Three volcanic arcs have been the source of New Zealand's volcanic activity since the Neogene: Northland arc, Coromandel Volcanic Zone (CVZ) and Taupō Volcanic Zone (TVZ). The eruption chronology for the Quaternary, sourced by the TVZ, is well studied and established, whereas the volcanic evolution of the precursor arc systems, like the CVZ (central activity c. 18 to 2 Ma), is poorly known due to limited accessibility to, or identification of, onshore volcanic deposits and their sources. Here, we investigate the marine tephra record of the Neogene, mostly sourced by the CVZ, of cores from IODP Exp. 375 (Sites U1520 and U1526), ODP Leg 181 (Sites 1123, 1124 and 1125), IODP Leg 329 (Site U1371) and DSDP Leg 90 (Site 594) offshore of New Zealand. In total, we identify 306 primary tephra layers in the marine sediments. Multi‐approach age models (e.g. biostratigraphy, zircon ages) are used in combination with geochemical fingerprinting (major and trace element compositions) and the stratigraphic context of each marine tephra layer to establish 168 tie‐lines between marine tephra layers from different holes and sites. Following this approach, we identify 208 explosive volcanic events in the Neogene between c. 17.5 and 2.6 Ma. This is the first comprehensive study of New Zealand's Neogene explosive volcanism established from tephrochronostratigraphic studies, which reveals continuous volcanic activity between c. 12 and 2.6 Ma with an abrupt compositional change at c. 4.5 Ma, potentially associated with the transition from CVZ to TVZ.
N2 - Plain Language Summary: Since 18 Ma, volcanic activity in New Zealand is dominantly sourced by the Coromandel Volcanic Zone (CVZ). Most caldera systems of the CVZ identified so far are located on Coromandel Peninsula in the NW of North Island, New Zealand, but studies of the CVZ are rare mainly due to the limited accessibility of its volcanic deposits, as well as missing stratigraphic continuity between different outcrops and the volcanic source. Here, our ocean drilling tephra record—mainly volcanic ash from explosive eruptions, distributed and falling out over the ocean—has a great potential to reveal the eruption history of the CVZ because it is preserved in marine sediments in a nearly undisturbed stratigraphic context. We analyzed ∼400 marine tephra layers from multiple ocean sediment cores off the coast of New Zealand for their geochemical glass compositions and identified 306 as largely undisturbed ash deposits. These primary ash deposits correspond to a total number of 208 Neogene volcanic events. Different dating methods result in a continuous marine tephra record for the last 12 Ma, equivalent to a unique and most complete eruptive history for the CVZ. This enables us to further unravel changes in the composition of the associated magmas with time. N2 - Key Points:New Zealand's Neogene explosive volcanism based on the marine tephra record
Geochemical fingerprinting of marine tephra layers across the study area to establish volcanic events
Insights into geochemical variations with time, repose times and spatiotemporal distribution