1 00:00:03,840 --> 00:00:06,800 This is Geology Bites with Oliver Strimpel. 2 00:00:08,360 --> 00:00:11,280 A subduction zone can last for a very long time. 3 00:00:12,560 --> 00:00:16,680 During that time, it can move forward, backward, or sideways 4 00:00:16,840 --> 00:00:20,560 and get stuck in place. It can even change direction. 5 00:00:21,560 --> 00:00:25,920 What governs how a subduction zone evolves, and how do the 6 00:00:25,920 --> 00:00:29,120 various kinds of evolution manifest themselves on the 7 00:00:29,120 --> 00:00:32,479 surface? Claudio Fachena has been 8 00:00:32,479 --> 00:00:36,240 studying how convergent margins evolve for over 30 years, 9 00:00:36,720 --> 00:00:39,600 concentrating particularly on the Mediterranean region. 10 00:00:40,720 --> 00:00:44,080 He is head of the Lithospheric Dynamics section at the 11 00:00:44,080 --> 00:00:49,520 Helmholtz Centre for Geosciences at GFZ in Potsdam in Germany, 12 00:00:50,040 --> 00:00:53,080 and also a professor at the Department of Science at Roma 13 00:00:53,080 --> 00:00:57,000 Trey University. Claudio Fachena, welcome to 14 00:00:57,000 --> 00:00:59,080 Geology Bytes. Thank you, Oliver. 15 00:00:59,160 --> 00:01:02,800 I'm very happy to be here. We've talked about subduction 16 00:01:02,800 --> 00:01:07,720 zones in previous episodes of the podcast, especially the ones 17 00:01:07,760 --> 00:01:12,480 with Jeff Abbas, David Bercavici, and Laurent Jolivet. 18 00:01:13,360 --> 00:01:18,480 But can you refresh us on what a subduction zone is and what the 19 00:01:18,480 --> 00:01:20,840 basic mechanism is that drives them? 20 00:01:21,320 --> 00:01:24,040 Yeah, sure. At larger scale we know mantle 21 00:01:24,040 --> 00:01:27,440 convection is a drive to dissipate the heat inside the 22 00:01:27,480 --> 00:01:30,080 Earth. So one of the consequence of 23 00:01:30,080 --> 00:01:34,840 that is the formation of a cold shell we call lithosphere on the 24 00:01:34,840 --> 00:01:38,880 outer part of the earth. And so those plates we call it 25 00:01:38,920 --> 00:01:44,600 oceanic Lithosphere is created a Ridge and then once it started a 26 00:01:44,600 --> 00:01:49,160 mid oceanic Ridge where the moth material rise spread apart and 27 00:01:49,160 --> 00:01:52,200 cooled down forming new oceanic sea floor. 28 00:01:53,200 --> 00:01:58,560 Now the leaders fear age became colder and eventually denser 29 00:01:58,600 --> 00:02:02,720 than the hotter softer material that is beneath it. 30 00:02:03,520 --> 00:02:07,880 And so after 20 or 30 million years approximately, it's going 31 00:02:07,880 --> 00:02:11,280 to be denser. And so it get dense enough to 32 00:02:11,280 --> 00:02:15,480 start sinking back into the mantle cell. 33 00:02:15,800 --> 00:02:20,360 Imagine to have a slab of metal or any dense material sinking 34 00:02:20,360 --> 00:02:23,440 in, falling into honey. So the slab is sinking because 35 00:02:23,440 --> 00:02:27,120 it's denser, but its motion is resisted by the viscosity of the 36 00:02:27,120 --> 00:02:30,680 mantle, almost like honey could resist a heavy object falling 37 00:02:30,680 --> 00:02:33,360 into that. So the speed at which the 38 00:02:33,360 --> 00:02:38,640 subduction zone go depends on two things, the density 39 00:02:38,640 --> 00:02:42,360 constraints that is scaling with the age of the literature and 40 00:02:42,360 --> 00:02:48,640 the viscosity of the mantle. Now the slab is now attached to 41 00:02:48,640 --> 00:02:54,320 the lidosphere and so for it sinks it has to bend over and 42 00:02:54,320 --> 00:02:58,000 this require energy. So the bending resistance is a 43 00:02:58,000 --> 00:03:01,200 big part of what control the dynamic of subduction. 44 00:03:01,920 --> 00:03:08,120 So in simple way, a subduction zone is where a cold, cold and 45 00:03:08,120 --> 00:03:12,480 dense lidosphere dive back into the mantle, driven by the 46 00:03:12,480 --> 00:03:16,920 gravity and resisted by the viscosity and by plants trend. 47 00:03:17,600 --> 00:03:21,040 I've said that subduction zones can last a long time. 48 00:03:21,680 --> 00:03:24,920 How long are we? Talking, subduction is the 49 00:03:24,920 --> 00:03:29,520 longest running tectonic process on Earth, so it can last 50 00:03:29,520 --> 00:03:32,440 millions or even hundreds of millions of years. 51 00:03:32,760 --> 00:03:36,680 For example, the unden subduction zone where the Nazca 52 00:03:36,680 --> 00:03:40,440 play now is sinking down below South America. 53 00:03:41,000 --> 00:03:43,640 We know before it was the Farayam play, it's been 54 00:03:43,640 --> 00:03:47,200 subducting for almost a couple of hundreds of million year. 55 00:03:47,760 --> 00:03:51,400 And also where you have India colliding with Eurasia along 56 00:03:51,400 --> 00:03:55,280 this big subduction zone, we know that the subduction was 57 00:03:55,280 --> 00:03:57,040 more than hundreds of million years. 58 00:03:57,720 --> 00:04:00,480 But here's the key. Subduction is unsteady. 59 00:04:00,800 --> 00:04:04,880 It change its speed, even the way it happened can shift 60 00:04:04,880 --> 00:04:08,600 dramatically and sometimes it's last for very few millions of 61 00:04:08,600 --> 00:04:12,440 years. Can you categorize the various 62 00:04:12,440 --> 00:04:15,320 ways in which subduction zones evolve? 63 00:04:15,840 --> 00:04:20,440 Sure, subduction zone, a highly dynamic process and highly 64 00:04:20,440 --> 00:04:24,760 unsteady. It's a 3D system, so a slab is 65 00:04:24,760 --> 00:04:29,520 never fixed in one place. So slab don't just sink straight 66 00:04:29,520 --> 00:04:33,800 down into the mantle of gravity but they move also sideways or 67 00:04:33,800 --> 00:04:37,800 laterally. The sideways motion is driven by 68 00:04:37,800 --> 00:04:41,880 play motion, mantle flow and the force within the slab itself. 69 00:04:42,400 --> 00:04:46,760 Now there is several way that the trench in the slab is 70 00:04:46,760 --> 00:04:49,800 moving. For example, one is slab 71 00:04:49,800 --> 00:04:53,240 rollback. So the slab move backward into 72 00:04:53,240 --> 00:04:55,840 the mantle and we call it slab rollback. 73 00:04:56,440 --> 00:04:59,840 And when the trench, which is the surface expression of 74 00:04:59,840 --> 00:05:04,520 subduction, also move backward, it retreats toward the 75 00:05:04,520 --> 00:05:09,440 subducting plate. The trench can also move forward 76 00:05:09,440 --> 00:05:14,600 or can be even stationary. So in forward motion, the slab 77 00:05:14,600 --> 00:05:16,880 is advancing toward the upper plate. 78 00:05:17,720 --> 00:05:21,760 Occasionally we can also have the case where the slab might 79 00:05:21,760 --> 00:05:26,520 break off, twist or stop and so the subduction in this case can 80 00:05:26,520 --> 00:05:29,720 shift to a new location, flip direction. 81 00:05:30,080 --> 00:05:33,200 And this is a process could we call polarity reversal. 82 00:05:34,040 --> 00:05:36,720 There are two important takeaways here. 83 00:05:36,800 --> 00:05:40,960 First, the movement of the subduction zone, it's not steady 84 00:05:41,280 --> 00:05:45,240 but it change over time. And 2nd subduction zone and 85 00:05:45,240 --> 00:05:48,920 never act alone, is never alone, but interact with the 86 00:05:48,920 --> 00:05:53,560 neighbourhood's lab. So the behaviour of one slab can 87 00:05:53,560 --> 00:05:56,000 be affected by another close by one. 88 00:05:56,600 --> 00:06:00,160 It's many regions, there are several subduction zone next to 89 00:06:00,160 --> 00:06:04,200 each other, and this can be for example in opposite direction, 90 00:06:04,240 --> 00:06:08,000 outward or inward. So the interaction between the 91 00:06:08,000 --> 00:06:11,200 slabs in this case became really complicated. 92 00:06:11,600 --> 00:06:13,880 Let's talk about each of these in turn. 93 00:06:13,880 --> 00:06:18,080 Then. What causes slab rollback or 94 00:06:18,160 --> 00:06:21,720 retreat of the trench? And when that happens, how does 95 00:06:21,720 --> 00:06:24,640 that manifest in the surface geology? 96 00:06:25,200 --> 00:06:29,040 This is a fascinating tectonic process that shapes some of the 97 00:06:29,120 --> 00:06:32,640 most acted zone on Earth, so it's very important. 98 00:06:32,840 --> 00:06:36,760 So what is that? A slab rollback happen when a 99 00:06:36,760 --> 00:06:40,000 subducting plate sink into the mountain and start moving 100 00:06:40,120 --> 00:06:43,920 backward. So at the surface, this goes the 101 00:06:43,920 --> 00:06:47,680 trench to retreat. So you should think like pulling 102 00:06:47,680 --> 00:06:53,560 a carpet down and back and the hedge move away from you as it 103 00:06:53,560 --> 00:06:56,080 rolls up. And this is simply because the 104 00:06:56,080 --> 00:06:59,080 slab is inclined toward the upper plate. 105 00:06:59,080 --> 00:07:02,880 So if you're pulling down even the tendency will be to retreat. 106 00:07:03,600 --> 00:07:08,000 Now all subduction zone in theory should have the tendency 107 00:07:08,000 --> 00:07:10,520 to Mcgrive backwards for this reason. 108 00:07:11,080 --> 00:07:15,960 The problem is that one of the key feature that we see when the 109 00:07:15,960 --> 00:07:20,440 slab rollback is that you push the trench away from the upper 110 00:07:20,440 --> 00:07:24,360 plate and so you create extension of formation, what we 111 00:07:24,360 --> 00:07:27,680 call Becker Basin. When you say Becker Basin, 112 00:07:27,920 --> 00:07:31,680 that's happening in front of the subduction zone and how, how 113 00:07:31,680 --> 00:07:34,360 does that work? So they're overriding plates, 114 00:07:34,360 --> 00:07:39,160 stretches and even split apart creating a new ocean. 115 00:07:39,360 --> 00:07:42,200 And there are several place where we can observe that. 116 00:07:42,200 --> 00:07:46,080 For example, along the Tonga branch, you have the Low basin, 117 00:07:46,480 --> 00:07:51,400 which is actually the fastest rollback area on the planet or 118 00:07:51,400 --> 00:07:56,440 in the GNC, but also in the Sandwich just South of South 119 00:07:56,440 --> 00:07:59,320 America. In the past, almost all the 120 00:07:59,320 --> 00:08:02,040 Western Pacific underwent extension. 121 00:08:03,160 --> 00:08:06,440 But there is something that is very interesting in the story. 122 00:08:07,000 --> 00:08:12,200 When we start looking at the age of this basin, we realize that 123 00:08:12,200 --> 00:08:16,080 this tension stretching on the upper plate, which are reflected 124 00:08:16,080 --> 00:08:18,960 by the fact that you have the trench retreat, don't last 125 00:08:18,960 --> 00:08:23,280 forever, but they're usually lasting for 10 or 20 million 126 00:08:23,280 --> 00:08:26,960 year. So that means that the motion of 127 00:08:26,960 --> 00:08:31,720 the trench for some time was highly retreating and then stop 128 00:08:32,120 --> 00:08:37,880 or slow down almost completely. So and after a pose of say few 129 00:08:37,880 --> 00:08:43,120 millions of year is start again. So this stop and go behaviour 130 00:08:43,120 --> 00:08:47,880 sometimes happen three times in some region like along the 131 00:08:47,880 --> 00:08:51,240 Ejuboni Mariana system. This is, I think, very 132 00:08:51,240 --> 00:08:54,640 fascinating because it's giving us the opportunity to understand 133 00:08:54,640 --> 00:08:56,960 better the dynamic of the system. 134 00:08:57,600 --> 00:09:00,440 If you wonder where the slab Robeck is happening right now, 135 00:09:00,480 --> 00:09:03,440 then you can look at probably the Tonga is the best place, 136 00:09:03,560 --> 00:09:06,720 which is one of the fastest. So you mentioned the Tonga 137 00:09:06,720 --> 00:09:10,320 Trench and you also mentioned the Izu Bonin Trench. 138 00:09:10,320 --> 00:09:13,040 Where is that? The Tonga Trench is the 139 00:09:13,040 --> 00:09:16,800 Southwest Pacific and the Izu Bonin Mariana. 140 00:09:17,120 --> 00:09:21,400 It's just South of Japan and then it's a very long feature 141 00:09:21,720 --> 00:09:24,200 that is standing almost north-south. 142 00:09:24,320 --> 00:09:28,400 So all this area, the western Pacific is bounded by the 143 00:09:28,400 --> 00:09:31,640 subduction zone of the Pacific, which is one of the fastest 144 00:09:31,640 --> 00:09:35,560 plate on Earth, underwent an enormous black carcass tension 145 00:09:36,080 --> 00:09:40,240 between say 30 million year, 40 million year and now is still 146 00:09:40,240 --> 00:09:42,480 active. That is one of the most 147 00:09:42,480 --> 00:09:45,240 spectacular evidence of lab rollback on Earth. 148 00:09:45,920 --> 00:09:49,600 What happens when subduction zones do the opposite and they 149 00:09:49,600 --> 00:09:52,520 advance? Why does that occur and how does 150 00:09:52,520 --> 00:09:55,680 that manifest on the surface? Well, this is only more 151 00:09:55,680 --> 00:10:00,280 complicated to understand in some region again in the Izuboni 152 00:10:00,280 --> 00:10:04,720 Mariana, which is was retreating for a long time and in the last 153 00:10:05,120 --> 00:10:09,760 5 million years start advancing. It's probably related to the 154 00:10:09,760 --> 00:10:13,680 fact that you have a multiple subduction zone lining up side 155 00:10:13,680 --> 00:10:16,920 by side and they are dipping on the same direction. 156 00:10:17,480 --> 00:10:23,040 So the motion of one of the slab can help pull the other forward 157 00:10:23,280 --> 00:10:27,600 like a little train. If the one in front move and 158 00:10:27,600 --> 00:10:31,640 it's pulling down the flipping slates, then it drags the other 159 00:10:31,640 --> 00:10:33,680 along. And so in the last five million 160 00:10:33,680 --> 00:10:38,280 year, the Izuboni Mariana for a long time was retreating, now 161 00:10:38,280 --> 00:10:40,600 changes motion and start advancing. 162 00:10:40,600 --> 00:10:43,080 Sorry, when you say dragging along, is it because it's next 163 00:10:43,080 --> 00:10:46,400 to it laterally dragging it or is it in front of it? 164 00:10:46,560 --> 00:10:50,800 Front of it, in front of it, and this has been recognized long 165 00:10:50,800 --> 00:10:54,520 time ago, but the effect of the front was lab, which is the 166 00:10:54,520 --> 00:10:58,640 Lucas lab, which is retreating at the moment, is consuming the 167 00:10:58,640 --> 00:11:03,160 plate between the two and then is kind of sucking the other 168 00:11:03,160 --> 00:11:07,320 trench, which is incredible. And so you have a complete 169 00:11:07,320 --> 00:11:10,040 reverse of moisture. So those labs are really 170 00:11:10,080 --> 00:11:12,160 floating into the mount all laterally. 171 00:11:12,280 --> 00:11:15,960 There are other extreme case of trench advance and those are, 172 00:11:15,960 --> 00:11:18,920 for example, happening during continental collision. 173 00:11:19,000 --> 00:11:22,680 One of the best example of it, it's not a subduction zone, it's 174 00:11:22,680 --> 00:11:25,400 a collisional zone. In this case, it's a continental 175 00:11:25,400 --> 00:11:28,960 lithosphere that is advancing toward the upper plate that 176 00:11:29,080 --> 00:11:33,360 India is indenting into Asia, creating this enormous mountain 177 00:11:33,400 --> 00:11:36,400 belt. So you got India crashing into 178 00:11:36,400 --> 00:11:40,160 Asia, but at the same time the Australian plate is subducting 179 00:11:40,200 --> 00:11:43,120 on the net from the southeast Java, Sumatra. 180 00:11:43,360 --> 00:11:46,960 So this sideway or lateral subduction, combine it with the 181 00:11:46,960 --> 00:11:52,640 mantle flow will push India frontward and crossing creation 182 00:11:52,640 --> 00:11:55,040 of the largest mountain belt in the world. 183 00:11:56,080 --> 00:11:58,360 So what does it look like at the surface? 184 00:11:58,360 --> 00:12:02,360 In trench advanced cases you often have intense crustal 185 00:12:02,360 --> 00:12:05,840 deformation, uplift, compression. 186 00:12:06,080 --> 00:12:10,760 You can have closure of Bayesian that it's a power spool way to 187 00:12:10,760 --> 00:12:14,280 having compression of force, very different from stretching 188 00:12:14,280 --> 00:12:19,560 during rollback. So in short, trench advance is 189 00:12:19,560 --> 00:12:23,440 less common than rollback, but when it does happen, it usually 190 00:12:23,440 --> 00:12:27,440 means that the tonic system is changing completely and moving 191 00:12:27,440 --> 00:12:32,560 from extension to compression. But it's also often caused by 192 00:12:32,560 --> 00:12:36,120 the influence neighborhoods, lab and Montal dynamics. 193 00:12:36,520 --> 00:12:40,840 I'm sure in the real world it's a bit of an oversimplification 194 00:12:40,840 --> 00:12:46,120 to say that subduction zones are either retreating or advancing. 195 00:12:46,800 --> 00:12:50,400 In his podcast episode, Laurent Jolivet describes some quite 196 00:12:50,400 --> 00:12:56,240 complex motions, including toroidal ones in 3D. 197 00:12:56,640 --> 00:13:00,920 Can you describe some of these more complicated motions? 198 00:13:01,480 --> 00:13:04,280 Sure, I will try. Let's talk about what happened 199 00:13:04,280 --> 00:13:07,280 in the mantle as his labs sink into it. 200 00:13:08,160 --> 00:13:13,200 So as the slab dive into the mantle itself is flowing from 201 00:13:13,200 --> 00:13:18,080 areas of high pressure toward areas of low pressure created by 202 00:13:18,080 --> 00:13:21,920 the slab itself. We usually break this mantle 203 00:13:21,920 --> 00:13:26,600 motion in two main component. The first one we call the 204 00:13:26,600 --> 00:13:31,760 poloidal component and just the vertical flow, the classical up 205 00:13:31,760 --> 00:13:35,240 and down. But then in 3D we have this 206 00:13:35,240 --> 00:13:38,720 other component, that is the toroidal component, that is the 207 00:13:38,720 --> 00:13:43,240 horizontal zwiggling flow, which tend to show up along the edge 208 00:13:43,240 --> 00:13:47,120 of the slab. So when this toroidal flow 209 00:13:47,120 --> 00:13:51,000 happened, if you're moving a spoon inside of a pot full of 210 00:13:51,000 --> 00:13:55,280 honey, you can see around the edge of the spoon, you will see 211 00:13:55,280 --> 00:13:59,000 the little vertex. And this is actually the kind of 212 00:13:59,000 --> 00:14:02,400 motion we are talking about and we are expecting to have into 213 00:14:02,400 --> 00:14:05,400 the mantle. If there are slab windows, so 214 00:14:05,520 --> 00:14:10,320 area where the slab is broken off, also a gap in the plate or 215 00:14:10,320 --> 00:14:16,040 near the slab edge, the mantle has space to flow inside and 216 00:14:16,040 --> 00:14:18,280 around the side. And this is creating the 217 00:14:18,280 --> 00:14:22,080 toroidal flow. It's a 3D feature and what is 218 00:14:22,080 --> 00:14:26,760 really fascinating is that this flow is not just deep into the 219 00:14:26,760 --> 00:14:32,040 mantle, but we have effect on the surface and it LED, for 220 00:14:32,040 --> 00:14:36,160 example, lateral deformation. For example, a large trice leaf 221 00:14:36,160 --> 00:14:40,320 folds on that produce a large earthquake rock shifting 222 00:14:40,320 --> 00:14:44,720 sideways, twisting or stretching in a very unusual pattern. 223 00:14:44,720 --> 00:14:49,680 So sometimes are very complicated to imagine when slab 224 00:14:49,680 --> 00:14:54,880 break into pieces or tear apart that slab is not a continuous 225 00:14:54,880 --> 00:14:57,560 feature. This effect are specially very 226 00:14:57,560 --> 00:15:00,680 pronounced. And so for example, Lauren was 227 00:15:00,680 --> 00:15:03,400 mentioned in the Mediterranean, this is a case where the slab 228 00:15:03,400 --> 00:15:07,480 are very small and so you have edges where this mantle is 229 00:15:07,480 --> 00:15:12,160 flowing during trench rollback. And so you're pushing basically 230 00:15:12,160 --> 00:15:15,480 the material that is below the slab on the side. 231 00:15:16,120 --> 00:15:19,240 And this is flowing over this abductance lab changing 232 00:15:19,240 --> 00:15:21,400 completely also the composition of the mountain. 233 00:15:22,120 --> 00:15:25,280 They had the Tongas lab. As we mentioned before, this is 234 00:15:25,280 --> 00:15:28,840 an area where you really have a lot of toroidal fluid that's 235 00:15:28,840 --> 00:15:32,480 been recognized nearby Samoa. Now, for example, you can have 236 00:15:32,480 --> 00:15:36,000 it in the Antilles or or for example, if you go at the edge 237 00:15:36,000 --> 00:15:39,720 of the abductance lab below the Andes in Patagonia on the Drake 238 00:15:39,720 --> 00:15:43,360 Passage between Antarctica and the South America, we have a 239 00:15:43,360 --> 00:15:46,600 slab break. And in this area we to have a 240 00:15:46,600 --> 00:15:50,280 big flow of Pacific mantle into different. 241 00:15:51,280 --> 00:15:54,240 So even if those flow are really deep into the mantle, their 242 00:15:54,240 --> 00:15:56,880 fingerprint on the surface are quite impressive. 243 00:15:57,080 --> 00:16:01,200 And so understanding them help us to really piece together the 244 00:16:01,280 --> 00:16:04,000 big picture of the mantle circuit on the Earth. 245 00:16:04,600 --> 00:16:09,240 All that present day examples of subduction zones that move 246 00:16:09,520 --> 00:16:13,880 laterally sideways or in a generally more complex fashion 247 00:16:13,880 --> 00:16:17,720 than either forward or backward. So yes, lateral motions lab is 248 00:16:17,720 --> 00:16:21,360 happening everywhere. Oliver subduction zone rally 249 00:16:21,360 --> 00:16:24,840 just sinks straight down and the trench are never stationary. 250 00:16:24,840 --> 00:16:29,080 Really what makes things tricky is how the different part of the 251 00:16:29,080 --> 00:16:32,800 slab interacting with each other with nearby slabs and reading 252 00:16:32,800 --> 00:16:36,120 the motion of the trench gave us the possibility to understand 253 00:16:36,120 --> 00:16:38,920 the slab dynamics. For example, one portion of the 254 00:16:38,920 --> 00:16:41,960 slab is advancing while the other one is retreating, and 255 00:16:41,960 --> 00:16:44,760 this created vortex and a complex dynamic in the 256 00:16:44,760 --> 00:16:46,640 overriding plate. For example, example, if you go 257 00:16:46,960 --> 00:16:50,600 to New Zealand, and we will discuss about that further on, 258 00:16:50,840 --> 00:16:54,240 then you go near the Alps, we have a strong collision of the 259 00:16:54,240 --> 00:16:57,000 plateau. But when you move northward, so 260 00:16:57,000 --> 00:16:59,680 the trench here is transpressional and is advancing 261 00:16:59,680 --> 00:17:01,880 a little bit. And if you move N, then you have 262 00:17:01,880 --> 00:17:05,079 a Becker region. So you move from compression to 263 00:17:05,079 --> 00:17:09,040 extension on the upper plate and the trench is more advancing or 264 00:17:09,040 --> 00:17:12,240 moving laterally to the South and is retreating to the north. 265 00:17:12,839 --> 00:17:16,040 The same picture is observed in other area like in the 266 00:17:16,040 --> 00:17:19,839 Mediterranean for example, if you go in Greece from the Lanic 267 00:17:19,839 --> 00:17:23,240 trench, which is retreating, you move north or along the other 268 00:17:23,240 --> 00:17:27,079 the Attic plates say going to where Venice say, and below the 269 00:17:27,079 --> 00:17:28,880 Dinarites, then you have compression. 270 00:17:28,880 --> 00:17:31,960 So you're moving lateral from compression zone where the 271 00:17:31,960 --> 00:17:35,320 trench is stationary is advancing toward the South. 272 00:17:35,480 --> 00:17:38,400 In the Lanic the trench is retreating very fast and 273 00:17:38,400 --> 00:17:42,640 producing backpack extension. So the lateral slab motion 274 00:17:42,640 --> 00:17:45,880 combined with interaction between adjacent slab and 275 00:17:45,880 --> 00:17:49,040 overriding play create a patchwork of tectonic setting 276 00:17:49,040 --> 00:17:54,200 that from mountain building to rifting and extension and so all 277 00:17:54,200 --> 00:17:57,240 connected on this 3D dynamic picture. 278 00:17:58,160 --> 00:18:02,560 I think the most surprising kind of subduction zone evolution is 279 00:18:02,560 --> 00:18:06,120 when the polarity of the subduction reverses. 280 00:18:06,520 --> 00:18:10,040 That is, a down going plate subducting in One Direction 281 00:18:10,320 --> 00:18:14,520 flips to becoming the overriding plate, with the formerly 282 00:18:14,680 --> 00:18:18,320 overriding plate subducting under it in the opposite 283 00:18:18,320 --> 00:18:21,120 direction. What makes that happen? 284 00:18:21,760 --> 00:18:25,080 Well this is a quite common mechanism as well. 285 00:18:25,480 --> 00:18:29,800 So it happen when you have a buoyant Fisher that is arriving 286 00:18:29,800 --> 00:18:34,200 a trench and it doesn't want to subduct and so you stop 287 00:18:34,200 --> 00:18:37,920 subduction somehow. In this case what you can have 288 00:18:38,040 --> 00:18:41,200 this is because I'm in a continental crust or a volcanic 289 00:18:41,200 --> 00:18:45,760 arc or a thick buoyant plateau is more buoyant and so it cannot 290 00:18:45,760 --> 00:18:50,400 descend down into the mountain. And now if you stop subduction, 291 00:18:50,480 --> 00:18:52,680 then you probably is followed by break off. 292 00:18:52,960 --> 00:18:57,160 And so this lab is falling down and the subduction will end. 293 00:18:57,600 --> 00:19:01,960 Now if compressional forces keep going in this case, then you 294 00:19:01,960 --> 00:19:05,720 have the restart of subduction in another place nearby. 295 00:19:06,160 --> 00:19:09,720 And one of the things that that we observe happening is that you 296 00:19:09,720 --> 00:19:13,440 can have a reversal of subduction now on the opposite 297 00:19:13,440 --> 00:19:16,240 direction. So subduction will occur on the 298 00:19:16,240 --> 00:19:18,680 other side and an opposite direction. 299 00:19:19,040 --> 00:19:23,520 So all this can occur in some millions of years, not very 300 00:19:23,640 --> 00:19:27,240 rapid because you have to stop 1 subduction and initiate another 301 00:19:27,240 --> 00:19:30,720 one. For example Banatu trench in the 302 00:19:30,720 --> 00:19:34,480 South Pacific. So it's Nordo Tonga now. 303 00:19:34,520 --> 00:19:39,080 There was a a plateau arriving a trench, it stopped subduction 304 00:19:39,080 --> 00:19:41,400 somehow. The subduction was of the 305 00:19:41,400 --> 00:19:44,840 Pacific that was going below the Australian plate. 306 00:19:45,280 --> 00:19:48,840 Now after the subduction, the plateau arrived, we have a 307 00:19:48,840 --> 00:19:52,120 reversal of subduction. Now the subduction is is of the 308 00:19:52,120 --> 00:19:56,560 Australian plate that go below the Pacific somehow and 309 00:19:56,560 --> 00:19:59,600 formation of the Vanatu trench of the New Hebrides. 310 00:20:00,280 --> 00:20:05,600 So this is a case where we now observe A lateral transition of 311 00:20:05,600 --> 00:20:09,720 the reversal polarity from the Tonga that is plunging down 312 00:20:09,720 --> 00:20:13,320 toward the West to the New Hebrides that is plunging down 313 00:20:13,320 --> 00:20:16,240 to the northeast. And so it occurred because of 314 00:20:16,240 --> 00:20:19,400 polarity reversal. Now in other cases which is 315 00:20:19,400 --> 00:20:22,960 pretty well known is Taiwan where you had the arrival of 316 00:20:22,960 --> 00:20:27,080 volcanic arc which is the chalk, the subduction zone and then you 317 00:20:27,080 --> 00:20:30,240 have the start of the new subduction zone of the South 318 00:20:30,240 --> 00:20:34,680 China Sea now. This reversal of polarity seems 319 00:20:34,680 --> 00:20:38,040 to have happened during the Caledonian originy. 320 00:20:38,040 --> 00:20:42,040 Rob Strachan told us about that in his podcast episode. 321 00:20:42,440 --> 00:20:45,960 So it sounds from what you're saying that polarity reversal 322 00:20:45,960 --> 00:20:50,320 actually is fairly common. Well, it is very common, maybe 323 00:20:50,440 --> 00:20:54,040 even more common than what we thought actually also in 324 00:20:54,040 --> 00:20:57,680 Camchaca, for example, we had that also in the Caribbean, we 325 00:20:57,680 --> 00:21:02,160 had that the subduction below what is now Mexico, Costa Rica, 326 00:21:02,160 --> 00:21:06,880 Panama was interrupted for and then arrival of the big plateau, 327 00:21:06,880 --> 00:21:09,920 which is the Caribbean plateau with the reversal of that. 328 00:21:10,920 --> 00:21:14,560 Now the only problem we have is that during subduction, 329 00:21:14,560 --> 00:21:19,040 sometimes the formation of the upper plate is really intense 330 00:21:19,120 --> 00:21:22,800 and some of this element that tests for the holders, the 331 00:21:22,800 --> 00:21:28,320 subduction polarity reversal can be lost into this mechanism. 332 00:21:28,320 --> 00:21:32,440 And so for us geologists now becoming a little bit difficult 333 00:21:32,800 --> 00:21:36,520 sometimes to unravel the history in a very complete fashion. 334 00:21:36,920 --> 00:21:42,760 And so the subsequent subduction episode may obscure the phrases 335 00:21:42,800 --> 00:21:47,440 of the oldest one or process like that that may occur also 336 00:21:47,440 --> 00:21:51,640 rapidly like in 10, so 20 million year in geological time 337 00:21:51,640 --> 00:21:53,640 scale. Sometimes this is a rapid 338 00:21:53,640 --> 00:21:56,200 process. Another phenomenon that we see 339 00:21:56,200 --> 00:22:00,840 quite often is the reversal of subduction polarity, not in 340 00:22:00,840 --> 00:22:04,560 time, but in space. In other words, as you follow 341 00:22:04,560 --> 00:22:07,960 the subduction zone along the surface, the subduction flips 342 00:22:07,960 --> 00:22:11,000 direction at a certain point. And I think you already just 343 00:22:11,000 --> 00:22:15,640 mentioned the example of this happening in New Zealand, where 344 00:22:15,760 --> 00:22:20,240 to the north of New Zealand and in North Island, the Pacific 345 00:22:20,240 --> 00:22:23,040 Plate is subducting westward under the Australian Plate. 346 00:22:23,400 --> 00:22:28,480 And then as you go South and cross the Alpine Fault, the 347 00:22:28,480 --> 00:22:31,400 direction reverses with the Australian Plate subducting 348 00:22:31,480 --> 00:22:33,880 eastward under the Pacific Plate. 349 00:22:35,160 --> 00:22:36,640 Do we understand how this happens? 350 00:22:36,640 --> 00:22:39,960 It sounds from what you were suggesting that these two 351 00:22:40,160 --> 00:22:43,840 subduction zones used to be going in the same direction, but 352 00:22:43,840 --> 00:22:47,240 then one got blocked up and reversed. 353 00:22:47,720 --> 00:22:50,800 It's actually the same things. So it's triggered by the 354 00:22:50,800 --> 00:22:54,680 collision of a buoyant feature like oceanic plateau, a volcanic 355 00:22:54,680 --> 00:22:56,880 arc. Sometimes it just reflect the 356 00:22:56,880 --> 00:23:00,680 presence of a polygeographic distribution, so the way the 357 00:23:00,680 --> 00:23:04,960 oceanic basin were distributed or ranged in the past and this 358 00:23:04,960 --> 00:23:08,240 set the stage for how and where subduction will start down 359 00:23:08,240 --> 00:23:10,640 later. One example is the transition 360 00:23:10,640 --> 00:23:14,720 from the Alps to the Apennine in Europe where we observe a change 361 00:23:14,720 --> 00:23:17,480 in subduction direction over a relatively short distance. 362 00:23:17,480 --> 00:23:20,600 So in the Apennine you have a subduction of the Adria plate 363 00:23:20,600 --> 00:23:25,120 which is belonging to Africa domain say below Eurasia. 364 00:23:25,120 --> 00:23:27,800 Whereas when you go in the Alps is the other way around. 365 00:23:27,800 --> 00:23:30,680 So the there is the Eurasia that is subducting below. 366 00:23:31,280 --> 00:23:33,880 Another great example as I said is Taiwan. 367 00:23:33,880 --> 00:23:37,960 So in this East China Sea plate is being subducted back to the 368 00:23:37,960 --> 00:23:42,080 north is the Philippine plate that's subducting under the UQ 369 00:23:42,080 --> 00:23:44,560 trench. So another clear change in 370 00:23:44,560 --> 00:23:48,320 polarity along strike. And the Vanetto is the other 371 00:23:48,320 --> 00:23:50,760 example that I was mentioned before. 372 00:23:50,760 --> 00:23:57,640 So it's the same process along strike and on time that drive 373 00:23:57,640 --> 00:23:59,720 that. When we spoke earlier, you 374 00:23:59,720 --> 00:24:04,480 mentioned slab anchoring and how it plays a role in mountain 375 00:24:04,480 --> 00:24:08,800 building and basically in freezing a subduction zone in 376 00:24:08,800 --> 00:24:11,240 place. Can you explain that? 377 00:24:11,800 --> 00:24:14,080 Oh yes, sure. This is one of my passion. 378 00:24:14,160 --> 00:24:17,920 The health mantle is not uniform in terms of viscosity. 379 00:24:18,440 --> 00:24:22,480 So that means that the deep layer, especially the one below 380 00:24:22,480 --> 00:24:28,720 700 kilometers are more viscous than the other one, like 50 or 381 00:24:28,720 --> 00:24:33,280 30 times more viscous. So when a slab reached this 382 00:24:33,280 --> 00:24:35,760 depth, you can behave in two ways. 383 00:24:36,400 --> 00:24:41,880 Some of them do not penetrate and flatten out, other may 384 00:24:41,880 --> 00:24:44,240 penetrate. And this also depending on the 385 00:24:44,240 --> 00:24:49,160 way the slab arrive to hit this transition zone, whether it's 386 00:24:49,160 --> 00:24:54,240 more vertical or not. So if this lab I enter into the 387 00:24:54,240 --> 00:24:57,960 lower mantle, then it is more anchor, it cannot really move 388 00:24:57,960 --> 00:25:01,680 because it's more strict by the more viscous layer. 389 00:25:02,280 --> 00:25:04,320 Now there is also another effect. 390 00:25:04,320 --> 00:25:07,800 Once it penetrate into the lower mantle, then it trigger a very 391 00:25:07,800 --> 00:25:11,920 large scale convection cell more vigorous than what the one 392 00:25:11,920 --> 00:25:15,680 before in the upper mantle. So in this case the trench 393 00:25:15,760 --> 00:25:19,440 became in stationary and could be stationary for some 10s of 394 00:25:19,440 --> 00:25:23,520 millions of year until something new happened, maybe the slab 395 00:25:23,520 --> 00:25:26,640 broken off. This is intriguing because a 396 00:25:26,640 --> 00:25:31,360 good example of this case and the impact of the anchoring on 397 00:25:31,360 --> 00:25:35,600 the deformation on the upper plate we think is the case of 398 00:25:35,600 --> 00:25:39,280 the formation of the Undiscord era in South America. 399 00:25:39,760 --> 00:25:43,520 So there at least in the northern part where the Andes go 400 00:25:43,560 --> 00:25:47,600 up forming the Altiplano 4000 meters elevation. 401 00:25:47,920 --> 00:25:51,800 So in this area, the trench of the Nazca plate remain 402 00:25:51,800 --> 00:25:55,200 relatively stationary. And we think this is occurring 403 00:25:55,200 --> 00:25:58,120 because the slab penetrated anchors deep into the mountain 404 00:25:58,720 --> 00:26:01,760 and so you're resisting the motion of South America. 405 00:26:01,880 --> 00:26:05,840 So that the reason why you have the sort of collision where you 406 00:26:05,840 --> 00:26:08,800 create a mountain belt even if you don't have the collision 407 00:26:08,800 --> 00:26:11,720 between 2 continental plate, it's just because the trench is 408 00:26:11,720 --> 00:26:13,960 stationary and anchor deep into the mountain. 409 00:26:14,440 --> 00:26:17,600 Wow that's interesting. So instead of just creating a 410 00:26:17,680 --> 00:26:23,680 regular volcanic arc as most subduction zones do, we create a 411 00:26:23,680 --> 00:26:26,480 giant mountain chain? Because the slab is stuck in 412 00:26:26,480 --> 00:26:30,680 place continually generating volcanism in the same place over 413 00:26:30,680 --> 00:26:33,080 10s or even hundreds of millions of years. 414 00:26:33,760 --> 00:26:37,400 So it's still subducting downwards, driving continued 415 00:26:37,400 --> 00:26:40,720 volcanism in the Andes and releasing volatiles. 416 00:26:41,120 --> 00:26:45,160 Exactly if the motion of the velocity of that even further 417 00:26:45,240 --> 00:26:49,320 increase when the slab penetrate into the lower mantle dioza, we 418 00:26:49,320 --> 00:26:53,400 think that the slab penetrate after a period of stagnation 419 00:26:53,400 --> 00:26:56,880 where you accumulate a lot of dense material and then they may 420 00:26:57,160 --> 00:26:58,920 avalanche down into the lower mantle. 421 00:26:58,920 --> 00:27:02,680 In this case, you really can have also an acceleration and 422 00:27:02,680 --> 00:27:05,920 outplay motion. So that is super interesting. 423 00:27:05,920 --> 00:27:10,560 This is ultimately in my mind the reason why you created 424 00:27:10,800 --> 00:27:13,880 everything under compression until you create a 425 00:27:13,880 --> 00:27:16,360 supercontinent. But this is another story. 426 00:27:17,320 --> 00:27:22,800 What methods and observations do you use in your research to 427 00:27:22,800 --> 00:27:25,680 better understand the dynamics of subduction zones? 428 00:27:26,160 --> 00:27:30,440 This is a great question. One of the major tool used for 429 00:27:30,440 --> 00:27:34,360 imagining subduction zone adapt obviously is a seismology. 430 00:27:34,680 --> 00:27:37,960 So seismology can give us the current structure of subduction 431 00:27:37,960 --> 00:27:41,600 zone, not only the distribution of earthquake that go down to 432 00:27:41,600 --> 00:27:45,120 700 kilometre, but also using tomography. 433 00:27:45,400 --> 00:27:48,040 And so looking at the distribution of the cold 434 00:27:48,040 --> 00:27:52,320 material revealed by the path of seismic way they go faster then 435 00:27:52,320 --> 00:27:56,880 you can unravel the whole phase of subduction story. 436 00:27:57,640 --> 00:28:00,880 And there is also the active seismology where we're shooting 437 00:28:00,880 --> 00:28:03,920 and then we can record by seismometer and this is 438 00:28:03,920 --> 00:28:07,480 illuminating the upper part of the subduction zone. 439 00:28:07,480 --> 00:28:13,320 So checking at the first tenths of 15 kilometers more in detail 440 00:28:13,320 --> 00:28:15,560 what happened into the subduction zone, You know, 441 00:28:15,760 --> 00:28:20,240 subduction zone release most of the seismic energy on Earth and 442 00:28:20,240 --> 00:28:23,800 it's causing big earthquake. Only subduction zone can have 443 00:28:24,040 --> 00:28:27,040 none of the other faults will never reach this kind of 444 00:28:27,200 --> 00:28:29,280 magnitude. Just because the geometry of 445 00:28:29,280 --> 00:28:33,840 subduction zone is so large that you can start propagating the 446 00:28:33,840 --> 00:28:37,640 rupture for hundreds of kilometers with motion that are 447 00:28:37,640 --> 00:28:40,960 10s of meters. We really spend a lot of energy 448 00:28:40,960 --> 00:28:44,560 and time to understand how they work and so for that we're 449 00:28:44,560 --> 00:28:49,000 installing seismic station on the sea, geodetic station on the 450 00:28:49,000 --> 00:28:52,800 sea, and trying to images the mush on the plate with great 451 00:28:52,800 --> 00:28:56,400 accuracy. Now seductions are also doing 452 00:28:56,400 --> 00:28:59,400 something different. So not only seismology but 453 00:28:59,400 --> 00:29:04,120 geodesy, but also it's about recycling material and moving 454 00:29:04,120 --> 00:29:07,560 rocks. So like a machine that takes 455 00:29:07,560 --> 00:29:13,600 sediment, fluids and rock down to 10s of kilometers, and when 456 00:29:13,600 --> 00:29:17,000 you do that, they're releasing fluid and they're releasing 457 00:29:17,000 --> 00:29:21,560 volatiles that are recycled backward into the volcanic arc. 458 00:29:21,920 --> 00:29:26,320 And so petrology is a very important tool as well, because 459 00:29:26,400 --> 00:29:30,000 with that you can understand much better what kind of 460 00:29:30,040 --> 00:29:34,720 material is subducting and how metamorphism reflect the 461 00:29:34,720 --> 00:29:39,520 temperature of the subduction process at the interface between 462 00:29:39,520 --> 00:29:41,640 the two plates. So is that because you're 463 00:29:41,640 --> 00:29:45,880 studying the detailed geochemistry of the material 464 00:29:45,880 --> 00:29:48,600 that comes out of the volcanoes in the volcanic arc? 465 00:29:49,120 --> 00:29:52,160 This will tell us a lot about the how much sediment are 466 00:29:52,160 --> 00:29:55,560 subducting and then how much fluid are subducting. 467 00:29:55,560 --> 00:29:59,880 And so this story will help us to understand the circuit that 468 00:29:59,880 --> 00:30:03,600 you can have at the recycle of element like carbon dioxide, 469 00:30:03,600 --> 00:30:07,800 metals and many others. So there's a whole budget of 470 00:30:07,800 --> 00:30:11,160 chemical elements that you can trace it using chemistry on 471 00:30:11,160 --> 00:30:15,440 petrology of volcanic arc. But also sometimes the 472 00:30:15,440 --> 00:30:19,720 subduction interface down to 4 and 40 and 30 kilometer is 473 00:30:19,720 --> 00:30:22,720 exhumed later. And so when we go in the field 474 00:30:22,720 --> 00:30:27,000 that we can look at that and reconstruct the pressure, the 475 00:30:27,000 --> 00:30:31,600 temperature and the budget of fluid that occur during the 476 00:30:31,600 --> 00:30:33,600 motion on one plate below the other. 477 00:30:34,400 --> 00:30:38,160 And when you have all this information, then you can get 478 00:30:38,160 --> 00:30:41,440 into modeling. Now modeling is a fundamental 479 00:30:41,440 --> 00:30:47,280 tool that both experimental and numerical model to try to mimic 480 00:30:47,280 --> 00:30:50,200 and understanding the dynamic. Once we have reconstructed the 481 00:30:50,200 --> 00:30:53,880 kinematic and reconstructing the parameters controlling the 482 00:30:53,880 --> 00:30:57,880 process, we can go to our machine, to our laboratory, 483 00:30:57,880 --> 00:31:01,720 reconstructing and understanding what caused the motion of this 484 00:31:01,720 --> 00:31:05,640 lab into the mantle and what process are governing this lab 485 00:31:05,640 --> 00:31:08,680 dynamic. So it's a teamwork you have to 486 00:31:08,840 --> 00:31:12,680 combining observation, experiment and theory to build 487 00:31:12,680 --> 00:31:15,120 that complete picture of a subduction zone. 488 00:31:15,280 --> 00:31:18,640 And that's also what makes subduction zone so exciting, I 489 00:31:18,640 --> 00:31:21,560 think. The seismic data we've been 490 00:31:21,560 --> 00:31:25,720 talking about so far gives us information about seismic wave 491 00:31:25,720 --> 00:31:29,000 speeds, which is usually interpreted to reflect the 492 00:31:29,000 --> 00:31:31,920 temperature of the lithosphere and mantle traversed by the 493 00:31:31,920 --> 00:31:35,520 seismic waves. But can we also use the 494 00:31:35,520 --> 00:31:40,840 anisotropy of the seismic waves, IE the different speeds of 495 00:31:40,840 --> 00:31:45,040 differently polarized waves, to reveal some of the mantle flows 496 00:31:45,040 --> 00:31:48,040 you've been telling us about around the subducting slab? 497 00:31:48,480 --> 00:31:50,440 No, absolutely. Seismic anisotropy is a 498 00:31:50,440 --> 00:31:53,640 fundamental tool actually, because seismic anisotropy 499 00:31:53,640 --> 00:31:57,560 actually gave us an incremental of deformation. 500 00:31:57,560 --> 00:32:00,680 So it's not only an instantaneous picture like the 501 00:32:00,680 --> 00:32:03,960 one you can have with earthquake, but you can go back 502 00:32:03,960 --> 00:32:08,160 in time because to have a strong signal then you have to deform 503 00:32:08,400 --> 00:32:12,360 our mineral in a way to polarize sufficiently the waves. 504 00:32:12,920 --> 00:32:16,440 And so also for that, I think this is a very useful tool 505 00:32:16,440 --> 00:32:19,000 because this gave us a long term signal. 506 00:32:19,000 --> 00:32:22,680 It's not an Eastern tennis one. What are you working on at the 507 00:32:22,680 --> 00:32:25,760 moment? So Oliver, my driving research 508 00:32:25,760 --> 00:32:29,080 stimulus is understanding the coupling between deep mantle 509 00:32:29,080 --> 00:32:33,080 process and what we see at the surface, so the connection 510 00:32:33,080 --> 00:32:35,240 between surface process and the deep. 511 00:32:35,440 --> 00:32:39,200 And I do that especially on subduction margin and active 512 00:32:39,200 --> 00:32:42,800 zones because when you look at working in active area, then you 513 00:32:42,800 --> 00:32:46,440 can actually use information from geophysics to better 514 00:32:46,440 --> 00:32:50,200 constrain what is happening now. And with that, you can go back 515 00:32:50,200 --> 00:32:53,520 in the past. So at the moment, looking close 516 00:32:53,520 --> 00:32:57,760 at the formation around slab edges, for example, in Greece, 517 00:32:57,760 --> 00:33:01,720 where the dynamics are very completely fascinating, moving 518 00:33:01,720 --> 00:33:05,920 from compression to extension, but also the Andes. 519 00:33:05,920 --> 00:33:10,920 We have installed some 10s of years ago an observatory along 520 00:33:10,920 --> 00:33:14,000 the Northern Chile in the Atacama desert, where we have a 521 00:33:14,000 --> 00:33:18,800 big seismic gap and we hope to be able to capture signal for 522 00:33:18,800 --> 00:33:22,760 the preparatory phase. But we also working in Panama, 523 00:33:22,880 --> 00:33:26,520 Colombia region, where the Caribbean meet the Nazca's labs. 524 00:33:26,520 --> 00:33:28,840 So it's a highly 3 dimensional problem. 525 00:33:29,440 --> 00:33:34,440 But in this context, we are really trying to understand how 526 00:33:34,440 --> 00:33:38,520 subduction is modelling also on the surface and the landscape 527 00:33:38,880 --> 00:33:43,360 and how this reflect on biodiversity for the crew and 528 00:33:43,400 --> 00:33:47,080 and formation of the Panama strength dividing the Pacific 529 00:33:47,080 --> 00:33:50,960 and the Atlantic. Also we don't stop here because 530 00:33:50,960 --> 00:33:52,840 we're also working in collisional areas. 531 00:33:52,840 --> 00:33:57,040 So the region where we're working now is Pakistan in the 532 00:33:57,040 --> 00:34:00,560 northern Pakistan. There in the Karakoram, we have 533 00:34:00,640 --> 00:34:04,240 two subduction zone in the past. Now they are pretty close to 534 00:34:04,240 --> 00:34:06,640 each other in the region of Nanga Parbat. 535 00:34:07,120 --> 00:34:11,120 And in this area we can find the trace of both subduction zone 536 00:34:11,120 --> 00:34:16,600 and try to understand what bring this formation or this enormous 537 00:34:16,719 --> 00:34:19,760 mountain belt. I love mountains, so I'm moving 538 00:34:19,800 --> 00:34:21,719 region where there are high elevation. 539 00:34:21,960 --> 00:34:25,520 There you can see the surface expression of deep deformation 540 00:34:25,520 --> 00:34:29,280 and try understanding the best expression of subduction and 541 00:34:29,280 --> 00:34:33,159 collision on the surface. Claudia Fachena, thank you very 542 00:34:33,159 --> 00:34:36,000 much. Oliver, thanks a lot for tuning 543 00:34:36,000 --> 00:34:38,280 in. To see pictures and 544 00:34:38,280 --> 00:34:43,639 illustrations that support this podcast, go to geologybytes.com 545 00:34:43,800 --> 00:34:46,560 where you'll also find a subject matter index of all the 546 00:34:46,560 --> 00:34:48,040 episodes. There. 547 00:34:48,040 --> 00:34:51,639 You can also give me feedback which I welcome as well as sign 548 00:34:51,639 --> 00:34:54,080 U to get my emails about new eisodes.