in the subsurface. The vast majority of intrusive rock within the upper crust is in widespread sills, the emplacement of which may structurally isolate and dismember upper crustal strata from underlying basement, as well as spawning dyke assemblages of complex geometry. Interaction of dykes and shoaling sills with near-surface aquifers is implicated in development of mafic volcaniclastic deposits which, in better-studied provinces, comprise large vent complexes and substantial primary volcaniclastic deposits. Flood lavas generally postdate and overlie mafic volcaniclastic deposits, and are emplaced as pahoehoe flows at a grand scale (up to 104 km2) from eruptions lasting years to decades. As with modern Hawaiian analogues, pahoehoe flood lavas have erupted from fissure vents that sometimes show evidence of high lava fountains at times during eruption. In contrast to basaltic provinces, in which volcaniclastic deposits are significant but not dominant, silicic LIPs are dominated by deposits of explosive volcanism, although they also contain variably significant contributions from widespread lavas. Few vent sites have been identified for silicic eruptive units in LIPs, but it has been recognized that some ignimbrites have also been erupted from fissure-like vents. Although silicic LIPs are an important, albeit less common, expression of LIP events along continental margins, the large volumes of easily erodible primary volcaniclastic deposits result in these provinces also having a significant sedimentary signature in the geologic record. The inter-relationships between flood basalt lavas and volcaniclastic deposits during LIP formation can provide important constraints on the relative timings between LIP magmatism, extension, kilometre-scale uplift and palaeoenvironmental changes. Copyright IAVCEI 2009