Inside the volcano: Three-dimensional magmatic architecture of a buried shield volcano

Faye Walker,John Millett,Nick Schofield,Dave Jolley,Dougal A Jerram,Sverre Planke,Reidun Myklebust,Simon Holford

doi:10.1130/g47941.1

Abstract

AbstractThe nature and growth of magmatic plumbing systems are of fundamental importance to igneous geology. Traditionally, magma chambers have been viewed as rapidly emplaced bodies of molten rock or partially crystallized “magma mush” connected to the surface by a narrow cylindrical conduit (referred to as the “balloon-and-straw” model). Recent data suggest, however, that magma chambers beneath volcanoes are formed incrementally through amalgamation of smaller intrusions. Here we present the first high-resolution three-dimensional reconstruction of an ancient volcanic plumbing system as a large laccolithic complex. By integrating seismic reflection and gravity data, we show that the ∼200 km3 laccolith appears to have formed through partial amalgamation of smaller intrusions. The complex appears to have fed both surface volcanism and an extensive sill network beneath the volcanic edifice. Numerous sills are imaged within the volcanic conduit, indicating that magma stalled at various levels during its ascent. Our results reveal for the first time the entire multicomponent plumbing system within a large ancient shield volcano.

Highlights

Extensive study of modern shield volcanoes, e.g., in Hawaii and Iceland, has provided detailed understanding of surface processes associated with basaltic volcanism (Moore and Clague, 1992; Valentine and Gregg, 2008; Cashman and Sparks, 2013)
There is little geophysical evidence for large melt-dominated magma chambers in active volcanic areas, causing researchers to propose that large magma bodies are transient and that magmatic systems are instead dominated by partially crystalline “magma mush” with small melt fractions (Glazner et al, 2004; Annen et al, 2015; Sparks et al, 2019)
We present the first high-resolution 3-D seismic images of a subsurface shield volcano (Erlend; Fig. 1C; Fig. S1 in the Supplemental Material1) and its magmatic plumbing system, revealed by careful seismic mapping

Summary

INTRODUCTION

Extensive study of modern shield volcanoes, e.g., in Hawaii and Iceland, has provided detailed understanding of surface processes associated with basaltic volcanism (Moore and Clague, 1992; Valentine and Gregg, 2008; Cashman and Sparks, 2013). Knowledge of the internal three-dimensional (3-D) structure of volcanic edifices and how this influences the storage and transport of magma within plumbing systems is comparatively poor This is because these systems cannot be observed directly and are generally studied through incomplete eroded outcrops (e.g., Chambers and Pringle, 2001; Westerman et al, 2004; Emeleus and Bell, 2005; Galland et al, 2018). Magma chambers have traditionally been viewed as large, long-lived, geometrically simple bodies of molten rock, which are emplaced rapidly and slowly crystallize to form plutons (Glazner et al, 2004; Annen et al, 2015; Jerram and Bryan, 2018; Sparks et al, 2019).

Faroe Islands

METHODS

Findings

DISCUSSION