CHARACTERIZING SUBMARINE TO SUBAERIAL VOLCANISM FROM LITHOFACIES AT A PARASITIC VENT TO LYTTELTON VOLCANO AT TAYLOR'S MISTAKE BEACH, SOUTH ISLAND, NZ

Taylor’s Mistake Beach is on the northeastern flank of the Lyttelton Volcanic Complex (LVC) on Banks Peninsula, New Zealand, a peninsula created by basaltic intraplate volcanism, and is a previously undescribed exposure on the peninsula. Describing these facies for the first time, this research aims to show that this location demonstrates the submarine to subaerial volcanic transition in proximity to a parasitic vent and to build an emplacement event history.

Detailed descriptive fieldwork was performed in combinations with petrographic analyses—performed optically and with the assistance of ImageJ—to describe the lithofacies at a macro- and micro- scale.

Taylor’s Mistake is comprised of four main lithofacies that we characterize in this study; a pyroclastic deposit, a breccia with coherent dike fingers, a dike complex, and a lava deposit. These facies are porphyritic and basaltic but have very different structures and textures. We interpret the pyroclastic deposit to be subaerially erupted scoria in a cone as a parasitic vent. The breccia with pieces of coherent dike fingers is a hyaloclastite in which the coherent fingers reflect the last pulse of the injection of dike material. The lava is a basalt from a different vent source on the LVC, and the dike complex formed as episodic injections of magmatic material.

From these lithofacies’ properties and contact relationships, we present a likely event history for the formation at this outcrop. A scoria cone developed subaerially prior to other emplacements. Second, a dike intruded through the wet sediment to form a hyaloclastite mound that partially covered the scoria cone. Next, a lava from an uphill source flowed over the top of the scoria and hyaloclastite and deposited subaerially apart from the very base which deposited in a shallow submarine environment. Lastly, episodic diking forming the major dike feature occurred after the other facies had cooled.

The presence of a hyaloclastite is significant because evidence of submarine volcanism has not been previously described in published research for Banks Peninsula. The overall site provides access to the submarine to subaerial transition from proximal vent facies at a parasitic vent which can be used in future research as a proxy for modern processes.