Wide‐band magnetotelluric measurements across the Taupo Volcanic Zone, New Zealand‐Preliminary results

Ogawa, Yasuo; Bibby, H. M.; Caldwell, T. G.; Takakura, Shinichi; Uchida, Toshihiro; Matsushima, Nobuo; Bennie, S. L.; Tosha, Toshiyuki; Nishi, Yuji

doi:10.1029/1999gl010914

Cited by 42 publications

(49 citation statements)

References 14 publications

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“…Rhyolitic melts can be continually derived from mush zones over long-periods of time provided they are rejuvenated by the influx of hot mafic intrusions, which progressively reheat and lead to partial melting of the mush (Bachmann and Bergantz 2004). The mush zones in the TVZ could be the partial melt zones identified using seismic and magnetotelluric methods (Bannister et al 2004;Henrys et al 2003;Ogawa et al 1999), which reside in the lower crust at depths between 15 and 30 km. High seismicity has been recorded in recent times beneath the HLVZ (Bryan et al 1999).…”

Section: Source Of the Magmasmentioning

confidence: 99%

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

et al. 2006

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Post-10 ka rhyolitic eruptions from the Haroharo linear vent zone, Okataina Volcanic Centre, have occurred from several simultaneously active vents spread over 12 km. Two of the three eruption episodes have tapped multiple compositionally distinct homogeneous magma batches. Three magmas totalling~8 km 3 were erupted during the 9.5 ka Rotoma episode. The most evolved Rotoma magma (SiO 2 =76.5-77.9 wt%, Sr=96-112 ppm) erupted from a southeastern vent, and is characterised by a cummingtonite-dominant mineralogy, a temperature of 739±14°C, and f O 2 of NNO+0.52±0.11. The least evolved (SiO 2 =75.0-76.4 wt%, Sr=128-138 ppm, orthopyroxene+ hornblende-dominant) Rotoma magma erupted from several vents, and was hotter (764±18°C) and more reduced (NNO+0.40±0.13). The~11 km 3 Whakatane episode occurred at 5.6 ka and also erupted three magmas, each from a separate vent. The most evolved (SiO 2 = 73.3-76.2 wt%, Sr=88-100 ppm) Whakatane magma erupted from the southwestern (Makatiti) vent and is cummingtonite-dominant, cool (745±11°C), and reduced (NNO+0.34±0.08). The least evolved (SiO 2 =72.8-74.1 wt%, Sr=132-134 ppm) magma was erupted from the northeastern (Pararoa) vent and is characterised by an orthopyroxene+ hornblende-dominant mineralogy, temperature of 764±18°C, and f O 2 of NNO+0.40±0.13. Compositionally intermediate magmas were erupted during the Rotoma and Whakatane episodes are likely to be hybrids. A single~13 km 3 magma erupted during the intervening 8.1 ka Mamaku episode was relatively homogeneous in composition (SiO 2 =76.1-76.8 wt%, Sr= 104-112 ppm), temperature (736±18°C), and oxygen fugacity (NNO+0.19±0.12). Some of the vents tapped a single magma while others tapped several. Deposit stratigraphy suggests that the eruptions alternated between magmas, which were often simultaneously erupted from separate vents. Both effusive and explosive activity alternated, but was predominantly effusive (>75% erupted as lava domes and flows). The plumbing systems which fed the vents are inferred to be complex, with magma experiencing different conditions in the conduits. As the eruption of several magmas was essentially concurrent, the episodes were likely triggered by a common event such as magmatic intrusion or seismic disturbance.

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Section: Source Of the Magmasmentioning

confidence: 99%

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

et al. 2006

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“…We use natural electromagnetic fields in the frequency range between 10 KHz and 1 Hz. Electromagnetic methods are widely used for the imaging of active volcanoes because the resistivity is sensitive to the fluids and the clay alteration minerals (Ogawa and Takakura, 1990;Ogawa et al, 1992Ogawa et al, , 1998Ogawa et al, , 1999Pellerin et al, 1996;Di Maio et al, 1998;Kagiyama et al, 1999;Fuji-ta et al, 1999;Matsushima et al, 2001;Müller and Haak, 2004;Ç aglar andİşseven, 2004;Manzella et al, 2004;Oskooi et al, 2005;Aizawa et al, 2005). It must be noted, however, that the interpretation of the conductors as either fluids or clay minerals can lead to opposing conclusions on the hydrology because fluids require high permeability whereas clay alterations may imply low permeability.…”

Section: Introductionmentioning

confidence: 99%

Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system

et al. 2006

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Kusatsu-Shirane volcano, Japan, is known for its active phreatic eruptions. We have investigated its hydrothermal system by conducting audio-magnetotelluric soundings at 22 stations along a profile that extends across the volcano. The final two-dimensional model is characterized by two conductors. One is a 300-to 1000-m-thick conductor of 1-10 m, which is located on the eastern slope and covered with 200-m-thick resistive layers of Kusatsu-Shirane lava and pyroclastics. This conductor indicates the presence of a Montmorillonite-rich layer of Pliocene volcanic rocks that may function both as an impermeable floor for the shallow fluid path from the peak to the hot springs to the east and as an impermeable cap for the deeper fluid path from the summit region to the foot of the volcano. The second conductor is found at a depth of 1-2 km from the surface, at the peak of the volcano, and its resistivity is as low as 1 m or less. This low resistivity can be explained by fluids containing high concentrations of chloride and sulfate which were supplied from the magmatic gases. Micro-earthquakes cluster above this conductor, and the cut-off of the earthquakes corresponds to the top of the conductor. This conductor infers the presence of the fluid reservoir, and the upward release of these fluids from the reservoir through the conduit presumably triggers the micro-earthquakes at the peak area of the volcano. Crustal deformation modeling using GPS and leveling data of the past 10 years revealed that the center of the deflation coincides with the top of the second conductor, indicating that the fluid reservoir itself can be hosting the deformation.

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“…Ogawa et al, 1999) suggest that greywacke underlies most (or all) of the TVZ, drilling at Wairakei has never penetrated through the bottom of the volcanic materials. Within the basement, fracture permeability is a primary factor in determining the electrical properties.…”

Section: Resistivity Of Volcanic Rocksmentioning

confidence: 96%

“…Measurements have, however, been made close to the field and across the TVZ. These measurements provide images of the resistivity structure at great depth (∼30 km) from which can be deduced the thermal conditions beneath the geothermal systems of the TVZ (Ogawa et al, 1999;Ingham, 2005;Heise et al, 2007).…”

Section: Deep Structure and Heat Sourcesmentioning

confidence: 99%

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Investigations of deep resistivity structures at the Wairakei geothermal field

et al. 2009

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Wide‐band magnetotelluric measurements across the Taupo Volcanic Zone, New Zealand‐Preliminary results

Abstract: Abstract. The Taupo Volcanic Zone (TVZ) of New

Cited by 42 publications

References 14 publications

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system

Investigations of deep resistivity structures at the Wairakei geothermal field

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