Australian volcanic rocks reveal their secrets
They’re the key to understanding what lies 30 kilometres beneath the Earth’s surface. Amy Middleton reports.
The continental crust of a planet such as Earth serves as a geological timeline of its evolution.
While the Earth’s upper crust is relatively accessible, and therefore quite well known to science, the lower part of the crust remains somewhat mysterious.
Unlocking this mystery, which could affect how we prepare for our future on this planet, is a key research area for Robert Emo, a PhD student in geology at Brisbane-based university QUT, in Australia.
Emo studies ancient rocks that were spewed up by volcanoes once active across the state of Queensland, from as far as 30 kilometres below the Earth’s surface. This is remarkable when you consider that the deepest anyone has ever drilled down is 10 kilometres. These volcanic rocks are “the only direct samples we have of this part of the Earth,” Emo says.
Queensland is a unique terrain for this kind of study, according to Emo, because of the sheer abundance of lower crustal rock that can be found scattered across the eastern part of Australia.
“It covers such a large area and a large portion of our crust,” he says. “Some of the actual lavas are as young as around 10,000 years old, whereas others around central Queensland are believed to be about 30 million years old.”
In the lab, Emo creates images of a cross-section of each lower crustal rock using electron microscopes and microprobes, and examines the chemical composition using a mass spectrometer. He then dates the samples by firing laser beams at certain minerals to assess the rates of decay of elements within them.
These techniques are an area of expertise of Emo’s principal supervisor in the QUT Science and Engineering Faculty, Professor Balz Kamber. It’s something of a dream academic pairing: when Emo was completing his undergraduate degree at Trinity College in Dublin, Kamber held the Chair in Geology and Mineralogy there – and was also one of Emo’s lecturers.
Emo later honed his skills in Vancouver with research on some of the Earth’s oldest preserved rocks. Around this time, he was contacted by Kamber and encouraged to apply for the inaugural WH Bryan Earth Sciences PhD Scholarship at QUT, under his supervision. He was successful.
“Yeah, I would say I followed him [to Brisbane],” Emo laughes “It was definitely an exciting opportunity to be working with him.”
Originally from Switzerland, Kamber had previously worked at the University of Cambridge and the University of Oxford in the UK, the University of Queensland, and Laurentian University in Canada.
He is at the cutting edge of the latest thinking about the Earth’s geological evolution, recently publishing a paper in the journal Chemical Geology that suggested a new theory explaining why diamonds formed as precious gemstones rather than just lumps of common graphite.
Kamber says research in earth sciences has really started to pique public interest in recent years. “At long last geology has become relevant to society – I had to wait 25 years for that. We all want electric cars, solar cells, fancy new gizmos – all of these require materials that are found by a geologist.
“We [also] want to know more about climate. The only way we can predict the future climate is to know about the past.”
If the answers to our future problems are locked in Earth’s lower crust, this geology super-team is working to find them.