Three-Dimensional Seismic Imaging of Ancient Submarine Lava Flows: An Example From the Southern Australian Margin

Submarine lava flows are the most common surficial igneous rock on the Earth. However, they are inherently more difficult to study than their subaerial counterparts due to their inaccessibility. In this study we use newly-acquired 3D (three-dimensional) seismic reflection data to document the distribution and morphology of 26 ancient, buried lava flows within the Middle Eocene-aged Bight Basin Igneous Complex, offshore southern Australia. Many of these lava flows are associated with volcanoes that vary from 60−625 m in height and 0.3−10 km in diameter. Well data and seismic-stratigraphic relationships suggest that the lava flows and volcanoes were emplaced offshore in water depths of <300 m. The lava flows range from 0.5−34 km in length and 1−15 km in width and are typified by tabular and dendritic forms. This morphological variation may result from differing lava effusion rates and/or the volumes of lava erupted. We demonstrate that: 1) the dendritic flows contain complex lava distribution systems and kipukas, features never-before observed from seismic data; and 2) the distribution and morphology of the lava flows was strongly controlled by the emplacement of magmatic intrusion-induced forced folds. This suggests that magmatic intrusions may play an important role in controlling the distribution of lava flows elsewhere. Our study highlights the usefulness of seismic data in studying the manifestation of submarine volcanism, and provides quantitative data on the extent and distribution of an ancient submarine volcanic province along the southern Australian margin.