Monogenetic basaltic edifices: their architecture, volcanology and importance in hydrocarbon basins

Abstract

Flood basalt provinces host significant hydrocarbon reserves. The provinces are produced during fissure eruptions which construct volcanic edifices atop an erupting dyke. The edifices are important components of volcanic-affected hydrocarbon basins; they provide insights into the underlying structural and magmatic plumbing systems, as well as acting as fluid migration pathways after burial. Furthermore, the edifices host a wealth of volcanological evidence that can be used to derive information relating to eruption dynamics such as eruption column height, mass flux and duration; as well as providing insights into the effects of eruptions on the environment. However, the location of the fissures in many hydrocarbon basins is poorly constrained. Furthermore, few studies have characterised the internal architecture of the edifices produced during fissure eruptions. This thesis uses field, seismic and well data to characterise the architecture of monogenetic basaltic edifices and understand their temporal and spatial evolution.
Field studies along a dissected Holocene fissure, Northeast Iceland, reveal that a scoria-agglutinate cone, spatter ramparts and a scoria rampart were constructed during Hawaiian-style lava fountaining. These edifices are analogous to those formed in the 1783 Laki eruption. Data gathered in this study can be used to recognise fissure-derived edifices in other volcanic provinces. I then contrast these dyke-fed edifices with rootless cones; a morphologically similar volcanic edifice produced during explosive interaction between inflating pāhoehoe lava and unconsolidated sediment. This thesis reveals that rootless cones can be distinguished from dyke-fed edifices on the basis of their juvenile clast morphology and clast density. This allows us to better recognise dyke-proximal locations. Lastly, I use exceptional quality 3D seismic and well data to show how a series of submarine monogenetic volcanoes evolved; progressing from a maar-forming stage, to a pillow volcano and tuff-cone-building stage as the confining pressure decreased above the growing edifices. These insights allow us to distinguish volcanic edifices from similar non-volcanic edifices in other seismic data sets, and also indicates that our understanding of submarine volcanism has previously been biased towards recognition of constructional features.