Geological Society of Australia
Victoria Division

General Meeting
Thursday 25th August at 6:15 p.m.
Fritz Loewe Theatre, School of Earth Sciences, University of Melbourne
Talk will be proceeded by drinks from 5:30 pm in the 4th floor tearoom, cost $2.

Student's Night


Tzu-Ying Kuo

Ph.D. candidate, School of Earth Sciences, The University of Melbourne.

The composition of altered oceanic crust (AOC) revisited

Altered oceanic crust (AOC) is a key reservoir in the Earth’s geochemical evolution, and knowledge of its composition is critical for the interpretation of both subduction zone and intra-plate magmatic products. Although global compilations of mid-ocean-ridge basalt (MORB) and ocean island basalt (OIB) data have previously been assembled to investigate mantle phenomena, most studies on AOC are usually limited to individual drill sites or locations. A broader and more comprehensive multi-element/isotope study of AOC compositions at the global scale that would permit comparisons between multiple sites exhibiting variable alteration impacts has yet to be undertaken. To address this issue, we have conducted a global survey of AOC compositions by 1) obtaining new trace element and Sr-Nd-Hf-Pb isotope data for selected AOC samples from ten DSDP/ODP/IODP Sites, and 2) combining these data with a review and compilation of previously published information. These data should promote an increased understanding of the role that AOC plays in subduction zone and deep mantle recycling (OIB) processes.

A total of 112 new samples have been analysed in this project for trace elements, Sr, Nd, Pb, Hf isotopes, and these have been combined with (generally less comprehensive) data from 3,147 literature analyses. Preliminary results indicate that relatively immobile elements as well as Nd and Hf isotopes generally display consistency with regional MORB character, whereas the contents of mobile elements are highly variable between samples and Sites. Overall, the new results compare well with previous data, with geochemical variations mainly controlled by lithology, coupled with the extent and type of alteration. Furthermore, the extent of alteration appears to be predominantly linked with crustal spreading rates. Broad correlations are observed in Nd and Hf isotope systematics, which may be indicative of mantle source evolution. Several different mean compositions of AOC, calculated by various approaches, will be compiled.


Jeremy Lee
Master of Science student, School of Earth Sciences, The University of Melbourne.
Pillow lavas in Timor: insights from fieldwork and geochemistry

The island of Timor is found in the area affected by the collision between the northwestern edge of the Australian continent and the Banda (Island) Arc subduction complex. Political instability following the Indonesian invasion of Timor-Leste in 1975 prevented detailed geological research for almost thirty years until Timor-Leste gained independence in 2002. Although research and fieldwork has since resumed, the tectonic models describing the formation of Timor remain uncertain.

The Oecusse (also Ocussi) district is a coastal pene-enclave of Timor-Leste and lies within Indonesian West Timor. It contains brilliant exposures of ocean floor pillow lavas outcropping as steep mountainous terrain.  Relative to other parts of Timor, Oecusse has not been regularly visited and its geology remains poorly studied. A six-week field season in Oecusse was conducted in cooperation with the Timorese government as part of a national mapping program run by the University of Melbourne.

This study is focused on the unmetamorphosed pillow lavas throughout Timor, but predominantly on the main body found in northern Oecusse.  We present a new dataset from whole-rock major/trace element and Sr-Nd-Pb-Hf isotopic analyses matched with field observations to differentiate and characterise the various lavas found throughout Timor. The main body of pillow lavas display island arc
E-MORB signatures, as suggested by the trace element and isotopic compositions. This is consistent with a supra-subduction zone ophiolite signature and is likely the result of mixing during post-collisional extension between a MORB-source and subducted material from the Australian margin. This new dataset will help to better constrain the tectonic history of Timor.

Michael Sephton

Ph.D. candidate, Department of Ecology, Environment and Evolution, La Trobe University.

Preliminary results from experiments with cement slurries to control acid mine drainage in waste rocks from the Brukunga mine in South Australia

The use of cements or grouts for geotechnical stabilisation of mine voids is well documented, but the effectiveness of cements and grouts in controlling sulfide oxidation has received comparatively little attention from researchers.

In this study, a range of Portland cement slurries were applied directly to waste rocks from the Brukunga Mine in South Australia to test effectiveness in controlling acid mine drainage generation.  This paper focuses on the results from three columns used as a control group with no cement application, and another three columns, subjected to application of a cement slurry with a water cement ratio of 1.0.

Cement slurry application caused the pH to increase to almost 12 in the first leach before stabilizing at around 8 after 2 months, at the same time reducing sulfur loads by around 75% and reducing acidity, iron, aluminium, magnesium, copper, zinc and manganese to undetectable levels.  These improvements have been sustained for around 12 months since cementing, and monitoring is continuing.

Higher Calcium, sodium and potassium concentrations in the leachates from the cemented rocks indicates that the cement is dissolving slowly whilst neutralizing the acidity produced by the lower rates of pyrite oxidation in these rocks.


Catherine Wheller

Ph.D. candidate, School of Earth Sciences, The University of Melbourne.

Conditions of formation for the granulites of southern Madagascar

In a suite of rocks collected from southern Madagascar is a sapphirine-bearing rock, the class of which has been assigned UHT (ultra-high temperature) status, with conditions greater than 950-1000°C at 8-11kbar. This rock has a low variance mineral assemblage that is ideal for establishing metamorphic conditions: sapphirine-orthopyroxene-magnetite-sillimanite-ilmenite-K-feldspar-quartz + melt. In a similar area, rocks with a peak mineral assemblage of garnet-magnetite-sillimanite-ilmenite-K-feldspar-quartz + melt are recorded.   Clearly oxidised, the conditions can be thought of in terms of T-M(O)-M(H2O), with the primary aim being to determine the PT of formation of these mineral assemblages. Ferric iron is included in the latest activity-composition model for sapphirine (Wheller & Powell, 2014) and is crucial for modelling sapphirine-bearing rocks in oxidised terranes.
Pseudosections in PT (pressure-temperature space) reveal the conditions of formation of the mineral assemblages, and overlapping conditions point towards consistent PT estimates of ~ 7.5-8.5kbar at 900-950°C. Difficulties in modelling the low variance sapphirine-bearing assemblage has been qualitatively resolved by thinking of the petrology as equilibrating in local domains of sapphirine + quartz (melt present) and orthopyroxene + sillimanite (melt absent).    

KFMASHTO compatibility diagrams are used to show alternative mineral assemblages at these PT conditions for other rock compositions.  If these rocks are representative, it does not appear that this is a UHT terrane.


Geological Heritage Issues in the News

The Geological Heritage Subcommittee of GSAV is concerned about the recurrence of rock crushing on the significant lava flows in western Victoria. Rock crushing appears to have been resumed on a property south of Hamilton on the Bydauk Lava Flow and this has hit the news both in The Age and the local Hamilton paper, The Standard.

The Harman Valley lava flow is the most recent of the flows from Mt Napier and has several significant features. Some of these features can be seen from the lookout on the Hamilton-Port Fairy Road. Not all features are threatened as some are in National Parks and other reserves but several features on private land are under threat.

The features in the Harman Valley and their significance (in brackets) are: HM002 Mt Napier (National); HM 001 Byaduk Caves (State); HM 036 The Great Barrier, Harman Valley (National); HM004 Wallacedale Tumuli (International). Many of the features can be viewed from the Harman Valley Lookout (HM 054) on the Hamilton - Port Fairy road which looks up the Harman Valley towards the volcano of Mount Napier. The mountain is a composite volcano with a broad, timbered, lava shield capped by a steeper, bare, scoria cone formed by explosive activity at the end of the eruption.  Below the lookout one can see the lava flow (about 36,000 years old) that came down the valley from the mountain. This flow was fed by lava tubes, some of which can be entered at the Byaduk Caves. One can see a lava channel below and to the right of the lookout. The flow is the best example of a valley constrained lava flow in Australia.

Unfortunately there is very little protection for geological sites in Victoria, especially on private land. As most protection does not involve destroying the features many farmers and landowners are  sympathetic, but occasionally we see people who are unable to co-operate. This appears to be the case here. There is no state government supported data base of sites; GSAV manages the only database for the entire state.

The subcommittee is currently investigating what further we can do, but lack of heritage legislation and limited planning laws restrict what is possible. We will keep you posted!

Susan White
Chair, Heritage Subcommittee


The 2016 Selwyn Symposium
Supercontinent assembly through breakup: An Eastern Gondwana Perspective.

The Selwyn Symposium will be held on September 29 at the Earth Sciences Building, University of Melbourne (corner Swanston & Elgin Streets, Parkville). Registration is now open.

This symposium brings together the latest research on the assembly of Gondwana and the subsequent controls that this had on disintegration of the supercontinent particularly focussing on eastern Gondwana (Australia, Zealandia). Talks will be given by Dr George Gibson, Andrew Merdith, Prof. Alan Collins, Dr David Moore, Prof. Nick Rawlinson, Dr Steven Boger, Dr Jo Whittaker, Dr Hamish Campbell, Dr Simon Holford, Dr Milo Barham and Dr Ian Duddy.

The Symposium will conclude with the presentation of the Selwyn Medal, followed by the Selwyn Public Lecture, given by Dr Hamish Campbell, presenting Did the entire New Zealand land mass sink beneath the waves 23 million years ago? The Symposium dinner will be held at Cafe Italia from 7:45 pm.

Further details are available at

Books Available

A selection of GSA publications will be available at the August meeting. They cover a range of topics. Free to a good home!

Forthcoming events

Unless otherwise noted, all 2016 talks will be held at the Fritz Loewe Theatre, School of Earth Sciences, University of Melbourne.

August 25th: Monthly meeting:
Students Night: Michael Sephton, Catherine Wheller, Tzu-Ying Kuo and Jeremy Lee.

September 29th: Selwyn Symposium
Supercontinent Assembly Through Breakup: An Eastern Gondwana Perspective.
More information:

October 27th: Monthly meeting:
Associate Professor John Paterson:

The Emu Bay Shale Konservat-Lagerstätte: A view of Cambrian Life from East Gondwana

Student Scholarships

The GSAV are pleased to offer scholarships for honours and postgraduate students in geological sciences for assistance with travel costs associated with attending conferences (fieldwork excluded). The number and value of the scholarships awarded each year is made at the discretion of the GSA Victoria committee. Up to $500 for travel within Australia and between Australia and New Zealand and $700 for travel elsewhere is available, paid half before and half after the conference. More information, including the eligibility criteria and application form, is available at

Contributions to The Victorian Geologist

If there are any events, happenings, news, or views that would be of interest to the membership, please send your details and information to Kieran Iles at
Newsletter deadline: First Friday of the month, except for December and January.

Contribute to TAG

It is member contributions which make TAG (The Australian Geologist) a member magazine – please keep the contributions coming and assist with informing all of the membership (not just your Division) about your activities.

Please send your news to:

About the GSA Victoria Division

General information about the Geological Society of Australia and GSA Victoria Division can be found at and
Contact details for the GSAV Committee can be found at

Copyright © 2016 GSA Victoria, All rights reserved.

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