Abstract
Information about birth and early eruptions of composite volcanoes is scarce, but erosion has revealed very early deposits of the Dunedin Volcano, and we apply anisotropy of magnetic susceptibility (AMS) techniques to retrieve information about the earliest known, submarine, eruptive centre. Although AMS has been used to recover information from subaerial eruptions, and to examine turbidites, this is its first use in investigating depositional processes and the source location for submarine volcaniclastic deposits. AMS fabrics of the deposits, emplaced by submarine eruption‐fed density currents, show basal portions of the currents were decoupled from more‐buoyant upper parts. Triangulation of AMS vectors and orientations yields a vent site location, with some imprecision reflecting the chaotic nature of deposits rapidly aggraded within 500 m of the source vent. This method elucidates depositional processes of subaqueous volcanic currents as well as subaerial ones, while still yielding sufficient consistency for triangulation of flow source sites.
Plain Language Summary
The early histories of volcanoes are difficult to reconstruct, as rocks from the earliest eruptions are buried by later eruptions. The Dunedin Volcano (active 16–11 million years ago), has been eroded back so that deposits from early eruptions are exposed along the coasts. We used a rock‐magnetic technique, anisotropy of magnetic susceptibility (AMS) on a submarine eruption deposit, to locate the vent of origin active early in the life of the Dunedin Volcano. This is the first time this technique has been applied to rocks formed by submarine eruptions. AMS fabrics suggest that the source vent was located <500 m southwest of the present‐day coastline. AMS results show that parts of the deposit were formed by chaotic eruption‐fed currents, while other parts were formed as the eruption‐fed current separated into a denser base layer and a more dilute top layer.
Key Points
We apply anisotropy of magnetic susceptibility (AMS) to submarine eruption deposits from the early life of the Dunedin Volcano, active 16–11 Ma
This is the first time this rock‐magnetic technique is used on submarine eruption deposits to investigate flow processes
Triangulation of AMS vectors indicates the source submarine vent was located within 500 m southwest of the present day coastline