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Article Dans Une Revue Journal of Volcanology and Geothermal Research Année : 2018

Physical and mechanical property relationships of a shallow intrusion and volcanic host rock, Pinnacle Ridge, Mt. Ruapehu, New Zealand

S.P. Mordensky
  • Fonction : Auteur
M.C. Villeneuve
  • Fonction : Auteur
B.M. Kennedy
  • Fonction : Auteur
Michael Heap
  • Fonction : Auteur
  • PersonId : 923962
D.M. Gravley
  • Fonction : Auteur
T. Reuschlé

Résumé

Shallow magmatic intrusions are prevalent in volcanic settings worldwide. Understanding how these intrusions interact and influence their volcanic host rocks is therefore relevant to many engineering geology, geothermal, and volcanological applications. In this study, we present the most comprehensive dataset for a shallow intrusion and its host rock in a volcanic setting to date, detailing the mechanical and physical properties of volcanic rocks from Pinnacle Ridge, Mt. Ruapehu, New Zealand. Based on the geomechanical properties of 194 measured samples, we identify seven geotechnical units: (1) unaltered dense coherent lava, (2) altered dense coherent lava, (3) unaltered brecciated lava margin, (4) altered brecciated lava margin, (5) unaltered intrusion, (6) altered intrusion, and (7) hydrothermal veining. We detail the mineralogy (andesite compositions ranging from primary to an advanced argillic alteration assemblage), porosity (0.7–31%), permeability (10−21–10−12 m2), elastic wave velocities (1994–5615 m/s), uniaxial compressive strength (1–332 MPa) of these geotechnical units. Our laboratory analyses indicate that primary lithology is the predominant control on the physical and mechanical properties of the geotechnical units. Additionally, the data suggest that there is a correlation between distance to the largest intrusion; this is particularly evident for the measurements on the brecciated lava margin samples. Towards the largest intrusion, this breccia shows decreasing porosity (30.92 to 5.49%) and permeability (10−12 to 10−17 m2) and increasing elastic wave velocities (1994 to 4157 m/s) and uniaxial compressive strength (3 to 61 MPa). Thin-section analysis suggests that these correlations are due to mineral precipitation within fractures and pores in the brecciated lava margins. These correlations with distance to the largest intrusion are not shared by the altered intrusions or dense coherent lavas. We suggest that the high primary permeability of the unaltered breccia facilitated efficient hydrothermal fluid circulation and mineral precipitation adjacent to the intrusion. The other geotechnical units are less affected because hydrothermal fluid flow, alteration, and mineral precipitation were limited due to low initial permeability (10−21–10−16 m2). Our study shows that the initial properties of the host rock (i.e. porosity and permeability) control the extent of hydrothermal alteration and the susceptibility to modifications of rock geomechanical properties. Modifications to porosity and permeability can influence edifice-scale behaviour; for example, a reduction in permeability can result in pore pressure augmentation, which exerts a primary control on volcanic slope stability, seismicity, and eruptive behaviour. This study provides the most comprehensive and complete geomechanical properties data suite on a shallow intrusion in volcanic host rock to date and will support monitoring and modelling of volcanic hazards associated with shallow igneous intrusions.
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Dates et versions

hal-01937200 , version 1 (28-11-2018)

Identifiants

Citer

S.P. Mordensky, M.C. Villeneuve, B.M. Kennedy, Michael Heap, D.M. Gravley, et al.. Physical and mechanical property relationships of a shallow intrusion and volcanic host rock, Pinnacle Ridge, Mt. Ruapehu, New Zealand. Journal of Volcanology and Geothermal Research, 2018, 359, pp.1 - 20. ⟨10.1016/j.jvolgeores.2018.05.020⟩. ⟨hal-01937200⟩
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