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Volcanic hydrothermal systems on andesitic composite volcanoes -- Mineralogy, 3D architecture and their use to understand flank collapse activity

Gabor Kereszturi1 , Antonio M. Álvarez-Valero2, Nessa D'Mello1,3, Mercedes Suárez Barrios2, Rachelle Sanchez1, Craig Miller4 and Daniel A. Coulthard Jr1

  • Affiliations: 1Volcanic Risk Solutions, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand; 2Department of Geology, University of Salamanca, Spain; 3Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, USA; 4GNS Science, Wairakei Research Centre, Taupo, New Zealand 

  • Presentation type: Talk [Invited]

  • Presentation time: Thursday 10:30 - 10:45, Room R290

  • Programme No: 3.8.1

  • Theme 3 > Session 8

Abstract

Volcanic hydrothermal systems are common to many andesitic composite volcanoes, yet their evolution, mineralogy, and significance often remain underexplored. This study highlights new approaches to understand the evolution of composite volcanoes by leveraging insights gained from geological mapping of hydrothermally altered deposits. We applied extensive field work and sampling, combined Scanning Electron Microscopy, Shortwave Infrared reflectance spectroscopy, X-Ray Diffraction, stable isotope systematics, X-Ray Fluorescence, thermodynamic modelling, airborne and close-range hyperspectral imaging and aeromagnetic surveys. Using Ruapehu (New Zealand) as a case study, we demonstrate how such analyses can provide critical information for improving volcanic hazard assessments. Our research examines fossil and active hydrothermal systems exposed in the southern sector of Ruapehu that show a diverse suite of weathering and hydrothermal mineralogy formed since 160 ky. Most of these are located with the Wahianoa Formation (160-80 ky), ranging from deeper phyllic- (>220 °C and more neutral pH) to shallower argillic alteration zones (80-200°C and low pH). This transition reflects variations in fluid temperature and pH within the exposed fossil hydrothermal system. Additionally, the outcrops reveal a complete lateral progression, from core alteration zones to more distal regions characterized by intermediate argillic and supergene alterations, featuring abundant goethite/hematite, and phyllosilicate mineral assemblages. We found a complex interplay between volcano growth/evolution and hydrothermal alteration history. A new model has been proposed to integrate hydrothermal alteration history into the Mt Ruapehu's evolution that can better depict ongoing alteration processes and triggers for flank instability and volcanic hazards associated with hydrothermal systems.