Geology and hot springs of Tikitere and Taheke hydrothermal fields, Rotorua

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Espanola, O.S. 1974 Geology and hot springs of Tikitere and Taheke hydrothermal fields, Rotorua, New Zealand. Lower Hutt: New Zealand Geological Survey. Report NZGS 68. 76 p.

Abstract: The Tikitere and Taheke hydrothermal fields in the Taupo Volcanic Zone of the North Island, New Zealand are genetically related to rhyolite volcanism. Active surface hydrothermal activity at Tikitere covers 24.8 ha, and is confined within a north-east trending major graben. The surface heat flow is believed to be controlled by buried normal faults trending parallel to the graben and/or possibly by ring structures on the margins of Rotorua and Haroharo calderas. The structure controlling the location of the Taheke hydrothermal field is not clear. Present evidence does not preclude a deep connection between Tikitere and Taheke fields.The oldest rocks exposed are Haparangi-Rhyolite domes and pumice breccia (Pokopoko Breccia) which pre-date voluminous outpourings of Mamaku Ignimbrite. Buried rhyolites from beneath Tikitere are known only from blocks in hydrothermal explosion breccia, and in the Rotokawa tephra. Rotoiti Breccia, an unconsolidated rhyolitic pumice breccia erupted from Okataina Volcanic Centre to the east, covered the area to depths of about 90 m and obscures underlying structures and formations. Younger Holocene tephras from volcanic vents east and south, in turn mantle the Rotoiti Breccia.The surface thermal manifestations at Tikitere and Taheke are generally characteristic of steam-heated, shallow ground water. Hot pools and spring water are strongly acid, discoloured, typically with high sulphate and low chloride concentrations. Some hot springs at lower elevations close to Lake Rotoiti discharge clear, slightly acid and relatively high chloride water. These springs suggest that chloride-bicaerbonate water underlies the area, and the same inference is drawn from the past intense silification of Rotoiti Breccia throughout the Tikitere field and to the north.Two prehistoric and one historic hydrothermal eruptions are known to have occurred at Tikitere. Breccia from those hydrothermal explosions were identified at Ruahine Crater, at three coalescing explosion craters north of Hell's Gate, and at Spring 6. The cause of the explosions is not definitely known, but fluctuations in hydrostatic pressure and rate of flow from hot springs are likely causes.Sites for four deep wells at Tikitere are suggested to test for steam production, and help define sub-surface geological parameters related to the hydrothermal field.