Category Archives: Geology education

New ideas in science can take ages to be understood and accepted

When recently participating in the jury process for the assessment of a student’s PhD thesis on palaeoweathering and surficial albitization in Spain (see previous article; https://bit.ly/2MmRMDZ), I summarized the difficulties faced by me and my students over many years in getting our observations and interpretations published and eventually (though perhaps reluctantly) accepted by the geological community in Europe . This story began almost 50 years ago when my detailed studies of albitization in surficial landscapes across France and elsewhere in western Europe commenced. The alteration had long been recognized but never seriously investigated. My story begins:

“During 1976-79 J-J Yerle completed a PhD on uranium deposits hosted in Permo-Carboniferous sediments in Rouergue (SW Massif Central). It included studies of core from numerous drillholes and was accompanied by extensive mineralogical analyses using X-ray diffraction. The major results were as follows: a fine-grained facies containing ~90% albite with no quartz or K-feldspar was encountered in the core; it appeared to have developed by albitization accompanied by chloritisation of biotite, but the intensity of the alteration decreased with depth and eventually disappeared. Dr Yerle initially considered a syn-sedimentary model for the albitization but K-Ar dating pointed to a Triassic age which suggested a palaeoweathering model post-dating sedimentation. None of our colleagues could accept this interpretation: five days before the formal defence of Dr Yerle’s thesis one colleague entreated the Institute Director to cancel the proceedings.

“From 1978-86 Dr J-M Schmitt was employed by the Ecole des Mines de Paris and commenced a doctorat es Sciences thesis on a uranium mine hosted in a gneiss in northern Rouergue focussing on albitization. He was able to demonstrate a clear decrease in the abundance of albite with depth in the profile; the geopetalcharacteristics of the profile, particularly its termination at depth where alteration was restricted only to fractures; and radiochronological data defining a Triassic age for the alteration. However, even this scholarly work did not convince colleagues and associates. On the contrary, many petrographers were opposed to the interpretation on the basis that they ‘knew’ that albitization could develop only at depth and at high temperatures – albite ‘could not’ form at low temperatures.

“During 1982-86 J-Y Clément undertook another PhD thesis on uranium deposits hosted in the Permian Lodève Basin, South of Rouergue. Here, the host sediments are clastics with interstratified ash layers. The base of the sequence is dark coloured and greenish; the top is red. This colour change had been thought of as an original facies character of the sequence. Dr Clément carefully described a profile consisting of an uppermost clay-enriched zone, an underlying zone in which the only feldspar present was pure albite (together with analcime); and a deeper zone containing secondary albite + Kfeldspar. The alteration did not persist at depth. All alteration horizons were discordant with the stratigraphy and were preserved under a Triassic sedimentary cover, which led to them being attributed to an infra-Triassic age. Dr Clement correlated this profile and the accompanying alteration with Dr Schmitt’s Rouergue albitization, the latter occurring on the continental surface upstream of the basin where weathering had persisted after the deposition of the early Trias in the basin. Yet, these observations and results were not convincing for many of our geologist colleagues.

“During the period from 1986 until 2000, about 15 years, we did little further work on the albitization because of our critics: other angles of ‘attack’ on the alteration profiles had to be found. One such approach came from numerous hikes in the Hercynian mountains and across Triassic palaeosurfaces. A first clue came from a visit to the albitized Delamerian (Cambrian) granites on the southern coast of South Australia. Then some traverses through the Morvan where the hilly terrain made it possible to better appreciate the widespread albitized profiles: these are characterised by fresh, unaltered granites in valleys and pervasive red albitized facies on higher slopes and hilltops. The same features were examined further north on the Brittany coast and the Vosges Massif, as well as in every part of the Massif Central, the Maures Massif on the French Riviera, at several places in the Alps, around Mont-Blanc, in Central the Spanish Massif and later in Morocco.

*Red albitised granites on the Brittany coast*

“1997 was the ‘tipping point’ when I went to Barcelona for field work on the Monjuic silification. Dr David Gomez-Gras showed me the paleoweathering features below the Trias. At each site I was more and more excited by the red facies thought to be the result of Triassic palaeoweathering: associated with it were magnificent albitized profiles. A plan was made to bring Dr David Parcerisa to Fontainebleau to undertake post-doctoral research on the Morvan.

“From 2000-2010, with Dr Parcerisa in Fontainebleau, there was a substantial renewal of energy in research on the Morvan albitized profiles. The work included substantial field mapping and sampling and detailed petrographic studies supplemented by cathodoluminescence. This gave a clear demonstration of a geopetal profile for the albitization. But a paper we submitted for publication describing these observations and data was rejected by a reviewer known as a specialist in albitization in sandstone reservoirs. One particular dismissive comment from him was that ‘the authors have no experience in albitization and do not even know what albitization means’. Unfortunately, this is an entrenched opinion offered by so-called peer reviewers on many papers with new ideas and interpretations submitted for publication nowadays.

During the same period, I had a PhD student (Catherine Recordel) working on paleomagnetic dating of the Siderolithic palaeoweathering profiles on the Massif Central but we struggled to get results. I suggested that she try to date the red albitized facies and this was successful and, eventually, so was the palaeomagnetic dating of the Siderolithic palaeoweathering profiles. Dr Ricordel’s paper on the age of the Morvan profile was accepted and this turned out to be the pass for Dr Parcerisa to publish his paper on his petrographic studies! One step forward – but yet some colleagues were still not convinced. One petrologist who worked for 30 years on the episyénite albitized facies in the Massif Central told me that he didn’t believe in paleomagnetic dating!

“From 2005-2010 we continued with paleomagnetic dating. Management in Mines-ParisTech Geoscience decided to promote research on the albitized profiles before I retired, for which I am grateful. We started with post-doctoral research by Dr Christine Franke and later complemented it with a PhD study by Kouakou Yao. Dr Yao’s research was focussed on the Sudetes Massif in Southern Poland. Paleomagnetic dating was also undertaken in the Sudetes, Vosges and Catalonia Massifs. All produced Triassic ages for the albitization . Extensive drilling in Norway, and additional drilling programs in the Maures Massif, generated very promising cores through albitized profiles. Later, causal exploration showed albitized geopetal profiles in Ireland, Cornwall and Galicia.

“During the 2010s Dr Carles Fàbrega started research on his thesis and made a significant contribution by means of radiometric dating and isotope analyses of single minerals. He confirmed the Triassic age for the albitic palaeoweathering profiles and also generated, for the first time, a temperature evaluation consistent with alteration in a palaeosurface or somewhat deeper regolith environment. This has been a major additional cornerstone for the subject.

“In conclusion: Max Plank said: ‘A new truth in science never succeeds in triumphing by convincing its adversaries and bringing them to see the light, but rather because finally these adversaries die and a new generation grows, to whom this truth is familiar.’ There is the hope!

“This story evolved over 45 years and there are some lessons about research that extend from it.

First you need a basis in field studies to apply your ideas: without fieldwork ideas remain dreams in geology and there are no new ideas. Observations in the field dictate what is possible (or not) and provides new facts.
You never can predict where or when new ideas will arise, and what they might be. Progress in research is always due to opportunities, field opportunities, meeting with people with different experiences, and opportunities to insert an idea into another’s research program. Opportunities must be taken as theyarise.
The essence of research is not to find out what others have already shown, but to innovate and to follow different pathways: from this springs the excitement of a quest for the unknown.
Finally, there is always risk-taking. This is one difficulty of the multiple research programs that abound at present. These research programs all aim to guide researchers and limit risk (mostly financial risk, of course) and so they tend to deviate as little as possible from what is already known. It is a brave agency who will award funds to those who are either little-known or whose proposal does not conform to the orthodoxy. This approach does not lead to novelty. It curbs imagination and creativity.
Research is like an unique artwork, a painting or a poem, and it should embody a quest for understanding and a captivating story.

(See also preceding companion article)

Dr Medard Thiry, December 2020

Surficial albitization – palaeoweathering preserved beneath the extensive Triassic unconformity in Western Europe

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One form of albitization consists of the replacement (albitization) of Ca-bearing plagioclase by secondary Na-plagioclase (i.e. albite) and is typically accompanied by alteration of biotite to chlorite and the staining of the rock by iron oxide pigments. In crystalline rocks, albitization is rather widespread but is traditionally considered result from deep and high-temperature metasomatic alteration linked to magma cooling during exhumation. Studies of albitization have principally been undertaken by petrologists who are mostly interested in the origin and emplacement of granites and naturally focus on aspects of their petrography and the details of their parageneses in this context. They interpret albitization to be a ‘window’ to post magmatic processes.

But albitization can also be a consequence of surficial weathering. The example we studied in Spain (Fig. 1) is widespread and spatially and temporally associated with a Triassic palaeosurface. Its occurrence forces a completely different point of view about this form of alteration. A major gap separates the two points of view about albitization and our findings have exposed a ‘cultural barrier’ that has to be breached in order to advance knowledge about this process, particularly where it is found in crystalline rocks. Key foci in the scientific exchange ought to include the geometry of the alteration in the field, petrographic observations detailing stages in the alteration, and the dating of these stages.

Figure 1. Field locations of albitized granites below the Triassic unconformity in Spain. (a) Guilleries Massif. (b) Roc de Frausa Massif. CCR: Catalan Coastal Ranges. From Fabrega et al. (2019).

The outcrop scale

The albitization we have studied in granites is characterised by reddening due to impregnation of the feldspars by iron oxides (Fig. 2). It results in: (1) a pervasive coloration distributed rather homogeneously within the rock volume, (2) fracture-bound red to pinkish granite facies or (3) spotting when the alteration is weak, resulting in pinkish spots distributed within non-reddened rock.

Figure 2. Strongly albitized Variscan red granites below the Triassic unconformity in the Guilleries Massif, NE Spain.

In terms of structure, a vertical profile of albitized granite, with a typical thickness around 150-200 m, occurs below the Triassic unconformity in the Guilleries and Roc de Frausa Massifs in NE Spain (Fig. 3). The most intense alteration occurs at the top, immediately below the unconformity, and progressively decreases in intensity with depth. From the top to the bottom, the alteration facies change from red to pink and ultimately spotted. Unaltered granites are found below (Fig. 3).

Figure 3. Vertical structure and facies evolution of the albitization profile. Intensity of alteration decreases with depth. (a) Mesozoic sedimentary cover. (b) Red facies. (c) Pink facies. (d) Spotted facies. After Parcerisa et al. (2010).

The microscope scale

Microscope observations of the albitized granites show a suite of reactions in the major minerals including plagioclase albitization, K-feldspar microclinization, biotite chloritization and quartz recrystallization. Albitization affects the primary plagioclase, where the Ca-bearing cores of the crystals are pseudomorphosed by secondary albite along twin planes and micro-fractures (Fig. 4a, b). Within this secondary albite, part of the calcium released during plagioclase replacement forms small patches of secondary calcite. Primary K-feldspar crystals are partially pseudomorphosed by secondary microcline (Fig. 4a). Biotite and is replaced by secondary chlorite (which contains large numbers of apatite inclusions compared with primary biotite; Fig. 4c), secondary titanite and anatase. Clusters of rare-earth carbonate minerals, probably synchisite-Ce, can be seen inside the secondary porosity of albitized plagioclase and microclinized orthoclase in backscattered electron-microscope images (Fig. 4d). Secondary quartz partially replaces primary quartz in the upper part of the profile (Fig. 4e). Primary and secondary monazite occur at the reaction front between albitized and unaltered granite (Fig. 4f).

Figure 4. Cathodoluminescence and SEM images of albitized granite. Ab1: Primary plagioclase. Ab2: Secondary albite. Ap: Apatite. Cal2: Secondary calcite. Chl2: Secondary chlorite. Kfs1: Primary K-feldspar. Kfs2: Microclinized K-feldspar. Mnz1: Primary monazite. Mnz2: Secondary monazite. Qtz1: Primary quartz. Qtz2: Secondary quartz. Syn2: Secondary Synchysite-(Ce). Tit2: Secondary titanite. From Fabrega et al. (2019).

Age dating

Dating of albitized profiles has been conducted at different sites through Europe using a variety of dating methods, including: (1) K-Ar dating of albite and K-feldspar (Bonhomme et al., 1980; Schmitt et al., 1984); (2) palaeomagnetism of Fe-oxides (Ricordel et al., 2007; Parcerisa et al., 2010; Thiry et al., 2011; Yao et al. 2011, Franke et al., 2011, Yao, 2013) and, most recently, (3) K-Ar microprobe dating of albite and K-feldspar and electron microprobe U-Th-Pb dating of monazite (Fabrega et al., 2019). All have established that the albitization and associated alteration occurred during the Late Permian to Early Triassic, around 250 Ma, while the Variscan granites were exposed at the landsurface.

Thus, the red-stained albitization relates specifically to the Triassic palaeosurface and was preserved beneath it by a Mesozoic and Cenozoic sediment cover. The alteration profiles are palaeoweathering features relating to surficial weathering and were nor much eroded. The geopetal organization (decreasing intensity of albitization with depth ending in alteration confined to fractures) is characteristic of weathering and alteration under the influence of geomorphology, climate, and groundwater.

Palaeoenvironmental setting of the alteration

The morphology of the alteration profile and its proximity to the Permo-Triassic palaeosurface suggests that the responsible fluids were Na-rich groundwaters (Fig. 5a). The depth of the alteration profile, the long-lasting tectonic stability in the region, and the continental scale abundance of saline environments in the Permo-Triassic period were probably key factors in the development of this near-surface weathering event across Europe. The albitization profiles remained preserved below the Triassic sedimentary cover or, in some cases (Fig. 5b), directly at the surface. In contrast to the non-albitized granites usually decompose to sandy material when exposed to surface conditions, the albitized granite has an increased resistance to weathering and erosion.

Figure 5. Permo-Triassic setting that facilitated the development (a) and preservation (b) of albitization. From Fabrega et al. (2019.

Extent of the Late Permian to Early Triassic palaeoweathering

Thus far, this form of palaeoweathering has been observed in Morocco, the Catalan Coastal Ranges, Eastern Pyrenees, Galicia and La Mancha in Spain; Corsica, the Maures, French Central Massif (Fig. 6), Morvan, the Alps, the Vosges and Brittany in France; in Germany; Great-Britain and Ireland; Sudetes in Poland; and in the Oslo Fiord in Norway.

Summary

We have demonstrated that the albitized facies are of surficial origin and bound to the weathering (geochemical) environment linked to the Triassic palaeosurface. This dramatically changes ideas about the geomorphic evolution of the basement areas over a large part of western Europe and is a major contribution to the geodynamic modeling of the region.Indeed, reconstruction of palaeosurfaces is a unique tool in unravelling the evolution of ancient continents. Extending age data from the better-known sedimentary basin deposits to adjacent crystalline basement landscapes (particularly of palaeoweathering features) provides the possibility to set the correct framework for geodynamical models (Fig. 6).

Figure 6. Occurrence of dated palaeoweathering profiles on the French Massif Central crystalline basement. After Thiry et al. (2012).

References

Bonhomme, M., Yerle, J.-J., Thiry, M., 1980. Datation K-Ar de fractions fines associées aux minéralisations. Le cas du bassin uranifère permo-houiller de Brousse-Broquiès (Aveyron, France).- C.R. Acad. Sc., Paris, 291, sér. D, p. 121-123.
Fàbrega, C., Parcerisa, D., Thiry, M., Franke, M., Gurenko, A., Gòmez-Gras, D., Solé, J., Travé, A., 2019. Permian–Triassic red‑stained albitized profles in the granitic basement of NE Spain: evidence for deep alteration related to the Triassic palaeosurface. International Journal of Earth Sciences, https://doi.org/10.1007/s00531-019-01764-0.
Franke, C., Yao, K.F.E., Thiry, M., Gomez-Gras, D., Ihlen, P., Kadzialko-Hofmokl, M., Jelenska, M., Parcerisa, D., Fabrega, C., Lagroix, F., Turniak, C., Szuskiewicez, A., 2011. Réstitution de la paléosurface triasique par datation des ré-aimantations inscrites dans les massifs paléozoïques européens. 13ème Congrès français de Sédimentologie, Dijon, Publ. ASF, Paris, 68, p. 137.
Parcerisa, D., Casas, L., Franke, F., Gómez-Gras, D, Lacasa, G., Nunez, J.A., Thiry, M., 2010. Geomorphological stability of Permo-Triasic albitized profiles – Case study of the Montseny-Guilleries High (NE Iberia). Geophysical Research Abstracts, 12, EGU2010, EGU General Assembly 2010, 2 p.
Parcerisa D, Thiry M, Schmitt JM (2010b) Albitization related to the Triassic unconformity in igneous rocks of the Morvan Massif (France). Int J Earth Sci 99:527–544. doi: 10.1007/s00531-008-0405-1.
Ricordel, C., Parcerisa, D., Thiry, M., Moreau, M.‑G., Gómez-Gras, D., 2007. Triassic magnetic overprints related to albitization in granites from the Morvan massif (France). Palaeogeography, Palaeoclimatology, Palaeoecology, 251, p. 268-282, doi:10.1016/j.palaeo.2007.04.001.
Schmitt, J.-M., Baubron, J.-C., Bonhomme, M.-G., 1984. Pétrographie et Datations K-Ar des Transformations Minérales Affectant le Gîte Uranifère de Bertholène (Aveyron—France). Mineralium Deposita, 19(2), 123-131.
Thiry, M., Franke, C., Vercruysse, C., Kissel, C., Edel, J.-B., Bruhlet, J., 2011. Datation des paléoaltérations du massif cristallin des Vosges : implications pour l’évolution géodynamique du massif. 13ème Congrès français de Sédimentologie, Dijon, Publ. ASF, Paris, 68, p. 318
Thiry, M., Ricordel-Prognon, C., Franke, C., Brulhet, J., 2012. Modernité des paléosurfaces : leur rapport à la géodynamique. in : Cojan I., Grosheny D., Parize O. (eds) Expression de l’innovation en géosciences, Une journée avec Bernard Beaudoin, Paris, Presses des Mines, Collection Sciences de la Terre et de l’Environnement, p. 113-125.
Yao, K.F.E., 2013. Albitization and oxidation of the granitoïd rocks related to the Triassic paleosurface in the Sudetes (SW Poland). Thesis École Nationale Supérieure des Mines de Paris in Paris (France) and Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy in Warsaw (Poland). 164 p. http://pastel.archives-ouvertes.fr/pastel-00971314.
Yao, K.F.E ., Franke, C., Thiry, M., Aleksandrowski, P., Szuszkiewicz, A., Turniak, K., 2011. Albitization as record of the Triassic Paleosurface in the Sudetic Crystalline basement (Poland). Geophysical Research Abstracts, 13, EGU 2011, EGU General Assembly 2011, Vienna, Austria, Geophysical Research Abstracts, Vol. 13, EGU2011-5930.

See also the companion article following (https://bit.ly/3puuvPk )

Dr Carles Fàbrega (Departament d’Enginyeria Minera, Industrial i TIC, Escola
Politècnica Superior d’Enginyeria de Manresa, Spain)

Sir Douglas Mawson, University of Adelaide

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Overview

Douglas Mawson was born on May 5, 1882 at Shipley in Yorkshire and migrated in 1884 to Australia with his parents Robert and Margaret and older brother William. From 1895 to 1898, William and Douglas attended Fort Street Model Public School in Sydney, one of the best public secondary schools in Australia. From 1899 to 1901, Douglas Mawson studied Mining Engineering at the University of Sydney, graduating on April 19, 1902. Mawson’s best results were in geology under the influence of TW Edgeworth David, the charismatic Professor of Geology at the time. This was the start of a lifelong friendship and professional association, which ended only on David’s death on August 28, 1934 (Corbett 1998, 2000).

In 1902 Mawson commenced a Bachelor of Science degree, majoring in geology. This was interrupted by him spending several months (April to September 1903) studying the geology of the New Hebrides (modern Vanuatu) at the behest of Edgeworth David. Mawson graduated with a Bachelor of Science in early 1905 and commenced an appointment as Lecturer in Mineralogy and Petrology at the University of Adelaide on March 1, 1905. The only other geologist at Adelaide University at the time was 60 year old Walter Howchin.

After arrival in Adelaide, Mawson was very active and in particular studied the geology of the Broken Hill area and the neighbouring Olary area in South Australia. Here Mawson found Precambrian rocks that he considered to have been deposited by glacial action. He wished to see modern glacial activity and in late 1907 contacted Edgeworth David, and through him, Ernest Shackleton, the leader of the 1907-1909 British Antarctic Expedition (BAE). As a result, he was appointed as physicist to the expedition. The BAE was based on Ross Island. Highlights of this expedition for Mawson were participation in the first ascent of Antarctica’s only active volcano, the 3794m high Mt Erebus, and membership of the first party (with Edgeworth David and Alistair Mackay) to reach the vicinity of the South Magnetic Pole. David and Mawson returned to Australia as heroes.

Later in 1909, Mawson found time to continue his Broken Hill studies and completed his doctorate before the end of the year. While working in Broken Hill, Mawson met Paquita Delprat, a daughter of Guillaume Delprat, the General Manager of BHP, whom he later married. Mawson visited London in late 1909 and unsuccessfully tried to persuade Scott to land him at Cape Adare, in order to study the geology of the area. He then organised the Australasian Antarctic Expedition (AAE), the story of which has been well documented by Mawson (1964), Ayres (1999), Hall (2000), Fitzsimons (2011) and particularly by Riffenburgh (2011) who gives the most comprehensive account. The AAE was most notable for Mawson surviving and struggling back to the base at Commonwealth Bay after the deaths of Belgrave Ninnis and Xavier Mertz, his sledging companions on the Far Eastern Party. The boat had already left and Mawson was obliged to stay in Antarctica for another twelve months with six members of his party, led by Cecil Madigan, who had stayed behind. As part of the AAE, bases were also established on Macquarie Island and the Shackleton Ice Shelf. The AAE saw the first use of radio communications with Antarctica.

Mawson was knighted in 1914. He was in the UK from 1916 as part of the war effort, returning to Adelaide in April 1919 where he was appointed Professor of Geology and Mineralogy at the University of Adelaide in 1921, a position he held until his retirement in 1952. For the next few years Mawson was involved in raising funds to pay off the debts of the AAE and in organising the publication of the scientific reports resulting from the expedition. He was an enthusiastic field geologist and did considerable field work in the Broken Hill/Olary and Flinders Ranges areas, usually accompanied by students.

In the summers of 1929-30 and 1930-31, Mawson led the ship-based British, Australian and New Zealand Antarctic Research Expedition (BANZARE) using the Discovery, the ship used by Scott in his first expedition in 1901-04. This was a largely marine science, oceanography and biology expedition, but included landing on Heard Island and a visit to Mawson’s old headquarters at Commonwealth Bay. On the second voyage, Mawson claimed formal possession of King George V Land on behalf of Britain. This is the basis of the present Australian claim to what is termed the Australian Antarctic Territory, which represents about 40% of Antarctica.

Mawson continued his field work in the Flinders Ranges in the 1930s and 1940s. He was a driving force in the establishment of ANARE (Australian National Antarctic Research Expeditions) that still runs the Australian Antarctic research activities. He continued to publish research papers until his death on October 14, 1958.

Memorabilia

The University of Adelaide and the adjacent South Australian Museum have displays where Mawson memorabilia can be viewed.

The Tate Museum in the Mawson Laboratories in the University at the corner of Frome Road and Victoria Drive has a display showcasing Mawson’s Antarctic activities on its southern wall. Some of the rocks collected on the Australasian Antarctic Expedition of 1911-14 are housed in the display cases and there is a substantial further collection in the basement crypt archive (where some sample boxes containing these specimens are as yet unopened). One of the AAE sledges is on the north wall of the Tate Museum.

On North Terrace, at the entrance to the University just west of the Bonython Building, there is a bust of Mawson which was unveiled in 1982 on the occasion of the Fourth International Symposium on Antarctic Earth Sciences, held in Adelaide to commemorate the centenary of Mawson’s birth. At the foot of the bust are two large boulders: one is charnockite from near Mawson Station in Antarctica and the other is pegmatite from Arkaroola in the northern Flinders Ranges.

A recently revamped Australian Polar Exhibit at the South Australian Museum, just to the west along North Terrace, deals with Mawson’s three visits to Antarctica, as well as his work in the Flinders Ranges. There are numerous artifacts from this work as well as some general information on Antarctica. There is also reference to the other two major Australian polar explorers from the pre-World War II era, namely Hubert Wilkins and John Rymill, both of whom were born in South Australia.

Selected references

Ayres, P, 1999. Mawson. A life. (The Miegunyah Press, Carlton South).
Cooper, BJ & Jago, JB, 2007. Mawson’s earliest (1906) report on the geology of the Flinders Ranges. Transactions of the Royal Society of South Australia, 132, 167-174.
Corbett, DWP, 1998. Douglas Mawson: The geologist as explorer. Records of the SouthAustralian Museum, 30,107-136.
Corbett, DWP, 2000. A staunch but testing friendship: Douglas Mawson and T.W.Edgeworth David. Records of the South Australian Museum, 33,49-70.
Fitzsimons, P, 2011. Mawson and the Ice Men of the Heroic Age: Scott, Shackleton andAmundsen. (William Heinemann, North Sydney).
Hall, L, 2000. Douglas Mawson: The life of an explorer. (New Holland, Sydney).
Jacka, FJ, 1986. Mawson, Sir Douglas (1882-1958). Australian Dictionary of Biography. (http://adb.anu.edu.au/biography/mawson-sir-douglas-7531).
Jago, JB & Pharaoh, MD, 2016. Pre-Antarctic Mawson in South Australia and western New South Wales. Transactions of the Royal Society of South Australia, 140, 107-128.
Jago, JB, Pharaoh, MD & Wilson-Roberts, CL, 2005. Douglas Mawson’s first major geological expedition: The New Hebrides, 1903. Earth Sciences History, 24,93-111.
Mawson, D, 1915. The Home of the Blizzard. 2 volumes. (William Heinemann, London).
Mawson, P, 1964. Mawson of the Antarctic. (Longmans, London).
Riffenburgh, B, 2011. Aurora. Douglas Mawson and the Australian Antarctic Expedition1911-14. (The Erskine Press, Norwich).
The Adelie Blizzard: Mawson’s Forgotten Newspaper, 1913, edited by Archie McLean. Reproduced by The Friends of the State Library of South Australia, 2010.

Author: Professor Jim Jago, School of Natural and Built Environments, University of South Australia. jim.jago@unisa.edu.au

The Giles Complex intrusions, central Australia

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Long-term Research Program initiated by Professor Bob Nesbitt between 1963 – 1970 in the Department of Geology & Mineralogy, The University of Adelaide

R.W. Nesbitt, Emeritus Professor, University of Southampton, UK (Nov 2017)

Brief overview

The Giles Complex is an iconic geological province straddling the junction of South Australia, Western Australia and Northern Territory. It was explored by Reg Sprigg and his colleagues in the 1950s as part of a mining company (Southwestern Mining) evaluation of its mineral potential and the SA sector was later mapped by the South Australian Geological Survey in the late 1950s. These early geological studies were essentially exploratory, setting out the distribution of the major rock types, but they provided little detail of the geological evolution and origin of these ancient rocks. In 1963, the area, being a remote and scientifically challenging geological province, provided an exciting challenge to a small University of Adelaide group. An important consideration at the time was the fact that as a University-based group we were not inhibited by State boundaries which allowed us to examine the whole igneous province on both sides of the WA-SA border. Several years of field studies, petrological, mineralogical and geochemical research were undertaken by me and my colleagues and post-graduate students in the Department of Geology & Mineralogy. The results were summarized in post-graduate research theses, reported at National and International conferences, and published widely in scientific journals (list attached). The theses and rock samples collected over the many field seasons, together with the respective thin and polished sections for petrographic study, are archived in the Mawson Collection in the Mawson Building.

This comprehensive suite of studies was largely completed in the early 1970s with later follow-up isotopic studies by Chris Gray when based at the ANU and later at La Trobe. The area was re-surveyed by the Australian Geological Survey Organisation (AGSO, Commonwealth Government) in 1987 and 1990 (AGSO Bulletin 239, 1996) which built on the work of Adelaide University.

Later work by the Geological Survey of Western Australia (http://www.dmp.wa.gov.au/Geological-Survey/West-Musgrave-Province-21418.aspx) was restricted to the Western Australian sector of the Complex. In South Australia, further studies have been significantly restricted because access is controlled by the local indigenous population.

Simplified geological map showing the location and distribution of the Giles Complex Intrusions (after Nesbitt et al, 1970)

Scientific significance & outcomes

The major outcomes of the work carried out by the Adelaide University group can be summarized as follows:

The intrusive rocks of the Giles Complex were emplaced as a series of individual mafic-dominated sheets of varying dimensions, some as large as 25km in length and 4km thickness. The present outcrop area occurs over an area of about 2,500 sq.km.
The intrusions were emplaced at varying depths in the crust with those in the east of the Complex being at deep crustal depths progressing to shallow depths in the west. The mapping and subsequent laboratory studies demonstrated that the Giles Complex rocks present an east to west vertical section of continental crust with the volcanics (at Tollu in Western Australia) representing the final extrusive sequence. Petrographic studies by Goode and Moore demonstrated that the layered intrusions in South Australia were emplaced at pressures equivalent to 30 to 40 km depth. Such pressures indicate that the intrusions were emplaced near the base of the continental crust with subsequent geological events bringing them to their present surface position.
The Adelaide group, working with isotope geochemists at the Australian National University (Compston & Nesbitt 1967) were the first to determine the age of the Giles Complex rocks as 1060 Ma. This age has been subsequently verified by The Geological Survey of Western Australia using the latest zircon dating techniques (1040 to 1090 Ma) and AGSO in Canberra (1080 Ma)
The intrusions were emplaced into already deformed high-grade gneisses and granulites representing at least one previous major tectonic event and, after emplacement, were subsequently deformed into varying orientations with some (e.g. Mt Davies) being overturned.
Studies by Moore (1973) and Goode (1978) confirm that shortly after consolidation, magma chambers in the east suffered high temperature-high pressure strain in localised areas. These zones (sometimes more than 100 metres across) point to major deformation events deep in the crust which were responsible for the disruption of the original intrusions. Such zones are marked by spectacular gneissic deformation structures where most of the original minerals have been totally recrystallized leaving residual highly deformed crystals or augen within a fine-grained groundmass.
Field studies demonstrate that during cooling, the magma-crystal mix behaved like aqueous sediments producing characteristic structures such as cross-bedding, slumping, load structures and ripple marks. This phenomenon was modelled by Goode in a series of important papers (1967a, b, c). Using this model allowed us to determine the original orientation of the magma bodies prior to the deformation event. Laboratory studies on fractionation trends in mineral groups also confirmed this interpretation (e.g. Kleeman & Nesbitt 1967).
In several areas, the contacts of the intrusions, particularly in the east, are well exposed. Given that the intrusions crystallised from high temperature magmas (> 1100°C) one would expect a strong cooling reaction where the magma reacted to the host country rock. The fact that this reaction is surprisingly muted indicates that the temperature difference was small and this in turn indicates the host rocks were at high pressure at emplacement. Field and petrographic studies at the margins of Mt Davies has revealed the presence of incipient melting producing granophyre veins and inclusions. On-going research using laser ICPMS isotopic techniques is aimed at understanding the degree of involvement of the host granulite rocks.

Ongoing research

The next stage of research is to understand how these intrusions fit into the evolution of continental Australia. The presence of such large quantities of magma in the continental crust is indicative of a major mantle melting event and may provide a model for the Large Igneous Provinces (LIPS) which mark major tectonic events in several continents (e.g. the Deccan and Siberian Traps).

Publications & theses from the Giles Complex team 1964 – 2007

Publications

Collerson, K.D., Oliver, R.L. & Rutland R.W.R. (1972). An example of structural and metamorphic relationships in the Musgrave Orogenic Belt, central Australia. J. geol. Soc. Aust. 18, 379-394.

Compston, W. & Nesbitt, R.W. (1967). Isotopic age of the Tollu Volcanics, W.A. J. geol. Soc. Aust. 14, 235-238.

Facer, R.A. (1967). A preliminary study of the magnetic properties of rocks from the Giles Complex, central Australia. Australian J. Science 30, 237-238.

Facer, R.A. (1970). Magnetic properties of the Giles Complex, central Australia. Search 1, 76-77.

Facer R.A. (1971). Magnetic properties of rocks from the Giles Complex, central Australia. Royal Society of NSW Journal and Proceedings 104, 45-61.

Facer, R.A. (1971). Intrusion and magnetization of the Giles Complex, central Australia. Geophysical Journal of the Royal Astronomical Society 22(5), 517-520.

Goode, A.D.T. & Krieg G.W. (1967). The geology of the Ewarara Intrusion, Giles Complex, central Australia. J. geol. Soc. Aust. 14, 185-194.

Goode, A.D.T. & Nesbitt, R.W. (1969). Granulites and basic intrusions of part of the Eastern Tomkinson Ranges, central Australia. Spec. Pub. Geol. Soc. Aust. 2, 279-281.

Goode, A.D.T & Moore A.C. (1975). High pressure crystallisation of the Ewarara, Kalka and Gosse Pile intrusions, Giles Complex, central Australia. Contr. Mineral. Petrol. 51, 77-97.

Goode A.D.T. (1975). A transgressive picrite suite from the western Musgrave Block, central Australia. J. geol. Soc. Aust. 22, 187-194.

Goode, A.D.T. (1976a). Small scale primary igneous cumulus igneous layering in the Kalka layered intrusion, Giles complex, central Australia. J. Petrol. 17, 379-397.

Goode, A.D.T. (1976b). Sedimentary structures and magma current velocities in the Kalka layered intrusion, central Australia. J. Petrol. 17, 546-558.

Goode A.D.T. (1976c). Vertical igneous layering in the Ewarara layered intrusion, central Australia. Geol. Mag, 114, 365-374.

Goode, A.D.T. (1977). Flotation and remelting of plagioclase in the Kalka intrusion, central Australia: petrological implications for anorthosite genesis. Earth & Planetary Science Letters 34 (3), 375-380.

Goode, A.D.T. (1978). High temperature, high strain rate deformation in the lower crustal Kalka intrusion, Central Australia. Contr.Mineral. Petrol. 66, 137-148.

Gray, C.M (1977). The geochemistry of central Australian granulites in relation to the chemical and isotopic effects of granulite facies metamorphism. Contr. Mineral. Petrol. 65, 79-89.

Gray, C M. (1978). Geochronology of granulite-facies gneisses in the Western Musgrave Block, Central Australia. J. Geol. Soc. Aust. 25, 403-414.

Gray, C.M. (1987). Strontium isotopic constraints on the origin of Proterozoic anorthosites. Precambrian Research 37, 173-189.

Gray C.M. & Compston W. (1978). A rubidium-strontium chronology of the metamorphism and prehistory of central Australian granulites. Geochim. Cosmochim. Acta 42, 1735-1747.

Gray, C. M. & Goode, A.D.T. (1981). Strontium isotopic resolution of magma dynamics in a layered intrusion. Nature 294, 155-158.

Gray, C.M. & Goode, A.D.T. (1989). The Kalka layered intrusion, Central Australia: a strontium isotopic history of contamination and magma dynamics. Contr. Mineral. Petrol. 103, 35-43.

Gray, C.M., Cliff, R.A. & Goode, A.D.T. (1981). Neodymium-strontium isotopic evidence for extreme contamination in a layered basic intrusion. Earth Planet. Sci. Letts 56, 189-198

Kleeman, J.D. & Nesbitt, R.W. (1967). X-ray measurements on some plagioclases from the Mt. Davies Intrusion, South Australia. J. geol. Soc. Aust. 14, 39-42.

Moore, A.C. & Goode, A.D.T (2007). Petrography and origin of granulite‐facies rocks in the Western Musgrave Block, Central Australia. J. geol. Soc. Aust. 25, 341-358.

Moore, A.C. (1968). Rutile exsolution in orthopyroxene. Contr. Mineral. Petrol. 17, 233-236.

Moore, A.C. (1969). Corona textures in granulites from the Tomkinson Ranges, central Australia. Spec. Publ. Geol. Soc. Aust. 2, 361-366.

Moore, A.C. (1970). Descriptive terminology for the textures of rocks in granulite facies terrains. Lithos 3, 123-127.

Moore, A.C. (1971a). Corundum-ilmenite and corundum-spinel associations in granulite facies rocks from central Australia. J. geol. Soc. Aust. 17, 227-230.

Moore, A.C. (1971b). Some aspects of the geology of the Gosse Pile Ultramafic intrusion. J. geol. Soc. Aust. 18, 69-80.

Moore, A.C. (1971c). Mineralogy of the Gosse Pile ultramafic intrusion, central Australia. Plagioclase. J. geol. Soc. Aust. 18, 115-126.

Moore, A.C. (1971d). Mineralogy of the Gosse Pile ultramafic intrusion, central Australia. Pyroxenes. J. geol. Soc. Aust. 18, 243-258.

Moore, A.C. (1973). Studies of igneous and tectonic textures and layering in the rocks of the Gosse Pile intrusion, central Australia. J. Petrol. 14, 49-80.

Nesbitt, R.W. & Kleeman, A.W. (1964). Layered intrusions of the Giles Complex. Nature 203, 391-393.

Nesbitt, R.W. & Talbot, J.L. (1966). The layered ultrabasic and basic rocks of the Giles Complex, central Australia. Contr. Mineral. Petrol. 13, 1-11.

Nesbitt, R.W. (1966). The Giles Complex, an example of a deeply eroded volcanic zone. Bull. Volcanogique 29, 271-282.

Nesbitt, R.W., Goode, A.D.T., Moore, A.C. & Hopwood, T.P. (1970). The Giles Complex, central Australia; a stratified sequence of mafic and ultramafic intrusions. Geol. Soc. S. Africa Spec. Publ. 1, 547-564.

Oliver, R.L., Collerson, K.D. & Nesbitt, R.W. (1969). Precambrian geology of the Musgrave Block. Excursion Guide No 13, ANZAS 1969, 37-40.

PhD theses

Bell, T.H. (1973). Mylonite development in the Woodroffe Thrust, central Australia. Unpubl. PhD thesis University of Adelaide.

Collerson K.D. (1972). High grade metamorphic and structural relationships near Amata, Musgrave Ranges, central Australia. Unpubl. PhD thesis University of Adelaide.

Facer, R.K. (1969). Magnetic properties of the Giles Complex, central Australia. Unpubl. PhD thesis University of Sydney.

Goode A.D.T. (1970). The petrology and structure of the Kalka and Ewarara layered basic intrusions, Giles Complex, central Australia. Unpubl. PhD thesis University of Adelaide.

Gray, C.M. (1971). Strontium isotopic studies in granulites. Unpubl. PhD thesis Australian National University.

Moore A.C. (1970). The geology of the Gosse Pile ultramafic intrusions and the surrounding granulites, Tomkinson Ranges, Central Australia. Unpubl. PhD thesis University of Adelaide.

Honours theses

Barnes, L. (1968). The petrography and geochemistry of some high grade metamorphic rocks from the Mt Davies-Giles region, central Australia. Unpubl. Honours thesis University of Adelaide.

Blight D.F. (1969). The geology, petrology and geochemistry of an area south of Tollu, W.A. Unpubl. Honours thesis University of Adelaide.

Bowden, P.R. (1969). Geology of the Tollu area Western Australia. Unpubl. Honours thesis University of Adelaide.

Coin, C.D.A. (1970). A study of the granulite facies terrain near Amata. Unpubl. Honours thesis University of Adelaide.

Goode, A.D.T. & Kreig, G.W. (1965). The geology of the Ewarara intrusion, Giles Complex, central Australia. Unpubl. Honours thesis, University of Adelaide.

Gray, C.M. (1967). The geology, petrology and geochemistry of the Teizi meta-anorthosite. Unpubl. Honours thesis University of Adelaide.

Kleeman J.D. (1964). Studies on the X-ray diffraction, analysis and geochemistry of plagioclase from the Mt Davies igneous intrusion. Unpubl. Honours thesis University of Adelaide.

Miller, C. (1966). A geochemical study of clinopyroxenes from the igneous intrusion South Davies, N.W. South Australia. Unpubl. Honours thesis University of Adelaide.

Smith, P.C. (1970). The geology of the Hinckley Ranges, W.A. Unpubl. Honours thesis University of Adelaide.

Steele, R.J. (1966). Gravimetric investigation of the Mt Davies and Gosse Pile intrusions of the Giles Complex. Unpubl. Honours thesis University of Adelaide.

Yong, S.K. (1964). The distribution of trace elements Ni, Cu, Sr, Cr, and Mn in the Mt Davies basic intrusion of South Australia. Unpubl. Honours thesis University of Adelaide.

A Lesson Learned

2 Replies

Field observations

As part of ongoing studies of the nature and distribution of Permian glacigene sediments on Fleurieu Peninsula, we were shown to a location just below the plateau surface near Spring Mount, west of ‘Minnawarra’ Homestead (Fig. 1). Here, on a north-facing spur high in the landscape, adjacent to scattered outcrops of extensively weathered and ferruginised bedrock, there was a surface scatter of rounded cobbles and pebbles cascading down towards a small dam in the valley. We would normally be looking for just this type of geological occurrence as evidence for Permian glacigene sediments from which the cobbles and pebbles (erratics, outwash gravels) would have been eroded. This site was somewhat removed from the usual locations of Permian sediments that are common nearby at lower elevations in the Inman Valley to the south, and in the Hindmarsh Tiers and Myponga valleys to the north. Nevertheless, the scatter of rounded clasts was distinctive.

Figure 1: Location map. Site studied marked by red star.

On closer examination, the clasts were commonly of quartzite and fine-grained gneissic rocks but we could not identify any granite cobbles: boulders and cobbles of Encounter Bay Granites are very common in the Permian deposits along the northern margins of the Inman valley, for example. In addition, many of the cobbles and pebbles here were somewhat oblate in shape.

We traced the scatter of clasts downhill towards a small dam. On the eastern side of the dam a shallow cutting had been made in the hillslope to provide vehicular access to the dam.

Figure 2: Pebbles and cobbles eroding from a bleached and weathered sand-silt material exposed at the base of a Xanthorrhea.

Figure 3: Scatter of pebbles and cobbles eroding from a bleached, weathered and somewhat ferruginised sand-silt material. Note the oblate character of many of the cobbles.

Various exposures en route to the cutting, for example on the downslope side of a Xanthorrhea (grass-tree), revealed cobbles and pebbles weathering from a bleached, weathered and generally poorly consolidated sand-silt matrix (Fig. 2), which is very like the situation we have observed in Permian glacigene deposits. First observations on approaching the cutting by the dam confirmed these relationships (Fig. 3). At the cutting, however, the actual field relationships of the clasts and the matrix are more clearly seen and the clasts tend to have a well defined ‘imbricate’ orientation in the host matrix (Fig. 4). Immediately to the east in the cutting the relationships become clear: the clasts are actually contained within steeply dipping weathered bedrock. Their oblate shape and orientation is a function of deformation of the bedrock and they are aligned parallel to the steeply dipping layering represented by schistosity roughly parallel to bedding (Fig. 5). The weathering of the bedrock, which is related to its occurrence in close proximity to the deeply weathered pre-Tertiary summit surface of Fleurieu Peninsula, and which is particularly characteristic of the area around Spring Mount, has extensively altered the rock matrix but apparently little affected most of the contained clasts.

Some outcrops in the small tributary immediately to the west of the dam are of weathered and ferruginised schist and gneiss, but there are no rock clasts evident.

Figure 4: Pebbles and cobbles with a clearly defined ‘imbricate’ habit within the bleached, weathered and somewhat ferruginised sand-silt matrix.

Figure 5: Pebbles and cobbles, now seen as significantly deformed parallel to the cleavage in steeply dipping bedrock which has been strongly altered by weathering.

Clearly, the geology is not reflective of Permian glacigene deposits but of weathered and altered bedrock most likely to be the basal Proterozoic conglomerate that unconformably overlies the Barossa Complex basement inlier in this region. Reference to the geological map (Fig. 6) confirms this possibility. The essentially unweathered conglomerate, which is also spectacularly deformed, is well-exposed in the Inman Valley at Grey Spur, just south of the Spring Mount locality. The same formation (assigned to the Aldgate Sandstone; SARIG mapping) is exposed on the coastline at Lady Bay, south of Normanville, but the deformation here has been very intense and the contained cobbles and pebbles are significantly deformed.

Conclusion

The ‘lesson learned’ is that all is not as it initially may seem in field geology, and jumping to conclusions is not recommended. A close examination of field relationships in any locality, together with questioning of initial conclusions and gathering of all available evidence, might actually uncover an interesting story that would otherwise be missed.

Figure 6: Geological map showing site location (red star) and distribution of basal Proterozoic conglomerate (Nol Aldgate Sandstone). Geology as follows: Orange-brown (Lb) = basement Barossa Complex; dark brown (NoI, Nds, Nl etc) = Proterozoic; pale brown (Eec, Eeb etc) = Cambrian Kanmantoo Group; blue (CP-j) = Permian glacigene sediments; orange (T) = undifferentiated Tertiary weathered zone materials; yellow (Q) = undifferentiated Quaternary alluvials.

A R Milnes

R P Bourman