Spatio-temporal associations between dike intrusions and fault ruptures in the Tongariro Volcanic Center, New Zealand

Abstract

Crustal extension of the southern portion of the Taupo Rift in the Central North Island of New Zealand is mostly accommodated by normal faulting and rare dike intrusions. To better understand how extension is accommodated and how volcanoes and faults interact, we provide a new integration of the tectonic and volcanic history of this young section of the Taupo Rift from geological evidence. Fault acceleration and deceleration apparently coincide with episodes of voluminous volcanic eruptions during the last 100 ka. Using geological data, we detect three modes of volcano-fault interactions active during different periods: (1) increased volcanism (eruptive volume) coupled with increased fault slip-rate (e.g., 26–11 cal kyr BP); (2) increased volcanism, but decreased adjacent fault activity (e.g., 11–10 cal kyr BP Pahoka-Mangamate “unzipping” period); and (3) decreased volcanism (low rates and volumes), but increased fault slip-rate (e.g., 45–25 cal kyr BP). The availability of melt production at depth is a first-order factor controlling the geodynamic processes of coeval fault slip-rate and magma volume variations within this rift. We hypothesize that progressive shallowing of magma drives transition of mode (1) to (2); i.e., maintaining high volcanic rates but decreasing fault slip. Second-order interactions, such as stress-transfer, is modelled by simple Coulomb stress transfer scenarios to other faults and volcanoes surrounding rift elements. Our results strongly suggest that fluctuations in magma input through time strongly influence both eruption frequency and seismic cycles in volcanic rifts. Time-dependent seismic hazard models must consider the influence of magmatic processes in fault parameters (e.g. temporal slip-rate variations) in continental rifting environments.