1 00:00:04,120 --> 00:00:07,000 This is Geology Bites with Oliver Stremple. 2 00:00:08,320 --> 00:00:12,200 What events in the geological past were responsible for 3 00:00:12,200 --> 00:00:17,000 shaping Central Europe? In earlier episodes I talked to 4 00:00:17,000 --> 00:00:19,880 of Liniman about the assembly of Central Europe during the 5 00:00:19,880 --> 00:00:24,280 Paleozoic and with Rob Butler on the origin of the Alps in the 6 00:00:24,280 --> 00:00:29,000 much more recent past. Here we talk about two orogenies 7 00:00:29,000 --> 00:00:31,480 that also played a key role in the story. 8 00:00:32,439 --> 00:00:35,920 First, the Codomian orogeny that lasted from the late 9 00:00:35,920 --> 00:00:40,480 Neoproterozoic to the early Cambrian, IE from about 700 10 00:00:40,480 --> 00:00:44,120 million years ago to about 425,000,000 years ago. 11 00:00:45,360 --> 00:00:49,640 And 2nd, the Veriskan orogeny that took place in the late 12 00:00:49,640 --> 00:00:54,360 Paleozoic from about 380 to 280 million years ago. 13 00:00:56,360 --> 00:00:59,680 Yuri Jacques has been studying the geology of Central Europe 14 00:00:59,680 --> 00:01:04,400 for over 25 years, using methods ranging from structural studies 15 00:01:04,400 --> 00:01:08,200 in the field to detrital zircon geochronology. 16 00:01:09,080 --> 00:01:11,720 He is a professor at the Institute of Geology and 17 00:01:11,720 --> 00:01:14,640 Palaeontology at Charles University in Prague. 18 00:01:15,840 --> 00:01:18,120 Yuri Jacques, welcome to Geology Bites. 19 00:01:18,840 --> 00:01:21,000 Thank you very much for inviting me. 20 00:01:21,000 --> 00:01:23,600 I'm glad to be here in this podcast. 21 00:01:24,120 --> 00:01:27,760 Before we talk about individual orogenies, let's try to place 22 00:01:27,760 --> 00:01:31,160 this in the wider tectonic context of the assembly and 23 00:01:31,160 --> 00:01:35,360 breakup of supercontinents. The so-called Wilson cycle that 24 00:01:35,400 --> 00:01:39,160 you break up a supercontinent and then it reforms roughly 25 00:01:39,160 --> 00:01:43,120 every 500 million years or so. This period that we're talking 26 00:01:43,120 --> 00:01:45,600 about, how does that fit into the Wilson cycle? 27 00:01:45,960 --> 00:01:49,960 This Wilson cycle would be positioned on a time axis 28 00:01:50,200 --> 00:01:53,960 between the supercontinent Rodinia and supercontinent 29 00:01:53,960 --> 00:01:56,840 Pangaea. So in the Mesoproterozoic and 30 00:01:56,840 --> 00:02:01,400 Allenoproterozoic times, we have here supercontinent Rodinia 31 00:02:01,400 --> 00:02:04,560 which broke up. And part of this, one of the 32 00:02:04,800 --> 00:02:07,280 results of this breakup was Gondwana. 33 00:02:07,800 --> 00:02:11,680 And then and we'll probably talk about it more, was Pangaea, 34 00:02:11,680 --> 00:02:14,200 which formed during late Paulozoic. 35 00:02:14,480 --> 00:02:18,160 So all the processes we will be talking about occurred in 36 00:02:18,160 --> 00:02:20,240 between. So we are in terms of a 37 00:02:20,240 --> 00:02:24,680 supercontinent cycle in between Rodinia and Pangaea. 38 00:02:25,000 --> 00:02:29,280 In terms of Wilson cycle, it's a little bit more complicated 39 00:02:29,280 --> 00:02:32,280 because Wilson cycle, it's only one of the forms of 40 00:02:32,520 --> 00:02:34,920 supercontinent breakup and assembly. 41 00:02:35,120 --> 00:02:38,520 So it implies that you create an ocean and then you close the 42 00:02:38,520 --> 00:02:41,640 same ocean. Here what we have the record in 43 00:02:41,640 --> 00:02:44,640 Central Europe, it was much more complex. 44 00:02:44,640 --> 00:02:47,680 There are more oceanic basins, more terrains involved. 45 00:02:47,680 --> 00:02:51,320 So the history is, say, more complex than the simple Wilson 46 00:02:51,320 --> 00:02:53,960 cycle. But in terms of supercontinent 47 00:02:53,960 --> 00:02:58,160 cycle, we can track processes which happened from the breakup 48 00:02:58,160 --> 00:03:00,920 of Rodinia to the assembly of Pangaea. 49 00:03:01,480 --> 00:03:07,120 So Europe today is part of Eurasia, so that is itself a 50 00:03:07,120 --> 00:03:09,480 pretty massive continental block. 51 00:03:09,920 --> 00:03:13,200 So during the assembly of Europe, was this leading to 52 00:03:13,360 --> 00:03:17,360 greater and greater amalgamation of terrains that eventually 53 00:03:17,880 --> 00:03:20,920 including the Caledonian Neurogene and then after the 54 00:03:20,920 --> 00:03:23,520 Voriscon, sort of basically led to the formation of Pangaea? 55 00:03:23,520 --> 00:03:25,880 Is that really this very high level picture? 56 00:03:26,440 --> 00:03:31,520 On a larger scale you are right, but on a smaller scale we should 57 00:03:31,520 --> 00:03:34,840 not forgot the Kadhomian Originae, which actually form 58 00:03:34,840 --> 00:03:39,680 much of crust which we see now in Western and Eastern Europe. 59 00:03:39,680 --> 00:03:44,080 And the younger Variscan Originae simply recycled this 60 00:03:44,080 --> 00:03:47,200 material. So I would argue that the main 61 00:03:47,200 --> 00:03:51,360 crustal forming event, maybe even most important crustal 62 00:03:51,360 --> 00:03:55,840 forming event, was the Kadhomian Originae at the late Proterozoic 63 00:03:55,840 --> 00:04:00,080 to Aleppozoic times. It really created new crust, the 64 00:04:00,080 --> 00:04:03,000 Variscan origin. It was collisional and it 65 00:04:03,320 --> 00:04:05,760 largely recycled this Cadomian basement. 66 00:04:06,480 --> 00:04:09,320 OK, so let's talk about the Cadomian orogeny. 67 00:04:09,960 --> 00:04:12,960 Can you walk us through a little bit more about what happened? 68 00:04:13,760 --> 00:04:17,000 So first of all, it should be mentioned that although the 69 00:04:17,760 --> 00:04:21,160 Kadomi and Origeniae was first defined in Europe, it was more 70 00:04:21,160 --> 00:04:23,520 likely a global scale Origenic event. 71 00:04:23,560 --> 00:04:26,400 Because it has been proposed that at the end of 72 00:04:26,400 --> 00:04:30,240 Neoproterozoic and in the beginning of Palazzoic we are 73 00:04:30,240 --> 00:04:35,240 talking about processes that happened about 750 to 500 74 00:04:35,240 --> 00:04:38,560 million years ago. Almost entire Gondwana was 75 00:04:38,560 --> 00:04:43,480 surrounded by broadly coeval and linked Origenic belts. 76 00:04:44,320 --> 00:04:49,000 So what we now call the Avalonian Cadomian belt was only 77 00:04:49,000 --> 00:04:51,880 one segment of a global origenic system. 78 00:04:52,560 --> 00:04:57,480 And key feature of this global origenic was subduction of large 79 00:04:57,480 --> 00:05:02,160 oceanic plates beneath the Gondwana mainland, forming sort 80 00:05:02,160 --> 00:05:06,800 of subductions of girdle and in effect subduction controlled 81 00:05:06,800 --> 00:05:12,480 formation of extensive tracts of accretionary edges, volcanic 82 00:05:12,480 --> 00:05:17,440 arcs, back arc basins which were attached to the upper overriding 83 00:05:17,440 --> 00:05:20,960 plate. So in terms of recent analogy, 84 00:05:21,200 --> 00:05:24,600 this is pretty much similar what we see now in the Western 85 00:05:24,720 --> 00:05:26,680 Pacific. In the Western Pacific, then 86 00:05:26,680 --> 00:05:28,720 yeah, it's OK. You get subduction and you get 87 00:05:28,720 --> 00:05:32,560 all the the consequences or corollaries associated with 88 00:05:32,560 --> 00:05:36,280 subduction. So do we see those today? 89 00:05:36,400 --> 00:05:39,400 Can we find the remnants of those in Europe? 90 00:05:39,480 --> 00:05:42,720 I mean, can we see accretionary wedges or where volcanic arks 91 00:05:42,720 --> 00:05:46,000 used to be, or remnants of mountain chains? 92 00:05:46,280 --> 00:05:50,040 Yes, we do. And actually, if you look on a 93 00:05:50,040 --> 00:05:53,520 geologic map of Europe, the fragments of the former 94 00:05:53,840 --> 00:05:58,520 Avalonian, Kadumi and Belp are now scattered all over Western 95 00:05:58,520 --> 00:06:02,360 and central Europe, with the main exposures being the Iberian 96 00:06:02,360 --> 00:06:07,280 massive in Spain and Portugal, Armorican massive in France, and 97 00:06:07,280 --> 00:06:09,880 of course the Bohemian must sit here in Central Europe. 98 00:06:10,400 --> 00:06:14,600 However, we find them frequently also within the Alpine originic 99 00:06:14,600 --> 00:06:18,520 system. So they were recycled during the 100 00:06:18,520 --> 00:06:21,440 Variscan origin and again recycled during the Alpine 101 00:06:21,440 --> 00:06:25,040 origin. And in this case they extend 102 00:06:25,040 --> 00:06:29,600 farther east and South into the Alps, Carpathians, and even 103 00:06:29,600 --> 00:06:34,280 farther into Bulgaria, Greece, Turkey, and even to Iran. 104 00:06:34,560 --> 00:06:39,880 So in all these places we find the relics or fragments of the 105 00:06:39,880 --> 00:06:44,400 former accretionary orogenic belt of the former Avalonian 106 00:06:44,400 --> 00:06:49,880 Kadamian active margin. And I would argue that in here 107 00:06:49,880 --> 00:06:54,760 in Bohemian Massif, we have one of the best preserved fragments 108 00:06:55,200 --> 00:07:01,040 of this margin, because we have here a relic of an Ophelite, we 109 00:07:01,040 --> 00:07:04,360 have a relic of an accretionary which very well preserved. 110 00:07:04,400 --> 00:07:08,960 We have a relic of volcanic island arc and also probably the 111 00:07:09,480 --> 00:07:13,240 arc basin, all in their original relationships. 112 00:07:13,560 --> 00:07:17,080 So we can study very well the Caribbean processes here in the 113 00:07:17,080 --> 00:07:20,320 Bohemian Massif. OK, there you have them still in 114 00:07:20,320 --> 00:07:22,560 their original relationship. I was going to ask you about 115 00:07:22,560 --> 00:07:24,720 that because it sounds like there's been an awful lot of 116 00:07:24,720 --> 00:07:28,720 processing that's taking place afterwards, with all fragments 117 00:07:28,720 --> 00:07:32,360 appearing from as far away as Spain to France and then to the 118 00:07:32,360 --> 00:07:35,920 central parts of Europe. So how do we reconstruct what 119 00:07:35,920 --> 00:07:39,240 happened during the orogeny? How do we kind of manage to wind 120 00:07:39,240 --> 00:07:42,800 the clock backwards and see how all the parts fit together? 121 00:07:43,680 --> 00:07:48,400 Yeah, there is several lines of evidence and there are several 122 00:07:48,400 --> 00:07:51,600 sort of principal things we can recognize in the rock record. 123 00:07:52,000 --> 00:07:57,120 First is what is called the Kadumian unconformity, which has 124 00:07:57,120 --> 00:07:59,240 been discovered here in Central Europe. 125 00:07:59,240 --> 00:08:04,800 It was noticed in second-half of 19th century and later formally 126 00:08:04,800 --> 00:08:10,280 defined in France in 1921. So it it's the major evidence 127 00:08:10,280 --> 00:08:14,720 that the Kadumian originator took place before Cambrian or or 128 00:08:14,720 --> 00:08:18,560 the vision, because what we see is that we have folded and 129 00:08:18,560 --> 00:08:23,280 deformed metamorphose basement complexes which are overlined by 130 00:08:23,280 --> 00:08:26,720 Foscilliferose on the formed Cambrian or even auto vision 131 00:08:26,720 --> 00:08:30,480 strata. Nowadays we have a lot of data 132 00:08:30,480 --> 00:08:35,039 available, which consists of Geo chronologic data, usually in 133 00:08:35,039 --> 00:08:40,280 sediments, the trital zircon ages, which allow us to define 134 00:08:40,320 --> 00:08:42,559 what's called maximum depositional age. 135 00:08:42,960 --> 00:08:47,200 So we can sort of put some time constraints on the age of 136 00:08:47,200 --> 00:08:51,680 deposition and deformation. Even in these rocks which do not 137 00:08:51,680 --> 00:08:55,400 contain any fossils, we have geochemistry which allows 138 00:08:55,400 --> 00:08:58,840 especially geochemistry or volcanic rocks, which allows us 139 00:08:58,840 --> 00:09:04,760 to interpret them as either volcanic arcs built on thin 140 00:09:04,960 --> 00:09:08,160 continental margin or on oceanic rust. 141 00:09:08,800 --> 00:09:13,640 We also have pieces or fragments of the subducting plate which 142 00:09:13,640 --> 00:09:17,480 were incorporated into the accretionary wedge probably or 143 00:09:17,480 --> 00:09:19,760 they form seamounts on the sea floor. 144 00:09:20,000 --> 00:09:23,400 And of course during subduction it's very difficult to subduct 145 00:09:23,680 --> 00:09:28,120 these asperities. So they they are created and 146 00:09:28,120 --> 00:09:31,480 mixed with the terrigenio sediments of the accretionary 147 00:09:31,480 --> 00:09:34,440 wedge. So there is enough pieces of 148 00:09:34,640 --> 00:09:39,800 evidence to argue that it was a Pacific type margin with active 149 00:09:39,800 --> 00:09:44,480 protracted subduction where an unknown oceanic plate which is 150 00:09:45,160 --> 00:09:49,520 almost completely gone to the mantle was subducted beneath 151 00:09:49,520 --> 00:09:53,000 Gunvana creating these accretionary wedges, island arc 152 00:09:53,000 --> 00:09:57,400 etcetera. So now as compared to 20 or 30 153 00:09:57,400 --> 00:09:59,360 years ago, we have a lot of data. 154 00:09:59,960 --> 00:10:04,720 The Geo chronology also allows us to set a time scales or set a 155 00:10:04,760 --> 00:10:09,600 time frame for this process. So if we focus on the Central 156 00:10:09,680 --> 00:10:12,840 Europe here, the academia and origina and the subduction 157 00:10:12,840 --> 00:10:18,520 started probably around 636 hundred, 20 million years ago. 158 00:10:19,120 --> 00:10:22,200 And what's interesting, it continued into Cambrian. 159 00:10:22,200 --> 00:10:27,200 So the end of subjection was probably at around 525,000,000 160 00:10:27,200 --> 00:10:30,200 years ago. So at the moment now at this 161 00:10:30,200 --> 00:10:32,800 stage of research, we have a lot of data. 162 00:10:33,840 --> 00:10:37,320 What about paleomagnetism? And do we know roughly at what 163 00:10:37,320 --> 00:10:39,680 latitude all these events took place? 164 00:10:40,280 --> 00:10:44,640 Paleomagnetism doesn't work good in these rocks because they are 165 00:10:44,640 --> 00:10:47,200 quite old. They have been remagnetized 166 00:10:47,200 --> 00:10:50,080 several times. But if we want to estimate a 167 00:10:50,080 --> 00:10:54,600 palaeolatitude, we can simply use the overlying strata because 168 00:10:54,600 --> 00:10:57,360 we have Cambrian or auto vision on top of it. 169 00:10:57,760 --> 00:11:02,800 So we can use palaeontological data, biogeography, but also in 170 00:11:02,800 --> 00:11:07,000 upper auto vision which is directly overlying the Cadomian 171 00:11:07,000 --> 00:11:10,240 basement. We have glacial marine sediments 172 00:11:10,560 --> 00:11:15,960 which argue for proximity to Gondwana because there must have 173 00:11:15,960 --> 00:11:19,840 been an continental continental glacier available. 174 00:11:20,280 --> 00:11:23,920 So putting it all together, that's a good argument for 175 00:11:24,200 --> 00:11:29,440 southern latitudes on the margin of Gondwana and based on mostly 176 00:11:29,440 --> 00:11:33,320 the Trito zircon Geo chronology and comparison of the Trito 177 00:11:33,320 --> 00:11:40,880 zircon ages in Cadomian basement with those in Africa and South 178 00:11:40,880 --> 00:11:43,640 America. So potential source areas. 179 00:11:44,080 --> 00:11:47,040 The most common view is that what constitutes Central Europe 180 00:11:47,040 --> 00:11:51,400 was somewhere close to West Africa, so sourced from West 181 00:11:51,400 --> 00:11:56,520 African Craton or Trans Saharan belt, so Northwest, Northwest 182 00:11:56,520 --> 00:11:58,680 Africa. So we have pretty much good 183 00:11:58,680 --> 00:12:03,200 constraints on where the terrains which are now in 184 00:12:03,200 --> 00:12:07,240 Central Europe were positioned at the end of no Proterozoic. 185 00:12:07,640 --> 00:12:12,120 So let's run the geological clock forward now, after this 186 00:12:12,120 --> 00:12:14,080 period that you've been describing in the end of the 187 00:12:14,080 --> 00:12:18,600 subduction, what happened next? Yeah, that's actually very 188 00:12:18,600 --> 00:12:23,640 difficult question because how exactly the Kadomian origin 189 00:12:23,640 --> 00:12:28,600 ended, it has long been a matter of debate and several other 190 00:12:28,600 --> 00:12:30,480 contrasting models have been proposed. 191 00:12:30,960 --> 00:12:34,120 And I would say that it has not been resolved until now. 192 00:12:34,480 --> 00:12:38,920 For example, Damien Announce and Brandon Murphy proposed a model 193 00:12:38,920 --> 00:12:43,320 of an interaction of the Caribbean active margin with 194 00:12:43,600 --> 00:12:49,080 migrating mid ocean Ridge and a change to a transform regime and 195 00:12:49,080 --> 00:12:52,280 later to a passive margin from the auto vision onwards. 196 00:12:52,720 --> 00:12:57,160 And what also seems likely that Avalonia are rifted completely 197 00:12:57,160 --> 00:13:02,360 away from its original position next to South America or 198 00:13:02,360 --> 00:13:07,360 Gondwana opening a Rake Ocean, and then collided with Laurentia 199 00:13:07,360 --> 00:13:11,040 and Baltica, what we now call the Caledonian origin. 200 00:13:11,720 --> 00:13:15,640 However, great debate exists to what happened to the other 201 00:13:15,640 --> 00:13:20,480 Karumean terrains, whether they also were completely detached 202 00:13:20,480 --> 00:13:24,960 from Gondwana and drifted northwards as entirely separate 203 00:13:24,960 --> 00:13:28,720 islands within the Rake ocean, or inmate attached to Gondwana 204 00:13:28,720 --> 00:13:31,000 at all times during the early Apollo's weeks. 205 00:13:31,000 --> 00:13:35,800 So this debate actually is rather important for the 206 00:13:35,800 --> 00:13:38,960 reconstruction of Prevariskan Palo geography. 207 00:13:39,520 --> 00:13:43,840 How many oceans and how many continental blocks were involved 208 00:13:44,360 --> 00:13:46,920 in the subsequent variscanerogene? 209 00:13:47,400 --> 00:13:51,760 The model I like and I prefer the moment is the one with the 210 00:13:51,760 --> 00:13:55,840 migrating mid ocean Ridge which intersected the Caribbean 211 00:13:55,840 --> 00:14:01,280 subduction zone because it's nicely explains the termination 212 00:14:01,280 --> 00:14:05,160 of Arc activity which was diachronous from West to east, 213 00:14:05,480 --> 00:14:09,520 but we cannot be sure. So again, to step back a little 214 00:14:09,520 --> 00:14:13,120 bit, so we had these series of events which you say we now have 215 00:14:13,120 --> 00:14:16,960 a fairly good evidence to be able to constrain what happened 216 00:14:16,960 --> 00:14:21,320 during the Codomian androgyny and we can roughly say how 217 00:14:21,320 --> 00:14:22,880 things looked at the end of that. 218 00:14:23,600 --> 00:14:25,880 And you say what's open to debate is what happened next. 219 00:14:25,880 --> 00:14:29,200 But at what point, running the clock still further forward, do 220 00:14:29,200 --> 00:14:32,320 we feel like we have enough evidence to say, well, at least 221 00:14:32,320 --> 00:14:36,720 now we know where all these terrains are positioned and what 222 00:14:36,720 --> 00:14:39,560 happened, and it's just that we have to somehow figure out what 223 00:14:39,560 --> 00:14:42,240 happened in between, starting with the end of the Kadoni and 224 00:14:42,240 --> 00:14:45,920 Orogeny? If you look at the end of Kadoni 225 00:14:45,920 --> 00:14:51,080 and Orogeny here in Central Europe, what we see is granitic 226 00:14:51,080 --> 00:14:55,640 plutonism. So large bodies of granitic 227 00:14:55,640 --> 00:15:01,960 magma intruding into the former accretionary wedge at about 525 228 00:15:02,320 --> 00:15:07,240 till 500, which is a sort of strange because accretionary 229 00:15:07,240 --> 00:15:12,600 wedges are typically very cold regions of Earth's crust because 230 00:15:12,600 --> 00:15:15,440 they are underlined by cold subducting oceanic place. 231 00:15:15,440 --> 00:15:18,640 So there is no heat source. So we need a heat source to 232 00:15:18,680 --> 00:15:24,240 explain the granitic platonism. One of the models that's what I 233 00:15:24,240 --> 00:15:29,600 was talking about is that Rich intersected the subduction zone, 234 00:15:29,600 --> 00:15:31,600 which would explain the heat source. 235 00:15:31,960 --> 00:15:38,360 So you can find more recent examples of mid ocean ridges 236 00:15:38,360 --> 00:15:41,440 intersecting subduction zones and creating sort of what's 237 00:15:41,440 --> 00:15:45,240 called slab window. So the so the slab sort of is 238 00:15:45,360 --> 00:15:50,200 detached and you can get a hot asthenosphere into the base of 239 00:15:50,720 --> 00:15:54,720 of cold accretionary watch and that's what we think happened 240 00:15:55,120 --> 00:15:58,560 during Cambrian. So we have this, we need to 241 00:15:58,560 --> 00:16:02,600 explain this heat source. And the next stage was the 242 00:16:02,600 --> 00:16:07,040 passive margin which is evidenced by Auto vision or 243 00:16:07,040 --> 00:16:10,720 Basil auto vision sediments, Basil auto vision beds which 244 00:16:10,920 --> 00:16:15,400 overlie the academia basement. So we have a very good record 245 00:16:15,520 --> 00:16:19,320 actually from the end of Proteosaic to the beginning of 246 00:16:19,320 --> 00:16:22,120 auto Vision. So we see the end of horogeny, 247 00:16:22,200 --> 00:16:26,080 some heat input and granitic plutonism and volcanism. 248 00:16:26,600 --> 00:16:30,400 And then we see passive margin, clearly passive margin sediments 249 00:16:30,680 --> 00:16:35,360 of earlier division age. But all these are indirect 250 00:16:35,480 --> 00:16:39,120 inferences. So moving the clock forward a 251 00:16:39,120 --> 00:16:42,640 little bit, then we come to the Veriskan Horogeny, right? 252 00:16:43,480 --> 00:16:49,320 So if we move onwards to early Polozoic, the key geodynamic 253 00:16:49,320 --> 00:16:53,280 process at the time was continental drift of Gondwana to 254 00:16:53,280 --> 00:16:57,640 the north together with the former Cadomian terrains at this 255 00:16:57,640 --> 00:17:00,520 margin. So Gondwana and anything which 256 00:17:00,520 --> 00:17:03,480 was north of it. So all these terrains formed 257 00:17:03,480 --> 00:17:07,599 previously during Cadomian origini moved N towards 258 00:17:07,599 --> 00:17:11,760 Laurentia, Baltica and Avalonia which were assembled during the 259 00:17:11,760 --> 00:17:14,040 Cadogian origini to form La Russia. 260 00:17:14,560 --> 00:17:19,119 So now we have two major converging mega continents, 261 00:17:19,119 --> 00:17:23,839 Gunvana and La Russia moving towards each other and closing 262 00:17:23,839 --> 00:17:27,720 the rake ocean in between and other smaller oceanic basins. 263 00:17:28,160 --> 00:17:32,080 As we discussed before, it's not entirely clear how many 264 00:17:32,080 --> 00:17:35,920 continental fragments or microplates and how many oceanic 265 00:17:35,920 --> 00:17:39,400 basins were involved in the various scan origin and in the 266 00:17:39,400 --> 00:17:42,960 various scan collision. And it's another a matter of 267 00:17:42,960 --> 00:17:45,960 debate. So it has been widely debated 268 00:17:45,960 --> 00:17:49,760 for decades. Nevertheless, I would emphasize 269 00:17:49,760 --> 00:17:53,040 that this process was significantly different from 270 00:17:53,040 --> 00:17:57,280 Cadomia and origini because it was a truly collisional origini. 271 00:17:57,280 --> 00:18:02,480 So we had a two major continents on each side of an ocean and 272 00:18:02,480 --> 00:18:06,800 after closure of the ocean the continents collided and this 273 00:18:06,880 --> 00:18:11,960 continental collision culminated during Devonian to Carboniferous 274 00:18:12,320 --> 00:18:17,240 and resulted in the formation of the Variscanorogenic belt and in 275 00:18:17,240 --> 00:18:19,800 turn in the formation of supercontinent Pangaea. 276 00:18:20,520 --> 00:18:25,000 So what is now in Central Europe was right in the heart of the 277 00:18:25,000 --> 00:18:28,240 Variscan belt and in the heart of Pangaea. 278 00:18:28,720 --> 00:18:32,240 And at the time, Central Europe was positioned somewhere near 279 00:18:32,240 --> 00:18:37,160 the equator because we have carbon ferrous coal basins which 280 00:18:37,320 --> 00:18:40,040 overlie the eroded Variscan basement. 281 00:18:40,160 --> 00:18:44,800 So you said that the Variscan then was really a kind of head 282 00:18:44,800 --> 00:18:48,400 on collision of two continents, whereas the the Cadomian you say 283 00:18:48,400 --> 00:18:52,520 was more accretionary, there wasn't actually the same kind of 284 00:18:52,600 --> 00:18:55,360 perpendicular motion if you like between the plates that created 285 00:18:55,360 --> 00:18:59,880 a Himalayan scale type mountain range as the Variscan might have 286 00:18:59,880 --> 00:19:02,360 done at the time. Yes, exactly. 287 00:19:02,360 --> 00:19:05,720 That's why we call it accretionary origin, because 288 00:19:05,960 --> 00:19:09,760 there was probably a large oceanic plate subducting beneath 289 00:19:09,760 --> 00:19:14,360 Gunvana, but there was no major continent on the other side. 290 00:19:14,720 --> 00:19:20,800 So we have protracted oceanic subduction lasting for 10s or 291 00:19:20,800 --> 00:19:23,400 maybe even more than 100 millions of years. 292 00:19:24,000 --> 00:19:28,960 However, it should be noted that oceanic plates are never smooth. 293 00:19:29,400 --> 00:19:33,400 So the oceanic plates which subducts carriers, for example 294 00:19:33,400 --> 00:19:38,280 seamounts, it can carry oceanic plateaus, it can carry intra 295 00:19:38,280 --> 00:19:43,360 oceanic volcanic arcs or sedimentary basins and all this 296 00:19:43,360 --> 00:19:46,320 material is very difficult to subduct. 297 00:19:46,560 --> 00:19:51,760 So it accretes, it makes the oceanic plate thicker and it's 298 00:19:51,760 --> 00:19:54,520 buoyant. So it's difficult to subduct. 299 00:19:54,520 --> 00:19:58,560 So it rather accretes to the overriding continental margin, 300 00:19:58,840 --> 00:20:01,920 and this is exactly what we think might have happened. 301 00:20:02,400 --> 00:20:05,720 During paduma and orogeny, in contrast, the Variscan orogenic 302 00:20:05,720 --> 00:20:10,720 Lee levels collision orogeny. So everything we know from other 303 00:20:10,720 --> 00:20:14,040 collision orogenic belts like the Alps and Himalayas. 304 00:20:14,040 --> 00:20:19,240 So closure of an ocean, first high pressure metamorphism 305 00:20:20,040 --> 00:20:23,880 creating high topography, high orogenic topography, maybe even 306 00:20:23,880 --> 00:20:29,040 an orogenic plateau like in the present day Tibet up to final 307 00:20:29,040 --> 00:20:32,720 collapse, erosion and exhumation of high grade metamorphic 308 00:20:32,720 --> 00:20:37,800 complexes. So everything of this we have 309 00:20:37,800 --> 00:20:40,840 recorded here in Central Europe. So and that's why the Vorisic 310 00:20:40,840 --> 00:20:45,200 neurogenes sort of world classic area for orogenic research. 311 00:20:45,600 --> 00:20:47,240 Yeah. So the best evidence for the 312 00:20:47,240 --> 00:20:51,240 vorisic neurogeny is in Central or Eastern Europe, is that what 313 00:20:51,240 --> 00:20:54,200 you're saying? I wouldn't say the best, but we 314 00:20:54,200 --> 00:20:58,800 have very well preserved all the Eurogenic zones. 315 00:20:58,800 --> 00:21:02,000 So if you would go across on collisional origin, you would 316 00:21:02,000 --> 00:21:05,880 start in a four land and you would go to the sort of central 317 00:21:05,880 --> 00:21:11,520 axial zone which was uplifted and then there is of course the 318 00:21:11,520 --> 00:21:15,000 deepest erosion and we are very well preserved this origenic 319 00:21:15,000 --> 00:21:18,040 architecture. So if you would go from north to 320 00:21:18,040 --> 00:21:21,360 South across the various kanorogenic belt, you would 321 00:21:21,360 --> 00:21:27,040 start in four land basins, very low grade thick successions of 322 00:21:27,040 --> 00:21:30,920 silicyclastic sediments. Then you would enter a low grade 323 00:21:31,040 --> 00:21:34,880 metamorphic complexes and then if you would be in deep and you 324 00:21:34,880 --> 00:21:40,560 can step into the orogenic interior which is now exhumed 325 00:21:40,800 --> 00:21:44,680 originally very deep rocks which formed the thickened orogenic 326 00:21:44,680 --> 00:21:48,760 root with granulites and migmatites and other high grade 327 00:21:48,760 --> 00:21:51,320 rocks. And all this is very well 328 00:21:51,320 --> 00:21:54,280 exposed and very well preserved here in Bohemian Massif. 329 00:21:54,280 --> 00:21:58,120 So that's and in Central Europe. So that's why it has been 330 00:21:58,120 --> 00:22:01,520 studied for decades. So if you go from north to 331 00:22:01,520 --> 00:22:04,000 South, you say you go through all these regions. 332 00:22:04,000 --> 00:22:05,600 What kind of distance are we talking about? 333 00:22:05,600 --> 00:22:08,680 If you were going to do your transect, do a trek from top to 334 00:22:08,680 --> 00:22:10,840 bottom, where would you start and where would you finish? 335 00:22:11,520 --> 00:22:15,920 You would start somewhere in very South of Poland and then 336 00:22:16,160 --> 00:22:20,280 end up in Austria, northern Austria, and it's about, let's 337 00:22:20,280 --> 00:22:24,080 say 300 kilometers. But then should be noted that 338 00:22:24,080 --> 00:22:27,760 it's not the end of the origin. So it's the end of the exposure 339 00:22:28,200 --> 00:22:31,200 of the origin, because the various can origin continues 340 00:22:31,320 --> 00:22:36,200 underneath the Molas basin of the Alps and goes farther South 341 00:22:36,240 --> 00:22:39,000 and of course continues into the Alps. 342 00:22:39,400 --> 00:22:43,960 But there it was revoked during Alpine origin, whereas to the 343 00:22:43,960 --> 00:22:50,080 north of the Alps the Alpine overprint was only localized and 344 00:22:50,080 --> 00:22:54,200 it was more reactivation not affected by the Alpine 345 00:22:54,200 --> 00:22:56,120 neurogeny. But the Alpine neurogeny was a 346 00:22:56,120 --> 00:22:58,400 bit further West. So you say if you start in 347 00:22:58,400 --> 00:23:01,360 Poland and you go down towards Austria, you said the Veriska 348 00:23:01,360 --> 00:23:04,240 neurogeny extends to where the Alpine neurogeny is today. 349 00:23:04,240 --> 00:23:06,960 So it actually extended further W as well as north to South. 350 00:23:07,560 --> 00:23:10,680 Yeah, you are right. You know, if he would look at 351 00:23:10,680 --> 00:23:15,920 the, let's say geologic map of the world in Carboniferous, the 352 00:23:15,920 --> 00:23:18,800 Veriskan origin was rather extensive. 353 00:23:18,800 --> 00:23:23,880 So the length could have been like 8 to 10,000 kilometers, 354 00:23:24,200 --> 00:23:26,600 maybe even more. So it was a really extensive 355 00:23:26,600 --> 00:23:30,680 origenic belt. So we found a remnants or pieces 356 00:23:30,680 --> 00:23:34,720 almost everywhere. But I'm now talking about those 357 00:23:35,360 --> 00:23:40,240 parts or fragments which which are exposed and which escaped 358 00:23:40,240 --> 00:23:44,200 the Alpine over print. So you can see them emerging 359 00:23:44,200 --> 00:23:48,960 from below, from, you know, largely covered in much of 360 00:23:48,960 --> 00:23:52,480 Western Europe by younger Mesozoic and Tertiary sediments. 361 00:23:52,880 --> 00:23:55,840 So you have several places, several, we call it massives, 362 00:23:56,280 --> 00:24:00,520 which project upward from younger sediments and that's 363 00:24:00,520 --> 00:24:03,680 where we can study the various kind of region at best. 364 00:24:04,080 --> 00:24:07,520 Is it the case then that even though we have a Himalayan scale 365 00:24:07,520 --> 00:24:10,520 mountain range at the end of the Variscan that none of the 366 00:24:10,520 --> 00:24:14,640 topography that we see today either in Central Europe going 367 00:24:14,640 --> 00:24:18,520 down from Poland to Austria or indeed in the periphery of the 368 00:24:18,520 --> 00:24:22,720 Alps, none of that is actually as old as the Variscan? 369 00:24:22,720 --> 00:24:24,520 That's all much more recently created. 370 00:24:24,520 --> 00:24:26,760 Is that right? Yeah, that's right. 371 00:24:26,760 --> 00:24:32,360 Nothing left from that because it has been about 300,000,000 372 00:24:32,360 --> 00:24:34,920 years since the end of the various canerogenes. 373 00:24:34,920 --> 00:24:38,800 So and even on geological time scale, this is a very long time 374 00:24:38,800 --> 00:24:42,800 span, so long enough for erosion to completely vipe out the 375 00:24:42,800 --> 00:24:46,000 original topography. So much of the present day 376 00:24:46,000 --> 00:24:49,480 topography and much of the present day relief which we see 377 00:24:49,480 --> 00:24:54,040 here in Central Europe is due to reactivation from Alpine 378 00:24:54,040 --> 00:24:57,920 originally because we are Alpine fall and which is still ongoing. 379 00:24:58,320 --> 00:25:02,040 So we see here several phases of compressional reactivation doing 380 00:25:02,040 --> 00:25:07,440 credentials and Sinosaic. And also we had here an episode 381 00:25:07,440 --> 00:25:12,000 of Tertiary rifting which led to the thinning of the lithosphere, 382 00:25:12,120 --> 00:25:16,200 some volcanism and we have some rift related cold basins. 383 00:25:16,320 --> 00:25:19,080 So that's the most recent relief. 384 00:25:19,480 --> 00:25:23,080 Nothing left from the Variscan Originae, of course. 385 00:25:23,080 --> 00:25:26,320 It's too long time. But the reactivation took place 386 00:25:26,320 --> 00:25:30,320 along faults that may have been active during the variscan 387 00:25:30,320 --> 00:25:32,280 because there were I guess zones of weakness. 388 00:25:32,800 --> 00:25:35,000 Yes, exactly. Especially at the end of 389 00:25:35,000 --> 00:25:39,240 Variscan Originae and there was a major phase of strike slip 390 00:25:39,240 --> 00:25:44,200 faulting and some of these faults run for tents or even 391 00:25:44,360 --> 00:25:47,440 several hundreds of kilometers and they penetrate through the 392 00:25:47,880 --> 00:25:50,600 whole crust. So these are large features 393 00:25:50,960 --> 00:25:54,000 which were there before the Alpine origin and they are easy 394 00:25:54,000 --> 00:25:58,600 to reactivate. So compressional stress from the 395 00:25:58,600 --> 00:26:03,080 Alpine origin reactivated these faults quite significantly in 396 00:26:03,080 --> 00:26:05,920 some places. And we have a lot of evidence, 397 00:26:06,000 --> 00:26:09,960 efficient track dating that there was also significant block 398 00:26:09,960 --> 00:26:13,400 uplifts during Jurassic, Cretaceous and Tertiary. 399 00:26:13,840 --> 00:26:18,880 So there's plenty of evidence for movements in the Central 400 00:26:18,880 --> 00:26:21,240 Europe. But all this was along these 401 00:26:21,240 --> 00:26:24,720 brittle falls. There was no metamorphism, no 402 00:26:24,720 --> 00:26:30,200 magmatism and no ductile pervasive deformation related to 403 00:26:30,200 --> 00:26:34,240 the Alpine origin. So that's why we have very well 404 00:26:34,240 --> 00:26:36,880 preserved the older Origenic cycle, the various. 405 00:26:37,240 --> 00:26:39,280 Oh, I see. So the Alpine and Erogeny, 406 00:26:39,280 --> 00:26:42,400 although it completely shifted things around and there's a lot 407 00:26:42,400 --> 00:26:45,720 of structural change, there wasn't so much metamorphic 408 00:26:45,720 --> 00:26:48,320 change. Not at all actually, because the 409 00:26:48,320 --> 00:26:51,720 metamorphism happened in the Alps, but we are too far from 410 00:26:51,720 --> 00:26:55,240 the origin. But still the compression we we 411 00:26:55,240 --> 00:26:57,760 felt it. So there was some movement, but 412 00:26:57,760 --> 00:27:02,640 these were localized along, as you pointed out, along zones of 413 00:27:02,640 --> 00:27:05,640 weakness which were pre-existing faults. 414 00:27:06,400 --> 00:27:07,920 What are you working on at the moment? 415 00:27:08,440 --> 00:27:12,720 With my colleagues, we are working on 2 main projects. 416 00:27:12,760 --> 00:27:17,200 One is focused on what we're talking about a bit and it's 417 00:27:17,200 --> 00:27:21,080 reconstructing of terrain provenance, which formed at the 418 00:27:21,080 --> 00:27:24,920 northern margin of Ganwana using the tritozochondrial chronology. 419 00:27:25,240 --> 00:27:29,400 And we have now new project which started this year, which 420 00:27:29,400 --> 00:27:33,480 is focused on reconstruction of our key and supercontinent. 421 00:27:33,480 --> 00:27:38,440 So the field work will be in Canada and Wyoming and Finland. 422 00:27:38,960 --> 00:27:40,840 So 2 very different time periods. 423 00:27:40,840 --> 00:27:44,320 Very different time periods and very different field areas, but 424 00:27:44,880 --> 00:27:47,960 we enjoy both. Both are very interesting 425 00:27:48,000 --> 00:27:51,640 problems to solve. Yuri Jacques, thank you very 426 00:27:51,640 --> 00:27:53,160 much. Thank you very much. 427 00:27:54,280 --> 00:27:56,960 To see pictures and illustrations that support this 428 00:27:56,960 --> 00:28:02,280 podcast, go to geologybytes.com, where you'll also find a subject 429 00:28:02,280 --> 00:28:04,200 matter index of all the episodes. 430 00:28:04,640 --> 00:28:08,000 There you can also give me feedback which I welcome, as 431 00:28:08,000 --> 00:28:11,000 well as sign up to get my emails about new episodes.