Syn-eruptive alluvial and fluvial volcanogenic systems within an eroding Miocene volcanic complex, Lyttelton Volcano, Bank Peninsula, New Zealand

摘要

The Diamond Harbour Volcanic Group (DHVG; 8.1-5.8 Ma) was deposited during the last stage of volcanism on Banks Peninsula, New Zealand. Interbedded with eruptives of the DHVG are volcanogenic sequences that constrain erosional extent, processes, timing, and degradation of Lyttelton Volcano. Such phases of erosion and deposition are commonly recorded in volcanic ring plains, but exposures within the highly eroded Lyttelton Volcano provide an excellent example of degradation processes and deposition in the interior of an eroding volcano. At Black Point, eastern Lyttelton Harbour, the Hays Bay Volcanogenic Sequence of the DHVG comprises interbedded conglomerate and sandstone, formed by debris flows to stream flows in an E-W valley-controlled alluvial fan system. Volcanogenic sequences elsewhere around Lyttelton Harbour are formed from multiple alluvial fan systems depositing into a braided alluvial/fluvial, single outlet depositional basin, indicating the inception of a NNE draining proto-Lyttelton Harbour by 8.1 Ma.