MEDIAL TO DISTAL INTERACTIONS AND DEPOSITS OF THE LYTTELTON VOLCANIC COMPLEX, SOUTH ISLAND, NEW ZEALAND

Medial to distal interactions and facies can provide insight into volcanic growth processes, mechanisms of lava transport, eruptive processes, and emplacement environments including subaerial versus subaqueous settings. To date, submarine volcanism has yet to be identified in the Lyttelton Volcanic Complex, Banks Peninsula, New Zealand. Detailed field mapping of four sites of the shore platform coupled with photographic analysis was used to characterise the constructional medial to distal flank sequences exposed in the now heavily eroded Lyttelton Volcanic Complex. Deposits along the shore platform include lava flow contacts, brecciated and fragmented zones, channel-like and tube-like flow structures, levee-like structures, zones of reworked ashy sediment, potentially glassy and frothy chilled margins, irregular jointing, and pseudopillow-like structures. Pseudopillow structures and fracture systems, frothy chilled margins, potentially glassy chilled margins, and evidence of aqueous reworking of volcaniclastic and sedimentary materials indicate the occurrence of lava-water interactions during the time of emplacement from approximately 12 to 9.7 mya. We interpret that these interactions are submarine, and that relative paleo sea level during volcanism was within approximately 5m of modern sea level, which correlates with global sea level data. Trends and strike and dips of lava flow features and channels indicate it is unlikely the lava flows and volcanic deposits were sourced from the central vent region of the Lyttelton Volcanic Complex, but from a source to the south-west, in the Mt. Evans area. This sequence / exposure in Camp Bay provides evidence that the Lyttelton Volcanic Complex was an oceanic island, and that eruptions at this evolving volcanic complex interacted with seawater that may have influenced eruptive processes and deposition.