Origin and diagenetic priming of a potential slow-slip trigger zone in volcaniclastic deposits flanking a seamount on the subducting plate, Hikurangi margin, New Zealand

Slow-slip megathrust events in the Hikurangi forearc region may be related to seamount subduction. IODP Expedition 375 drilled flank of Tūranganui Knoll, a Cretaceous east subduction zone containing units analogous intervals associated with subducted seamounts. Detailed investigations volcaniclastic Unit V at Site U1520, based on scanned core images, petrographic observations, point-counting, and μXRF mapping, reveal that it is mafic succession rich clay minerals which are products multiphased history diagenetic alteration. This unit interpreted as resulting from downslope transport debris submarine eruptions. In contrast, most volcanic clasts recovered nearby U1526, near top subaerial eruptions reworked by wave action. shallow water sedimentary package experienced minimal clay-mineral alteration more extensive early carbonate cementation. Differences clast origins, depositional settings histories these highlight heterogeneity systems Plateau. However, presence voluminous hydrous clays within thick, altered flanking U1520 provides ready source for excess pore fluids enable slow-slip along zone.