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GeoTalk: The life and death of an ocean – is the Atlantic Ocean on its way to closing?

GeoTalk: The life and death of an ocean – is the Atlantic Ocean on its way to closing?

Geotalk is a regular feature highlighting early career researchers and their work. Following the EGU General Assembly, we spoke to João Duarte, the winner of a 2017 Arne Richter Award for Outstanding Early Career Scientists.  João is a pioneer in his field. He has innovatively combined tectonic, marine geology and analogue modelling techniques to further our understanding of subduction initiation and wrench tectonics. Not only that, he is a keen science communicator who believes in fostering the next generation of Earth scientists.

Thank you for talking to us today! Could you introduce yourself and tell us a little more about your career path so far?

I am a geologist by training. I gained my undergraduate degree from the University of Lisbon and I stayed there to research geodynamics as part of my PhD which I finished in 2012. As I was coming to the end of writing up my thesis I moved to Monash University, in 2011, to start a postdoc.

Yes! I worked on my PhD and a postdoc at the same time, but I was only really finishing up. My thesis was almost ready. When I moved to Australia the defence was outstanding, but otherwise I was almost done.

My PhD thesis focused on the reactivation of the SW Iberian margin. It was the very first time I came across the problem of subduction initiation and that has become a big focus of my career to date.

My postdoc came to an end in 2015 and I moved back to Portugal and took up a position at the Faculty of Sciences of the University of Lisbon where I’ve started building my own research group [more on that later on in the interview].

I’ve always been passionate about science. It started when I was a kid, I’ve always been interested in popular science. My favourite writers are Isaac Asimov and Carl Sagan.

During EGU 2017, you received an Arne Richter Award for Outstanding Young Scientists for your work on subduction initiation and wrench tectonics. What brought you to study this particular field?

On the morning of the 1st of November 1755, All Saints Day, when many Portuguese citizens found themselves at church attending mass, one of the most powerful earthquakes ever document struck off the coast of Portugal, close to Lisbon.

It was gigantic, with an estimated magnitude (Mw) 8.5 or 9. It triggered three tsunami waves which travelled up the Tagus River, flooding Lisbon harbour and the downtown area. The waves reached the United Kingdom and spread across the Atlantic towards North America too.

The combined death toll as a result of the ground shaking, tsunamis and associated fires may have exceeded 100,000 people.

The event happened during the Enlightenment period, so many philosophers and visionaries rushed to try and understand the earthquake. Their information gathering efforts are really the beginning of modern seismology.

But the 1755 event wasn’t an isolated one. There was another powerful earthquake off the coast of Portugal 200 years later, in 1969. It registered a magnitude (Mw) of 7.8.

This earthquake coincided with the development of the theory of plate tectonics. While Wegener proposed the idea of continental drift in 1912, it wasn’t until the mid-1960s that the theory really took hold.

People knew by then that the margins of the plates along the Pacific were active – the area is famous for its powerful earthquakes, explosive volcanoes and high mountain ranges. Both the 2004 Indian Ocean and 2011 Thoku (Japan) earthquakes and tsunamis were triggered at active margins.

But the margins of the Atlantic are passive [where the plates are not actively colliding with or sinking below one another, so tectonic activity – such as earthquakes and volcanoes – is minimal]. So, it was really strange that we could have such high magnitude quakes around Portugal.

A large European project was put together to produce a map of the SW Iberian margin and the Holy Grail would be to locate the source of the 1755 quake. The core of my PhD was to compile all the ocean floor and sub-seafloor data and produce a new map of the main tectonic structures of the margin.

Tectonic map of the SW Iberia margin. In grey the deformation front of the GibraltarArc, in white the strike-slip fault associated with the Azores-Gibraltar fracture zone, and in yellow the new set of thrust faults that mark the reactivation of the margin (Duarte et al., 2013, Geology)

What did the new map reveal?

Already in the 70s and later in the late 90s, researchers started to wonder if this margin could be in a transition between passive to active: could an old passive margin be reactivated? If so, could this mean a new subduction zone is starting somewhere offshore Portugal?

The processes which lead a passive margin to become active were unclear and controversial. All the places where subduction is starting are linked to locations where plates are known to be converging already.

The occurrence of the high magnitude earthquakes, along with the fact that there is structural evidence (folding, faulting and independent tectonic blocks) of a subduction zone in the western Mediterranean (the Gibraltar Arc) suggested that it was possible that a new subduction system was forming in the SW Iberian margin.

The new ocean floor and seismic data revealed three active tectonic systems, which were included in the map. The map shows the margin is being reactivated and allowed identifying the mechanism by which it could happen: ‘Subduction invasion’ or ‘subduction infection’ (a term first introduced by Mueller and Phillips, 1991).

I’d like to stress though, that the map and its findings are the culmination of many years of work and ideas, by many people. My work simply connected all the dots to try to build a bigger picture.

So, what does ‘subduction infection and invasion’ involve?

Subduction zones, probably, don’t start spontaneously, but rather they are induced from locations where another subduction system (or an external force, such as  a collisional belt) already exists.

For example, if a narrow bridge of land connects an ocean (as is often the case) where subduction is active to one where the margins are passive. The active subduction zones from one can invade the passive margins and activate them. You see this in the other side of the Atlantic (where subduction zones have migrated from the Pacific), in the Scotia and the Lesser Antilles arcs.

We also know this has happened in past. But Iberia might be the only place where it is happening currently. And that is fascinating!

Earlier on you said that the ‘Holy Grail’ moment of the map would be if you could find the source of the 1755 earthquake. Did you?

No. Not entirely. The source of the earthquake is probably a complex fault, where multiple faults ruptured to generate the quake, not just one (as is commonly thought).

In your medal lecture at the General Assembly in 2017 (and in your papers) you allude to the fact that the reactivation of the SW Iberian margin has even bigger implications. You suggest that staring of subduction process in the arcs of the Atlantic could ultimately lead to the ocean closing altogether?

The Wilson cycle defines the lifecycle of an ocean: first it opens and spreads, then its passive margins founder and new subduction zones develop; finally, it consumes itself and closes.

So, the question is: if subduction zones are starting in the Atlantic will it eventually close?

There are a few things to consider:

The ocean floor age is limited. It seems that it has to start to disappear after about ~ 200 million years (the oldest oceanic lithosphere is ~ 270 million years old). Passive margins in the Earth history also had life spans of the order of ~ 200 Ma, suggesting that this may not be a coincidence. I suspect that there is a dynamic reason for this…

Most researchers agree that the next major oceanic basin which is set to close is the Pacific. The Americas (to the east) are moving towards East Asia and Australia at a rate of 3-4 cm yr-1, so it should close in roughly 300 million years.

We also know that the Atlantic has been opening for 200 million years already. If you believe that the closing of the Pacific indicates that continental masses have been slowly gliding towards each other to form the next supercontinent (a theory know as extroversion); then the Atlantic has to continue to open until the Pacific closes. This would mean that ocean floor rocks in the Atlantic would be very old (up to 500 million years old!) – highly unlikely given the oldest existing oceanic rocks are 270 million years old.

The map I made during my PhD showed that the Atlantic oceanic lithosphere is already starting to break-up and is weakened.

All the pieces combined, I think the most likely outcome is that the Pacific and the Atlantic will close at the same time. This scenario would require other oceanic basins to form, and that’s possible in the existing Indian Ocean and/or the Southern Ocean. Present-day continents would be brought together to form a new supercontinent, which we called Aurica.

Aurica – the hypothetical future supercontinent formed as the result of the simultaneous closure of the Atlantic and the Pacific oceans (Duarte et al., 2016, Geological Magazine).

If you take into consideration present-day plate velocities the supercontinent could be fully formed in approximately 300 million years’ time. We expect Aurica to be centred slightly north of the equator, with Australia and the Americas forming the core of the landmass.

With those findings, it is obvious why subduction has been a recurring theme in your career as a researcher. But what sparked your initial interest in geology and then tectonics in general?

I spent a lot of time outdoors as a kid. I was always curious and fascinated by the outdoor world. I joined the scouts when I was eight. We used to camp and explore caves by candle-light!

When I was 14 I took up speleology; there are lots of caves in the region I grew up in, in Portugal. As amateurs, my speleology group participated in archaeological and palaeontological work. The rocks in the region are mainly of Jurassic age and contain lots of fossils (including some really nice dinosaurs).

The outdoors became part of me.

I knew early on that I didn’t want a boaring job with lots of routine. I wanted a career that would allow me to discover new things.

Geology was the most obvious choice when picking a degree. I felt it offered me a great way to stay in touch with the other sciences too – physics via geophysics and biology through palaeontology.

In my 2nd year at university, I was invited to help in an analogue lab looking at problems in structural geology and geodynamics.

I was always attracted to the bigger picture. Plate tectonics unifies everything. I like how by studying tectonics you can link a lot of little things and then bring them together to look at the bigger picture.

What advice do you have for early career scientists?

When I found out about the award I was shocked because I wasn’t expecting it at all.

I always felt I wasn’t doing enough [in terms of research output]. I think that early career scientists are being pushed to limits that are unreasonable; the competition is intense. It’s not always obvious, but there is a lot of pressure to publish. But there are also a lot of very good people whose publication record doesn’t necessarily reflect their skill as a scientist.

The award made me realise I was probably doing enough!

Moving to Australia was KEY. Moving and creating collaborations with different people will make you unique. You don’t want to stay in the same institution. [By doing so] you become very linear. There are a number of schemes available (like Marie Curie and Erasmus) which allow you to move. Use these to the fullest. Moving allows you to see problems from different perspectives. And you will become more unique as a scientist.

There a lot of bright young scientist – never have we had so many – we are all unique, but you have to find the uniqueness in yourself. Most of all have fun. Do science for the right reasons and remember that people still recognise honest hard work (the award showed me that).

Interview by Laura Roberts, EGU Communications Officer.

References

Duarte, J. C., Rosas, F, M., Terrinha, P., Schellart W, P., Boutelier, D., Gutscher, M-A., and Ribeiro, A.,: Are subduction zones invading the Atlantic? Evidence from the southwest Iberia margin, GEOLOGY, 41, 8, 839–842, https://

Duarte, J. C., and Schellart W, P.,: Plate Boundaries and Natural Hazards, Geophysical Monograph, 219 (First Edition), ISBN: 978-1-119-05397–2, 2016

Duarte, J., Schellart, W., & Rosas, F.,: The future of Earth’s oceans: Consequences of subduction initiation in the Atlantic and implications for supercontinent formation, Geological Magazine, 1–14,  https://doi.org/10.1017/S0016756816000716, 2016.

Purdy, G.M.,: The Eastern End of the Azores-Gibraltar Plate Boundary, GJI, 43, 3, 973–1000, https://doi.org/10.1111/j.1365-246X.1975.tb06206.x, 1975

Mueller, S., Phillips, R, J.,: On The initiation of subduction, JGR, 96, B1, 651-665, https://doi.org/10.1029/90JB02237, 1991

Ribeiro, A., Cabral, J., Baptista, R., and Matias, L.,: Stress pattern in Portugal mainland and the adjacent Atlantic region, West Iberia, Tectonics, 15, 3, 641–659, https://doi.org/10.1029/95TC03683, 1996

 

 

 

 

 

Imaggeo on Mondays: Lava highway in Kanaga Island

Imaggeo on Mondays: Lava highway in Kanaga Island

On a rare sunny day, Mattia Pistone (a researcher at the Smithsonian Institution in Washington DC) was able to capture this spectacular shot of Kanaga, a stratovolcano in the remote Western Aleutians, which is usually veiled by thick cloud.

The Western Aleutians form a chain of 14 large and 55 small volcanic islands, belonging to one of the most extended volcanic archipelagos on Earth (1900 km), stretching from Alaska across the northern Pacific towards the shores of Russia.

As part of a team of researchers, Mattia spent three grueling weeks in the isolated region. Being one of the most extended volcanic arc systems on Earth, the Aleutians can shed light on one of the most fundamental questions in the Earth sciences: how do continents form?

The Earth’s landmasses are made of continental crust, which is thought to be largely andesitic in composition. That could mean it is dominated by a silicon-rich rock, of magmatic origin, which is fine grained and usually light to dark grey in colour. However, basaltic magmas derived from the Earth’s upper mantle and erupted at active volcanoes contribute to chemistry of the continental crust. The fact that continental crust bears the chemical hallmarks of both suggests that the formation of new continents must somehow be linked to motion of magma and its chemistry.

Establishing the link between magma generation, transport, emplacement, and eruption can therefore significantly improve our understanding of crust-forming processes associated with plate tectonics, and, particularly, help determining the architecture and composition of the continental crust. The Alaska-Aleutian archipelago is a natural laboratory which offers a variable range of volcanic rocks. The islands present a perfect opportunity for scientists to try and understand the origin of continents.

By collecting samples of volcanic ash erupted at Kanaga and other volcanoes of the Aleutian arc, Mattia and his colleagues are currently investigating the origin of this volcanic ash. Understanding its chemistry allow the team to get a clearer idea of the conditions that were present while the magma was forming and ascending, for example, how much water and iron were present.

The team were based on the Maritime Maid research vessel, and hoped from island to island collecting samples and taking measurements of volcanic activity as part of a large research consortium called GeoPRISMS, funded by the National Science Foundation. The field work was supported by a Bell 407 helicopter and its crew.

Today’s featured image shows an andesitic lava flow erupted in 1906. The volcanic deposits were explored during the field geological mission by Mattia and the team. Kanaga last erupted in 1994. Ash from that eruption was found in the nearby island of Adak. Even at present, there is a highly active system of fumaroles at the summit of the volcano.

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo on Mondays: Deep in the Himalayas

Deep in the Himalayas . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu).

The Himalayas: vast, formidable and home to the Earth’s highest peaks. The mountain range stretches inexorably through Indian, Bhutan, Nepal, China (Tibet) and Pakistan separating the Tibetan Plateau to the north from India’s alluvial plains to the south.

India, as we know it today, started life much further south, as an island not far off the coast of Australia. It was separated from Asia (on the Eurasian plate) by the Tethys Ocean, a vast body of water which  wrapped, almost entirely, around the supercontinent Pangea. As the supercontinent started to break up, some 200 million years ago, India began its slow (in human terms, but quite fast geologically speaking) journey north towards Asia.

Moving at speeds between 9 to 16 cm per year (for comparison, human hair grows roughly 15 cm per year), by 80 million years ago, India was located 6,400 km south of Asia. The Tethys was being slowly subducted under the Asian plate and would eventually close (disappear) all together some 30 million years later, when the Indian plate collided against Asia and the Himalayas began to uplift.

The closing and subduction of the Tethyan Ocean, followed by the collision of the two continents produced the Himalayas. The mountain range is divided into six parallel belts, each of which has distinct lithotectonic zones. They are highly complex and represent a long history of tectonic processes and deformation events.

The high peaks of Nepal and China attract a fair share of the limelight, offering thrill seeking adventurers the possibility to get close to (if not scale) the highest mountains on Earth. But lesser known areas of the Himalayas also offer a window into the geological past of the planet and breathtaking scenes for intrepid people too.

Today’s photograph features a valley deep in the Indian Himalayas, and illustrates some geological, geomorphological and other phenomena’s together with a small village that was built inside this glacier curved valley.

 

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo on Mondays: recreating geological processes in the lab

Imaggeo on Mondays: recreating geological processes in the lab

Many of the processes which take place on Earth happen over very long time scales, certainly when compared to the life span of a person. The same is true for geographical scale. Many of the processes which dominate how our planet behaves are difficult to visualise given the vast distances (and depths) over which they occur.

To overcome this difficulty, scientists have developed and resorted to a number of tools; from geological mapping right through to generating computer models. One such tool dates back some two centuries: analogue experiments. Initially they started off as roughly scaled experiments to test a range of hypothesis. Famously, James Hutton used analogue models to prove that the folding of originally horizontal strata is the result of lateral compression. With time they have become increasingly sophisticated, allowing researchers to replicate a vast range of conditions and environments which lead to a better understanding of how our planet works.

Today’s Imaggeo on Monday’s image, by Stephane Dominguez, a researcher Chargé de Recherche CNRS, in Montpellier, shows the final evolution stage of an analog experiment dedicated to the study of Relief Dynamics – how surface topography comes to be – and what role tectonics, erosion and sedimentation play in the formation of landscapes. In such experiments, typical scaling is 1cm = a few hundred meters and 1s = a few tens of years.

In this particular experiment “we used a specific granular material mixture (made of water saturated silica, microbeads, PVC and graphite powders, to simulate a portion of the upper terrestrial crust submitted to tectonic extension (where the crust is being stretched, such as at, but not limited to, continental rifts and divergent plate boundries),”explains Stephane.

At the same time, the research team used a rainfall system to project micro water droplets on the model surface. This causes water runoff to initiate and starts the growing reliefs to be eroded.

“We obtain a very realistic morphology that continuously evolves in response to complex interactions between surface deformation (induced by normal fault activity – caused by the stretching of the crust) and surface processes (erosion, sediment transport and deposition).”

 

References

Ranalli, G.: Experimental tectonics: from Sir James Hall to the present, Journal of Geodynamics, 32, 65-76.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

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