Culture
Jiří Žák on the Orogenies that Shaped Central Europe
In this episode of Geology Bites, Oliver Stremple interviews Professor Jiří Žák about the significant orogenic events that shaped Central Europe, focusing on the Codomian and Varyskan orogenies. T...
Jiří Žák on the Orogenies that Shaped Central Europe
Culture •
0:00 / 0:00
Interactive Transcript
spk_0
This is geology bites with Oliver Stremple.
spk_0
What events in the geological past were responsible for shaping central Europe?
spk_0
In earlier episodes I talked to Ulf Lindemann about the assembly of central Europe during
spk_0
the Paleozoic and with Rob Butler on the origin of the Alps in the much more recent past.
spk_0
Here we talk about two Arrogynes that also played a key role in the story.
spk_0
First the Codomian Arrogyny that lasted from the late Neoprotrozoic to the early Cambrian,
spk_0
i.e. from about 700 million years ago to about 425 million years ago,
spk_0
and second the Varyskin Arrogyny that took place in the late Paleozoic from about 380 to 280 million years ago.
spk_0
Yuri Juck has been studying the geology of central Europe for over 25 years using methods
spk_0
ranging from structural studies in the field to detritle Zergon geochronology.
spk_0
He is a professor at the Institute of Geology and Pallionology at Charles University in Prague.
spk_0
Yuri Juck, welcome to geology bites.
spk_0
Thank you very much for inviting me. I'm glad to be here in this podcast.
spk_0
Before we talk about individual Arrogynes, let's try to place this in the wider tectonic context
spk_0
of the assembly and breakup of supercontinence, the so-called Wilson cycle that you break up a supercontinent
spk_0
and then it reforms roughly every 500 million years or so.
spk_0
This period that we're talking about, how does that fit into the Wilson cycle?
spk_0
This Wilson cycle would be positioned on a time axis between the supercontinent Rodinia
spk_0
and supercontinent Pangaea. In the Mesopotamian and the Mesopotamian and the Mesopotamian times
spk_0
we have here a supercontinent Rodinia which broke up and part of the results of this breakup was Gondvana
spk_0
and then we'll probably talk about it more, which was Pangaea which formed during late Paleozoic.
spk_0
All the processes we'll be talking about occurred in between.
spk_0
So we are in terms of a supercontinent cycle in between Rodinia and Pangaea.
spk_0
In terms of Wilson cycle it's a little bit more complicated because Wilson cycle it's only one of the forms of supercontinent breakup and assembly
spk_0
so it implies that you create an ocean and then you close the same ocean.
spk_0
Here what we have the record in Central Europe it was much more complex.
spk_0
There are more oceanic basins, more terrains involved so the history is so more complex than the simple Wilson cycle.
spk_0
But in terms of supercontinent cycle we can track processes which happened from the breakup of Rodinia to the assembly of Pangaea.
spk_0
So Europe today is part of Eurasia so that is itself a pretty massive continental block.
spk_0
So during the assembly of Europe was this leading to greater and greater malgamation of terrains that eventually including the Caledonian Rogy and then after the Vyriscan
spk_0
sort of basically led to the formation of Pangaea. Is that really this very high level picture?
spk_0
On a larger scale we were right but on a smaller scale we should not forget the Codomian origin which actually formed much of crust
spk_0
which we see now in western and eastern Europe and the younger Vyriscan origin a simply recycled this material.
spk_0
So I would argue that the main crustal forming event, maybe even most important crustal forming event was the Codomian origin and the late Proterozoic to Elipolosovic times.
spk_0
It really created new crust. The Vyriscan origin was collisional and it largely recycled this Codomian basement.
spk_0
Okay so let's talk about the Codomian Arrogyny. Can you walk us through a little bit more about what happened?
spk_0
So first of all it should be mentioned that although the Codomian origin was first defined in Europe it was more likely a global scale orrgynic event
spk_0
because it has been proposed that at the end of no Proterozoic and in the beginning of Pallerozoic we are talking about processes that happened about 750 to 500 million years ago.
spk_0
Almost entire Gondvana was surrounded by broadly co-evil and linked originic belts.
spk_0
So what we now call the Avolonian Codomian belt was only one segment of a global orrgynic system.
spk_0
And key feature of this global orrgyn was subduction of large oceanic plates beneath the Gondvana mainland forming sort of subduction on girdle.
spk_0
And in effect the subduction controlled formation of extensive tracks of accretionary villages, volcanic arcs, back arc basins which were attached to the upper overriding plate.
spk_0
So in terms of recent analogy this is pretty much similar what we see now in the western Pacific.
spk_0
In the western Pacific then yes, okay you get subduction and you get all the consequences or corollaries associated with subduction.
spk_0
So do we see those today? Can we find the remnants of those in Europe? I mean can we see accretionary wedges or where volcanic arcs used to be or remnants of mountain chains?
spk_0
Yes we do and Akchale if you look on a geologic map of Europe the fragments of the former Avolonian Codomian belt are now scattered all over western and central Europe with the main exposures being the Iberian Massif in Spain and Portugal, Armory Conmasif in France and of course the Bohemian Massif here in central Europe.
spk_0
However we find them frequently also within the Alpine originic system. So they were recycled during the Varscan origin and again recycled during the Alpine originate.
spk_0
And in this case they extend further east and south into the Alps, Carpathians and even further into Bulgaria, Greece, Turkey and even to Iran.
spk_0
So in all these places we find the relics or fragments of the former accretionary originic belt of the former Avolonian Codomian active margin and I would argue that in here in Bohemian Massif we have one of the best preserved fragments of this margin because we have here a relict of an Ophelite.
spk_0
We have a relict of an accretionary belt, we have a relict of volcanic island arc and also probably the Becart Basin all in their original relationships.
spk_0
So we can study where well the Codomian processes here in the Bohemian Massif.
spk_0
Okay there you have them still in their original relationship. I was going to ask you about that because it sounds like there's been awful lot of processing that's taken place afterwards with all fragments appearing from as far away as Spain and the rest of the world.
spk_0
So we are going to France and then to the central parts of Europe. So how do we reconstruct what happened during the Orogyny? How do we get them managed to wind the clock backwards and see how all the parts fit together?
spk_0
Yeah there is several lines of evidence and there are several sort of principle things we can recognize in the rock record.
spk_0
First is what is called the Codomian Unconformity which has been discovered here in Central Europe. It was noticed in second half of 19th century and later formally defined in France in 1921.
spk_0
So it's the major evidence that the Codomian originate took place before Cambrian or Barbivian because what we see is that we have folded and deformed metamorphosed basement complexes which are overlined by fossiliferous and deformed Cambrian or even Barbivian strata.
spk_0
Nowadays we have a lot of data available which consists of geochronologic data that usually incitement the tritles or conages which allow us to define what's called maximum deposition of age.
spk_0
So we can sort of put some time constraints on the age of deposition and deformation even in these rocks which do not contain any fossils.
spk_0
We have geochemistry which allows especially geochemistry of volcanic rocks which allows us to interpret them as either volcanic arcs built on thinned continental margin or on oceanic rust.
spk_0
We also have pieces or fragments of the subducting plate which were incorporated into the accretionary wedge, probably or they form sea mounts on the sea floor and of course during subduction it's very difficult to subduct these asperities.
spk_0
So they are accreted and mixed with the terryginial sediments of the accretionary wedge.
spk_0
So there is enough pieces of evidence to argue that it was a pacific type margin with active protracted subduction where an unknown oceanic plate which is almost completely gone to the mantle was subjected beneath Gondwana creating these accretionary wedges, island arc etc.
spk_0
So now as compared to 20 or 30 years ago we have a lot of data.
spk_0
The geochronology also allows us to set time scales or set time frame for this process.
spk_0
So if we focus on the central Europe here the Codomian origin and the subduction started probably around 630, 620 million years ago.
spk_0
And what's interesting it continued into Cambrian so the end of subduction was probably around 525 million years ago.
spk_0
So at the moment now at the stage of research we have a lot of data.
spk_0
What about paleo magnetism and do we know roughly at well latitude all these events took place?
spk_0
Paleo magnetism doesn't work good in these rocks because they are quite old they have been remagnetized several times.
spk_0
But if we want to estimate a paleo lotitude we can simply use the overlying strata because we have Cambrian or Ordovician on top of it.
spk_0
So we can use paleontological data, biogereography but also an upper ordovician which is directly overlying the Codomian basement.
spk_0
We have glacial marine sediments which argue for proximity to Gondvana because there must have been a continental glacier available.
spk_0
So putting it all together that's a good argument for southern latitudes on the margin of Gondvana.
spk_0
And based on mostly the Tritosircon Geo-Hornology and comparison of the Tritosircon ages in Codomian basement with those in Africa and South America so potential source areas.
spk_0
The most common view is that what constitutes Central Europe was somewhere close to West Africa so sourced from West African Crathon or Transaharan Belt.
spk_0
So Northwest Africa. So we have pretty much good constraints on where the terrains which are now in Central Europe were positioned at the end of no-perturacy.
spk_0
So let's run the geological clock forward now after this period that you've been describing in the end of the subduction. What happened next?
spk_0
Yeah that's actually a very difficult question because how exactly the Codomian orrigenic ended? It has long been a matter of debate and several rather contrasting models have been proposed.
spk_0
And I would say that there has not been resolved until now. For example Damian Nance and Brandon Malfe proposed a model of an interaction of the Codomian active margin with migrating mid ocean rich and a change to a transform regime and later to a passive margin from the other vision onwards.
spk_0
And it also seems likely that Avallonia rifted completely away from its original position next to South America or Guendvana opening a rake ocean and then collided with Lower Ensure and Baltica, what we now call the Codonia orrigena.
spk_0
However, great debate exists to what happened to the other Codomian terrains whether they also were completely detached from Guendvana and drifted northwards as entirely separate islands within the rake ocean or it may attach to Guendvana at all times during the early Apollo week.
spk_0
So this debate actually is rather important for the reconstruction of Prevariska and Apollo Geography, how many oceans and how many continental blocks were involved in the subsequent Varyskan orrigena.
spk_0
The model I like and I prefer the moment is the one with the migrating mid ocean rich which intersected the Codomian subduction zone because it nicely explains the termination of arc activity which was diacronos from west to east but we cannot be sure.
spk_0
So again to step back a little bit so we had these series of events which you say we now have a fairly good evidence to be able to constrain what happened during the Codomian and rogyny and we can roughly say how things looked at the end of that.
spk_0
And you say what's open to debate is what happened next but at what point running the clock still further forward do we feel like we have enough evidence to say well at least now we know where all these terrains are positioned and what happened and it's just that we have to somehow figure out what happened in between.
spk_0
Starting with the end of the Codomian orrogyny.
spk_0
I feel look at the end of Codomian orrigena here in central Europe what we see is granitech plutonism so large bodies of granitech magma intruding into the former accretionary wedge at about 525,000.
spk_0
Which is a sort of strange because accretionary wedges are typically very cold regions of earth crust because they are underlined by cold, subducting oceanic place so there is no heat source.
spk_0
So we need a heat source to explain the granitech plutonism.
spk_0
One of the models that's what I was talking about is that rich intersected the subduction zone which would explain the heat source.
spk_0
So you can find more recent examples of mid ocean ridges intersecting subduction zones and creating sort of what's called slab window.
spk_0
So the slab sort of is detached and you can get a hot austenosphere into the base of cold accretionary wedge.
spk_0
And that's what we think happened during Cambrian.
spk_0
So we need to explain this heat source and the next stage was the passive margin which is evidenced by all-dovish and orrbuzzle-ordovish and sediments,
spk_0
which overlie the cadomian basement.
spk_0
So we have a very good record actually from the end of protezoic to the beginning of orrbison.
spk_0
So we see the end of orrbison some heat input and granitech plutonism and volcanism and then we see passive margin, clearly passive margin sediments of early orrbison age.
spk_0
But all these are indirect inferences.
spk_0
So moving the clock forward a little bit then we come to the veriscan arrogenee, right?
spk_0
So if we move onwards to alipalozoic, the key geodynamic process at the time was continental drift of gondvana to the north.
spk_0
Together with the former cadomian terrains at its margin, so gondvana and anything which was north of it,
spk_0
so all these terrains formed previously during cadomian orrbison, moved north to our slorantia Baltica and Avalonia,
spk_0
which were assembled during the cadomian orrbison to form La Roussia.
spk_0
So now we have two major converging mega-continents, gondvana and La Roussia moving towards each other and closing the rake ocean in between,
spk_0
another small oceanic basins. As we discussed before, it's not entirely clear how many continental fragments or microplates and how many oceanic basins were involved in the veriscan orrgene and in the veriscan collision.
spk_0
And it's another matter of debate, so it has been widely debated for decades.
spk_0
Nevertheless, I would emphasize that this process was significantly different from cadomian orrgene because it was a truly collisional orrgene.
spk_0
So we had a two major continents on each side of an ocean and after closure of the ocean, the continents collided.
spk_0
And this continental collision culminated during Davonia and to Carboniferos and resulted in the formation of the veriscan orrgene belt and in turn in the formation of supercontinent Pangaea.
spk_0
So what is now in central Europe was right in the heart of the veriscan belt and in the heart of Pangaea and at a time central Europe was positioned somewhere near the equator
spk_0
because we have Carboniferos, coal basins which overlaid eroded veriscan baseman.
spk_0
So you said that the veriscan then was really a head on collision of two continents, whereas the cadomian you say was more accretionary.
spk_0
There wasn't actually the same kind of perpendicular motion if you like between the plates that created a Himalayan scale type mountain range as the veriscan might have done at the time.
spk_0
Yes, exactly. That's why we call it accretionary origin because there was probably a large oceanic plate subducting Binhit Gunvana, but there was no major continent on the other side.
spk_0
So we have a protracted oceanic subduction lasting for tens or maybe even more than 100 millions of years.
spk_0
However, it should be noted that oceanic plates are never smooth. So the oceanic plates which subducts, for example, sea mounts, it can carry oceanic plateaus, it can carry intra-oceanic volcanic arcs or sedimentary basins.
spk_0
And all this material is very difficult to subduct. So it accretes, it makes the oceanic plate thicker and it's buoyant. So it's difficult to subduct.
spk_0
So it rather accretes to the overriding continental margin. And this is exactly what we think might have happened during cadomian origin.
spk_0
In contrast, the veriscan originic level is a collisional orogene. So everything we know from other collisional orginic belts like the Alps and Himalaya.
spk_0
So closure of an ocean first, high pressure, metamorphism, creating high topography, high orginic topography, maybe even an orginic plateau like in the present day to bed, up to final collapse or ocean, an exhumation of high-grade metamorphic complexes.
spk_0
So everything of this we have recorded here in central Europe. So that's why the veriscan origin is sort of vortglo sick area for orginic research.
spk_0
Yes, so the best evidence for the veriscan orogene is in central or eastern Europe, is that what you're saying?
spk_0
I wouldn't say the best, but we have very well preserved all the orginic zones. So if you would go across an collisional orgin, you would start in a foreland and you would go to the sort of central axial zone which was uplifted and then there is of course the deepest erosion.
spk_0
And we are very well preserved this orginic architecture. So if you would go from north to south across the veriscan orginic belt, you would start in foreland basins, very low, great thick succession of celestial ecstasysthmens, then you would enter a low-grade metamorphic complexes.
spk_0
And then if you would be in the you can step into the orginic interior which is now exhumed, originally very deep rocks which formed the thickened orginic root with granulites and mickmatites and other high-grade rocks.
spk_0
And all this is very well exposed and very well preserved here in Bohemian Massif. So that's an in central Europe. So that's why it has been studied for decades.
spk_0
So if you go from north to south you say you go through all these regions or kind of distance are we talking about if you were going to do your transect, do a trek from top to bottom, where would you start and where would you finish?
spk_0
You would start somewhere in very south of Poland and then end up in Austria, not in Austria. And it's about let's say 300 kilometers.
spk_0
But then should be noted that it's not the end of the orgin. So it's the end of the exposure of the orgin because the very scourgene continues underneath the mollus basin of the orbs and goes farther south and of course continues into the orbs.
spk_0
But there it was reworked during Alpine orgini. Whereas to the north of the orbs the Alpine overprint was only localized.
spk_0
And it was more free activation, not affected by the Alpine orgini.
spk_0
But the Alpine orgin was a bit further west. So you say if you start in Poland and you go down towards Austria, you said the risk in a orgin extends to where the Alpine orgini is today. So it actually extended further west as well as north to south.
spk_0
Yeah, you're right. You know, if he would look at the, let's say geologic map of the world in Carboniferos, the very scourgene was rather extensive.
spk_0
So the length could have been like 8 to 10,000 kilometers maybe in the mollus. So it was a really extensive orginic belt.
spk_0
So we found a ruminants or pieces almost everywhere. But I'm now talking about those parts or fragments which are exposed and which escaped the Alpine overprint.
spk_0
So you can see them emerging from below from largely covered in much of Eastern Europe by younger Mesozoic and Torshary sediments.
spk_0
So you have several places, several, we call it massive, which project upvart from younger sediments and that's where we can study the very scourgene at best.
spk_0
Is it the case then that even though we had a Himalayan scale mountain range at the end of the Vyrskin that none of the topography that we see today either in central Europe going down from Poland to Austria or indeed in the periphery of the Alps, none of that is actually as old as the Vyrskin.
spk_0
That's all much more recently created, is that right?
spk_0
Yeah, that's right. Nothing left from that because it has been about 300 million years since the end of the Vyrskin originates.
spk_0
So and even on geological timescale this is a very long time span. So long enough for erosion to completely wipe out the original topography.
spk_0
So much of the present day topography and much of the present day relief, which we see here in central Europe is due to reactivation from Alpine originate because we are Alpine forland, which is still ongoing.
spk_0
So we see here several phases of compression reactivation during critiches and senozoic.
spk_0
And also we had here an episode of tertiary rifting which led to the thinning of the litosphere, some volcanism, and we have some rift related called basins.
spk_0
So that's the most recent relief. Nothing left from the Vyrskin originate, of course. It's too long time.
spk_0
But the reactivation took place along faults that may have been active during the Vyrskin because they were, I guess, zones of weakness.
spk_0
Yes, exactly. Especially at the end of Vyrskin originate there was a major phase of strike slip faulting and some of these faults run for tens or even several hundreds of kilometers and they penetrate through the whole crust.
spk_0
So these are large features which were there before the Alpine originate and they are easy to reactivate.
spk_0
So compressional stress from the Alpine originate reactivated these faults quite significantly in some places.
spk_0
And we have a lot of evidence, efficient track dating that there was also significant block uplifts during Jurassic critiches and tertiary.
spk_0
So there is plenty of evidence for movements in the central Europe, but all this was along these brittle faults. There was no metamorphism, no magnetism, and no ductile pervasive deformation related to the Alpine originate.
spk_0
So that's why we have very well preserved the older originic cycle, the Vyrskin one.
spk_0
Oh, I see. So the Alpine originate, although it completely shifted things around and there's a lot of structural change, there wasn't so much metamorphic change.
spk_0
Not at all, actually, because the metamorphism happened in the Alps, but we are too far from the origin. But still the compression we felt it.
spk_0
So there were some movements, but these were localized along, as you pointed out, along zones of weakness, which were pre-existing faults.
spk_0
What are you working on at the moment?
spk_0
With my colleagues, we are working on two main projects. One is focused on what we're talking about a bit.
spk_0
And it's reconstructing of terrain provenance, which formed at the Northern margin of Gondwana using the Tritazir Conjechroge.
spk_0
And we have now a new project which has started this year, which is focused on reconstruction of archaea and supercontinent.
spk_0
So the fieldwork will be in Canada and Wyoming and Finland.
spk_0
So two very different time periods.
spk_0
Very different time periods and very different field areas, but we enjoy both.
spk_0
Both are very interesting problems to solve.
spk_0
Yuri Jaak, thank you very much.
spk_0
Thank you very much.
spk_0
To see pictures and illustrations that support this podcast, go to GeologyBytes.com, where you'll also find a subject matter index of all the episodes.
spk_0
There you can also give me feedback, which I welcome, as well as sign up to get my emails about new episodes.