Structure and fluid flow in andesitic systems of the Taupo volcanic zone; a framework to unravel subseafloor hydrothermal flow pathways at Brothers volcano, Kermadec Arc?

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Author(s): Massiot, Cecile; Kissling, Warwick; Nicol, Andrew; McNamara, David D.
International Ocean Discovery Program (IODP), Expedition 376 Scientists
Author Affiliation(s): Primary:
GNS Science, Lower Hutt, New Zealand
University of Canterbury, New Zealand
National University of Ireland, Ireland
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The subduction of the Hikurangi plateau beneath the Indo-Australian plate is associated with arc volcanism and hydrothermal systems both onshore (Taupo Volcanic Zone) and offshore (Kermadec arc) New Zealand. While the Taupo Volcanic Zone offers large exposures of active volcanoes and geothermal drilling data, the subsurface of the Kermadec arc was explored for the first time at Brothers volcano this year as part of IODP Expedition 376. Here we present the preliminary structural interpretation of the borehole image log acquired at Brothers volcano alongside structural patterns observed in andesitic systems of the Taupo Volcanic Zone. Terrestrial laser scanning of a recent (∼6000 years) lava flow of the Mt Ruapehu volcano, located at the southern tip of the Taupo Volcanic Zone, reveals a highly connected fracture system of cooling joints partially connected to surrounding breccias. Borehole image log interpretation and statistical analysis of three boreholes of the Rotokawa Geothermal Field, hosted in a buried andesitic volcano in the Central Taupo Volcanic Zone, highlight the interaction between cooling joints formed during emplacement of the lavas, and tectonic faults and stresses of the intra-arc Taupo Rift. Numerical models of discrete fracture networks consistent with fracture orientation, linear density, and fracture thickness observed in drill cores and borehole image logs from the Rotokawa Geothermal Field indicate the presence of numerous flow pathways of variable tortuosity. These pathways support the circulation of subsurface geothermal fluids through open fractures, and provide the loci for mineral precipitation. The variable residence time of fluids through these pathways potentially allows for fast fluid flow travel in the pathways of low tortuosity, as well as mineralisation in pathways more geometrically complex. Inferences from these generic numerical models based on onshore andesitic geothermal systems will be used for future interpretation of fluid circulation through fractures at the submarine Brothers volcano.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; Andesites; Australasia; Brothers Volcano; Expedition 376; Hydrothermal conditions; Igneous rocks; International Ocean Discovery Program; Kermadec Islands; Kermadec Trench; New Zealand; North Island; Pacific Ocean; South Pacific; Taupo volcanic zone; Volcanic rocks; Volcanoes; West Pacific Ocean Islands
Record ID: 2019050473
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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