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Tectonics and Structural Geology

Tectonics and Structural Geology

Meeting Plate Tectonics – Cesar Ranero

Meeting Plate Tectonics – Cesar Ranero

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Cesar Ranero


Prof. Cesar Ranero is an Earth Science researcher, currently Head of Barcelona Center for Subsurface Imaging (Barcelona-CSI). He owns a degree in Structural Geology and Petrology from the Basque country and he later completed his PhD in Barcelona, emerging himself in Geophysics. Prof. Ranero’s research is marked by a multidisciplinary approach, applying physical methodologies to understand geological processes.

Scientist also have to look for collaboration with the industry.

Ranero giving an outreach talk on fossil fuels at the Centre de Cultura Contemporània de Barcelona (CCCB). Credit: Cesar Ranero

Hi Cesar, after doing research for few decades, what is, at present, your main research interest?

My research interest covers mainly active processes, I am not so interested in regional geology. I see regional geology as a necessary step to understand processes but the main goal of our group is to understand geological processes. For instance, a great interest in our group is the seismogenic zone and the generation of great earthquakes. We have very good examples in the Iberian peninsula, such as the famous 1755 Lisbon earthquake. Yet, nobody knows where the big fault that created this earthquake is located. We have a lot of research to do. But, often to understand local geology you need to integrate it in the big-picture view of processes. This is why we are mainly interested in those processes rather than in regional geology.

The more you know, the more you realize that nearly everything is to be discovered.

Further, I am interested in interacting with the industry. The geological/geophysical community is a relatively small community (compared to medicine, for example). There is out there quite a few industry groups that are doing very similar things in terms of methodologies and approaches (communities working in oil & gas exploration, or the ones working on carbon sequestration, or geothermal energy production…) All these communities have quite a bit of history in the development of methodologies. They usually have much more money and very talented people developing new methodologies. It is very necessary that we participate in their interests. They are often showing interest in what we do. By going to their meetings and talking to them, you can build fruitful interactions. Scientists also have to look for collaboration with the industry, because at the end of the day it is a place where some of our students can find a good job and make a career.

How would you describe your approach and methods?

The approach in our group is multidisciplinary, we combine complementary methodologies. But it is also important to be aware of proper methods to interpret geophysical data (you have to understand different geological methods, for instance, the methods used in structural geology).

Poststack finite-difference time migration line showing the structure of the Cocos plate across the ocean trench slope. Ranero et al., 2003, Bending-related faulting and mantle serpentinization at the Middle America trench, Nature, 425, 6956, 367.

 

What would you say is your favorite aspect of your research?

What stroke me since I started my PhD is how much good work has been done, but how much more needs to be done.
We know a lot because there were many talented people before doing a lot of work. But actually, if you have a sceptical mind, the more you know, the more you realize that nearly everything is to be discovered. If you look at the last 10 years, you realize that a lot of what has been published is incremental science and much had been laid down in previous publications. But also, there are a whole series of new topics coming out and you have to pay attention because those are the topics that really mean a substantial jump forward. Every year there are several new interesting things coming. For example, earthquake phenomena have been an amazing topic in the last years, all these new phenomena explaining how plate boundaries slip. You have to keep a sceptical mind and at the same time search for those topics.

You have to have a sceptical mind.

Why is your research relevant, what are the real world applications?

This is always a good question. We do a lot of basic research and there is always the philosophical question on whether basic research is relevant… When we discovered the laser, nobody knew how relevant this would be in the future. Now, we can not live without it! I am sure that there is a percentage of basic science discovery that might not have any real-world application. But in many cases, it does. Much of what we do contributes to the understanding of natural hazards. But also, we contribute to resolving problems industries and society are concerned with.

Prestack depth migration of a Sonne-81 line projected on bathymetry perspective. Ranero & von Huene, 2000, Subduction erosion along the Middle America convergent margin, Nature, 404, 6779, 748.

 

At this point of your career, what do you consider to be your biggest academic achievement?

I would like to think that it is the next one! (laughs)

I am proud to have been elected as a fellow of the American Geophysical Union. It means I have done something relevant that is appreciated by my peers, and at the same time, it is a great motivation to work even harder in the future.

Also, I have some nice papers that I am proud of (tectonics of subduction zones, the role of fluids on earthquakes, serpentinization of the outer rise). My view is that for most people, after you finish your career and you look back at your many publications, probably only 3-4 papers are really worth it and seriously contributed brand new material.

What would you say is the main problem that you solved during your most recent project?

Since I came back to Spain, 12 years ago, I started to work a lot in the Mediterranean. For many years, the Mediterranean had been a place where people did not want to work because it is too complex. With the help of German groups and others, our group has been able to characterize for the first time the nature of the crust in many systems in the Mediterranean. We have added a new layer of information to understand the evolution of the whole Mediterranean region. I am quite happy with that, we are producing quite a few papers and have some very new ideas, and we have also started to put that together with fieldwork. There has been a lot of on-land work all around the Mediterranean, but rather limited modern geophysical data on the nearby basins. For example, the Apennines are very well known, but the nearby Tyrrhenian, not so much… We worked with the Italian and the German groups and found some new, interesting geological observations.

Cartoon showing a conceptual model of the structure and metamorphic evolution of subducting lithosphere formed at a fast spreading center. Ranero et al., 2005, Relationship between bend-faulting at trenches and intermediate-depth seismicity, Geochem. Geophys. Geosyst., 6, Q12002, doi:10.1029/2005GC000997.

The biggest challenge is to have time to think about new observations of
high quality that challenges the conventional view
.

After being many years active in the academia, looking back, what would you change to improve how science in your field is done?

I think there are significant differences depending on the country, even within Europe, in terms of funding: how research is done, how research careers develop… Some countries, like Germany and France, are doing relatively good in terms of funding. Other countries, like Spain, Italy or Portugal are not. These countries do not have a well-organized structure for funding, so for researchers is difficult to know how to organize funding around their research to succeed. The people that do well, that work hard, that produce, should have the certainty that they will be able to move forward. But today there is a lot of uncertainty, and in these countries, there’s no warranty that people who deserve it, will have their chances. This is a major problem for ECR, and I think a better structure funding and more funding opportunities for ECR are needed.

Regarding European-funded projects, as for example those of the European Research Council, these programs are extremely prestigious, and only the very top are getting these very well funded grants. And yet, it is unclear to me, at least in my community, that the results and papers produced in the context of these programs are of higher quality than those in other funding programs. So, is it unclear to me that this is a system that we should sustain, but that we shall see in the next years. Talking to others, I get the perception that it is now becoming somewhat too prestigious, people even hesitate to submit proposals because they have to invest loads of time into it and is a huge effort that might not even pass the first evaluation, and review comments appear somewhat indecisive. But I might be wrong on this one.

What you just exposed, goes to some extent in line with my next question: What are the biggest challenges right now in your field?

As for the scientific challenges, I think we can look back at the Plate Tectonic revolution. How did it happen? Before it happened, many observations did not have a good explanation because we were lacking the right data. Then, almost suddenly, we got three datasets that nobody had seen before: magnetometers and echo sonars of higher quality coming from the second-world-war related research, and a worldwide seismological network for monitoring within the frame of the Nuclear Weapon Ban Treaty. And of course, these data landed on the right people. But, in my opinion, it was the access to the right data that provided a whole new view on geology.

So, perhaps the biggest challenge we have now is to be able to produce new methodologies of high resolution to look deeper into the Earth. We need to use high-quality new data sets and new observations that could allow to actually challenge the conventional views.

This is very complicated, particularly in the academic world we live in now. Currently, people have to write several papers for their PhD, and immediately after, in the postdoc period, they have to produce a massive number of papers to at least have a chance. In these circumstances, you can simply not think long enough in a complicated problem. There’s little time to think about what the main fundamental problems are that you want to solve. You have to be a paper-producing machine, and this is detrimental to their quality. You might manage to be someone that is highly productive but, in that frame, it is unlikely that you will often produce major quality. There’s too much pressure on ECRs. So, a challenge is to have time to think about how to obtain new observations of high quality that can change conventional views.

Pre-stack depth-migrated line IAM11, with arrows and numbers indicating the average dips of the block-bounding fault segments exhumed during rifting. Ranero & Pérez-Gussinyé, 2010, Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins, Nature, 468, 7321, 294.

You have to be a paper-producing machine, and this is detrimental to their quality.

What were your motivating grounds, starting as an Early Career Researcher? Did you always saw yourself staying in academia?

I actually thought of going to the industry when I finished university. But I was lucky enough to be introduced to Enric Banda, my PhD supervisor, who had a big picture of geosciences, and he made a real impression on me and made me change my goals. Once I started my career in science, I quickly realized that there was a lot to be done. After two-three years into my PhD, thanks to a nice data set and some good results that were coming out, I definitely saw myself staying in academia. I looked for funding before finishing my PhD and I was lucky to get a Marie Curie, which was not even called like that at the time. I was lucky to work with relatively large groups, and with good funding. There was a good moment, also for industry. Funding was not a major issue for me for many years, so I could spend my time doing the research I wanted. At present, early careers are much more complicated, and you have to really like it to keep on pushing for it.

What advice would you like to give the ECS?

Be ambitious, think big. Don’t be afraid of making mistakes. And above all, be sceptical, completely sceptical about everything. Don’t pretend you know more about what you know, but be sceptical. Because, almost for sure, no matter who did the work, it can be improved, and in most cases, to a great extent. And be open, talk to everybody.

 

Researchers of the Barcelona Center for Subsurface Imaging. Credit: Cesar Ranero

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Anne Davaille

Meeting Plate Tectonics – Anne Davaille

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Anne Davaille


Anne Davaille majored in Physics and continued with a PhD in Theoretical Physics of Fluids, jointly at the University Pierre et Marie Curie and the Institut de Physique du Globe de Paris (IPGP). She investigates convection in strongly temperature-dependent fluids. After her PhD, she went to Yale for a postdoc and she currently holds a CNRS-position at the FAST Laboratory of University Paris-Sud, France.

Research is ideas plus craftmanship. It should be fun and you have to enjoy it to do it.

Anne Davaille. Credit: Anne Davaille.

Anne, what are your research interests and what methods do you use for your research?

Fluid mechanics is my main research area. I study convection in complex fluids, and I use this framework to understand mantle convection and the convective evolution and cooling of planets. My main approach is through laboratory experiments. But then I use and/or build some theory to interpret the experimental results, to derive a physical understanding, and finally to make inferences for geodynamics. All the way, numerics are also involved, to treat the experimental results, or to quantitatively apply the results to planets.

 

No matter what fancy stuff you do, if your data is not good, you are losing on what you are going to get

You have significantly advanced fluid dynamics within the geosciences. Up until now, what do you consider your biggest scientific achievement?

It is probably the works that we did on thermo-chemical plumes in two-layer convection models. We showed that convection in a mantle heterogeneous in density and viscosity could produce several types of plumes, and therefore several types of hotspots. More recently, we have been able to observe different ways of subduction initiation from convection in complex fluids. Plume-induced subduction could be occurring on Venus right now, and might have been important in the Archean Earth. On the side, I am also very happy with the techniques we developed to measure simultaneously and in situ the temperature and velocity fields in the experiments. It really helped us to push lab experiments forward and get a quantitative understanding of the processes we observed.

Different types of plumes and hotspots, depending on the presence of density heterogeneities in the mantle. From Davaille, Nature, 402, 756-760, 1999; and Davaille, Girard & Le Bars, EPSL, 203, 621-634, 2002.

 

After all the time you have spent in science, you have seen many questions answered and more questions rise. What is the biggest challenge in your field that we face today?

Until now, we still have not solved the question ‘why do we have plate tectonics?’ from a physical point of view. On what scale do we need to look for that answer? Grain scale? Or meso-scale, since the lithosphere is quite heterogeneous (e.g. faults, dikes,…)? To get plate tectonic behavior, and therefore the strong localization of deformation, we need a non-Newtonian rheology. From my experience, fluids presenting this particular behaviour are very often mixtures, and their effective behaviour on the large scale can be quite different from their local microscopic behaviour. Moreover, the history of this structure can also strongly influence the large-scale behaviour. With the theoretical understanding we have today, we still cannot model well these behaviours, and therefore answer the plate-tectonics question. I don’t know if we shalll find the answer in theory first, I don’t think that is necessary. It will require most probably a mix of theory, numerics, and data, both experimental (where you can observe and measure all the scales, from the grain to convection) and geological (the “field truth”). Once we do have that answer, we shall gain a better understanding of the other planets and satellites as well.

Plume-induced subduction obtained in FAST laboratory in a climatic chamber. From Davaille, Smrekar & Tomlinson, Nature Geosc., 10, 349-355, 2017.

The one thing we really should stop doing is having this frantic will to publish

Your field of expertise has changed over the years. Is there something you would still like to change?

Oh yes, there are some things I would like to change. The one thing we really should stop doing is having this frantic will to publish. It is an extremely bad habit and it does not generate good research. Especially for the young people that still need to develop ideas and skills, they need time to think and make mistakes, which is not possible with the current mindset of fast publishing. Fast publishing is not beautiful, nor efficient for creative research. Even though the world wants things always faster, doing it faster is not human. We should stop this. What I find the most important is that my work should be strong enough so that people understand what I did and can use this to build on it and move further. For this we need time.

Different regimes of convection in strongly temperature-dependent fluids as a function of the viscosity ratio and the intensity of convection (Rayleigh number). The temperature structure in the sugar syrups is visualized by Thermochromic Liquid Crystals. From Androvandi, Davaille, Liamre, Fouquier & Marais, Phys. Earth Planet. Int., 188, 132-141, 2011.

 

When you were in the Early Stages of our career, what were your expectations for your future?

When I was 7 years old, I learned about plate tectonics. Later, the operation FAMOUS was happening and at this young age I found that fantastic and I wanted to know more. That was one of the reasons why I went into physics. I think that during my career I have been very lucky. Once I got my degree, I thought that before getting a job, I wanted to do a PhD in a very specific topic ‘Convection in complex fluids and planets’. After that we would see. I did not really have any expectations, but I thought, if I can do it maybe it will work and that would be great. Somehow it worked and so I continued working in it, and it is still great fun!

You have to be very demanding, very rigorous if you want to succeed

The last question for today’s Early Career Scientists: what advice would you like to give the ECS that would like to stay in science?

Well, first I think that research is ideas plus craftmanship. It should be fun and you have to enjoy it to do it. But craftmanship is demanding. I have a small anecdote here. I once did an internship at Schlumberger. I worked with experiments and my supervisor at the time told me ‘if you put shit in, -(meaning noise)-, you will get shit out’. My advice would therefore be that no matter what fancy stuff you do, if your data is not good, you are losing on what you are going to get. So for experimental or numerical modelling, if you are not demanding, or only short-term, you may get away with it for a while, but on the long run, you will not last. You have to be very demanding, very rigorous. I think that’s the best way to succeed.

 

Anne Davaille. Credit: Anne Davaille.

Interview conducted by Anouk Beniest

Minds over Methods: Mineral reactions in the lab

CL image of a sheared quartz-muscovite gouge. Credit: André Niemeijer.

Mineral reactions in the lab

André Niemeijer, Assistant Professor, Department of Earth Sciences at Utrecht University, the Netherlands

In this blogpost we will go on a tour of the High Pressure and Temperature (HPT) Laboratory at Utrecht University and learn about some of the interesting science done there.

André Niemeijer next to a striated fault surface. Credit: André Niemeijer.

André’s main interest is fault friction and all the various processes that are involved in the seismic cycle. This includes the evolution of fault strength over long and short timescales, the evolution of fault permeability and the effects of fluids. His current research is aimed at understanding earthquake nucleation and propagation by obtaining a better understanding of the microphysical processes that control friction of fault rocks under in-situ conditions of pressure, temperature and fluid pressure.

Most of the deformation in the Earth’s brittle crust occurs on and along faults. Fault movement produces fine-grained wear material or gouge, which is very prone to fluid-rock interactions and mineral reactions (Wintsch, 1995). It has long been recognized that the presence of a fluid allows for deformation to occur at much lower differential stresses than without.

Pressure solution

One of the mechanisms by which this deformation occurs is pressure solution (alternatively termed “solution-transfer creep” or “dissolution-precipitation creep”). This mechanism operates through the dissolution of materials at sites of elevated stress, diffusion along grain boundaries and re-precipitation at low stress sites (e.g. pores). Pressure solution is an important diagenetic process in sandstones and carbonates as evidenced by the presence of stylolites in many carbonate rocks, which are often used as counter tops and floors (particularly in banks, I noticed). In addition, it has been suggested that pressure solution plays an important role in the accommodation of (slow) shear deformation of faults (Rutter & Mainprice, 1979) and possibly in controlling the recurrence interval of earthquakes (Angevine, 1982).

Fluid-rock interactions in the lab

Experimentally, it is challenging to activate pressure solution or mineral reactions in the laboratory, because they are typically slow processes. Moreover, it is difficult to find evidence of their operation. We have used a unique hydrothermal rotary shear apparatus, which is capable of temperatures up to 700 °C to activate pressure solution in fine-grained quartz gouges. We were able to prove that new material was precipitated by using a combination of state-of-art electron microscopy techniques that involve cathodoluminescence (CL).

The hydrothermal rotary shear apparatus at the HPT laboratory at Utrecht University, the Netherlands. Credit: André Niemeijer.

Signature of pressure solution

The CL signal of a mineral depends on the type and level of impurities and defects that are present. We used quartz derived from a single crystal which showed relatively uniform CL. Because our apparatus has various metal alloy parts, small amounts of aluminium are present in the fluid. Aluminium can be incorporated in newly precipitated quartz, which gives a different CL signal. This allows us to map the locations where quartz has newly formed and link this to the experimental data. Taken together, we can use these to derive and constrain microphysical models for fault slip that can be used to extrapolate to natural conditions (e.g. Chen & Spiers 2016, van den Ende et al., 2018).

RGB overlay of secondary electron and cathodoluminescence signals in a deformed quartz sample. Newly precipitated quartz shows up in a blue colour. Credit: Maartje Hamers.

Mineral reactions

Outcrops of natural faults often show evidence for enhanced mineral reactions with increasing shear strain. For instance, the Zuccale fault (Isle of Elba, Italy) has a high content of talc in the highest strained portion of the fault (Collettini & Holdsworth, 2004). Talc is a frictionally weak mineral and its presence in the Zuccale fault provides an explanation for the possibility of slip along this low-angle normal fault. We were able to produce talc experimentally from mixtures of dolomite and quartz in only 3-5 days of shearing at low velocity. This shearing was accompanied by major weakening, with friction dropping from 0.8 to as low as 0.3. The reaction to talc is sensitive to temperature and fluid composition. At slightly higher temperature, we produced diopside and forsterite which are frictionally unstable and generated audible laboratory earthquakes.

Identifying reaction products

We tried a whole range of different analytical techniques to identify the reaction products. Despite the obvious frictional weakening that we observed, talc was only observed in two samples with x-ray diffraction (XRD). Fourier-transform Infrared analysis, on the other hand, proved to be very sensitive to talc and has the big advantage that only a small amount of material is needed (~70 mg). Electron microscopy with EDS-analysis (Energy Dispersive X-ray Spectroscopy) proved helpful to some extent, because it shows the phase distribution. However, the small size of reaction products gives a mixed chemistry, which complicates the identification of reaction products. Finally, to positively identify the various phases in the different samples, we employed Raman mapping.

RGB overlays of EDS analyses of samples deformed at 300 °C (left) and 500 °C (right). Dolomite appears in yellow, quartz in blue, calcite in red, talc in cyan in the left image, while dolomite is orange, calcite is red, diopside is purple and forsterite is cyan in the right image. Credit: André Niemeijer.

Outlook

Our studies have shown that reactions can be quite rapid in fine-grained fault gouges. These reactions can have a profound effect on both fault strength and stability but are typically ignored in large-scale models of the seismic cycle. Incorporating reactions requires models that can account for the effect of stress and grain size reduction on the development of faults, which is not an easy task, but is a necessary ingredient to understand the long-term behavior of faults.

References

  • Angevine, C. L., Turcotte DL, Furnish MD. (1982) Pressure solution lithification as a mechanism for the stick-slip behavior of faults. Tectonics 1 (2), 151-160 doi:10.1029/TC001i002p00151.
  • Chen, J. and Spiers CJ. (2016) Rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model. Journal of Geophysical Research: Solid Earth 121 (12), 8642-8665 doi:10.1002/2016JB013470.
  • Collettini, C. and Holdsworth RE. (2004) Fault zone weakening and character of slip along low-angle normal faults: Insights from the Zuccale fault, Elba, Italy. Journal of the Geological Society 161 (6), 1039-1051 doi:10.1144/0016-764903-179.
  • E H Rutter, D H Mainprice (1979)On the possibility of slow fault slip controlled by a diffusive mass transfer process. Gerlands Beitr. Geophysik, Leipzig 88 (1979) 2, S. 154-162.
  • van den Ende, M. P. A., Chen J, Ampuero J., Niemeijer AR. (2018) A comparison between rate-and-state friction and microphysical models, based on numerical simulations of fault slip. Tectonophysics 733, 273-295 doi:10.1016/j.tecto.2017.11.040.
  • Wintsch, R. P., Christoffersen R, Kronenberg AK. (1995) Fluid-rock reaction weakening of fault zones. Journal of Geophysical Research: Solid Earth 100 (B7), 13021-13032 doi:10.1029/94JB02622.

Meeting Plate Tectonics – Roger Buck

Meeting Plate Tectonics – Roger Buck

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Roger Buck


Roger Buck is a Research Professor at the Lamont-Doherty Earth Observatory at Columbia University, in New York. His interest lies in developing theoretical models for processes that affect the solid earth. He also studies deformation patterns and topography on other planets, such as Venus.

The key is to look for areas where new data shows that there are important things we don’t understand, things that still surprise us.

After being active for several decades, what is currently your main research interest? How would you describe your approach and methods?

Broadly, I work in Geodynamics. In a lot of different aspects to it. I started doing work on planetary science and mantle convection. Now I work mostly on the mechanics of faulting and of magmatic dike intrusions, particularly focussed on continent breakup and mid-ocean ridges.

 

Roger Buck – Deploying GPS instruments to understand the mechanics of dike intrusions in Afar, Ethiopia. Credits: Roger Buck

 

What would you say is the favourite aspect of your research?

What I find really satisfying is trying to find geologic phenomena or structures that look very complicated, but where there is actually a fairly simple underlying physical mechanism. It is particularly satisfying to find a fairly simple mathematical expression describing the mechanics of processes that otherwise might look quite complicated.

I always hope that, on the long term, explaining things better is good in itself

Why is your research relevant? What are the possible real world applications?

That’s difficult to say in a lot of cases. Just explaining how structures got to be there might not have immediate effects. But, I always hope that on the long term explaining things better is good in itself. Understanding how the Earth works can help us dealing with hazard mitigation. Some of the work that we are doing recently deals with the tectonic processes that are related with earthquakes. That might help us understand the different kinds of earthquakes that happen in different areas.

 

Roger Buck – Physical experiment with gelatin, testing how magma intrusion could trigger continental breakup. Credit: Roger Buck

What do you consider to be your greatest academic achievement?

In airplanes, I tell people that “I work on areas that are splitting apart and on what allows them to split apart”. Probably the single cleanest example was a controversy that came up in the 1980s about what people often refer to as “low angle normal faults” that are associated with rocks brought up from great depth in the crust in core complexes. Over a number of papers, we showed that a lot of these structures that are low angle now, probably initiated at high angles, in ways that are very easy to understand mechanically. They evolved in a way that it’s just a consequence of normal extensional faults extending over long distances. It was very satisfying to chip away that problem from a kinematic viewpoint, and then from a more basic, mechanical point of view. Much of his work was done with excellent colleagues, like Luc Lavier and lately with Jean-Arthur Olive, on numerical simulations of these processes.

 

What would you say is the main problem that you solved during your most recent project?

I’ve been working with a very bright student on the Tōhoku earthquake that happened in March 2011 in Japan, where there was really unprecedented data (the Japanese had many geophysical instruments both on land and underwater). One of the things that was unexpected was that in the upper plate, in the lithosphere above the subduction interphase, the predominant aftershocks over a broad region (about 200 km wide) were extensional earthquakes. This had never been seen before. We have been working with simple ideas and numerical models to explain these extensional earthquakes. Our idea is that it is related to the long term (millions of years timescale) changes in the dip angle of subduction that basically bend the upper plate. We don’t have a clear connection with the extensional deformation that might have been related to the excessive size of the tsunami that was produced, but there could be some relationship. We certainly have not solved this problem but we have a promising hypothesis for one part of the Tōhoku earthquake.

It is very important to continue support for very basic work.

After being many years active in academia, looking back, what would you change to improve how science in your field is done?

Oh, that’s a hard question. A lot of things over the years have been done very well, I think. Like fostering international collaboration in science and that there has been fairly healthy support for science, in a lot of countries, including the United States. It is very important to continue support for very basic work. There has been a retreat from supporting multi-channel seismic work in the ocean in recent years, but this is one of the best ways for us to illuminate the structures produced by tectonic processes. At the same time, increased computer power allows us to get better resolution of structures, based on essentially the same data. However, we still need to collect new data.

The key for big advances is often new technologies

Roger Buck – Deploying seismometers across the Okavango Rift. View on the Victoria Falls. Credit: Roger Buck

 

What you just exposed, goes to some extent in line with my next question: What are the biggest challenges right now in your field?

Uh! These are pretty challenging questions, that’s for sure!

I think there are great and exciting challenges in things I don’t work on myself. The fact that geodesy has improved so much in recent decades and we are learning so much more about plate boundaries. I remember the wonderful talk of Jean-Philippe Avouac during the symposium in Paris, he emphasized how much we have learned. Many seismic gaps are in places where we don’t see traditional seismic activity: large earthquakes or fast earthquakes. We now know that they are slow earthquakes and slow slip events. Understanding where they occur and why we have different kinds of earthquakes in different places along subduction zones is an area that a lot of people have recognized is very important. I think the key to big advances is often new technologies. Geodesy, both on land and submarine, combined with imaging offers terrific hope for a better understanding of major earthquakes. For example, we don’t have a good clue on why some big subduction earthquakes produce very large tsunamis and others not so large tsunamis. These are huge challenges.

 

What were your motivating grounds, starting as an Early Career Researcher? Did you always see yourself staying in academia?

I was always kind of academically oriented. I liked the idea of doing research. I started in Physics and liked it a lot, and then I started taking Geology and liked Geology a lot! I was at university in the mid-1970s and there was a lot of excitement about applying plate tectonics to solve different problems and it seemed very exciting… I am definitely not a good field geologist, but I love being in the field. I think it is important for people doing theoretical work to actually understand the data that they are working with and where it comes from, and the great skill it takes to collect and interpret data. But I realized very quickly that this wasn’t my strength. The key is to look for areas where new data is showing that there are important things we don’t understand, things that still surprise us. That is one of the encouraging things that I’ve seen through my career: repeatedly, with new measurements, we had total surprises. We have seen things we did not expect.

Follow things where you have the potential to make some contribution

What is the best advice you ever received and what advice would like to you give to Early Career Students?

Oh boy!  One piece of advice I got about writing papers that deal with models is particularly good:  You should very clearly separate observations from model assumptions and model interpretations. Not mixing these three things up is something that I certainly struggle with it, but it is something that keeps papers clear and crisp.

The obvious piece of advice that you hear very often and that I certainly tell people: You are typically going to like things that you have some aptitude for. So, follow things where you have the potential to make some contribution. Find something that you really do feel good about doing and you are going to feel good about it if you are somewhat capable of doing it.

 

Roger Buck in Egypt – Credit: Roger Buck

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Roland Bürgmann

Meeting Plate Tectonics – Roland Bürgmann

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Roland Bürgmann


 

Roland Bürgmann is Professor of Geophysics at the University of California, Berkeley. He has been teaching and doing research in Berkeley for around 20 years. He started studying Geology in Germany (Universität Tübingen) and then continued his studies in the US, obtaining his PhD in Geomechanics and Crustal Deformation from Stanford University.

 

After being active for several decades in your field, where is your main research interest currently? How would you describe your approach and methods?

My current research is on active tectonics. Really the idea is to study deformation processes in the Earth related to fault systems and the earthquake cycle, but also all kinds of systems that produce active deformation like volcanoes, landslides, or land subsidence. We study those especially with geodetic tools, and also with seismology and field observations. So, I don’t tie myself to any particular observational technique, I’m really just interested in better understanding the kinematics and dynamics of deformation processes of all kinds in the Earth.

The key indication that you are doing the right thing is that you love what you’re doing

What would you say is your favourite aspect of your research?

Research really means being able to work with people. Research is not a solitary thing, a lot of it is about thinking of problems and trying to solve them. Not by yourself, but by having the opportunity to work with students and postdocs. That really enriches research immensely. I see this as one of the most enjoyable and valuable aspects of academic research.

Why is your research relevant? What are the possible real-world applications?

I guess with what we do it is relatively easy to point out real-world applications because we address natural hazards. Earthquakes, volcanoes, landslides… everybody is somewhat worried about those. On the other hand, we have to admit that often the research we do is not going to directly impact or save lives. My wife is a cancer surgeon and she might have improved or even saved a life or two every week. For us, it is much more like we are pushing on a research problem, and we do see the long-term relevance when it comes to ultimately being able to mitigate and better understand earthquake hazards and some of these other hazardous processes.

Research is not a solitary thing

Roland with his group after running a trail race (an annual tradition) Credit: Roland Bürgmann

 

What do you consider to be your biggest academic achievement?

Bürgmann, Hilley, Ferretti, & Novali (2006). Resolving vertical tectonics in the San Francisco Bay Area from permanent scatterer InSAR and GPS analysis. Geology, 34(3), 221.

My biggest academic achievement, I’m sure is still to come (laughs). That’s a tough question… you couldn’t really say, well this is “the one” finding or study that is the most important one… I think overall the work I’ve done that relates to better understanding the whole earthquake cycle; we’ve done a lot of work on postseismic deformation, fault slip, stress interactions, rheology… but it’s all incremental. I don’t feel like we have made “this one” discovery that people would always associate with me.

What would you say is the main problem that you solved during your most recent project?

One of my most recent projects is related to landslide physics. We use InSAR to study the landslide deformation, and rely on precipitation records and pore-pressure diffusion models to calculate what the fluid pressure is in the landslides. We can quite directly relate that and explain the time lag between precipitation and landsliding.

I think that this is a useful contribution. In a paper that we are about to publish, we were able to do that in the years prior to a landslide that then failed catastrophically. So there the hope is that this will actually allow us to understand what is it that gets a landslide over the brink. Landslides can keep moving steadily over the years, decade for decade, but what is it that makes one fail catastrophically? So this study, we hope can help to contribute to better understanding that.

 We should do more […] interdisciplinary studies

Looking back, what would you change to improve how science in your field is done today?

Something that we are doing already, which I think is really important and we should do more of, are truly interdisciplinary studies. I’m a strong believer in that, and I do think that geomorphologists need to talk to geophysicists, and to the modellers … Ideally, all of us should know enough about these other fields so that we can really optimize how we can see the whole system. I do think there is much more left to be done when it comes to that. Allowing us to speak the same language and joining forces when it comes to really understanding how the Earth works, not to limit oneself to just one problem, one process, and therefore one approach to understand it.

 

After all the time you have spent in science, you have seen some questions answered and more questions raised. What are the biggest challenges right now in your field?

Bürgmann, Rosen & Fielding (2000). Synthetic Aperture Radar Interferometry to Measure Earth’s Surface Topography and Its Deformation. Annual Review of Earth and Planetary Sciences, 28(1), 169–209.

Scientifically, we like to understand what we study in the simplest possible way. We try not to “over-model” what we observe, really just trying to get at the key underlying processes and principles. On the other hand, we got so much data now from all kinds of observational systems that seem to be trying to tell us much more. This suggests we should be upscaling the model complexity, and try to understand multiple processes at the same time. That is both exciting and seems dangerous. Whenever I see climate scientists with their models that incorporate hundreds of different processes, everything from turbulence in the atmosphere to particles in the air and many other things, that just seems scary and something that you would not want to do with what we study in geophysics. But I do see the need that we have to make our models and ways of understanding the Earth more complicated. Doing that consciously but well, that’s a big challenge.

 

What were your motivating grounds, starting as an Early Career Researcher?

The biggest influences ultimately are people. It was highly enthusiastic role models that made me get really excited about what I’m doing and made me change my career path. I wanted to study other things in my freshman year when I started studying geology. Over the years, I got to work with enthusiastic and inspiring mentors that made all the difference. Ultimately we are social animals and it does make a huge difference to have those kinds of influences in your early career.

We all have our insecurities

So you always saw yourself staying in academia?

I wasn’t sure. I definitely considered alternative career paths. I meant to do an industry internship, which ended up not working out because I ended up working at the US Geological Survey that summer instead. I think I kind of knew I wanted to be in academia, but you really don’t know. You don’t know if you are good enough. We all have our insecurities and everything that comes with that, from impostor syndrome to what not. But it certainly always felt natural to me. The key indication that you are doing the right thing is that you love what you’re doing.

 

Following to what you just exposed, is there any other advice would you give to Early Career Students?

When it comes to giving advice, I always say, research in academia is the best possible job. Period. But only if you enjoy doing that. If research stresses you beyond normal stress levels, if it does not give you true pleasure, then maybe it is not the right thing. I totally appreciate how that is not necessarily true for everybody. Maybe you are meant for a more structured environment, where you don’t have to make up your days’ work on your own, every day. But if you are happy with that, it really is the greatest thing in the world. It does not feel like a job.

 

Credit: Roland Bürgmann

Interview conducted by David Fernández-Blanco

Minds over Methods: Massively dilatant faults in Iceland – from surface to subsurface structures

Minds over Methods: Massively dilatant faults in Iceland – from surface to subsurface structures
In this Minds over Methods we don’t have one, but two scientists talking about their research! Michael Kettermann and Christopher Weismüller, both from Aachen University, explain us about the multidisciplinary approach they use to understand more about massively dilatant faults. How do they form and what do they look like at depth?

Massively dilatant faults in Iceland – from surface to subsurface structures

Michael Kettermann & Christopher Weismüller, RWTH Aachen University

Michael (left) and Christopher (right) in the field. Credit: Michael Kettermann and Marianne Sophie Hollinetz.

Iceland is a volcanic island in a unique setting on the Mid-Atlantic Ridge, separating the Eurasian and North American plates. A deep mantle plume lies beneath Iceland, and the combination of rift and plume leads to very active basaltic volcanism. Ubiquitous features along the rift zone are normal faults, often exquisitely exposed at the surface. Normal faults in basalts are also common in many volcanic provinces, like Hawaii, the East African Rift, and along mid ocean ridges. These faults often form as massively dilatant faults (MDF), which show apertures up to tens of meters at the surface and supposedly have large volumes of open voids in the subsurface.

Figure 1. View along-strike a massively dilatant fault in layered basalt. The geometry of the vertical fault faces is prescribed by the cooling joints. Several basalt columns have been loosened and dropped into the fault, now being stuck in the fault (top) or filling the cavity (bottom). Opening width < 3 m. Credit: Michael Kettermann.

These openings form pathways for fluids like magma or hydrothermal waters and consequently are of importance for volcanic plumbing systems, mineralization and geothermal energy supply.

Iceland provides a perfect natural laboratory to study MDF. Due to its position on the Mid-Atlantic Ridge, Iceland is cut by extensional fault systems roughly from southwest to north. A wide range of oblique extensional to pure extensional faults can be observed mostly in flood basalts, but also in sub-glacially formed hyaloclastites (weaker volcanic sediments), pillow lavas and occasionally sediment layers formed in warmer times. Outcropping rocks in Iceland are younger than 20 Ma distal from the rift (eastern and western Iceland), while tectonic and corresponding volcanic activity at the ridge (central Iceland) constantly causes the formation of new rocks. The rough climate hinders soil formation and vegetation to overgrow faults, providing unique outcrop conditions.

While it is relatively easy to access and study the faults at surface level, investigations into the subsurface are much more challenging. Direct observations are only possible down to depths of some tens of meters by climbing into the fractures. Cavities are often filled with rubble, sediments, water or snow (Fig. 1). Steep, open fractures with meter-scale aperture are hard to detect with geophysical methods (seismic reflection/refraction, ground penetrating radar, electrical resistivity tomography) at depths greater than some meters.

We therefore started the massively dilatant fault project, a multidisciplinary, integrated project bringing together remote sensing, fieldwork, analogue modelling and numerical simulations. In essence, we utilize a modelling approach to recreate the structure and evolution of MDF at depth, using real 3D surface data as input and comparison data set.

 

Drone mapping and photogrammetry

In a first step, we capture and analyse the surface expressions of MDF at a number of representative fault areas in Iceland. To this end, we flew 27 drone surveys during our five weeks long field season in summer 2017, covering a total length of more than 42 km of faults. Luckily, in the Icelandic summer the days are very long, so the National Park Service allowed us to fly the drones early in the morning and late in the evening outside of tourist hours. For each area, we took several hundred to thousands of overlapping photographs (e.g. Fig. 2). We processed these sets with photogrammetry software, applying the Structure from Motion (SfM) technique. SfM is an increasingly popular, fast and cheap technique to reconstruct high-resolution 3D information from 2D images. This allows us to recreate digital elevation models and ortho-rectified photo-mosaics of the faults in resolutions better than 15 cm per pixel (Fig. 3). The largest area at the famous Thingvellir fissure swarm covers a length of almost 7 km with an average resolution of 11 cm per pixel.

We use these digital elevation models and ortho-photos to retrieve a wide range of structural data. Mapping the fault traces in a GIS software allows for the measurement of fault opening width, throw, orientation and length. From throw and aperture, we can then estimate the fault dip at depth. Digital elevation models further provide surface dip data that we then compare with observations from analogue models.

Figure 2. A drone photograph facing South of the Almannagjá fault in Thingvellir, where the Thingvallavegur road crosses the fault. The Almannagjá fault resembles the western shoulder of the Thingvellir graben system with locally > 50 m opening width and 40 m vertical offset. Credit: Christopher Weismüller. .

Figure 3. Digital elevation model created from drone photographs using photogrammetry software. It contains the faults at Sandvik on the Reykjanes Peninsula (SW Iceland). The detail panes (red square) show the DEM (right) at a higher zoom level and the corresponding ortho-rectified photograph (left). The bridge crossing the fault depicted in the detail panes is a famous touristic spot, known as „The bridge between the continents“, since the fault symbolically divides the North American and Eurasion plates. Credit: Michael Kettermann.

 

 

 

 

 

 

 

Figure 4. Sideview of an analogue model showing three timesteps of the development of a massivley dilatant fault and associated fractures in hemihydrate (Bücken, 2017). Note the tilted block developing at the surface of the model and the dilatant jogs and voids in the subsurface. The opening at the surface is not directly linked to the fault at depth, but caused by the rotation of the tilted block. Credit: Daniel Bücken..

Modelling approach

For the analogue modelling approach on the hundreds to thousand meter scale, we use cohesive powders as modelling material (Bücken, 2017). Especially hemihydrate powder has been proven suited to model dilatant fractures (Holland et al., 2006; Kettermann et al., 2016; van Gent et al., 2010) as it has a well characterized true cohesion and tensile strength. Faults in Iceland transform from opening mode fractures to shear mode faults at depth when overburden stress is high enough. As we are interested in the upper dilatant parts of the faults, i.e. above the shear mode faulting, we chose a basement-fault controlled approach, where a rigid basement represents the shear mode fault. It moves down-dip along a predefined surface, deforming the powder sieved on top. The basement fault dip follows the data we derived from the field and is set to 60° – 65°. The scale of the models calculates from strength and weight of the natural prototype and the modelling material. 1 cm of powder equals about 50 m of basalt.

 

Comparison of models and nature

Results show a close similarity between field and experiment at the surface structures. Open fractures form with large apertures at the surface and often we observe the formation of tilted blocks (Fig. 4). The existence and scaled dimensional similarity of fractures and tilted blocks in the field and using a scaled material suggest a validity of other observations in the models. Glass sidewalls in the analogue models provide the opportunity to examine how the faults evolve at depth. We observe that large caves form underneath these blocks and we predict that these must exist in the field as well, albeit potentially filled with rubble. Our models corroborate earlier predictions that extensional faults are open down to 800 – 1000 m (Gudmundsson and Bäckström, 1991). We also learned that below that, a hybrid failure zone exists where dilational jogs, open extensional fractures between shear mode faults, provide lateral pathways for magma or water, even at depths where the overburden stress prevents the formation of purely extensional faults.

 

Outlook

The previously shown experiments investigated MDF at a larger scale in purely dip-slip kinematics. However, faults at rifts often have strike-slip components, forming normal faults with oblique kinematics. In further experiments, we therefore explored the effect of varying basement fault obliquities, i.e. the range between dip-slip normal faults and strike-slip faults (Bitsch, 2017). As expected, early phases of faulting are dominated by Riedel shears. Surprisingly, the surface structure of mature faults, however, does not change distinctly up to obliquities of 60°, but the subsurface connectivity decreases with increasing obliquity.

Figure 5. Analogue model resembling successive layers of lava flows with cooling joints created by carefully stacking several layers of dried corn starch slurry (Winhausen, 2018). The dip of the basement fault is prescribed by the apparatus. The fault geometry generated in the model is very similar to the ones observed in Iceland. Large cavities develop and are partially refilled by loosened columns, as shown in figure 1. Tensile fractures develop on the surface of the footwall, similar to the hemihydrate model and the field. Credit: Lisa Winhausen.

Zooming in on the faults, an inherent mechanical anisotropy (orthotropy) of basalts gains more influence on the macroscale structure of faults. Due to the shrinking during cooling of flood basalts, polygonal to blocky columns form and present regular weak zones in the rockmass. Introducing mechanical anisotropy into a stronger modelling material (dried corn-starch slurry) beautifully illustrates how the small-scale structure of the faults is affected by the layering of flood basalts and cooling fractures therein (Fig. 5; Winhausen, 2018). Close to the surface the strong basalt does not fracture, but propagating faults rather localize at the pre-existing cooling joints. This causes a jagged structure of the fault, formation of caves, and eroded basalt columns filling the opening fractures.

We are currently working on implementing all these learning points into discrete element simulations, where we can adjust material properties in a way that allows for modelling deeper parts of the faults with better mechanical control.

 

 

References

Bitsch, N.D., 2017. Massively dilatant faults in oblique rift settings – an analogue modeling study (MSc Thesis). RWTH Aachen University, Germany, Aachen.

Bücken, D.H., 2017. Effect of mechanical stratigraphy on normal fault evolution – Insights from analogue models and natural examples in Iceland (MSc Thesis). RWTH Aachen University.

Gudmundsson, A., Bäckström, K., 1991. Structure and development of the Sveinagja graben, Northeast Iceland. Tectonophysics 200, 111–125. https://doi.org/10.1016/0040-1951(91)90009-H

Holland, M., Urai, J.L., Martel, S., 2006. The internal structure of fault zones in basaltic sequences. Earth Planet. Sci. Lett. 248, 301–315. https://doi.org/10.1016/j.epsl.2006.05.035

Kettermann, M., von Hagke, C., van Gent, H.W., Grützner, C., Urai, J.L., 2016. Dilatant normal faulting in jointed cohesive rocks: a physical model study. Solid Earth 7, 843–856. https://doi.org/10.5194/se-7-843-2016

van Gent, H.W., Holland, M., Urai, J.L., Loosveld, R., 2010. Evolution of fault zones in carbonates with mechanical stratigraphy – Insights from scale models using layered cohesive powder. J. Struct. Geol. 32, 1375–1391. https://doi.org/10.1016/j.jsg.2009.05.006

Winhausen, L., 2018. Influence of columnar joints on normal fault geometry and evolution An analog modeling study Master Thesis (MSc thesis). RWTH Aachen University.

Meeting Plate Tectonics – Walter Roest

Meeting Plate Tectonics – Walter Roest

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Walter Roest 


Walter Roest was born in Dordrecht, The Netherlands. He has had an impressive international career that started with an MSc in Physics and then Geophysics at Utrecht University in the Netherlands. He was the last one to obtain a PhD in Marine Geophysics from the Vening Meinesz laboratory for Marine Geophysics at Utrecht University, which closed afterwards. His career continued in Halifax, Canada where he contributed to geophysical data processing and interpretation, and subsequently in Ottawa, where he spent 12 years of his career in aeromagnetics. Since 2002 he is based at IFREMER in Brest, France, where he is active as a Marine Geophysicist.

 

Walter Roest – Credit: IFREMER annuaire

Walter, what was your reason to go into Earth Sciences? 

As a young adolescent, I wanted to become a physics teacher. That was my main reason to start with my studies in Physics in 1976. In 1978 an advertisement for a scientific cruise appeared. I applied and was allowed to embark, but unfortunately, the cruise got cancelled. There was another opening in 1979, which was aborted after a fire in the engine room. As a result, as an undergraduate, I had no real plan for about 6 months, until they proposed me to participate in the construction of a seismic streamer for the laboratory. After that, I was convinced that I wanted to work at sea. I got some opportunities abroad, so I basically dropped my physics-teacher wishes and continued in Geosciences.

Throughout my career I have never really planned anything, I never had any clear expectations neither

When you were very early in your career as a scientist, what kind of expectations did you have?

Throughout my career I have never really planned anything, I never had any clear expectations neither. Opportunities arose, in my case not in the Netherlands but in Canada and so I moved continents. I left the data acquisition at sea for a while. When I didn’t find a job after my PostDoc position I got the opportunity to go into aeromagnetics. Many years later, when I saw an advertisement for a position at IFREMER, the French marine research institute, I just applied. I thought I didn’t have any chance, but I was lucky enough to get the position! My career has been mainly a concatenation of events that happened.

It is very important to have knowledge on how data is collected.

What research interests, approaches and methods did you develop during your career?

Müller, D., et al., 2008. Geochemistry, Geophysics, Geosystems, 9. Q04006.

My research interests lie within global tectonics, using empirical research tools that are closely connected to data. It is very important to have knowledge on how data is collected. I try therefore to go on a research cruise at least once a year, so I stay updated about the newest data acquisition and processing techniques. I’m not so much interested in very detailed processes, but I’d rather try to understand the large scale tectonic setting of an area.

 

You have been around, working in quite some different fields. What accomplishment in your career are you most proud of?

Interesting question! I think I’m most proud of the Müller et al., 2008 paper I co-authored. It was published in G-cubed. We started this project in 1987 with a first edition of the ‘digital global plate tectonics map of the world’ in 1997. It basically took 20 years of work and I think the publication is a fantastic result, used and cited by many researchers. It shows that hard work pays off!

As soon as you can, start international collaborations […] they give you a different view on the world.

After all these years in the field of plate tectonics, you have seen many questions solved, but also arise. What do you think are the biggest challenges today?

Many questions still remain about the initiation of subduction. We basically do not understand how this works. Recently, we had two cruises in the South-East Pacific where we acquireseismic data to figure out how subduction starts. Also in terms of plate boundaries, there still many questions. For example between North and South America, we don’t exactly know where the plate boundary is, nor the style of deformation that is associated with it.

[…] you should force yourself to go a bit further every time you do something and make yourself capable of reflecting on the things you have done.

One last question, Walter, what would be your advice to Early Career Scientists that aspire a career in geosciences?

I actually have multiple tips and tricks that might boost your (early) career. As soon as you can, start international collaborations. I have worked with Chinese, Russian, Brazilian and American research groups, amongst others. They give you a different view on the world. For example, when I first worked with the Russians, they did not think that seafloor spreading was happening, even though we together interpreted magnetic lineations as isochrons. Another advice is that you should force yourself to go a bit further every time you do something and make yourself capable of reflecting on the things you have done. A last advice: every now and then go to conferences by yourself, don’t stick with your group or the people you already know. You will have the best encounters. For example, I met Dietmar Müller with whom I eventually wrote many papers, at a poster session at the AGU in San Francisco in 1978. So even when you are shy, just go for it, get out there!

 

Interview conducted by Anouk Beniest

Meeting Plate Tectonics – Richard Gordon

Meeting Plate Tectonics – Richard Gordon

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Richard Gordon


Prof. Richard Gordon is currently Professor at Rice University (William Marsh Rice University in Houston, Texas). He researches on how several areas such as paleomagnetism, plate tectonics, lithospheric deformation and space geodesy are tied together. While a student, Professor Gordon used paleomagnetic data to calculate the minimum velocity of a plate or continent in the past. In 2002, he was awarded by the GSA with the Arthur L. Day Medal for contributions to the development of the plate tectonic model, especially for the recognition and quantification of diffuse oceanic plate boundaries.

There will be some heated debates in the AGU

After being active for several decades in this field, where lies currently your main research interest?

My interest is in processes in the lithosphere. This could mean Plate Tectonics, deformation of the lithosphere, absolute plate motions, how plates move relative to the hotspots, how much hotspots move between them and how they all move relative to the spin axis. Plate motions, how standard they are, how motions from a million years compare with plates motions we see over decades with space geodesy. My particular interest right now lies in working out the polar wander path of the Pacific plate, because it is a key missing part of the puzzle for understanding Cenozoic global tectonics, and Pacific tectonics. Those are some of the highlights.

How would you describe your approach, which methods do you while conducting your research?

A lot of it involves looking at data, using as many data and as diverse datasets as we can to test different hypotheses. A little tiny bit of it involves modelling. The main focus in our research group right now is on looking at marine magnetic anomalies in the Pacific and coming up with novel ways of process them in order to squeeze out information on where the paleomagnetic pole lies.

What would you say is the favourite aspect of your research?

When you discover something new about the Earth and understand the Earth better, and you are the first one to get that realization: that is such a high, that makes all the hard work worthwhile.

Kreemer and Gordon (2014). Pacific plate deformation from horizontal thermal contraction. Geology, 42 (10), 847-850.

Why do you think is your research relevant? What are the possible real world applications?

A lot of the work I’ve done has been about relative motion of the plates and motion across deep deforming zones, for example in the western US. Some of that work has been used and can be used more to help assess seismic hazards. The seismic moment releases energy over time and spaces related to how much the earthquakes move and how fast the plates move, I think this is a very important implication. I’m hoping, in the future, to relate true polar wander to global climate change. Maybe it will work, maybe not. But if it did, I think that would be really relevant.

What do you consider to be your biggest academic achievement?

(sighs)… That’s a tough one… Something I am very proud at was leading a group with a couple of my graduate students, to put together one new global set of plate velocities. We did a really careful job, went back to all of original data and analyzed the results. We were able to discover a lot of things. You can discover a lot of new things by going back and looking at the data. It was a big project and we were all really worn out at the end, but I think we are all very proud of that.

That work led to the discovery and quantification of motion across several diffuse oceanic plate boundaries. Such boundaries are globally significant and occupy 10% to 15% of the ocean floor. At the scale of the boundaries and boundary zones, the physics of deformation in them is very different from that for narrow oceanic plate boundaries.

C. DeMets, R. G. Gordon, D. F. Argus, S. Stein (1990). Current plate motions. Geophysical Journal International, 101 (2), 425–478

What would you say is the main problem that you solved during your most recent project?

We have some of the papers out and still some of them are in the pipeline, I will be talking about them in the AGU: We solved a problem that people didn’t think was a problem: what’s the paleolatitude of the Hawaiian hot spot, when the Emperor Seamount Chain was formed. What we showed is different from what everybody believed. We showed that it stayed in the same place, it did not change its latitude. So it is going to be very controversial and there may be some heated debates in the AGU and EGU, I am sure. But I am sure we have got this right!

After being many years active in the academia, looking back, what would you change to improve how science in your field is done?

The easy answer would be: more funding! (laughs) Also, more opportunities for young scientists.

What are the biggest challenges right now in your field?

For the project I am doing right now on paleomagnetism of the Pacific, one challenge is that we need more data from the Pacific. We can do better with more data. A lot of the data that we have is collected by ships. But we would like to have vector data, from airplanes or drones that can move fast enough. Finding better quality data than we have is a challenge. And this goes back to more funding (laughs).

I thought I was going to be a writer

Richard Gordon in 1971. Credit – East Side Union High School.

What were your motivating grounds, starting as an Early Career Student? Did you always see yourself staying in academia?

When I went to graduate school, I thought I was going to be a writer. A science writer, maybe a science-fiction writer too. Isaac Asimov was my role model! I thought I had to have a PhD to know enough to be a good science writer. But to do a PhD I had to do research. So I started doing it and got really excited about it. And I thought “Hey, I could do this! I’m pretty good at this!

I did an internship in the oil industry for a summer and I really liked that too, but I liked academics a lot more, so I made the decision to stay in academia. Although I am still keeping my options open to still become a science writer. Isaac Asimov actually was an assistant professor for I think 6 years. When he reached the point where he was earning more money from his writing than as a professor, he decided to become a full-time writer. But I never did the writing, I just got so excited about academia that I have been totally focused in that way.

A disproportionate number of new discoveries are made by early career scientists

What advice would like to you give to Early Career Scientists?

The first thing is: don’t get discouraged. Because part of being an academic is receiving critical feedback. The advantage for us is that the people who are giving us feedback are people who also are getting feedback from somebody else. Whereas in art & music, the critics don’t actually make the music or make the art, they are just professional critics. It doesn’t give them the perspective of the person who also has received critical feedback. Everyone is going to get criticism, and papers get rejected and proposals get rejected…just don´t let yourself get discouraged and do read the criticisms carefully. It may be mostly wrong but there will be a kernel of truth, which can help you write a better paper, write a better proposal or be a better scientist.

The other thing to remember is that a disproportionate number of new discoveries are made by early career scientist. The early career scientists own the future, the near future. And that is part of “don’t be discouraged” because if you’ve got bright ideas, you could be just around the corner of a big advance.

Those two things together are, I think, important.

Richard Gordon. Credit – Jeff Fitlow, Rice University.

 

Interview conducted by David Fernández-Blanco

Minds over Methods: Tectonochemistry of Melting Mud in the Mantle, evidence from the Oman/UAE ophiolite

Minds over Methods: Tectonochemistry of Melting Mud in the Mantle, evidence from the Oman/UAE ophiolite

For this first Minds over Methods of 2019, we invited Christopher Spencer, Senior Research Fellow at Curtin University in Australia, to tell us something about tectonochemistry. By applying geochemistry to tectonic processes, it is possible to get more insight into the different stages of the rock cycle. By combining fieldwork and geochemical analyses of the Oman/UAE ophiolite, Chris and his co-workers believe they found the first direct and in-situ evidence of sediment melting in the mantle.

 

Credit: Christopher Spencer

Tectonochemistry of Melting Mud in the Mantle, evidence from the Oman/UAE ophiolite

Christopher Spencer, Senior Research Fellow, Curtin University, Australia

The rock cycle is the first thing we learn in Geology 101. Magma and lava cool to form igneous rocks. Igneous rocks then erode to form sediment, which forms sedimentary rocks as it is compacted. Increasing pressure and heat then create metamorphic rocks, which eventually will melt. In each of the transitions described in the rock cycle, tectonics is usually involved. Granite batholiths form in subduction zones and are uplifted and eroded in collision zones. The sediments derived therefrom are deposited along continental margins that are often then returned to subduction zones where they contribute to new magmatic systems. There is a wide array of tools that we can use to evaluate the role of tectonics in the rock cycle, of which geochemistry is able to provide insight into each stage of the process.

Applying geochemistry to tectonics is (unsurprisingly) referred to as tectonochemistry. Similar to tectonophysics, where geophysics is applied to address large-scale tectonic questions, tectonochemistry provides a unique view into geochemical proxies of tectonic processes. The melting of sediment along convergent margins is a classic tectonochemical problem, as the unique chemical signature of sediment found in a granite provides unequivocal evidence for the melting of a sedimentary rock. In collisional systems, like the Himalaya, tectonochemistry has been used to constrain the melting of meta-sedimentary rocks as crustal thickening and decompression drives dehydration of micas which leads to melting. Collisional systems provide clear and in situ evidence for sediment melting.

Figure 1: Clockwise from top left: tourmaline-bearing leucogranite from the Himalaya in NW India, leucogranite dykes intruding meta-sedimentary rocks exposed at 5000m altitude, in situ melting of meta-pelite and formation of leucogranite, incongruent melting of muscovite + plagioclase + quartz to form leucogranite but leaving the biotite behind. Credit: Christopher Spencer.

 

Sediments are also thought to melt in subduction systems, but given the difficulty of accessing the asthenosphere directly, it is more challenging to constrain the processes occurring deep in a subduction zone. The incorporation of sediment in subduction zones is often constrained using the geochemistry of the resulting magmatic rocks. The chemical signature of sediment provides a clear indication of its incorporation in the magma, but it is often unclear whether the contamination is occurring in the asthenospheric wedge or in the upper crust. For example, many granite batholiths contain zircon grains that are foreign to the host magma and whose age spectra match the detrital zircon age spectra of the adjacent sedimentary units. This relationship is a clear indication that sedimentary contamination occurred in the upper crust. Unfortunately, the geochemical proxies used to establish the sedimentary contamination only provide indirect evidence for the subduction of sedimentary material into the asthenospheric wedge. Such indirect evidence includes seismic stratigraphy showing sedimentary units being subducted beneath the forearc and whiffs of sedimentary geochemical signals in arc volcanics. Although these evidences point towards sediment being subducted deep into the asthenospheric wedge where it melts and contaminates the magmas coming off the subducting slab, they do not preserve direct evidence of sediment melting in the mantle.

To acquire direct evidence of processes happening deep in the mantle, I set my sights on the Oman/UAE ophiolite, where a thick succession of mantle peridotite is preserved beneath a complete stratigraphic section of oceanic crust. Previous work has shown that this ophiolite not only preserves an intact record of oceanic crustal stratigraphy, but also geochemical features of a subduction zone in the oceanic crust. This implies the ophiolite formed in a supra-subduction setting, where during the earliest phase of subduction, extension in the upper plate caused rifting and formation of oceanic crust above a subduction zone.

 

Figure 2: Oceanic crustal stratigraphy of the Oman/UAE ophiolite comprised of (clockwise from top left): pillow basalts, sheeted dykes, layered gabbros, and mantle peridotite. Credit: Christopher Spencer.

 

During fieldwork in the ophiolite, while traversing the 8-15 km thickness of the mantle peridotite, I encountered a number of granitoid dykes that cross cut the peridotite, but do not cross the petrologic Moho. Many of these dykes contained tourmaline, muscovite, biotite, and even andalusite, minerals that would be expected from the melting of sedimentary material. Finding these minerals in the mantle indicates these grantoid dykes formed from the melting of sedimentary material and here they were within the mantle! Subsequent analysis of zircon grains from these granitoid dykes revealed the age of these dykes was equivalent to the age of the overlying ophiolite providing bullet-proof evidence that they intruded while the ophiolite was forming above a subduction zone. To provide the nail in the coffin for a sedimentary origin, I performed oxygen isotope analysis of the zircon and quartz. Sedimentary material has a distinct oxygen isotopic composition and igneous rocks that are thought to have experienced sediment contamination have δ18O values that lie along mixing lines between a sediment end member and the mantle. The oxygen isotopic analyses of the sub-Moho granitoids of the Oman/UAE ophiolite revealed the highest δ18O values ever measured in igneous rocks, providing unequivocal evidence that these granitoids represent pure sediment melts. In a paper published in Geology (Spencer et al., 2017), my coauthors and I argue these igneous rocks represent the first direct and in situ evidence of sediment melting in the mantle. Lucky for us, we have just scratched the surface of the exciting things left to learn about these fascinating granitoids and I look forward to the opportunity to return to the Oman/UAE ophiolite.

Figure 3: Sub-Moho granitoids of the Oman/UAE ophiolite: A) Cathodoluminescence image of a zircon shown with location and result of δ18O analyses. B) Photograph of sub-Moho granitoids. C) Hand sample of granite with tourmaline and lepidolite (lithium-bearing mica). Credit: Christopher Spencer.

 

Meeting Plate Tectonics – David Bercovici

Meeting Plate Tectonics – David Bercovici

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting David Bercovici


David Bercovici started his scientific career with a BSc in Physics, and eventually graduated with a PhD in geophysics and space physics [from UCLA]. He was a professor at the University of Hawaii from 1990 until 2000. In 1996 he received the James B. Macelwane Medal from the AGU for his contributions to geophysical sciences as a young scientist. Since 2001 he has been at Yale as a professor in Geology and Geophysics, and is currently Department Chair (for the 2nd time).  In the last few years he was elected to both the American Academy of Arts & Sciences and the US National Academy of Sciences.

 

For me, the biggest question I still would like to answer is: why do we have plate tectonics?

Could you briefly describe your research interests, David?

My research interests are in geophysical and geological fluid dynamics, especially to understand lithosphere and mantle dynamics. I’m mostly a theoretician, which means I do more pen and paper work developing theories and models of geophysical processes, not so much in the way of numerical simulations. My area of interest right now is understanding rock rheology at the grain scale in a physical way. For example, the softening feedback mechanisms we think are working on rocks to generate plate boundaries are quite complicated. However, if we are able to understand them for Earth, perhaps we can use them to understand the conditions for whether plate tectonics can occur on other planets, too. Mylonites are a good example of rocks that probably undergo a self-softening feedback, since it appears that deformation causes their mineral grains to shrink, which makes them softer, which then focusses or localizes their deformation, and so on.

 

You have been around for some time. What do you consider your biggest achievement within your field of expertise?

Overall I believe we’ve made a lot of progress in trying to understand why Earth has plate tectonics (and maybe why other planets in our solar system do not).  A lot of the physics necessary to advance this field relates to exotic rock rheologies, and this has involved a collaboration between experimental rock physicists and geodynamical theoreticians and modelers.  Rock physicists like my Yale colleague Shun Karato, David Kohlstedt (at the University of Minnesota) and Greg Hirth (at Brown University) have been a big influence on me.  I think my own contribution has been in developing ‘grain damage theory’ which describes how mineral grains evolve under deformation and cause weakening as we see in mylonites. I and my colleagues (most notably Yanick Ricard at the ENS-Lyon, but also former students William Landuyt now at Exxon and Brad Foley now at Penn State, and my two current collaborators Elvira Mulyukova at Yale and Phil Skemer at Washington University in St. Louis) have developed and continue to develop  theories for how grains damage. I consider the physics that we’ve developed for this a significant accomplishment.

 

Bercovici, D. & Ricard, Y., 2013. Earth and Planetary Science Letters, 275-288.

 

So besides your projects related to ‘damage physics’, do you have side-projects too?

David Bercovici – Credit: David Bercovici

Yes, I do! I currently have a project working on oscillations and magmatic waves in volcanic systems before eruptions with various colleagues (most notably Mark Jellinek at the University of British Columbia and Chloé Michaut at the ENS-Lyon).  And I have worked on problems that are related to the presence and circulation of water in the mantle. I and my colleague Shun Karato proposed the reasonably well-known (and controversial) transition zone water filter model. This theory argued that the upper and lower mantle are kept somewhat chemically distinct but without actual layering (which is usually required to explain the difference in basalts coming up at mid-ocean ridges versus ocean islands like Hawaii) by hydrous melting of material upwelling out of the transition zone, just at the 410 discontinuity. This melting then cleans the rising mantle of incompatible elements, much like a coffee filter (or maybe more like a hookah), allowing mid-ocean ridge basalts to look depleted.

One of the biggest challenges today is to predict and understand how other planets function.

You have quite some different interests! Overall, what do you consider the biggest scientific challenges in your field nowadays?

One of the biggest challenges today is to predict and understand how other planets function. Do they have plate tectonics or not? If not, could they have had plate tectonics at one time, and then why did it stop? We need to do tests and get data from other planetary and extra-solar bodies. Currently, we only have data from the Moon, Mercury, Mars and Venus (and also outer-solar system icy bodies). We are a long way from understanding our universe and the objects residing in it. I think that the model of plate tectonics as we know it nowadays is maybe just a recipe describing our own planet, but will not necessarily work for others.

Any model or code is only as good as the physics being used

 

So to get to there, what do you think could be improved in your field?

In geodynamics, constructing and using big numerical models is very popular nowadays. There is a danger here though, because users of these models do not always understand the physics behind the code they are using, and that some of this physics is incomplete. Any model or code is only as good as the physics being used, and we do not necessarily understand all this physics yet.   It is very important to understand how the numerical tool is constructed, or at least its limitations, and we really need to emphasize this. Ideally, everyone using a model would understand how the model works, but as codes become more complicated this becomes less practical or feasible. But at the very least, before you use a model, you should think about how to interpret it.  One can first develop a simpler theory or scaling-law to hypothesize or predict what the model might do, and then treat the numerical simulation like an experiment to test (and perhaps disprove or perhaps refine) this hypothesis.  This will make your study much more valuable and long-lasting.

 

You still have some time to continue your research. How do you see the remainder of your career?

I certainly hope to have some more discoveries coming up. You often have a broad idea or hypothesis that gives some direction where you should go, but you’re often surprised about what you discover along the way.  One of the things I work on now is the metal asteroid Psyche. One question is as such an asteroid freezes completely, can it sustain a magnetic field? This is a completely new direction for me and I find it very exciting! Whether my ideas will work or not, I can’t say yet. But sometimes my more successful ideas developed in a folder on my computer called ‘Cool or Stupid?’. One of my more well-known papers had that as a working title for a couple of years.

I was a terrible student.

What advice would you like to give today’s Early Career Scientists?

When I was an undergraduate and for some time in graduate school, I was a terrible student.  I didn’t even make it into graduate school at first! So my expectations were rather low.  Probably my one redeeming quality was that I was stubborn and persistent.  I figured I would continue to try to make it in graduate school until the university police were called to escort me off campus, which luckily never happened. My best advice is that if you feel you have found out what you want to do, be stubborn, but not so stubborn and rigid as not to learn new things and try ideas outside of your comfort zone.

My second advice is that you should ask yourself what big question do you want to answer in your life? What would you like written on your tombstone that you tried to accomplish?  Find yourself that question and make it your life goal. For me, the biggest question I still would like to answer is: why do we have plate tectonics?

Interview conducted by Anouk Beniest