Remobilised silicic tuffs in middle Pleistocene fluvial sediments, southern North Island, New Zealand

Abstract

Abstract Fluvial and lacustrine sediments of middle Pleistocene age (lower Matuyama Reversed Chron and Jaramillo Subchron) contain numerous thick silicic tuffs that have been deposited in the central southern North Island of New Zealand, 100–200 km from their source in the Taupo Volcanic Zone (TVZ). Sedimentary facies indicate most of the tuffs have been transported and deposited subaqueously in a distal braid‐plain environment. Individual emplacement events represent catastrophic floods involving vertical accretion up to 30 m. Sedimentation patterns reflect rapid volcaniclastic aggradation in response to volcanism, and intervening hiatuses. Over half of the tuffs examined are composed of reworked and mixed rhyolitic (SiO2 72–79 wt%) eruptive products. In addition, most contain brown glasses (SiO2 53–79 wt%) and minerals derived from a range of intermediate to silicic eruptives. Ages and characteristics of the tuffs indicate a major phase of volcanism before and during the Jaramillo Subchron, similar in chemical composition and reflecting common petrogenesis to late Pleistocene volcanism in the TVZ (i.e., frequent eruptions of voluminous, homogeneous rhyolites contemporaneous with subordinate intermediate eruptives). The emplacement of the tuffs in the East Coast region requires substantial transport routes through the present‐day Main Axial Ranges and points to considerable uplift in the last c. 0.91 Ma.