TS
Tectonics and Structural Geology

Structural Geology

Features from the field: Foliation

Features from the field: Foliation

Have you ever walked on a mountain trail, passing past outcrops of rocks and noticed that many rocks appear to be split along a well-defined orientation? If you have, you might have seen one of the most important structures in metamorphic rocks – called foliation.

The term ‘foliation’ derives from the Latin folium, meaning ‘leaf’. A rock with a foliation looks like a pile of ‘leaf-sheets’ that appear piled up one upon the other. Any set of planes that is pervasively repeated in a rock volume defines a foliation, irrespective of its origin, thickness or composition. In the example shown on top of the page, the rock easily splits along foliation surfaces that dip to the left. In this case, the foliation is defined by the preferred orientation of tiny platy minerals – called phyllosilicates – that cause the rock to break apart easily along a specific direction.

Triassic metabreccia from Punta Bianca (La Spezia, Italy). Note the foliation defined by deformed clasts of white marble. The image is 90 cm in width. Photo © Samuele Papeschi

In the example on the left, a deformed breccia, the foliation is defined by clasts that were flattened by tectonic forces and that are now all oriented parallel to each other.

There are many processes that can lead to the development of a foliation in rocks (I will save them for another post). What is important is that a foliation is a pure and simple geometric term, which means that you can use it to describe any pervasive set of planes in a rock, even if you don’t know their origin or composition.

Given this definition, foliations are not restricted just to metamorphic rocks. Bedding planes in sedimentary rocks define a foliation, and so do flow structures in volcanic rocks or compositional bands (schlieren) in intrusive rocks. This kind of foliation is called primary foliation – formed during deposition or igneous crystallization of rocks – to distinguish them from secondary (or tectonic) foliation that develops when rocks are deformed.

 

There is a foliation inside this granitic dyke from the Calamita Peninsula (Elba Island, Italy). In this case it is defined by black bands rich in tourmaline and changes in grain size. Photo © Samuele Papeschi

 

Tectonic foliations are widespread in metamorphic rocks. They form as a result of different processes, which require two basic ingredients:

  • First, you need deformation processes. Luckily, we are on a trembling planet and at depth rocks are squeezed by tectonic forces.
  • Second, you need heat and pressure. You can squeeze rocks as much as you want, but if temperature is not high enough, they will break rather than develop a foliation. Some rocks can deform at relatively low temperature (claystones for instance) while others -for example a granite, require several hundreds of degrees to start deforming.

If all the conditions above are satisfied, congratulations! Your rock will develop a foliation. During deformation, old grains rotate and parallelize with each other. Eventually, new minerals will grow already oriented parallel to the foliation. This is because the foliation plane lies perpendicular to the direction of maximum tectonic force (called stress in geology) and mineral grains find less resistance to their growth along the foliation plane. Difficult? Here is a sketched example, modified after Raymond (1995).

 

The progressive development of a foliation overprints primary structures leading to the development of a new, metamorphic structure. Redrawn after Raymond (1995).

 

The more deformation goes on, the more primary structures are obliterated. A foliation progressively overprints primary structures, becoming more and more penetrative as deformation continues. If rocks face only limited deformation or are deformed at relative low temperatures, they can preserve original structures, but if the intensity of deformation or temperature (or both) are high, primary structures will likely be destroyed.

We have barely started to scratch the surface of this interesting topic. In the next chapters of the ‘Features from the Field’ series I will look in greater detail at the complicated world of foliation. Stay tuned!

 

References and further reading

Dieterich, J.H., 1969. Origin of cleavage in folded rocks. American Journal of Science 267, 155-165.
Fossen, H., 2016. Structural Geology. Cambridge University Press.
Ramsay, J.G., and Huber, M.I., 1983. The techniques of Modern Structural Geology. Vol. 1: Strain Analysis. Academic Press, London.
Raymond, L. A., 1995. Petrology: the study of igneous, sedimentary, metamorphic rocks. Dubuque, IA : Wm. C. Brown (editors)

Minds over Methods: Virtual Microscopy for Geosciences

Minds over Methods: Virtual Microscopy for Geosciences
The next “Minds over Methods” blogpost is a group effort of Liene Spruženiece (left) – postdoctoral researcher at RWTH Aachen and her colleagues Joyce Schmatz, Simon Virgo and Janos L. Urai.

Credit: Liene Spruženiece

The Virtual Microscope is a collaborative project between RWTH Aachen University and Fraunhofer Institute for Applied Information Technology (Schmatz et al., 2010; Virgo et al., 2016).

In the multitude of tools to analyze rocks, the optical microscope is still one of the first go-to methods for rock characterization. A look on a petrographic thin section under an optical microscope gives a quick overview of the mineralogy and fabric of a rock and helps to determine the areas of interest for more detailed analysis with other methods. It is also a crucial part for teaching geology classes.

Most geoscience institutions already have a petrographic microscope that is equipped with a camera and maybe an automated stage for capturing image mosaics. However, these images make only limited use of the vast amount of information available, such as the overview of the sample fabric at different magnifications or the change of optical mineral properties (pleochroism and extinction behavior) with the rotation of polarizers. Although there have been recent developments in the field of virtual microscopy (NASA, 2007; The Open University; 2010; Tetley and Daczko, 2014), to our knowledge, none of the existing systems has been able to fully emulate a user experience in a virtual environment that is equal to using a traditional analogue microscope.

 

Figure 1. The setup of the PetroScan microscope. Credit: Fraunhofer FIT

How does it work?

The idea behind the virtual microscope is to capture the full information of entire rock thin-sections in a digital format, including the possibility to switch between plain light and crossed polarizers, rotate the polarizers and zoom everywhere in the sample at high magnifications.

The hardware part of our system consists of a fully automated petrographic microscope, connected to a computer (Figure 1). The software contains three modules; a PetroScan launcher for setting up the image acquisition, optimizer for combining and interpolating the scanned images and a viewer program (Figure 3).

 

Figure 2. Automated sample stage allows capturing high resolution images of entire thin sections by combining thousands of images taken sequentially along a predefined grid. Credit: Jochen Hürtgen

High-resolution mosaics (Figure 2) containing up to a million images can be acquired in a few hours. With crossed polarizers, the scans are performed for several rotation angles. The movement accuracy of the sample stage is about 10 nm. This ensures precise overlap of the scanned mosaics at different rotation angles, where each corresponding pixel has the same x-y coordinates. Thus, the images of each rotation angle are precisely overlapping and allow to interpolate the change in brightness values for every individual pixel in the mosaics, producing smooth curves (Figure 3) that reflect extinction behavior in minerals (Heilbronner and Pauli, 1993).  Each attribute of these interpolated curves (phase, amplitude) of the sample can be viewed at any rotation angle.

 

Quantification of optical images

Figure 3. Screenshot of the PetroScan TileViewer window showing a thin section that is scanned under crossed polarizers. On the right side the scanned image is overlain by the phase map, where each pixel is color-coded according to the mineral extinction angles. Credit: Liene Spruženiece, Joyce Schmatz, Simon Virgo and Janos L. Urai

Virtual microscopy offers powerful means for quantitative analysis of giga pixel images to extract multi-scale information. It has a resolution of up to few micrometers for areas in sizes of 10 square centimeters. In its current form the viewer software that we developed contains a built-in toolbox for displaying and tresholding the intensity, saturation and hue values of the scanned images. This can be used for a quick estimation of sample porosity or proportions of different minerals. In addition, the scans with interpolated crossed-polarizer rotation also contain information of the mineral extinction behavior that is used to produce a “phase map” (Figure 3). The “phase map” displays the variations in the mineral optical axis orientations. Although it cannot provide absolute values for the crystallographic orientations, it allows a clear distinction between differently oriented mineral grains and allows easy visualization of qualitative lattice misorientations inside individual mineral grains. Furthermore, import and export functions are incorporated in the image viewing software. Thus more advanced image analysis can be carried out in specifically designated external softwares (e.g. Fiji/ImageJ, GiS, Matlab, Python), then inserted back in the PetroScan viewer software.

 

Applications in teaching

Figure 4. Mineralogy and fabrics of the scanned samples can be segmented and quantified using built-in toolboxes. The recognition of features is greatly improved by the possibility to zoom in the samples, switch between the plain light and crossed polarizers and rotate the polarizers. Credit: Liene Spruženiece, Joyce Schmatz, Simon Virgo and Janos L. Urai

At RWTH Aachen University, virtual petrography has been used as a teaching tool for several years. For example, it is extensively used in the microtectonics course. Each class consists of a short introduction in some of the common rock microstructures, such as veins, cataclasites, mylonites, dissolution-precipitation features and others. This is followed by an hour-long presentation by a student group, where they describe and discuss the respective microstructure in a scanned thin-section, projected to a screen with a high-resolution beamer. The students use laser pointers for characterizing the features and origins of the microstructure, switch between views in plain-polarized or crossed-polarized light, zoom in and out across the sample, adjust illumination settings, rotate polarizers and do basic image analysis (Figure 4). This has proven to be a highly engaging teaching method. The students in the audience question the presenting group asking to provide a closer look or more details on any interesting microstructural feature. Often hypotheses are formed by the listeners and immediately tested by the presenters, allowing to perform an investigation and agree on a reasonable explanation at the end of the class. Virtual petrography can be especially important in teaching institutions that do not own well-equipped microscopy labs. It only requires a computer and a projector. The thin section scans and PetroScan viewing software will be available for download online. Thus, such a method will not incur additional costs to the institutions, at the same time will provide a large collection of a high variety of geological samples.

 

The vision

We imagine a world-wide community built around the platform of virtual microscopy, where the information from different analytical methods can be exchanged between users and stored in open databases, available for teaching or research purposes. Many advantages arise from such a transformation. Work can be carried out anywhere without a need to access microscopes, several users can simultaneously view the same samples, data can be easily quantified and integrated between different methods, and thin-section libraries can be shared and exchanged by the user community.

Further plans for developing this method include collaboration with the computer vision department at RWTH Aachen University in order to create deep learning algorithms that allows quick and precise segmentation of rock microfabrics, such as mineral content and distribution, grain boundaries, grain sizes, porosity, etc. This has been made possible by recently obtained funding from the RWTH Aachen University “Exploratory Research Space – ERS”. The final data set will be public and shared with communities.

 

Edited by Derya Gürer

 

References

Heilbronner, R.P., Pauli, C. (1993). Integrated spatial and orientation analysis of quartz c-axes by computer-aided microscopy. Journal of Structural Geology, 15, 369-382.

Tetley, M.G., Daczko, N.R. (2014). Virtual Petrographic Microscope: a multi-platform education and research software tool to analyse rock thin-sections. Australian Journal of Earth Sciences 61, 631-637.

NASA (2007). Virtual Microscope. Available at: http://virtual.itg.uiuc.edu/

Schmatz J., Urai J.L., Bublat, M., Berlage, T. (2010). PetroScan – Virtual microscopy. EGU General Assembly, EGU2010-10061.

The Open University (2010). The Virtual Microscope for Earth Sciences Project. Available at: http://www.virtualmicroscope.org/.

Virgo S., Heup, T., Urai J.L., Berlage, T. (2016). Virtual Petrography (ViP) – A virtual microscope for the geosciences. EGU General Assembly, EGU2016-14669.

Meeting Plate Tectonics – Jean-Philippe Avouac

Meeting Plate Tectonics – Jean-Philippe Avouac

These blogposts present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Get to know them, learn from their experience, discover the pieces of advice they share and find out where the newest challenges lie!


Meeting Jean-Philippe Avouac


Prof. Jean-Philippe Avouac initially studied mathematics and physics during his undergraduate and graduate degrees. Later he got more inclined towards geophysics and then he discovered Earth Sciences. During his Ph.D. at the Institut de Physique du Globe de Paris, advised by Paul Tapponnier, he immersed himself in geology and tectonic geomorphology. Currently, Jean-Philippe Avouac is a Professor of Geology at the California Institute of Technology.

Like living organisms, earthquakes have a life cycle: they nucleate, grow and arrest. There can be some lineage but each earthquake is a different being.

Fieldwork along the Kali Gandaki (Nepal) in 1999. Credit: Barbara Avouac

Where lies your main research interest?

I study crustal dynamics: How the crust is deforming as a result of earthquakes, but also as a result of viscous processes. I study the process of stress accumulation on faults, the release of this stress by earthquakes, as well as how earthquakes and other mechanisms of deformation are contributing to building the topography and geological structures in the long run.

 

How would you describe your approach and methodology?

In my group, we develop techniques to measure crustal deformation using in particular remote sensing and seismology. We were using radar images initially, and we have moved toward using more optical images with time and also GPS data… We try to reproduce the observations (geodetic deformation, kinematic models of seismic ruptures, gravity field…) using dynamic models to determine what are the forces and rheologies needed.

 

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

What I like most about my research is mentoring Ph.D. students and postdocs. I love matching their skills with good problems, problems that will be attractive to them and that will resonate with the currently hot questions in Earth Sciences. I really love doing that.

The other thing I love is to use what I learned as I student (maths and physics) to answer science questions arising from natural observations. I love that part when you look at nature, you observe something and try to measure it quantitatively and then you try to explain the observation with dynamic models. I really enjoy going back and forth between observations and modelling. And the field! I really like being in the field… This is an aspect of the job that really attracted me initially.

We built from what other researchers had done before, but we reached quite different conclusions […] that’s exciting!

Jean-Phillipe Avouac leading a field excursion in the Dzungar basin, 2006. Credit: Aurelia Hubert-Ferrari

 

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

A significant fraction of my research is relevant to seismic hazards. After my Ph.D., I worked for the Commissariat à l’Energie Atomique (CEA) for 10 years. I was conducting seismic hazard assessment studies for nuclear facilities. So, I have been exposed to the applied side of earthquake science and I like that some of the research we do in my group can help to improve the way we do seismic hazard assessments.

But what I really want to say is that I do not think relevance should drive academic research. In that regard, I should say that I don’t like much the way the funding system works today. I think there is too much emphasis on relevance to society. The idea that you start from stating problems of societal relevance, and only then see what kind of research we can do to solve this problem is not a good approach, in my opinion. I don’t think this is the way important scientific discoveries are made. You make discoveries by being curious, by observing nature with an open mind, by exploring new ideas and coming up with new concepts, or by observing something that is not explained in the current theoretical framework that we have and then you make use of the knowledge that you build after looking at these problems. There is no way you can clearly anticipate where the joyful exploration of an intriguing idea or observation can lead but we know from experience that the society benefits from curious scientific exploration. So, although I think there is relevance in what I am doing, I do not think that, in general, relevance to society should be driving academic research.

 

An outcome of Jean-Phillipe Ph.D Thesis, later published in Kinematic model of active deformation in Central Asia (Avouac and Tapponnier, GRL – 1993; doi: https://doi.org/10.1029/93GL00128).

I do not think relevance to society should drive academic research

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

People in my group work on many different projects that are all very exciting to me. I’m going to mention just one project though because I can not possibly list them all.

We have done a lot of work in the past to develop techniques to invert geodetic measurements for fault slip at depth. A postdoc and a graduate students in my group have moved on to improve the technique and use it to document slow slip events in Cascadia over the last 15 years. That was a daunting work but their hard work and perseverance have really paid back. The end result is amazing! We see how the slow slip event initiate, propagate, arrest, trigger one another… We built from what other researchers had done before us, but we reached quite different conclusions given that we now have a more complete view of the behaviour of the system –that’s exciting! I anticipate that we are going to learn a lot about the dynamics of slow-slip events, and maybe it will have important implications for regular earthquakes!

What do you consider to be your biggest academic achievement?

The research for which my group is probably best known is that we have done in the Himalaya. In particular, we have built a model of the seismic cycle that explains the observations that we have from seismology, geodesy, geomorphology and geology. We worked a lot on the Himalaya, in part because I love mountains, but also because it is a very unique setting to study orogenic processes which are still active today. There is really no better place where you can get geological constraints on the thermal and structural evolution of the range. There is a lot of erosion and it has been going on for a long time, so the rocks that have been brought to the surface have recorded the thermal and deformation history over tens of million years. Our research has helped understand how the Himalaya has formed as a result of seismic and aseismic deformation, and I think it has yielded important insight on orogenic processes and the seismic cycle in general.

By the way, I don’t mean that earthquakes are periodic. Like living organisms, earthquakes have a life cycle: they nucleate, grow and arrest. There can be some lineage but each earthquake is a different being.

Animation showing the process of stress build up and release associated to earthquakes along the Main Himalayan Thrust fault, along which India is thrust beneath the Himalaya and Tibet. Credit: Jean-Philippe Avouac, Tim Pyle and Kristel Chanard.

We tend to build walls between disciplines […] We would not have been able to discover plate tectonics without a deep cross-disciplinary dialogue

What do you think are the biggest challenges right now in your field?

As I mentioned before, the funding system is an issue. Funding agencies are clearly making a big mistake in prioritizing social relevance as a criterion to evaluate proposals. Aside from that, the challenge that we have in the Earth Sciences is that we tend to build walls between disciplines. Specialization is a natural drift, and you can make a very successful career in a particular field pushing further a particular analytical or modelling technique. Also, it is easier to get funding for what you are known to be good at. As a result, walls between disciplines are building with time. The vocabulary is evolving in each individual discipline and it is increasingly difficult to make major advancements that can bridge different disciplines. In my research, I try to navigate from one discipline to the other… but it is a challenge –while it can be key to make significant discoveries, it takes time and effort. There are fewer and fewer people making a carrier this way. It can be dangerous because of a dilution effect, but at some point, it is needed. Look at plate tectonics for example: it happened because of advances in different disciplines but most importantly because some scientists were aware of these advances and were able to connect them and derive a coherent global framework. We would not have been able to discover plate tectonics without a deep cross-disciplinary dialogue.

Another challenge is that nowadays we have a lot more data than we used to have. This is both an opportunity and a threat. There is a trend to produce more and more publications, that look very solid because they use a lot of data, but that are in fact very incremental. More of the same is not necessarily advancing knowledge at a fundamental level. We have to be imaginative with regard to how to process the increasing flux of data, but it should not come at the cost of being imaginative with regard to what they mean.

I do not like the way the funding system works today

When you were in the early stages of our career, what were your expectations? Did you always see yourself staying in academia?

After my Ph.D. I did not stay in academia. But even when outside academia, I kept doing research, because I had an appetite for it and was working in an environment where scientific curiosity was valued, even if science was not the main objective. Although I was not unhappy at all outside academia, I decided to go back to it since I found it more exciting for myself: I like to solve scientific questions but there is not so much I could solve without the help of students and postdocs. I didn’t consider staying in academia after my PhD because there were sides of the academic life I did not feel comfortable with… I was finding people in academia to be a bit… difficult sometimes, with big egos and not so open minded. Also, we are a very conservative community. There’s a reason for that, for we as scientists have to be sceptical and to push back new ideas and new observations. I guess I have now become now one of those crazy and conservative academic guys (laughs)!

 

Mapping and sampling Holocene terraces abandoned by rapid climate-driven incision in the Tianshan. Credit: Luca Malatesta

If you have a new idea… you will probably have a hard time

What advice would you like to share with Early Career Students?

My first advice is to be aware of the important questions that we should try to solve. Not because they are relevant but because they are interesting and because they are timely, given the tools and data that we have access to. Being aware of the really big questions is important because we tend to forget them sometimes as we become more specialized. And be also aware of the new techniques available, especially those that you could draw from other fields; computer science or medical imagery for example… It is important to be curious and see what is happening in other fields so that you can transfer new ideas and new techniques to your own field and give a try at answering big science questions.

Be curious, be adventurous. Take risks. Try things that might not work. You might be losing your time but it is also an opportunity to make real fundamental advancements. You can make a career by increments, but I think it is not as rewarding as taking risks and really solving a difficult problem.

Follow your own dreams and don’t be intimidated by peer pressure. If you put a new idea on the table, a really new one, first, you will probably have a hard time expressing it clearly… And second, peers will most probably push back, as they should. So do not be intimidated, believe in your ideas, and keep adjusting and pushing them forward. I see too many times students or postdocs who meltdown and get discouraged if they receive a negative comment after a presentation… – I would say, that could, in fact, be a good sign! You may be doing something different and maybe people are not understanding because there is something disturbing and really new!

 

Jean-Phillipe Avouac. Credit: Trish Reda.

 

Interview conducted by David Fernández-Blanco

Features from the Field: Boudinage

Features from the Field: Boudinage

The Features from the Field series is back! In our previous posts, we have shown how rocks can deform during ductile deformation, producing folds. Folds very commonly develop in rocks when rock layers are shortened by tectonic forces in a specific direction. On the other hand, when layers are extended, we develop boudins.

Saucisson is a dry cured sausage (boudin) from France. Did you know that geology is full of food analogies? Indeed, we love barbecues. Photo credits © Nate Grey (Flickr)

Boudins – the term comes from the French word for ‘sausage’ – are fragments of original layers that have been stretched and segmented. They develop in layers that are stronger and more resistant to deformation (i.e. more competent) than the surrounding rocks. In the example shown at the top of the page, the boudinated layer is made up of ‘strong’ amphibolites that are surrounded by relatively weaker quartzites. As you can see, the layering of the quartzites is deflected in the ‘pinches’, as if they where flowing in the gaps of the boudins during the extension. That’s it! During ductile deformation, rocks flow over millions of years in a plastic way.

Different rock types are characterized by a different strength during deformation, which is significantly influenced by temperature, pressure or -very important- presence of water. Boudinage is a very common structure which helps  the geologist understand ‘who is stronger than who?’ and helps them guess the physical conditions at which deformation took place.

Boudinage style can also vary enormously. For example, the eye-shaped boudins shown at the top of the page are called ‘pinch-and-swell’ structures. Indeed, you can notice that the boudins are not entirely separated and are connected by a very thin amphibolite layer, as if they were ‘pinched’ by a finger. This structure suggest that both the boudinated layer and the surrounding rocks are deforming in a ductile way.

However, fracturing can also play an important role in boudinage. In the example shown below, the top layer consists of strong quartz-metaconglomerate that has been boudinated within very weak phyllites (the bottom layer). The quartz-metaconglomerate is fragmented along symmetric (dextral and sinistral) fractures with an offset of several centimeters. The white material filling the gaps are vein of quartz that were deposited during the boudinage process. Note how the fractures are restricted to the metaconglomerate.

 

Symmetric boudinage of a quartz metaconglomerate in phyllites. The gaps of the boudins are filled with white quartz veins (Punta Bianca, La Spezia, Italy). Photo credits © Samuele Papeschi

 

Boudins can be symmetric, as in the example above, or asymmetric, as in the example below, where the boudinated layer is an amphibolite surrounded by weaker micaschists and quartzites. The boudins are separated by small scale sinistral shear fractures and systematically rotated clockwise. In this case, the geologist can obtain information about rock strength during deformation, but also on the sense of shear – which here is top to the right.

 

Asymmetric boudinage of amphibolite (the blackish layer) in dark grey biotite-micaschists and white quartzites (Elba Island, Italy). The amphibolite layers is fragmented by several, sinistral shear fractures. Photo credits © Samuele Papeschi

 

Rocks are not stretched in a single direction. Layers can also be flattened and stretched along 2 directions. When this occurs, you get fragmented boudins surrounded by 2 sets of fractures, as in the last example below. You already know that geologists like food analogies, so are you able to guess the name of this last structure? Yes, it is a chocolate tablet boudinage.

 

Chocolate tablet boudinage: a grey dolomite vein has been stretched along two, nearly-perpendicular, directions. The gaps between the boudins are filled by calcite deposited by fluids (Punta Bianca, La Spezia, Italy). Photo credits © Samuele Papeschi.

 

To sum it up, boudinage is a very important structure when studying rocks in the field, which gives us important insights about deformation, rock strength, pressure and temperature conditions and the sense of shear. Together with folds, lineations and foliations, it represents one of the most important features that can be described in the field.

Meeting Plate Tectonics – Dietmar Müller

Meeting Plate Tectonics – Dietmar Müller

These blogposts present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Get to know them, learn from their experience, discover the pieces of advice they share and find out where the newest challenges lie!


Meeting Dietmar Müller


Dietmar Müller is Professor of Geophysics at the University in Sydney and leads the EarthByte research group. He started his academic career in Germany at the University of Kiel and obtained his PhD in Earth Science at the Scripps Institution of Oceanography, UC San Diego, in 1993. Throughout his career he has straddled the boundary between geology, geophysics and computing.

Figure out what you actually enjoy doing and just go and do that.

You were educated in Germany and in the USA. How did you end up in Australia?

After I finished my PhD in 1993, I saw an advert for a lectureship in geophysics at the University of Sydney in EOS. I had never been to Australia and had no idea what life in Sydney might be like, but I thought, I might as well send off an application. A couple of months later I got a postcard from Sydney University, informing me that I had been shortlisted for the position. I thought this was vaguely interesting, but as a fresh PhD graduate, I mainly had my eyes on a couple of postdoctoral fellowships in Europe. Then I got a phone call for an interview. They had clearly decided that flying me to Sydney, all the way across the vast Pacific Ocean, was far too expensive. But they seemed to be interested in my vision for the future, and at the end of the phone interview they asked me: “If we offered the position to you, would you take it?” The thing is, this was the first real job anyone offered to me, so I thought, it’s probably a good idea to say “sure, why not”. Soon they faxed me a contract (these were not yet the days of the internet). Then I thought, hmm, what is this place actually like? So I went to the public library in San Diego and borrowed a VHS tape on Sydney. It included footage of Bondi Beach, Sydney Harbour and the Blue Mountains, with a few kangaroos and koalas thrown in for good measure. I thought this looks ok, it could be a liveable place. After I finally got my visa, I booked a 1-way flight to Sydney, and in late October 1993 I showed up in the Department of Geology and Geophysics and ran into a guy who turned out to be the Head of Department. He looked at the Scripps T-shirt I was wearing, and said: You must be the guy we hired! Of course, he had never seen me, so my T-shirt was my main identifying feature. Remarkably, over 25 years later, I am still there.

Dietmar settling into life in Australia in the 90s, mapping Devonian carbonates in Yass. Credit: unknown.

What is your main research interest? How would you describe your approach and methods?

I lead an Australian research effort, with many international links, to develop and continue to refine something that could be called a virtual Earth Laboratory. I have been an advocate for open-source software and open-access data during my entire career to make science transparent and reproducible. Based on these principles we have spearheaded the development of custom software and global data sets to reconstruct the Earth through time. To understand the Earth’s evolution we need to change our geographic reference system as we go back in time, because of plate tectonics. The plate tectonic revolution in the late 60s and 70s established the principles of how plate tectonics works. Applying these principles to build an Earth model is essentially what I have focussed my career on. I have always had a fascination with Earth evolution over geological time because its comprehension lies so far outside the everyday experience of humans. Most people cannot grasp the relevance of processes on vastly longer timescales than our own lifetime. But understanding the rhythms of Earth’s deep past and thinking about time like a geologist can perhaps give us the perspective we need for a more sustainable future. To dive into the Earth’s past, plate tectonics is indispensable. We need to be able to reconstruct geological data to their original environments. Doing this effectively requires open-source software and open-access data sets that can be shared amongst the community, enabling collaboration.

How do you build an open-source software system from scratch?

Dietmar Müller and Mike Gurnis in Altadena, 2006, taking a break from planning GPlates development. Credit: Melanie Symonds.

When I arrived in Sydney (over 25 years ago) there was no open software to build plate tectonic models, let alone to link plate motions to mantle convection models so that we can investigate the evolution of the entire plate-mantle system. I assembled a small team, partnering with Michael Gurnis at Caltech, to build the community GPlates software. This effort was initially supported by the Australian Partnership for Advanced Computing (APAC) enabling the development of GPlates1.0 on Linux and PCs and its Geographic Markup Language-based information model. In 2005, we managed to get a small educational grant from Apple Computers to develop the GPlates for Macs. We are lucky that shortly afterwards the AuScope National Collaborative Research Infrastructure was established which has supported GPlates development since 2007. That allowed us to fully develop reconstructions of plate boundary networks through time, which is essential for coupling plate tectonics to mantle convection models, as well as the 3D interactive visualisation of mantle volumes and lastly the functionality to model plate deformation, a key step beyond the classical rigid plate tectonic theory. We also developed a python library, pyGPlates, that allows users to link our plate models to many other forms of spatiotemporal data analysis and to other types of models, including geodynamic and paleoclimate models.

The slow carbon cycle is like slow cooking… over millions of years

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

Understanding the Earth as a system. I am interested in integrating observations from Plate Tectonics and mantle convection with landscape evolution and surface environments through time. I would like to adopt a definition of Earth System Science that actually includes the entire solid Earth, as well as the atmosphere, oceans and biosphere.

What are the real world applications of your research?

There are many applications of plate tectonics. They include understanding solid Earth evolution, palaeogeography, paleoclimate, paleoceanography, paleobiology, and spatiotemporal data mining, for instance for resource exploration. Most mineral deposits are associated with plate boundaries, so being able to link ore deposit formation with plate motions and the kinematic and geodynamic history of plate boundaries allows us to start understanding why certain mineral deposits form at specific windows in space and time, something we have recently started doing using the Andes as a case study.

Students will be entering a transformed workplace unlike any their parents knew

What do you consider to be your biggest academic achievement?

I am most well-known for my work on the age and palaeophysiogeography of the ocean basins. I started working on this as a PhD student. My thesis supervisor, John Sclater, made a name for himself with the first isochron map of the ocean basins. But there was no digital map. Having a digital grid, linked to a global plate model, was going to be critical for studying a whole range of processes from subduction, plate-mantle interaction, the evolution of ocean gateways through time, dynamic surface topography, and many others. I decided to synthesize all the data that we had available at the time to create the first digital map of the ocean basins, followed by a set of reconstructed paleo-age maps. This has enabled a lot of research, both my own and that of the community. For example, it has allowed us to look at the volume of the ocean basins through time (via the connection between the age and the depth of the ocean floor). A more recent achievement, fresh off the press, represents an epic decadal effort on part of the EarthByte group to complete a global plate model for the Mesozoic/Cenozoic period that includes plate deformation. Classical plate tectonics requires plates to be rigid and separated by narrow boundaries. It’s astonishing that it’s taken about 30 years since diffuse deformation was first widely recognised in the 80s to get to the point of systematically building a global model incorporating diffuse deformation for the geological past (soon to appear in Tectonics). It reveals that about a third of the continental crust has been deformed since the breakup of Pangea, about 77 million km2, partitioned into 65% extension and 35% compression. That roughly corresponds to the total area of North and South America and Africa together. The model can be used to investigate the evolution of crustal strain, thickness, topography, temperature, and heat flux, globally.

Total distributed continental deformation accumulated over 240 million years of rifting and crustal shortening. In Dietmar et al. (to come in 50th anniversary plate tectonics volume in Tectonics). A global plate model including lithospheric deformation along major rifts and orogens since the Triassic.

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

Recently, I became involved in the Deep Carbon Observatory. There are a few quite exciting problems involved in understanding the Earth’s deep carbon cycle and, being an area I have not traditionally worked in, it’s a new adventure for me to try to understand how plate tectonic drives the geological carbon cycle. One of the problems that we tackled in the course of connecting plate tectonics to the “slow carbon cycle” is to investigate seafloor weathering. The slow carbon cycle takes place over tens of millions of years, driven by a series of chemical reactions and tectonic activity and is part of Earth’s life insurance, as it has maintained the planet’s habitability throughout a series of hothouse climates punctuated by ice ages. We were able to build on ocean drilling results and laboratory experiments from other groups to understand how of the storage of C02 and carbon in the ocean crust changes through time, as a function of the age of the ocean crust and of the bottom water temperature, which is quite important, because temperature strongly modulates this process. This is something we published in Science Advances in 2018.It is quite a cool paper!

We actually need geochemists and geophysicists to work together

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

The biggest change in my time in academia is the emergence of artificial intelligence (AI) and data science as a universal, rapidly growing research area and set of tools to analyse big or complex data, to assimilate data into models and to quantify uncertainties in process models and predictions. There is an urgent need for all Earth science students to become literate in these areas. By the time this year’s first-year students will graduate, they will be entering a transformed workplace unlike any their parents knew. However, the need for changing staff profiles and undergraduate curricula are often recognised and implemented much more slowly than the evolution of the world outside of our ivory towers. But this change needs to happen.

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

Most of the problems that we are left with are complicated problems that aim at understanding the complexity of the Earth system. That could be anything from structural geology to understanding physical and chemical problems. An example is the field of geodynamics. It is mostly dominated by looking at the physics of mantle convection. And then there is another bunch of people who look at the chemistry of the mantle. These fields have not been properly connected. We actually need geochemists, geophysicists and geologists to work together to try to understand how the Earth system works. Then we need to connect deep Earth evolution to surface environments, understand the exchange of fluids and volatiles between the solid Earth and the oceans and atmosphere.

You actually have to be in for the long game

Building a geological time machine at the University of Sydney, 2009. Credit: Rhiannon McKeon

What was your motivation, starting as an Early Career Researcher? Did you always see yourself staying in academia?

As a kid I was inspired to become a scientist by taking long walks along Germany’s Baltic Sea beaches, picking up unusual rocks and fossils along the way, none of which really belonged there. They had all originated in Scandinavia, where they had been scraped off by moving glaciers and dropped much further south after being transported in the ice over 1000 km. I still have a small collection of these rocks and fossils which include remains of sea urchins and squids from the Cretaceous period and over 400 My old pieces of ancient reefs that had once been buried deeply in the Scandinavian crust. I always wanted to be an academic, I wanted to understand how the Earth works, over geological time. I never had any second thought about that. I can see today that students are often quite confused about what they want to do. Because they are unsure about where the future might take them, they don’t end up focussing on any one subject and are not necessarily inclined to acquire skills that are deep and broad enough to excel. If you want to be successful at anything, you need to become really good at something, and persevere. Be good at something that you actually enjoy, and be in it for the long game.

Who inspires you?

I am inspired by the pioneers of open source software and open access data. Open science is the key to forming global research teams and advancing studies of the Earth system. I am inspired by Paul Wessel at the University of Hawaii, who, together with his colleagues, built one of the most extensive geo-software systems, the Generic Mapping Tools, over the past ~30 years; I started using an early version of it during my PhD and am still using it! In terms of open access data, one of my heroes in Earth Sciences is David Sandwell at the Scripps Institution of Oceanography, who revolutionised our knowledge of the deep structure of the ocean basins by making his global satellite gravity maps freely available to the community. On the geochemistry side, Kerstin Lehnert at the Lamont-Doherty Earth Observatory has accomplished an amazing feat by leading the EarthChem database effort, and now the Interdisciplinary Earth Data Alliance, a nice example for bringing geochemistry and geophysics together.

What is the best advice you ever received?

Not long after I arrived at the University in Sydney, the then professor of geophysics pulled me aside and said: “I have one piece of advice for you: Stay away from University politics and just do your own thing“. That’s exactly what I have done and that’s the best advice I have ever received. It is easy to get carried away with politics at many different levels…

Stay away from University politics

What advice would you give to students?

You have to figure out what you enjoy and what you would like to do. You should not choose a career because you think this career will pay more money than another one, or it may seem there are more jobs in one field than another. The advice I would give to students is to try to figure out what you actually enjoy doing and just go and do that. The future will be driven by big and complex data analysis and simulation and modelling, but there will still be a need for people who can identify a rock. If you can do both, you’ll have a job without any doubt!

 

Dietmar Müller, November 2018 in his office. Credit: Jo Condon, AuScope

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Cesar Ranero

Meeting Plate Tectonics – Cesar Ranero

These blogposts present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Get to know them, learn from their experience, discover the pieces of advice they share and find out where the newest challenges lie!


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

Features from the field: Folding

Features from the field: Folding

Folding is one of the most common geologic phenomena in the world. I should start with defining the term ‘deformation’ in order to understand the folding process better.

In geology, deformation is an alteration of the size or shape of rocks. Deformation is caused by stress, the scientific term for force applied to a certain area. Stresses on rocks can stem from various sources, such as changes in temperature or moisture, shifts in the Earth’s plates, sediment buildup or even gravity.

Z folds in the Alba Syncline. Did they really make it? They are geologist so they can 🙂 Photo credit: by Erin Kennedy distrubted via  geology.blogs.brynmawr.

There are three types of rock deformation. Elastic deformation is temporary and is reversed when the source of stress is removed. Ductile deformation is irreversible, resulting in a permanent change to the shape or size of the rock that persists even when the stress stops. A fracture is considered as brittle deformation, whereas folding is considered as ductile deformation. The third one type is viscous deformation is the behavior of the fluids such as magma.

Certain factors determine which type of deformation rocks will exhibit when exposed to stress. These factors are rock type, strain rate, pressure and temperature. For instance, higher temperatures and pressures encourage ductile deformation. This is common deep within the Earth, where, due to higher temperatures and pressure than nearer the surface, rocks tend to be more ductile.

But, nowadays we find rocks from deep regions exposed at the surface. How? The answer is ‘uplift’, the balance between the rate of magma intrusion into the crust, erosion, and the relative densities of the continental crust and the mantle.

Anticline Trap. Anticline is a structural trap for petroleum.  Image reproduced from original source.

Folding is a manner for sedimentary and metamorphic rocks. Different layers in those rocks help geologist to understand structures.

Last but not least, Anticlines (type of folding) are important types of “structural traps” in petroleum geology.

To sum it up, Folds are significant structures for either in structural or economic geology. They are, moreover, remarkable phenomenon for people due to their great looking like many other geologic structure.

Features from the field: Slickenside Lineations

Features from the field: Slickenside Lineations

In this Tectonics and Structural Geology blog we will use different categories for our blog-posts. The first category we present to you is all about field geology: “Features from the field”. One of our bloggers, Mehmet Köküm, spends a lot of time in the field for his PhD and will share some of the features used in structural geology with us. This edition of ‘Features of the Field’ will be all about Slickenside lineations!

Paleostress Studies Reveals Deformation Mechanism 

It is assumed that faults are formed as pure strike slip or dip-slip faults. However, we widely come across oblique faults. If they are formed as pure strike-slip or dip-slip faults, then something should have affected its behavior. This can be done by many things, such as a change in tectonic regime or a block rotation. Many areas in the world have experienced several different tectonic regimes in the past. Faults should have been affected by these tectonic regime changes. A normal fault could have worked as a reverse fault in the past or vice versa. In other words, if we may figure out a faults’ past behavior, we could figure out the evolution of tectonic regimes in the related area.

Within this blog I will explain how structural geologists determine the behavior of a fault in the past and present. The principle purpose of my PhD project is to determine the deformation mechanism and the relation between past and present behavior of the East Anatolian Fault (EAF) by using paleostress analysis. The EAFZ is one of the most active intracontinental transform faults in Turkey.

During a field trip as part of my PhD project, one of the goals was to find slickenside lineation on a slip surface along the East Anatolian Fault in Turkey. Slicken-lines are series of parallel lines on a fault plane and represent the direction of relative displacement between the two blocks separated by the fault. Hence, direction and sense of slip can be obtained from slickenside lineation on a fault plane. Knowing this for numerous faults helps us to understand previous and present behavior of faults.

The aim of using slickenside lineation is to calculate the paleostress tensor. Paleostress tensors provide a dynamic interpretation (in terms of stress orientation) to the kinematic (movement) analysis of brittle features. Paleostress tensor analysis enables identification of the stress history of a studied area.

There are two principal types of slicken-lines: those that form by mechanical abrasion (striations) and those formed by mineral fibrous growth (mineral fiber lineations). The former can occur either in relief or groove on a fault surface. It can be a small quartz grain or larger grain causing striations on a fault surface. The latter developed due to crystal growth fibres or other grains being crystallized during fault slip. Most are made of calcite, quartz, gypsum etc. These two types of lineations are reliable criteria for calculating the paleostress tensor and common in low-grade metamorphic rocks and sedimentary rocks.

In this work, the key issue is to find and collect as much fault slip data sets as possible. In that sense, it is important to know what kind of rocks may include slicken-lines. Striations or slicken-lines are particularly found on limestone, sandstone and claystone. Moreover, mineral fiber lineations are seen most in limestone. Therefore, limestone should be investigated in more detail to collect fault slip data.

Paleostress studies require great care, effort, and attention in the field, but its outcomes for the behavior of the faults are important, since they reveal the tectonic evolution of the area. For this reason, many structural geologist touch on palestress studies in their work in order to relate observed structures to the causative tectonic forces.