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Tectonics and Structural Geology

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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

Minds over Methods: Reconstruction of salt tectonic features

Minds over Methods: Reconstruction of salt tectonic features

What is the influence of salt tectonics on the evolution of sedimentary basins and how can we reconstruct such salt features? Michael Warsitzka, PhD student at the Friedrich Schiller University of Jena, explains which complementary methods he uses to better understand salt structures and their relation to sedimentary basins. Enjoy!

 

Credit: Michael Warsitzka

Reconstruction of salt tectonic features from analogue models and geological cross-sections

Michael Warsitzka, PhD student, Institute of Geosciences, Friedrich Schiller University Jena

Salt tectonics, as a sub-discipline of structural geology, describe deformation structures developing due to the special deformation behaviour of salt (as synonym for a sequence of evaporitic rocks). Salt behaves like a viscous fluid over geological time scales and, therefore, it may flow due to lateral differences in thickness and density of the supra-salt layers. This influences the structural evolution of sedimentary basins, because salt flow can modify the amount of regional subsidence of the basin. Local sinks (“minibasins”) develop in regions from where salt is squeezed out and salt structure uplifts, e.g. diapirs or pillows evolve in regions of salt influx. Unfortunately, temporal changes of salt flow patterns are often difficult to reconstruct owing to enigmatic ductile deformation structures in salt layers. Understanding the evolution of salt-related structures requires either forward modelling techniques (e.g. physically scaled sandbox experiments) or restoration of sedimentary and tectonic structures of the supra-salt strata.

In my PhD thesis, I tried to integrate both, analogue modelling and restoration, to investigate salt structures and related minibasins developed in the realm of extensional basins. The sandbox model is a lab-scale, simplified representative of natural salt-bearing grabens, e.g. the Glückstadt Graben located in the North German Basin (Fig. 1). A viscous silicone putty and dry, granular sand were used to simulate ductile salt and brittle overburden sediments. Cross sections were cut through the model at the end of each experiment to conduct reconstruction of the final experimental structures. The material movements were monitored with a particle tracking velocimetry (PIV) technique at the sidewalls of the experimental box.

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Fig 1: 2D restoration of the supra-salt (post-Permian) strata in the Glückstadt Graben (Northern Germany). Credit: Michael Warsitzka

Using experimental and geological cross sections, structures in the overburden of the ductile layer can be reconstructed, if present-day layer geometries and lithologies of the overburden strata can be identified. From natural clastic and carbonatic sediments we know that they compact with burial, reducing the layer thickness. Therefore, the reconstruction procedure sequentially removes the uppermost layer and layers beneath are decompacted and shifted upwards to a horizontal surface (Fig. 2). The sequence of decompaction and upward shifting is then repeated until the earliest, post-salt stage is reached (Fig. 1). It intends to restore the initial position, shape and thickness of each reconstructed layer.

In analogue experiments, no decompaction is necessary, because the compressibility of the granular material is insignificant for depths of a few centimetre. Restoration can be directly applied to coloured granular layers revealing detailed layer geometries for each experimental period (Fig. 2a). The PIV technique displays coeval material movement and strain patterns occurring during the subsidence of the experimental minibasins (Fig. 2b). Based on the observation that the experimental structures resemble those reconstructed from the natural example (Glückstadt Graben during the Early Triassic, Fig. 1), it can be inferred that strain patterns observed in the experiments took place in a similar manner during the early stage of extensional basins. This demonstrates the advantage of applying both methods. First, original geometries of basin structures can be determined from the restoration and then reproduced in the model. If the restored geometries are suitably validated by the models, the kinematics observed in the model can be translated back to nature and help to understand the effect of salt flow on the regional subsidence pattern.

Fig 2: Result of an analogue model showing (a) reconstructed sand layers restored from a central cross section, and (b) monitored displacement and strain patterns in the viscous layer above the left basal normal fault. Credit: Michael Warsitzka

Minds over Methods: Sensing Earth’s gravity from space

Minds over Methods: Sensing Earth’s gravity from space

How can we learn more about the Earth’s interior by going into space? This edition of Minds over Methods discusses using satellite data to study the Earth’s lithospere. Anita Thea Saraswati, PhD student at the University of Montpellier, explains how information on the gravity of the Earth is obtained by satellites and how she uses this information to get to know more about the lithosperic structure in subduction zones.

 

Sensing Earth’s gravity from space

Anita Thea Saraswati – PhD student, Géosciences Montpellier

From the basic physics we all know that the value of the gravity is a constant 9.81 meter per second squared. This assumption would be true if the Earth were a smooth nonrotating spherical symmetric body made of uniform element and material. However, because of the Earth’s rotation, internal lateral density variation, and the diversity of the topography (including mountains, valleys, oceans and glaciers), the gravity  varies all over the surface. These tiny changes in gravity due to the mass variations could be a crucial hint for understanding the structure of the Earth, both on the surface and at depth.

The determination of Earth’s gravity field has benefited from various gravity satellite missions that have been launched recently. Among them are the Challenging Minisatellite Payload (CHAMP) (2000-2010), the Gravity Recovery and Climate Experiment (GRACE) (2002-recent), and most recently the Gravity field and steady-state Ocean Circulation Explorer (GOCE) (2009-2013). From these missions, finally a global high quality coverage of Earth’s gravity field became available. (Yay!)

GRACE observation data are very useful for the temporal analysis of changes in gravity. For example to detect the gravity signal before and after a big earthquake, like the Sumatra Mw 9.1 (2004) and Tohoku Mw 9.1 (2011) ones. By analyzing the changes of gravity signal during a certain period of time, it could also be used to detect the drought over a large scale area, which is used in several areas in Africa and Australia.

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Design of GOCE satellite observation. A geoid’s shape is showed on the bottom left. On the top right, the GOCE gravity gradients in six components. (Source : ESA)

 

Meanwhile, GOCE is very suitable for the construction of a static model of Earth’s gravity field. Since this satellite has a very low orbit, ~250 km above mean sea level, it has a better spatial resolution. Its accuracy is also better than the previous missions, up to 1 mGal. GOCE is equipped with a gradiometer, which measures the gravity acceleration in three directions (x, y, and z). Afterwards this information is processed into a gravity-gradient dataset containing six components (XX, XY, XZ, YY, YZ, ZZ).

This gravity gradient is the first derivative of the gravity acceleration, which provides us better information about the geometry of the earth’s structure than the gravity acceleration itself. For my PhD, I use this gravity gradient dataset to analyze the lithospheric structure of subduction zones. Before treating the GOCE observation data, I am developing a computational code to calculate the gravity and gravity gradient due to the effect of topography, also called the topographic reduction. The observed gravity and gravity gradient values will be reduced by this topography effect in order to get the anomaly signal. This means that only the signal due to other geodynamic phenomena over the observed area (e.g. slab, isostasy, mantle plum, etc.) is left. By doing further processing, we can obtain the lateral variations of the lithospheric structure in the study areas and then investigate the correlation with the occurrence of mega-earthquakes in these subduction zones.

Since there is still some ambiguity about the information that is produced by gravity data only, it is better to combine the use of them with others geophysical or geological measurements, e.g. seismic tomography measurements and magnetic field observations.

 

Global coverage of GOCE gravity gradient (in milliEötvös) in radial direction (ZZ) (Panet, I. et al., 2014)

 

Reference:

Panet, I., Pajot-Métivier, G., Greff-Lefftz, M., Métivier, L., Diament, M. and Mandea, M., 2014. Mapping the mass distribution of Earth/’s mantle using satellite-derived gravity gradients. Nature Geoscience7(2), pp.131-135.

Minds over Methods: studying dike propagation in the lab

Minds over Methods: studying dike propagation in the lab

Have you ever thought of using gelatin in the lab to simulate the brittle-elastic properties of the Earth’s crust? Stefano Urbani, PhD student at the university Roma Tre (Italy), uses it for his analogue experiments, in which he studies the controlling factors on dike propagation in the Earth’s crust. Although we share this topic with our sister division ‘Geochemistry, Mineralogy, Petrology & Volcanology (GMPV)’, we invited Stefano to contribute this post to ‘Minds over Methods’, in order to show you one of the many possibilities of analogue modelling. Enjoy!

 

dscn0024Using analogue models and field observations to study the controlling factors for dike propagation

Stefano Urbani, PhD student at Roma Tre University

The most efficient mechanism of magma transport in the cold lithosphere is flow through fractures in the elastic-brittle host rock. These fractures, or dikes, are commonly addressed as “sheet-like” intrusions as their thickness-length aspect ratio is in the range of 10-2 and 10-4 (fig.3).

Understanding their propagation and emplacement mechanisms is crucial to define how magma is transferred and erupted. Recent rifting events in Dabbahu (Afar, 2005-2010) and Bardarbunga (Iceland, 2014, fig.1) involved lateral dike propagation for tens of kilometers. This is not uncommon: eruptive vents can form far away from the magma chamber and can affect densely populated areas. Lateral dike propagation has also been observed in central volcanoes, like during the Etna 2001 eruption. Despite the fact that eruptive activity was mostly fed by a vertical dike to the summit of the volcano, several dikes propagated laterally from the central conduit and fed secondary eruptive fissures on the southern flank of the volcanic edifice (fig.2). Lateral propagation can hence occur at both local (i.e. central volcanoes) and regional (i.e. rift systems) scale, suggesting a common mechanism behind it.

fig-3mario-cipollini

Fig. 2 Lava flow near a provincial road, a few meters from hotels and souvenir shops, during the 2001 lateral eruption at Etna. Credit: Mario Cipollini

Therefore, it is of primary importance to evaluate the conditions that control dike propagation and/or arrest to try to better evaluate, and eventually reduce, the dike-induced volcanic risk. Our knowledge of magmatic systems is usually limited to surface observations, thus models are useful tools to better understand geological processes that cannot be observed directly. In particular, analogue modelling allows simulating natural processes using scaled materials that reproduce the rheological behavior (i.e ductile or brittle) of crust and mantle. In structural geology and tectonics analogue modelling is often used to understand the nature and mechanism of geological processes in a reasonable spatial and temporal scale.

d_grad_dike57_080Field evidence and theoretical models indicate that the direction of dike propagation is controlled by many factors including magma buoyancy and topographic loads. The relative weight of these factors in affecting vertical and lateral propagation of dikes is still unclear and poorly understood. My PhD project focuses on investigating the controlling factors on dike propagation by establishing a hierarchy among them and discriminating the conditions favoring vertical or lateral propagation of magma through dikes. I am applying my results to selected natural cases, like Bardarbunga (Iceland) and Etna (Italy). To achieve this goal, I performed analogue experiments on dike intrusion by injecting dyed water in a plexiglass box filled with pig-skin gelatin. The dyed water and the gelatin act as analogues for the magma and the crust, respectively. Pig-skin gelatin has been commonly used in the past to simulate the brittle crust, since at the high strain rates due to dike emplacement it shows brittle-elastic properties representative of the Earth’s crust. We record all the experiments with several cameras positioned at different angles, taking pictures every 10 seconds. This allows us to make a 3D reconstruction of the dike propagation during the experiment.

In order to have a complete understanding of the dike intrusion process it is essential to compare the laboratory results with natural examples. Hence, we went to the field and studied dikes outcropping in extinct and eroded volcanic areas, with the aim of reconstructing the magma flow direction (Fig. 3). This allows validating and interpreting correctly the observations made during the laboratory simulations of the natural process that we are investigating.

fig-1

Fig. 3 Outcrop of dikes intruding lava flows. Berufjordur eastern Iceland.

 

Minds over Methods: Numerical modelling

Minds over Methods: Numerical modelling

Minds over Methods is the second category of our T&S blog and is created to give you some more insights in the various research methods used in tectonics and structural geology. As a numerical modeller you might wonder sometimes how analogue modellers scale their models to nature, or maybe you would like to know more about how people use the Earth’s magnetic field to study tectonic processes. For each blog we invite an early career scientist to share the advantages and challenges of their method with us. In this way we are able to learn about methods we are not familiar with, which topics you can study using these various methods and maybe even get inspired to use a multi-disciplinary approach! This first edition of Minds over Methods deals with Numerical Modelling and is written by Anouk Beniest, PhD-student at IFP Energies Nouvelles (Paris).

 

Approaching the non-measurable

Anouk Beniest, PhD-student at IFP Energies Nouvelles, Paris

‘So, what is it that you’re investigating?’ It’s a question every scientist receives from time to time. In geosciences, the art of answering this question is to explain the rather abstract projects in normal words to the interested layman. Try this for example: “A long time ago, the South American and African Plate were stuck together, forming a massive continent, called Pangea, for many millions of years. Due to all sorts of forces, the two plates started to break apart and became separated. During this separation hot material from deep down in the earth rose to the surface increasing the temperature of the margins of the two continents. How exactly did this temperature change over time, since the separation until present-day? How did this change affect the basins along continental margins?”

These are legitimate questions and not easy to answer, since we cannot measure temperature at great depth or back in time. In this first post on numerical methods, we will be balancing between geology and geophysics, highlighting the possibilities and limits of numerical modelling.

The migration of ‘temperature’ through the lithosphere is a process that takes time and depends heavily on the scale you look at. Surface processes that affect the surface temperature can be measured and monitored, yielding interesting results on the present-day state and variations of the temperature. The influence of mantle convection cycles and radiogenic heat production are already more difficult to identify, take much more time to evolve and might not even affect the surface processes that much. Going back in time to identify a past thermal state of the earth seems almost impossible. This is where numerical models can be of use, to improve, for example, our understanding on the long-term behaviour of ‘temperature’.

Temperature is a parameter that affects and is affected by a variety of processes. When enough physical principles are combined in a numerical model, we can simulate how the temperature has evolved over time. All kinds of different parameters need to be identified and, most importantly, they need to make sense and apply to the observation or process you try to reproduce. Some of these parameters can be identified in the lab, like the density or conductivity of different rock types. Others need to be extracted from physical or geological observations or even estimated.

Once the parameters have been set, the model will calculate the thermal evolution. It is not an easy task to decide if a simulation approaches the ‘real’ history and if we can answer the questions posed above. We should always realise that thermal model results at best approach the real world. We can learn about the different ways temperature changes over time, but we should always be on the hunt to find measurements and observations that confirm what we have learned from the simulations.

temperature_quick