Transitions in Eruptive Style During the 2012 Deep Submarine Silicic Eruption of Havre Volcano, Kermadec Arc, New Zealand

Clark, Acacia1; Carey, Rebecca1; Jutzeler, Martin1; Mitchell, Samuel2

1University of Tasmania, Hobart, Australia, 2University of Bristol, Bristol, United Kingdom

Submarine eruptions are poorly understood compared to their subaerial counterparts due to challenges accessing and observing them. The 2012 silicic submarine eruption of Havre Volcano in the Kermadec Arc was the largest deep ocean eruption (~900 – 1220 meters below sea level) ever recorded.

The main vent transitioned in eruption style during the event. The current eruption framework describes the onset of magma disruption on the seafloor at high (107 kgs-1) eruption rates, which produced a large pumice raft (~1 km3) accompanied with a giant pumice seafloor deposit. This phase transitioned to an intermediate phase of unknown intensity that produced an ash-lapilli-block (ALB) deposit proximal to the vent. The final eruptive phase was low intensity (104 kgs-1) effusive magma emplacement that produced a 250 m-high dome complex (Dome OP) over the vent. Previous studies have focused on microtextures of these main phases to understand shallow conduit processes.

We have identified lobe deposits around Dome OP which stratigraphically sit above the ALB deposit but were emplaced prior to the end of the effusive phase. These deposits represent a transitional phase between high to low eruption rates. Detailed microtextural studies were conducted on four representative clasts from in-situ Dome OP together with three clasts from surrounding lobe deposits, and two dense end-member ALB clasts not previously studied.

Microlites of the same crystal types and habits are present in lobe deposits and in-situ Dome OP clasts, where they are most abundant. ALB clasts are microlite free with almost spherical vesicles. Clasts from lobe deposits have elongated vesicles with round edges and in-situ Dome clasts have elongated and flattened vesicles. ALB clasts have the highest vesicle number density, followed by lobe deposits and then in-situ Dome clasts. Rounded vapor-phase cristobalite is present in lobe deposits and in-situ Dome O clasts, whereas in-situ Dome P clasts contain an abundance of oblong cristobalite crystals that exist entirely within the groundmass. No discernible correlation could be made between vesicle size and cristobalite crystal size. Silicic submarine domes are morphologically and texturally similar to subaerial domes, indicating hydrostatic pressure has a minor role in outgassing and emplacement processes of lava domes.


Biography

Acacia graduated with a Bachelor of Science from the University of Sydney in 2015. After taking some time to explore Canada she returned to undertake her Honours at the University of Tasmania (UTAS) and graduated with First Class. She intends to begin her PhD at UTAS in late 2020.

Volcanic stratigraphy and eruption mechanisms from the last remaining outcrops at Wiri Mountain, Auckland Volcanic Field, New Zealand

Foote, April1, Németh, Károly2, Handley, Heather1

1Department of Earth and Planetary Sciences, Macquarie University, Sydney, Australia, 2Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand

Dispersed volcanic fields (commonly labelled as monogenetic volcanic fields) are of great interest in volcanology as they provide a relatively simple volcanic architecture to study regarding magma source to surface processes, edifice growth and subsequent destructions. The Auckland Volcanic Field (AVF) in New Zealand is among the few hundred documented dispersed volcanic fields worldwide that were active through the Holocene and can broadly be defined as a mafic intraplate monogenetic volcanic field. Recent research has highlighted that the transition between monogenetic and polygenetic volcanism is far more continuous than was originally thought, where volcanoes traditionally viewed as monogenetic are commonly found to have had multiple eruptions and complex magmatic plumbing systems.

This study focuses on the last remaining outcrops of Matukutūruru, or Wiri Mountain, one of the southernmost volcanic centres in the AVF. Wiri Mountain presents a unique situation where despite the large extent to which deposits have been removed, the remaining spectacular outcrops allow a clear picture to be formed, including analysis of stratigraphy and facies, vent location and extent of deposits, fragmentation depth, eruptive styles and their transitions and the eruption history of the volcanic centre.

Wiri Mountain has had a complex eruption history, beginning with a pre-existing tuff ring/maar landscape. An initial basal tuff ring was deposited by predominantly pyroclastic density currents with ballistic curtain deposits and some pyroclastic fall, through a debris filled vent that widened mostly at depth through the course of the eruptions. At least two smaller, satellite tuff rings were then deposited on the outer flanks of the first by a combination of pyroclastic density currents and pyroclastic fall, with a transition from phreatomagmatic to Strombolian eruptive style. A central scoria cone was then deposited within the initial tuff ring, followed by lava spatter and lava flows that covered the tuff rings, the scoria cone, and the surrounding area. This complex eruption history highlights the range and transition of eruptive styles leading to the production of multiple types of eruptive products and deposits that can be typical for the AVF.

The small magma volumes typical of monogenetic volcanism allow for significant influence of fragmentation and eruptive products by external water, resulting in a wide variety of volcanic landforms. However, based on the results of this study, volcanic activity at Wiri Mountain and the surrounding area of the southern end of the AVF was potentially more complex than would typically be expected from the textbook definition of monogenetic activity, with a large enough eruptive volume to allow a complex eruptive evolution over time, multiple satellite cones, and potential connections to nearby centres; highlighting the grey area on the concept boundary of monogenetic volcanism.


Biography

April Foote is a PhD candidate at Macquarie University. Her studies are based on the volcanology of the southern end of the Auckland Volcanic Field.

Geophysical and geochemical constraints on the formation of Holocene intraplate volcanism in East Asia

Ward, Jack F.1; Rosenbaum, Gideon1; Ubide, Teresa1; Wu, Jonny2; Caulfield, John T. 1,3; Sandiford, Mike4; Gürer, Derya1

1School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia, 2Department of Earth and Atmospheric Sciences, University of Houston, Houston, USA, 3Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane, Australia, 4School of Earth Sciences, University of Melbourne, Melbourne, Australia

East Asia contains many Holocene volcanic centres, several of which are located far (between 600 and 1500 km) from the Pacific and Philippine Sea plate subduction zones. The origin of these intraplate volcanoes, which include Jeju, Ulleungdo, Tianchi, Jingbohu, Erkeshan and Wudalianchi, remains enigmatic. Geodynamic processes proposed to explain the occurrence of the East Asian Holocene intraplate volcanoes include mantle plume activity, subduction processes with slab fluid involvement, and subduction processes without slab fluid involvement. Here, we evaluate a variety of geophysical datasets and a compilation of geochemical data to assess the feasibility of these mechanisms. High-resolution tomography data provide no evidence for the rise of deep-seated mantle plumes. Instead, the tomographic and seismic data highlight the stagnation of the Pacific slab at the 660 km discontinuity below Tianchi, Longgang, Jingbohu, Erkeshan and Wudalianchi. The geophysical data also provide evidence for the stagnation of the Philippine Sea slab at the 410 km discontinuity below Jeju and Ulleungdo. Although the intraplate volcanoes appear to be located above subducted slabs, the geochemical data do not provide evidence for melt generation due to slab metasomatism. Instead, the intraplate volcanoes are alkaline in composition and display primitive mantle normalised trace element characteristics comparable to those shown by ocean island basalts. In light of the absence of evidence for plume activity or slab metasomatism, we suggest that convective upwellings occurring at the edges of the Pacific and Philippine Sea slabs may be responsible for Holocene intraplate volcanism in East Asia. Because it is likely that the Pacific and Philippine Sea slabs have been stagnant in the mantle transition zone for millions of years, we speculate that slab-edge convection and volcanism may be driven by regional-scale tectonic events. We conclude by discussing possible Neogene–Quaternary tectonic events that may have contributed to the occurrence of East Asian Holocene intraplate volcanism. 


Biography

Jack Ward is a PhD student at the School of Earth and Environmental Sciences, The University of Queensland. He uses geophysical and geochemical data to better understand the processes that cause anomalous subduction-related magmatism.

Timescales of magma ascent recorded by olivine zoning patterns from Mount Leura and Mount Noorat, Newer Volcanics Province, Australia

Didonna, Rosa1, Handley, Heather1, Cas, Ray2, Fidel, Costa3, Murphy, Timothy1

1Department of Earth and Environmental Sciences, Macquarie University, Sydney, NSW, Australia 2School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, Australia 3Earth Observatory of Singapore, Nanyang Technological University, Singapore

Intraplate continental basaltic volcanic provinces (ICBVPs) occur on all continents, but the timescales of magmatic processes that lead to eruption in such settings are poorly understood due to the temporal infrequency and lack of spatial pattern in eruptions. Therefore, unravelling the timescale of magma ascent is a critical aspect to advance our understanding of volcanic hazard and risk. Here we focus on the Newer Volcanics Province (NVP) of SE Australia is an active intraplate basaltic province that contains over 400 volcanic centres. Volcanic landforms include maars, tuff rings, scoria cones, lava fields along with more complex eruption centres and the rate of activity has varied in space and time. Despite a large number of studies on the bulk-rock geochemistry and physical volcanology of the deposits (e.g. stratigraphy, eruption styles), few constraints are available on the timescales of magma ascent in the province.

We have investigated the olivine crystals within entrained mantle xenoliths and as individual crystals within the groundmass of basaltic volcanic rocks using compositional X-ray maps, backscattered electron (BSE) images and electron microprobe analyses (EMPA). We focus on NVP samples from Mount Leura (Lehurra kang) and Mount Noorat (Knorart) to shed a light on the dynamic processes that lead to the eruption and the relative timescales of magma ascent. Olivine crystals in mantle xenoliths are mainly unzoned with Mg#90 (Mg# = 100×Mg/[Mg+Fe]) with few crystals normally zoned (<Mg#75 rim). Olivine grains in the groundmass are commonly up to 1 mm in size and are mainly skeletal, with significant variation in Mg#, CaO, MnO and NiO content from core to rim. Olivine grains in the Mount Noorat samples are largely normally zoned with crystal interiors characterised by >Mg#90 and rims by <Mg#75. Olivine crystals from Mount Leura contain complexly zoned olivines suggesting a more complex crystallisation and transport history (Mg#77-79 cores and rims up to Mg#85). We model the chemical zonation patterns in olivine crystals that reveal a short time of magmatic processes before the eruption. The insight of magma storage, ascent and the pathway to the surface at NVP is a crucial information in understanding the volcanic hazard and mitigation risk in the region for which too little consideration is still given at the present.


Biography

Research Fellow in the Dept of Earth and Environmental Sciences at Macquarie University. PhD from Macquarie University in April 2020.

Research interests in igneous petrology and volcanology. Focus on crystal records of magmatic processes and timescales in the lead-up to volcanic eruptions combining field observations and detailed microscopy analytical techniques.

Newly identified mafic and felsic tuffs of the Shoalhaven and Talaterang Groups, southern Sydney Basin: their volcanic significance and palaeoecological impacts

Bann, Dr Glen1, Graham, Ian2, Jones, Brian1

1University of Wollongong, Wollongong, Australia, 2University of NSW, Kensington, Australia

A suite of newly identified mafic and felsic tuffs are described from the Shoalhaven and Talaterang Groups of the southern Sydney Basin. This includes the Clyde Coal Measures, Wasp Head, Pebbly Beach and Snapper Point Formations, Wandrawandian Siltstone, Nowra Sandstone, Berry Siltstone and the lower Broughton Formation. The tuffs are readily observed from outcrops in the field however, so far, have proved very difficult to discern in drill cores.

The mafic tuffs commonly comprise abundant biotite and muscovite grains, which are often deformed, K feldspar, plagioclase, volcanic quartz, with embayments, quartz shards and rare euhedral zircons. The felsic tuffs contain abundant volcanic and metamorphic quartz, plagioclase, more common pumaceous material, less micas and very rare or absent, shards. All tuffs contain carbonaceous material of various amounts and both are commonly reworked, although a lack of abrasion on the phenocrysts in the mafic tuffs suggests that the material has not travelled far from its source. Numerous dropstones of the same tuff material are common throughout the sequence, with volcanic types dominating in the east and metamorphic cratonic types in the west.

The Koo Lee Tuff Member, the largest of the mafic eruptions with a maximum thickness of almost 3m, is stratigraphically located within the lower Broughton Formation and due to its explosiveness and volume, has been deposited across a large area of the basin, hence outcrops in a number of locations. This provides the opportunity to identify eruption and emplacement mechanisms plus lateral changes in the deposit as well as providing a chronological time line through the southern Sydney Basin.

Volcanic detritus from island volcanoes to the south-east inundated sediment derived from the craton to the west during this period. Evidence from the presence of predominantly Cruziana ichnogenera and glendonites throughout the succussion, in addition to wavy contact surfaces beneath coarser sands and sporadic volcanic derived clasts suggest deposition was dominated by episodic storm activity in cold climate conditions with periodic coastal ice sheets depositing the clasts, or dropstones. Very fine-grained carbonaceous horizons indicate that deposition was also periodically dominated by extended low energy conditions. These deposits represent small or distant components of much larger volcaniclastic aprons surrounding a series of vents to the south-east. Evidence suggests a proximal source from island volcanoes ranging from mild Strombolian to the violently explosive Vulcanian or Plinean phreatomagmatic type eruptions. The association with the Late Permian Gerringong Volcanics and these earlier eruptions is presently unclear. The felsic eruptions are more distal, possibly associated with a large felsic provenance in the Zealandia craton to the south east.

The tuffs are often associated with trace fossil escape burrows, both successful and unsuccessful, and marine body death assemblages, commonly within the tuffs themselves but also found both below and above the tuffs. The effects of the eruptions and the tuffs on the local biota at the time will include changes in pH and Eh, elevated water and substrate temperatures, chemical toxicities such as Hg and As, during and post eruption, and an increase in turbidity. Effects will impact different species, with the more significant eruptions impacting everything. The more proximal eruptions, such as the Koo Lee Tuff, will also destroy habitat, displacing the animals.

It is therefore apparent that volcanism was controlling and dominating the deposition and conditions during early stages of the formation of the southern Sydney Basin.


Biography

This work has been ongoing since completing an Honours thesis on the early volcanism of the southern Sydney Basin in 1999, was drastically highjacked for many years by a PhD which had nothing to do with this, glad to be back and making interesting and challenging discoveries

Shallow Conduit and Vent Processes during the 1886 Basaltic Plinian Eruption at Tarawera, New Zealand

Moore, Hannah1, Carey, Dr Rebecca1, Houghton Dr Bruce2, Jutzeler, Dr Martin1, White, Dr James3

1School of Natural Sciences and CODES, University of Tasmania, TAS, Australia 2Department of Earth Sciences, University of Hawaii at Mānoa 3Department of Geology, University of Otago

The 1886 eruption of Tarawera, New Zealand, is one of four known examples of basaltic Plinian eruptions. During the climactic phase, a high Plinian eruption column was produced, fed by vents in four segments along an 8-km-long fissure across Mt Tarawera. This eruptive activity was simultaneous with other adjacent vents across the mountain that were in a low-intensity style of eruption. Here we present a detailed re-examination of microtextures from pyroclasts to constrain the ascent and degassing histories of the magma which influenced the Plinian versus low intensity styles of eruption along the Mt. Tarawera portion of the fissure. With this study, we aim to understand how this basaltic magma erupted at such high mass eruption rates. Scoria clasts and ash particles selected from stratigraphy proximal to the vent represent (1) a widespread endmember, sedimented from the Plinian column margin and (2) a localised endmember, sedimented from low intensity explosions, representing the lowest mass eruption rates. We also study clasts from a medial section, from which clasts were absolutely entrained into the Plinian plume and represent the highest mass eruption rates. The main differences in scoria clasts from different sites along the fissure segment are in microlite crystallinities: these are low within the proximal localised material (35–55 %), high within the proximal widespread material (95–99 %), and intermediate within the medial material (69–84 %). We suggest that, for vents erupting at Plinian intensity, there was a strong parabolic velocity profile across the conduit, which ensured that magma near conduit margins ascended slower, cooled faster and became more viscous than magma along the axis, leading to longer residence times and therefore more advanced degrees of outgassing and crystallisation. The highly viscous magma at the margins may have reduced permeability and therefore outgassing from magma along the axis, causing a build-up of pressure within the conduit, driving higher eruption rates, and leading to a Plinian eruption. Eruption products sedimented into the widespread proximal environment represent the collar of cooler, more crystallised magma, whereas products entrained into the high plume and sedimented into the medial location represents magma from the central axis. For vents erupting at low intensities, there were transient discrete explosions, where the most intense explosive eruptions cleared out the shallow conduit. These
episodic explosions allowed efficient outgassing from magma in the shallow conduit, but viscosity remained relatively low compared to Plinian magma.


Biography

Hannah Moore conducted her MSc degree in Volcanology at the University of Bristol. Hannah’s PhD research at the University of Tasmania is focussed on the 1886 basaltic Plinian eruption of Tarawera. She uses techniques such as field geology, textural analysis and physical volcanology to understand this unusual eruption.

About the GSA

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