Subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling, Lake Purrumbete Maar, Newer Volcanics Province, southeastern Australia

Jackson C van den Hove, Laurent Ailleres, Peter G Betts, Ray A F Cas

Research output: Contribution to journalArticleResearchpeer-review

7 Citations (Scopus)

Abstract

Lake Purrumbete Maar (LPM) is situated in the Late Cenozoic intraplate, basaltic Newer Volcanics Province, southeastern Australia. It is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake. Gellibrand Marl accidental lithics, which occurs to a maximum depth of 250 m below LPM, represent the deepest excavated host rock unit present in the volcanic succession. Irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption. High-resolution lake- and land-based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar. This is done to test the assumption, based on lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. The collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces (<1 mGal) associated with the maar, on an inherently unstable water body. The magnetic anomaly over LPM shows several irregularly shaped high magnetic anomalies. Four 2.5-D forward models transecting LPM were constructed based on the observed potential field data. Five coalesced vents forming an undulating shallow bowl-shaped diatreme contained within the Gellibrand Marl (240 m depth) were modelled to satisfy the observed magnetic response, while a large sill body at 350 m depth is modelled to satisfy the observed gravity response. A second forward model, completed to satisfy the observed magnetic response, also includes coalesced shallow bowl-shaped diatremes within the Gellibrand Maar, which then taper down to become thin and steep sided and extend down to the basement (1,050 m depth). Three-dimensional property and geometry inversions suggest the diatreme most likely extends to a greater depth than the initial maximum depth of 240 m. This suggests the lithic-based maximum diatreme depth inferred by accidental lithics present in the volcanic successions is an underestimate.
Original languageEnglish
Pages (from-to)142-159
Number of pages18
JournalJournal of Volcanology and Geothermal Research
Volume304
DOIs
Publication statusPublished - 2015

Keywords

  • Coalesced diatreme
  • Forward modelling
  • Maar
  • Potential field inversion

Cite this

@article{d6111397ab79482f919259cafda2563d,
title = "Subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling, Lake Purrumbete Maar, Newer Volcanics Province, southeastern Australia",
abstract = "Lake Purrumbete Maar (LPM) is situated in the Late Cenozoic intraplate, basaltic Newer Volcanics Province, southeastern Australia. It is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake. Gellibrand Marl accidental lithics, which occurs to a maximum depth of 250 m below LPM, represent the deepest excavated host rock unit present in the volcanic succession. Irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption. High-resolution lake- and land-based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar. This is done to test the assumption, based on lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. The collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces (<1 mGal) associated with the maar, on an inherently unstable water body. The magnetic anomaly over LPM shows several irregularly shaped high magnetic anomalies. Four 2.5-D forward models transecting LPM were constructed based on the observed potential field data. Five coalesced vents forming an undulating shallow bowl-shaped diatreme contained within the Gellibrand Marl (240 m depth) were modelled to satisfy the observed magnetic response, while a large sill body at 350 m depth is modelled to satisfy the observed gravity response. A second forward model, completed to satisfy the observed magnetic response, also includes coalesced shallow bowl-shaped diatremes within the Gellibrand Maar, which then taper down to become thin and steep sided and extend down to the basement (1,050 m depth). Three-dimensional property and geometry inversions suggest the diatreme most likely extends to a greater depth than the initial maximum depth of 240 m. This suggests the lithic-based maximum diatreme depth inferred by accidental lithics present in the volcanic successions is an underestimate.",
keywords = "Coalesced diatreme, Forward modelling, Maar, Potential field inversion",
author = "{van den Hove}, {Jackson C} and Laurent Ailleres and Betts, {Peter G} and Cas, {Ray A F}",
year = "2015",
doi = "10.1016/j.jvolgeores.2015.08.020",
language = "English",
volume = "304",
pages = "142--159",
journal = "Journal of Volcanology and Geothermal Research",
issn = "0377-0273",
publisher = "Elsevier",

}

TY - JOUR

T1 - Subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling, Lake Purrumbete Maar, Newer Volcanics Province, southeastern Australia

AU - van den Hove, Jackson C

AU - Ailleres, Laurent

AU - Betts, Peter G

AU - Cas, Ray A F

PY - 2015

Y1 - 2015

N2 - Lake Purrumbete Maar (LPM) is situated in the Late Cenozoic intraplate, basaltic Newer Volcanics Province, southeastern Australia. It is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake. Gellibrand Marl accidental lithics, which occurs to a maximum depth of 250 m below LPM, represent the deepest excavated host rock unit present in the volcanic succession. Irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption. High-resolution lake- and land-based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar. This is done to test the assumption, based on lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. The collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces (<1 mGal) associated with the maar, on an inherently unstable water body. The magnetic anomaly over LPM shows several irregularly shaped high magnetic anomalies. Four 2.5-D forward models transecting LPM were constructed based on the observed potential field data. Five coalesced vents forming an undulating shallow bowl-shaped diatreme contained within the Gellibrand Marl (240 m depth) were modelled to satisfy the observed magnetic response, while a large sill body at 350 m depth is modelled to satisfy the observed gravity response. A second forward model, completed to satisfy the observed magnetic response, also includes coalesced shallow bowl-shaped diatremes within the Gellibrand Maar, which then taper down to become thin and steep sided and extend down to the basement (1,050 m depth). Three-dimensional property and geometry inversions suggest the diatreme most likely extends to a greater depth than the initial maximum depth of 240 m. This suggests the lithic-based maximum diatreme depth inferred by accidental lithics present in the volcanic successions is an underestimate.

AB - Lake Purrumbete Maar (LPM) is situated in the Late Cenozoic intraplate, basaltic Newer Volcanics Province, southeastern Australia. It is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake. Gellibrand Marl accidental lithics, which occurs to a maximum depth of 250 m below LPM, represent the deepest excavated host rock unit present in the volcanic succession. Irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption. High-resolution lake- and land-based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar. This is done to test the assumption, based on lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. The collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces (<1 mGal) associated with the maar, on an inherently unstable water body. The magnetic anomaly over LPM shows several irregularly shaped high magnetic anomalies. Four 2.5-D forward models transecting LPM were constructed based on the observed potential field data. Five coalesced vents forming an undulating shallow bowl-shaped diatreme contained within the Gellibrand Marl (240 m depth) were modelled to satisfy the observed magnetic response, while a large sill body at 350 m depth is modelled to satisfy the observed gravity response. A second forward model, completed to satisfy the observed magnetic response, also includes coalesced shallow bowl-shaped diatremes within the Gellibrand Maar, which then taper down to become thin and steep sided and extend down to the basement (1,050 m depth). Three-dimensional property and geometry inversions suggest the diatreme most likely extends to a greater depth than the initial maximum depth of 240 m. This suggests the lithic-based maximum diatreme depth inferred by accidental lithics present in the volcanic successions is an underestimate.

KW - Coalesced diatreme

KW - Forward modelling

KW - Maar

KW - Potential field inversion

UR - http://goo.gl/4mq0lU

U2 - 10.1016/j.jvolgeores.2015.08.020

DO - 10.1016/j.jvolgeores.2015.08.020

M3 - Article

VL - 304

SP - 142

EP - 159

JO - Journal of Volcanology and Geothermal Research

JF - Journal of Volcanology and Geothermal Research

SN - 0377-0273

ER -