Seismic volcanostratigraphy of the Gascoyne margin, Western Australia

Abstract

Integrated interpretation of seismic, gravity, and magnetic data has revealed the presence of a large breakup-related volcanic complex on the rifted Gascoyne Margin, Western Australia. Using the concept of seismic volcanostratigraphy, we have identified three main volcanic seismic facies units related to the extrusive volcanism: 1) Landward Flows, 2) Seaward Dipping Reflections (SDR), and 3) Volcanic Protrusions. Additionally, we have identified four seismic facies units related to the tectonomagmatic evolution of the margin: 4) Domes, 5) Moho, 6) Top Underplating, and 7) Sill Intrusions. The Galah Rise comprises the majority of the volcanic complex and is dominated by 100–200 km long, NE-striking volcanic ridges surrounded by multiple sets of deep-marine emplaced SDRs. An estimated excess crustal volume of the 50 000 km 2 large Galah Rise is 350 000 km 3. The volcanic complex is located at the outer corner of a shear-rift margin setting. The magmatism is sparse on the shear margin, massive near the outer corner and decreases NE-wards along the rifted margin segment and away from the fracture zone. The Gascoyne Margin is comparable to the volcanic Vøring Margin, NE Atlantic, in terms of dimensions, structural setting and distribution of the volcanic seismic facies units. However, the along-margin variations in magmatism are more prominent on the Gascoyne Margin.