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tectonics

Imaggeo on Mondays: Mola de Lord

Imaggeo on Mondays: Mola de Lord

From the easterly Atlantic waters of the Bay of Biscay to the Catalan wild coast (Costa Brava) in the west, the Spanish Pyrenees stretch 430 km across the north of the country. At the foothills of the Catalan Pyrenees you’ll find the Pre-Pyrenees. Despite not reaching the soaring heights of the peaks of the Pyrenees, they nonetheless offer important insights into the geology of the range and stunning panoramas, such as the one featured as today’s Imaggeo on Mondays image. In today’s post, Sarah Weick, a researcher at the Georg August University in Göttingen, explains why the foothills of the mountain belt are a structural geologist’s playground.

The picture was taken from the top of the flat-topped mountain ‘Mola de Lord’, with a beautiful view over the turquoise-blue water of the river Cardener and growth folds, characterised by a significant increase in throw with depth, caused by their syn-sedimentary development The over 1000 m-high mountain belongs to Vall de Lord, close to the Sant Llorenc Growth Structure, formed of folded sedimentary rocks of marine and continental origin that developed from Eocene to Oligocene and display local angular unconformities (where horizontally parallel sedimentary rocks are deposited atop previously tilted layers). Moreover, it is excellently preserved as a structure in the footwall of the Pyrenees and helps to understand how sedimentary deposits are reorganized during the development of a syn-sedimentary growth structure and how they may distribute between the foreland basin and the mountain belt. Outcrops on the mountain top are of conglomeratic composition with clasts and fossilized nummulites – lense-shaped single-celled sea creatures with shells that lived from Paleocene to Oligocene.

As a geologist, Mola de Lord is not the only remarkable location in Catalonia. On a greater scale, the table mountain belongs to the Spanish Pyrenees. There, hikers can experience parts of untouched nature, and witness the mountain’s geological past: from eroded carbonate karsts with unique shapes to the Ebro basin.

The Pyrenees are located in southwest Europe on the border between France and Spain. The Upper Cretaceous to Miocene collision and subduction of the Iberian microplate under the European plate initiated the orogeny, which went through two main phases. The tectonic changes during the Alpine Orogeny that started 66 Ma ago and some earlier Jurassic activity, caused a compressive regime and thus produced a lot of pressure that caused folding on different scales and the continuing orogenic growth. Deformation occurred also after the collision. The orogenic basement can be described by inherited folded formations over a granitic basement.

 By Sarah Weick, researcher at the Georg August University in Göttingen.

 

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

Imaggeo on Mondays: Dragon Blood Tree

Imaggeo on Mondays: Dragon Blood Tree

On a small and isolated island in the Indian Ocean you’ll find an endemic population of Dragon Blood Trees (Dracaena cinnabari). Burly, with an interesting umbrella-shaped fractal canopy, these unique trees are a sight to behold.

To see them for yourself, you’ll have to travel to the little known Socotra archipelago. Off the coast of Somalia, but belonging to Yemen, the group of islands boast an impressive assortment of endemic plant life, making them know as the ‘Galapagos of the Middle East’.

Crucial to the uniqueness of the flora and fauna of the archipelago is Socotra’s geographical position and how it came to be there. The African plate extends out from the Horn of Africa, east of the Guardafui graben, in what is known as the Socotra Platform. Here you’ll find four islands, of which Socotra is the largest, as well as two scars of former islands which have been eroded away by wave action.

At in excess of 240 kilometres east of the Horn of Africa and 380 kilometres south of the Arabian Peninsula there is no getting away from the remoteness of the archipelago. Testament to this is the presence of seven endemic bird species on the island.

So how did the strange looking Dragon Blood Tress and other flora and fauna come to populate Socotra and its neighbours?

It is thought that until 43 million years ago, the Socotra archipelago remained largely submerged. Although there were some brief emergence events during the Jurassic/Cretaceous and Cretaceous/Tertiary, given the area was re-submerged after this time, they are considered of little importance.

Subsequently, Socotra Island continued to grow due to uplift. Despite changing sea depths, there are indications that land species could migrate over from mainland African and Arabia via land bridges and stepping stones. With ‘cousin’ species present in Somalia and Arabia, it’s likely the Dragon Blood Trees originated there in the distant past.

From 16,000 years ago onwards, the isolation of the archipelago grew due to a combination of further flooding of low-lying areas, the formation of large basins (namely the Guardafui and Brothers basin) and increasing distance from the mainland. Since then, the species on Socotra and its neighbouring islands have had time to evolve and adapt to their surroundings, become different, albeit sometimes closely related, to their continental counterparts.

It was only around the third century BC that Socotra started to emerge from its isolation after attracting the attention of the young Alexander the Great during one of his war campaigns. The island then became known in the Hellenic World and all the Mediterranean for being one of the main sources of incense, myrrh and dragon’s blood powder resin.

As Socotra commercial importance gradually faded away in the centuries to follow, Dragon’s Blood resin remained one of the main exports of the island. The resin was considered a precious ingredient of dyes, lacquers and varnishes, and the legend has it that Antonio Stradivari – the famous seventeenth century luthier from Cremona – used Socotra’s red resin to varnish his violins.

yemen

The landscape of the Socotra archipelago. Credit: Annalisa Molini via Flickr.

One thing is for sure, as Annalisa Molini’s (Assistant Professor at the Institute Center for Water and Environment, in Abu Dhabi), photographs attest to: Socotra island and it’s Dragon Blood Trees are stunning.

However, the remoteness of the Socotra archipelago and the current armed conflict in Yemen threaten to put at risk the island’s important and unique natural heritage; one that no doubt, should be protected and preserved.

References

M. Culek: Geological and morphological evolution of the Socotra Archipelago (Yemen) from the biogeographical view, Journal of Landscape Ecology, 6, 3, 84–108, DOI: 10.2478/jlecol-2014-0005, 2014

Brown, B.A. Mies, Vegetation Ecology of Socotra, Springer Netherlands, Dordrecht, 2012. doi:10.1007/978-94-007-4141-6.

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

Imaggeo on Mondays: An explosive cloud

Imaggeo on Mondays: An explosive cloud

One of the world’s most volcanically active regions is the Kamchatka Peninsula in eastern Russia. It is the subduction of the Pacific Plate under the Okhotsk microplate (belonging to the large North America Plate) which drives the volcanic and seismic hazard in this remote area. The surface expression of the subduction zone is the 2100 km long Kuril-Kamchatka volcanic arc: a chain of volcanic islands and mountains which form as a result of the sinking of a tectonic plate beneath another.  The arc extends from Hokkaido in Japan, across the Kamchatka Peninsula, through to the Commander Islands (Russia) to the Northwest. It is estimated that the Pacific Plate is moving towards the Okhotsk microplate at a rate of approximately 79mm per year, with variations in speed along the arc.

There are over 100 active volcanoes along the arc. Eruptions began during the late Pleistocene, some 126,000 years ago at a time when mammoths still roamed the vast northern frozen landscapes and the first modern humans walked the Earth.

Many of the volcanoes in the region continue to be active today. Amongst them is Karymsky volcano, the focus of this week’s Imaggeo on Mondays image. Towering in excess of 1500 m above sea level (a.s.l), the volcano is composed of layers of hardened lava and the deposits of scorching and fast moving clouds of volcanic debris knows as pyroclastic flows. You can see some careering down the flanks of the volcano in this image of the July 2004 eruption. The eruptive column is the result of a

“strong Vulcanian-type explosion, with the cloud quickly rising more than 1 km above the vent. The final height of the eruption cloud was approximately 3 km and in the image you can clearly see massive ballistic fallout from multiple hot avalanches on the volcanoes slopes,”

explains Alexander Belousov, a Senior Researcher at the Institute of Volcanology and Seismology in Russia and author of this week’s photograph.

 

USGS map of the Kuril-Kamchatka trench, showing earthquake locations and depth contours on downgoing slab. Credit: USGS, USGS summary of the 2013 Sea of Okhotsk earthquake, via Wikimedia Commons.

USGS map of the Kuril-Kamchatka trench, showing earthquake locations and depth contours on downgoing slab. Credit: USGS, USGS summary of the 2013 Sea of Okhotsk earthquake, via Wikimedia Commons.

If you pre-register for the 2015 General Assembly (Vienna, 12 – 17 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

GeoTalk: The mantle and models and measurements, oh my! Talking geophysics with Juan Carlos Afonso

This week in GeoTalk, we’re talking to Juan Carlos Afonso, a geophysicist from Macquarie University, Sydney. He explains how a holistic approach is crucial to understanding tectonic processes and how a little “LitMod philosophy” can go a long way to achieving this…

First, could you introduce yourself and tell us a little about what you are currently working on?

My name is Juan Carlos Afonso and I’m a geophysicist currently working at Macquarie University in Sydney, Australia.  My research interests lie in the fields of geophysics and geodynamics, and span many different geophysical and geological processes. My current research integrates a lot of different disciplines, such as mineral physics, petrology, geodynamics, lithospheric modelling, nonlinear inversion, and physics of the mantle, to explore and improve our understanding of lithospheric evolution and plate tectonics.

More specifically, I am interested in the thermochemical structure and evolution of the lithospheric mantle, the mechanical and geochemical interactions between tectonic plates and the sublithospheric upper mantle, and their effects on small- and large-scale tectonic processes. The lithosphere is critical to humans because it is the reservoir of most of the natural resources on which modern society depends, as well as the locus of important geological and biological process such as seismic activity, CO2-recycling, mineralisation events, and volcanism!

Juan Carlos out in the field! (Credit: Juan Carlos Afonso)

Juan Carlos out in the field! (Credit: Juan Carlos Afonso)

During EGU 2012, you received a Division Outstanding Young Scientists Award for your research into the lithosphere and its properties. Could you tell us a bit more about your work in this area?

First of all, it was such a humbling experience to receive this award. I really admire the previous awardees and it is a real honour to have received this award.

I was selected for this award based mainly on the work I did on combining different geophysical and geochemical datasets into a single conceptual framework that has become known as the “LitMod approach”. This theoretical and computational framework fully integrates geochemistry, mineral physics, thermodynamics, and geophysics in an internally-consistent manner*. And allows researchers from different disciplines – seismology, geodynamics, petrology, mineral physics, etc. – to construct models of the Earth that not only satisfy one particular set of observations, but a multitude of observations. This is of primary importance because it guarantees consistency between theories and models (i.e. you can’t cheat!), and results in better and more robust data interrogation and interpretation. This approach is being applied to a wide range of geodynamic and geophysical problems, from studying the water content of the mantle to inferring the thermal structure of Venus.

More recently, my colleagues and I presented the idea of multi-observable probabilistic inversion, a technique that is similar to CAT-scanning in medicine, but that we used to study the thermochemical (or thermo-chemical-mechanical) structure of the lithosphere and upper mantle. We showed that it is a feasible, powerful and general method that makes the most out of available datasets and helps reconcile disparate observations and interpretations. This unifying framework brings researchers from diverse disciplines together under a unique holistic platform where everything is connected to everything else and it will hopefully help understand the workings of the Earth in a more complete manner. But there is a lot of work yet to be done to achieve this!!

…and off duty! (Credit: Juan Carlos Afonso)

…and off duty! (Credit: Juan Carlos Afonso)

How can programmes like LitMod help improve our understanding of plate tectonics?

A great scientist recently said “Each single discipline within the geosciences has progressed tremendously over the 20th century; the problems now lie at the interfaces between the sub-disciplines and ensuring that all geoscientific data are honoured in integrated models. We are well beyond the time when scientists can present their interpretations based on mono-discipline thinking. We absolutely must think of the Earth as a single physico-chemical system that we are all observing with different tools.”  These sentences capture very well the spirit of the LitMod approach, which forces you to think about and interpret geoscientific data in a manner that ensures consistency (as much as possible!). I think one of the reasons for the interest in such an approach is the need for robust and easy-to-use tools that researchers from different disciplines can apply to their individual datasets (seismic, gravity, magnetotelluric, etc.) and explore the connections to other related datasets and disciplines  it helps researchers have a better understanding of the broader implications of their own models. It is also useful to petrologists interested in testing the geophysical and geodynamic implications of their petrological and geochemical models.

LitMod provides a platform wherein chemistry and physics are married such that models of lithosphere and sub-lithospheric mantle must be consistent with petrology, heat flow, topography, gravity, geoid, and seismic and electromagnetic observations. Too often we see models of the Earth, derived from a single dataset, that are incompatible with other observations. Some are better, some are worse. To have a model that explains all observations does not imply that the model is correct, but it does minimise the chances of being wrong! Plate tectonics and science in general use this concept to advance our knowledge of the Earth.

An important (if not the most important!) factor to mention here is that, as with any other project of this magnitude, LitMod would not be possible without the contribution of many scientists who unselfishly helped me to put things together. I’d like to thank Javier Fullea, James Connolly, Nick Rawlinson, Yingjie Yang, Alan Jones, Bill Griffin, Sue O’Reilly and Manel Fernandez for all their help and crucial input to the “LitMod philosophy”.

Sussing out an outcrop. (Credit: Juan Carlos Afonso)

Sussing out an outcrop. (Credit: Juan Carlos Afonso)

And importantly, how does it work?

The main idea is actually quite simple:  a valid physicochemical model of the Earth has to explain all available data in a consistent manner. In essence, this is one of the main steps of the scientific method, right? The LitMod approach is simply a way of constructing Earth models (either by forward or inverse modelling) that satisfy basic physical principles and observations. In a nutshell, LitMod says “you cannot try to fit an observation by changing one parameter of your model without having to change all other parameters in a physically and thermodynamically consistent way, which in turn will affect the prediction of all the other observations”. This is a nice idea, and it should provide robust results as long as what one thinks is consistent, is actually correct. At this stage, we are confident with most of our choices, but there still is much work to do to get a complete understanding of how to model all available datasets simultaneously and how much we can believe our results.

The problem lies in the details, of course, because it is not easy to explain all data consistently when our understanding of each individual dataset is incomplete to different degrees. Moreover, the resolution and sensitivities of different datasets are markedly different too. This problem has a potential solution though. We just need to study the individual problems more carefully (e.g. more laboratory experiments, field case studies, etc.) until we obtain an understanding of them that is similar to the others. In practise this is not straightforward, and many gaps still exist in the description of some problems. A current example, but not the only one, is the discrepancy between results obtained by the magnetotelluric and seismic methods. But even in this case, an integrated modelling approach helps us to isolate the root causes of these discrepancies and to propose new studies to remediate them; something that could not be done by analysing the data separately.

And don’t forget the computational problems, which I find particularly fascinating and frustrating at the same time. Surprisingly, there is not much written about formal joint inversions of multiple datasets; we are learning as we go, but that is what keeps it entertaining!

Lastly, what are your research plans for the future?

I cannot know for sure what I’ll be doing in 10 years (probably geochemistry!), but I can tell you what I’m going to be doing in the next 5-6. Besides continuing working on regional scale inversions with LitMod, I am currently starting to work on two fronts that may appear disconnected at a first glance, but are actually intimately related. The first front is the construction of whole-Earth thermo-chemical-mechanical models, similar to what we are doing with LitMod, but at planetary scale. The other is modelling multiphase reactive flow in the Earth’s mantle with some new numerical techniques. In the end, 5-6 years from now, I think these two fronts will coalesce into a single thick wall… but noone knows whether the wall will stand solid or collapse like a castle of cards… we have to try though!

Want to know more about LitMod? Check out these resources:

Afonso, J. C. , Fullea, J., Griffin, W. L. , Yang, Y., Jones, A. G. , Connolly, J. A. D., O’Reilly, S. Y.: 3D multi-observable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle. I: a priori petrological information and geophysical observables. J. Geophys. Res., 118, 2586–2617, 2013.

Afonso, J. C., Fullea, J., Yang, Y., Connolly, J. A. D., Jones, A. G.: 3D multi-observable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle. II: General methodology and resolution analysis. J. Geophys. Res., 118, 1650–1676, 2013.

Fullea, J., Afonso, J. C., Connolly, J. A. D., Fernàndez, M., García-Castellanos, D., Zeyen, H.: LitMod3D: an interactive 3D software to model the thermal, compositional, density, rheological, and seismological structure of the lithosphere and sublithospheric mantle. Geochem. Geophys. Geosyst., 10, 2009.

*What is an internally consistent model?

By “internal consistency” I mean that all calculated parameters (e.g. thermal conductivity, bulk modulus, etc.) and observables (e.g. dispersion curves, travel times, et.c) are only and ultimately dependent on temperature, pressure, and composition (the fundamental independent variables), while being linked together by robust and sound (typically nonlinear) physical theories. This guarantees that a local change in properties (like density), which may be required to improve the fitting of a particular observable, will also be reflected in all other observables in a thermodynamically and physically consistent manner. It also implies that no linearity between observables needs to be assumed; each observable responds according to its own governing physical theory (e.g. sound propagation).

If you’d like to suggest a scientist for an interview, please contact Sara Mynott.