Geophysical and volcanological insights into the subsurface morphology and eruptive histories of complex maar volcanoes within the Newer Volcanics Province, Western Victoria (original) (raw)
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Journal of Volcanology and Geothermal Research, 2015
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 upon lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. 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 irregular shaped high
Factors controlling the internal facies architecture of maar-diatreme volcanoes
Bulletin of Volcanology, 2013
Most if not all kimberlite pipes show a multitude of facies types, which imply that the pipes were emplaced under an episodic re-occurrence of eruptive phases, often with intermittent phases of volcanic quiescence. The majority of these facies can be related to either the fragmentation behaviour of the magma during emplacement or changing conditions during sedimentation of volcaniclastic deposits, as well as their alteration and compaction after deposition. An additional factor controlling pipe-facies architecture is the degree of mobility of the loci of explosions in the explosion chambers of the root zone or root zones at the base of the maar-diatreme volcano. In a growing pipe, the root zone moves downward and, with that movement, the overlying diatreme enlarges both in size and diameter. However, during the life span of the volcano, the explosion chamber can also move upward, back into the lower diatreme, where renewed explosions result in the destruction of older deposits and their structures. Next to vertical shifts of explosion chambers, the loci of explosions can also move laterally along the feeder dyke or dyke swarm. This mobility of explosion chambers results in a highly complex facies architecture in which a pipe can be composed of several separate root zones that are overlain by an amalgamated, crosscutting diatreme and maar crater with several lobes. Pipe complexity is amplified by periodic changes of the fragmentation behaviour and explosivity of kimberlite magma. Recent mapping and logging results of Canadian and African kimberlite pipes suggest that kimberlite magma fragmentation ranges from highly explosive with abundant entrained country rock fragments to weakly explosive spatter-like production with scarce xenoliths. On occasions, spatter may even reconstitute and form a texturally coherent deposit on the crater floor. In addition, ascending kimberlite magma can pass the loci of earlier fragmentation events in the root zone and intrudes as coherent hypabyssal kimberlite dykes in high pipe levels or forms extrusive lava lakes or flows on the crater floor or the syneruptive land surface, respectively. This highly variable emplacement behaviour is typical for basaltic maar-diatreme volcanoes and since similar deposits can also be found in kimberlites, it can be concluded that also the volcanological processes leading to these deposits are similar to the ones observed in basaltic pipes.
Introductory Chapter: Updates in Volcanology – From Volcano Modeling to Volcano Geology
Updates in Volcanology - From Volcano Modelling to Volcano Geology, 2016
The book "Updates in Volcanology: From volcano modelling to volcano geology" is composed of 13 book chapters provided by authors from a great variety of disciplines. Each of the book chapter genuinely reflects the diversity of volcanological researches in recent years and documents new look at geological problems associated with volcanism and volcanic hazard research. The chapters from this book represent perfectly the current trends in volcanology as a merging research directions from geophysical aspects of volcanology and its traditional field-based methods. The book chapters have been grouped into three sections. Section 1 is titled "Understanding the volcano system from petrology, geophysics to largescale experiments" and provides a total of five chapters covering geophysical aspects of volcanic researches including their geochemical perspectives. The section starts with a comprehensive summary on the volcanic plumbing systems we know today and their relevance to understand the volcanic behavior from the magmatic source to a magma fragmentation that provides pyroclasts to be transported and deposited away from their source. Volcanic plumbing systems commonly defined as a network of various magmatic intrusive bodies (sheet-or dyke-like) and diverse size and shape of magmatic storage places (chambers) that located between the primary source and the surface anywhere the geological conditions allow to stall magma migration toward the surface [1-7]. The magmatic plumbing system of a volcano is a complex array of injected melts where various chemical processes take place that are strongly or loosely linked to the primary melt source and/or interact with the wall rocks. This book chapter provides a detailed summary of the methods recently applied to harvest information about these complex system feeding volcanoes on the surface. This chapter provides a summary on the potentials and the limitations of each applied methodology commonly used in magmatic plumbing system studies and highlight the fact that magmatic plumbing systems are complex geo-environments where physical and
Most if not all kimberlite pipes show a multitude of facies types, which imply that the pipes were emplaced under an episodic re-occurrence of eruptive phases, often with intermittent phases of volcanic quiescence. The majority of these facies can be related to either the fragmentation behaviour of the magma during emplacement or changing conditions during sedimentation of volcaniclastic deposits, as well as their alteration and compaction after deposition. An additional factor controlling pipe-facies architecture is the degree of mobility of the loci of explosions in the explosion chambers of the root zone or root zones at the base of the maar-diatreme volcano. In a growing pipe, the root zone moves downward and, with that movement, the overlying diatreme enlarges both in size and diameter. However, during the life span of the volcano, the explosion chamber can also move upward, back into the lower diatreme, where renewed explosions result in the destruction of older deposits and their structures. Next to vertical shifts of explosion chambers, the loci of explosions can also move laterally along the feeder dyke or dyke swarm. This mobility of explosion chambers results in a highly complex facies architecture in which a pipe can be composed of several separate root zones that are overlain by an amalgamated , crosscutting diatreme and maar crater with several lobes. Pipe complexity is amplified by periodic changes of the fragmentation behaviour and explosivity of kimberlite magma. Recent mapping and logging results of Canadian and African kimberlite pipes suggest that kimberlite magma fragmentation ranges from highly explosive with abundant entrained country rock fragments to weakly explosive spatter-like production with scarce xenoliths. On occasions, spatter may even reconstitute and form a texturally coherent deposit on the crater floor. In addition, ascending kimberlite magma can pass the loci of earlier fragmentation events in the root zone and intrudes as coherent hypabyssal kimberlite dykes in high pipe levels or forms extrusive lava lakes or flows on the crater floor or the syneruptive land surface, respectively. This highly variable emplacement behaviour is typical for basaltic maar-diatreme volcanoes and since similar deposits can also be found in kimberlites, it can be concluded that also the volcanological processes leading to these deposits are similar to the ones observed in basaltic pipes.
Journal of Volcanology and Geothermal Research
Calculating the volume of magma involved in an eruption of a maar volcano is often hindered by the uncertainty of the volumes of maar–diatremes.We calculate the eruptive volumes of several complex monogenetic volcanic centres, utilising existing geophysical models to constrain the volumes of subsurface diatremes and conduits, and digital elevation models and drill hole data to constrain the volume of the ejecta rims.We focus our calculations on several maar volcanoes within theNewer Volcanics Province of south-eastern Australia including Ecklin maar, and the Red Rock and Mount Leura volcanic complexes. Based on an average componentry of the ejecta-rim, we estimate a dense rock equivalent magma volume of 0.04 × 109 m3, 0.17 × 109 m3 and 0.29 × 109 m3 for Ecklin maar, the Red Rock and Mount Leura volcanic complexes respectively. The Red Rock and Mount Leura volcanic complexes have magma volumes that are an order of magnitude higher than Ecklin maar, and exhibit far more complex eruptive histories with multiple vents and transitions between explosive phreatomagmatic, magmatic explosive and effusive styles. Based on the total tephra volumecomparisons of observed eruptions,we estimate a VEI of 2 for Ecklin, Mount Leura and Red Rock.
Bulletin of Volcanology, 2013
The ∼5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner. The facies are (1) coherent to vesicular fragmental alkali basalt (effusive/Hawaiian spatter and lava flows); (2) massive scoriaceous fine lapilli with coarse ash (Strombolian fallout); (3) bedded scoriaceous fine lapilli tuff (violent Strombolian fallout); (4) thin-medium bedded, undulating very fine lapilli in coarse ash (dry phreatomagmatic surge-modified fallout); (5) palagonite-altered, cross-bedded, medium lapilli to fine ash (wet phreatomagmatic base surges); and (6) massive, palagonite-altered, very poorly sorted tuff breccia and lapilli tuff (phreato-Vulcanian pyroclastic flows). Since most deposits are lithified, to quantify the grain size distributions (GSDs), image analysis was performed. The facies are distinct based on their GSDs and the fine ash to coarse+fine ash ratios. These provide insights into the fragmentation intensities and water-magma interaction efficiencies for each facies. The eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles, except for a "magmatic horizon" of effusive activity occurring at both ends of the volcanic complex simultaneously. The eruption foci are located along NW-SE trending lineaments, indicating that the complex was fed by multiple dykes following the subsurface structures related to the Tartwaup Fault System. Possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates, viscosity, crystallinity, degassing and magma discharge rate, as well as hydrological parameters.
Earth and Planetary Science Letters, 2013
Temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location. However, the relationship between the external and internal characteristics of volcanoes and sub-volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data. We use high-quality 2D seismic reflection data from the Ceduna Sub-basin, offshore southern Australia, to quantitatively analyse 56, pristinely-preserved, Eocene-age volcanogenic mounds, and a genetically-related network of sub-volcanic sills and laccoliths. Detailed seismic mapping has allowed the 3D geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised. Forty-six continental, basaltic shield volcanoes have been identified that have average flank dips of <121, basal diameters of 1.94–18.89 km, central summits that are 0.02– 1 km high and volumes that range from 0.06 to 57.21 km3. Parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material, suggesting that a series of temporally separate eruptions emanated from a central vent. The shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill-complex. Eight volcanogenic hydrothermal vents, which are also associated with the lateral tips of sills, were also recognised, and these appear to have formed from the seepage of intrusion-related hydrothermal fluids onto the seafloor via emplacement-induced fractures. This work highlights that deformation patterns preceding volcanic eruptions may (i) be offset from the eruption site; (ii) attributed to intrusions with complex morphologies; and/or (iii) reflect magma movement along pre-existing fracture systems. These complexities should therefore be considered in eruption forecasting models that link pre-eruption ground deformation to subterranean magma emplacement depth and volume. More generally, our study highlights the key role that seismic reflection data can play in understanding the geometry, distribution and evolution of ancient and modern volcanic systems.
Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins
Updates in Volcanology - Transdisciplinary Nature of Volcano Science, 2021
Our ability to investigate both the intrusive and extrusive parts of individual volcanoes has evolved with the increasing quality of seismic reflection datasets. Today, new seismic data and methods of seismic interpretation offer a unique opportunity to observe the entire architecture and stratigraphy of volcanic systems, with resolution down to tens of meters. This chapter summarises the methods used to extract the geomorphic aspects and spatio-temporal organisation of volcanic systems buried in sedimentary basins, with emphasis on the utility of 3D seismic reflection volumes. Based on descriptions and interpretations from key localities worldwide, we propose classification of buried volcanoes into three main geomorphic categories: (1) clusters of small-volume (<1 km3) craters and cones, (2) large (>5 km3) composite, shield and caldera volcanoes, and (3) voluminous lava fields (>10,000 km3). Our classification primarily describes the morphology, size and distribution of er...