Seismic imaging of ‘broken bridges’: linking seismic to outcrop-scale investigations of intrusive magma lobes

TLDR

Three‑dimensional seismic data reveal that sills consist of discrete magma lobes formed during emplacement, providing unprecedented insight into magma flow within sub‑volcanic systems. The study targets a large Faroe–Shetland Basin sill to identify and map ‘broken bridges’ between elongated magma lobes in three dimensions. Using high‑resolution seismic imaging, the authors locate and characterize broken‑bridge structures within the sill. The analysis shows that broken‑bridge structures are perpendicular to magma flow, linking seismic‑scale observations to outcrop‑scale processes and suggesting a scale‑invariant magmatic emplacement mechanism.

Abstract

Three-dimensional seismic datasets have provided unrivalled insights into magma flow within sub-volcanic systems. One of the key revelations is that sills appear to be constructed of a series of discrete magma lobes that form during the emplacement of magma into host-rock. We focus on a large sill, within the Faroe–Shetland Basin, North Atlantic, that is well imaged on seismic data, and identify the presence of ‘broken bridges’ within the sill, developed between elongate magma lobes, and reveal for the first time in three dimensions the development of broken bridges. Critically, by relating the imaged structures to key outcrop-scale examples we confirm that bridge and broken-bridge structures are oriented perpendicular to the magma flow direction. This work thus demonstrates a key link that can be made between seismic-scale investigation of intrusions and sub-seismic (outcrop-scale) processes, highlighting the seemingly scale-invariant nature of the magmatic emplacement process.