1 00:00:03,800 --> 00:00:06,800 This is Geology Bites with Oliver Strimpel. 2 00:00:08,200 --> 00:00:11,880 One of the most appealing aspects of geology is the way it 3 00:00:11,880 --> 00:00:16,280 can reveal the common origin of rocks that today are separated 4 00:00:16,280 --> 00:00:20,440 by thousands of miles. In a recent episode with Rob 5 00:00:20,440 --> 00:00:25,360 Strachan, we saw how a single, albeit extended orogeny, the 6 00:00:25,360 --> 00:00:30,000 Caledonian orogeny, formed rocks now in the northern British 7 00:00:30,000 --> 00:00:33,560 Isles, eastern Greenland, and western Norway. 8 00:00:34,440 --> 00:00:37,680 But the Appalachian Mountains are also part of this same 9 00:00:37,680 --> 00:00:41,600 story, even though they now lie across the Atlantic Ocean. 10 00:00:42,440 --> 00:00:46,360 These mountains stretch for over 2000 miles all the way from 11 00:00:46,360 --> 00:00:49,760 Newfoundland and Canada to central Alabama in the United 12 00:00:49,760 --> 00:00:53,600 States. Case Van Staal has been studying 13 00:00:53,600 --> 00:00:57,680 the Appalachians for over 35 years, focusing especially on 14 00:00:57,680 --> 00:01:00,240 the large scale tectonics of their formation. 15 00:01:01,280 --> 00:01:04,760 He is a Meritus scientist at the Geological Survey of Canada and 16 00:01:05,519 --> 00:01:08,800 an adjunct research professor in the Department of Earth and 17 00:01:08,800 --> 00:01:11,760 Environmental Sciences at the University of Waterloo in 18 00:01:11,760 --> 00:01:15,440 Ontario. Case van Staal, Welcome to 19 00:01:15,440 --> 00:01:17,720 Geology Bites. Thanks for inviting me. 20 00:01:18,320 --> 00:01:21,240 Since I said that the formation of the Appalachian Mountain belt 21 00:01:21,240 --> 00:01:25,440 is related to the Caledonian neurogeny, let me quickly recap 22 00:01:25,440 --> 00:01:28,840 the very high level tectonic context of thaterogeny. 23 00:01:29,920 --> 00:01:33,240 It took place between the final breakup of the supercontinent 24 00:01:33,240 --> 00:01:37,600 ridinia, about 600 million years ago and the formation of 25 00:01:37,600 --> 00:01:41,920 Pangaea. It could in some ways be viewed 26 00:01:41,920 --> 00:01:46,200 as a first stage in the assembly of the Pangaean supercontinent. 27 00:01:47,360 --> 00:01:53,080 So around 430 to 400 million years ago, three of the large 28 00:01:53,080 --> 00:01:56,560 continental masses that had rifted apart from Virginia 29 00:01:56,960 --> 00:02:01,960 collided and formed La Russia. Those colliding continental 30 00:02:01,960 --> 00:02:06,040 masses where Laurentia, which corresponds to present day North 31 00:02:06,040 --> 00:02:10,919 America, Greenland and Scotland, Baltica which corresponds to 32 00:02:10,919 --> 00:02:16,320 Scandinavia, and Avalonia and Ganderia which correspond to the 33 00:02:16,320 --> 00:02:21,000 various terrains preserved in Ireland, Wales and England and 34 00:02:21,000 --> 00:02:22,960 parts of mainland Northwest Europe. 35 00:02:24,160 --> 00:02:27,320 These collisions comprise the main phase of the Caledonian 36 00:02:27,320 --> 00:02:31,040 neurogeny. So getting back to the 37 00:02:31,040 --> 00:02:35,560 Appalachians, where these 3 continental masses also 38 00:02:35,560 --> 00:02:38,720 responsible for forming the Appalachians to the West. 39 00:02:39,200 --> 00:02:43,160 In part because Beltica was not involved in the Appalachians, 40 00:02:43,680 --> 00:02:46,360 but certainly Avalonia and Gondira were. 41 00:02:46,360 --> 00:02:49,640 But you forgot one thing which is actually quite important. 42 00:02:49,760 --> 00:02:53,200 You forgot the Taconic Grampian event, which is an Order Vision 43 00:02:53,200 --> 00:02:56,920 event that took place between 480 and 450,000,000 years ago. 44 00:02:57,480 --> 00:03:01,760 And actually that is one of the arguments that the processes 45 00:03:01,760 --> 00:03:05,400 that were taking place in the Caledonian orogeny and the 46 00:03:05,400 --> 00:03:09,920 Appalachian orogeny are related. Because this arrival of a 47 00:03:10,240 --> 00:03:13,680 terrain outboard of Laurentia with Laurentia on the lower 48 00:03:13,680 --> 00:03:15,960 plate. So Laurentia was the down going 49 00:03:15,960 --> 00:03:20,440 plate is very similar all the way from Norway into the sound 50 00:03:20,440 --> 00:03:23,840 of Appalachians. And so this event involved the 51 00:03:23,840 --> 00:03:28,040 abduction of Ophelites and the arrival of islet arcs to the 52 00:03:28,040 --> 00:03:31,760 Laurentian margin. And it is after that event that 53 00:03:31,760 --> 00:03:35,480 the subduction changed its polarity from South dipping 54 00:03:35,480 --> 00:03:38,920 because Laurentia was in an east West orientation at that time 55 00:03:39,440 --> 00:03:42,600 was lying very close to the equator and then subduction 56 00:03:42,600 --> 00:03:46,200 started to go in the nice Laurentia from South to north. 57 00:03:46,200 --> 00:03:50,160 So that event is the realization that the event that was very 58 00:03:50,160 --> 00:03:54,440 similar was one of the linkages between the Caledonian and 59 00:03:54,440 --> 00:03:56,120 Appalachian horogenes. OK. 60 00:03:56,120 --> 00:03:58,440 That was the tectonic Grampian events. 61 00:03:58,880 --> 00:04:02,440 When we spoke earlier, you said that you have probably seen more 62 00:04:02,440 --> 00:04:05,800 rocks in Ireland and Newfoundland than anyone. 63 00:04:06,760 --> 00:04:09,840 Was it the close relationship between the rocks on either side 64 00:04:09,840 --> 00:04:12,800 of the North Atlantic that initially LED us to this 65 00:04:12,800 --> 00:04:15,800 tectonic picture? Well, this is not a new idea. 66 00:04:15,880 --> 00:04:20,839 People have been commenting on the similarities between the 67 00:04:20,920 --> 00:04:25,160 geology and the British Isles and the Appalachians in North 68 00:04:25,160 --> 00:04:29,160 America for many years. Some of the people you can 69 00:04:29,160 --> 00:04:32,160 mention is Hank Williams in Newfoundland at Memorial 70 00:04:32,160 --> 00:04:35,440 University, and John Dewey was a professor at Oxford. 71 00:04:35,880 --> 00:04:39,280 And they early on, after the acceptance of plate tectonics in 72 00:04:39,280 --> 00:04:44,040 the 1960s, they started to realize that it was important to 73 00:04:44,200 --> 00:04:47,280 correlate these features because they saw that there was probably 74 00:04:47,320 --> 00:04:51,480 a similar tectonic history. Can you tell us just how the 75 00:04:51,480 --> 00:04:54,320 rocks on either side of the North Atlantic relate to each 76 00:04:54,320 --> 00:04:56,920 other? And do those relationships 77 00:04:56,920 --> 00:04:59,520 extend all the way down the entire length of the 78 00:04:59,520 --> 00:05:02,960 Appalachians? The rocks are similar even on a 79 00:05:02,960 --> 00:05:06,880 little logical level. But yes, certainly the rocks in 80 00:05:06,880 --> 00:05:09,520 the Northern Appalachians. So that's the rocks which 81 00:05:09,520 --> 00:05:12,320 stretch from Connecticut all the way to Newfoundland, and 82 00:05:12,400 --> 00:05:15,080 especially Newfoundland, because it's the closest to the British 83 00:05:15,080 --> 00:05:18,760 Isles, has a geology that is very similar to what you see in 84 00:05:18,760 --> 00:05:20,760 the British Isles, especially Ireland. 85 00:05:21,360 --> 00:05:25,320 So the correlations are based on tectonic setting of the rocks. 86 00:05:25,320 --> 00:05:29,640 So better a rock is an arc or a rift or a margin. 87 00:05:30,160 --> 00:05:33,160 And so we're correlating rocks of similar tectonic setting, 88 00:05:33,320 --> 00:05:37,120 looking at the provenance, looking at the tectonic 89 00:05:37,120 --> 00:05:39,640 histories of the rocks. So we're using all kinds of 90 00:05:39,640 --> 00:05:44,360 tools for that, paleontology and fossils in the rocks, the ages 91 00:05:44,360 --> 00:05:46,720 of the rocks. Let's talk a bit more about each 92 00:05:46,720 --> 00:05:51,600 of these types of relationship. How is the tectonic setting 93 00:05:51,960 --> 00:05:55,560 related across the Atlantic? Well, for instance, when we 94 00:05:55,560 --> 00:05:59,640 determine a rock, let's say this rock is an island arc and we use 95 00:05:59,800 --> 00:06:03,440 igneous geochemistry for that. And we see these rocks are very 96 00:06:03,440 --> 00:06:06,920 similar to modern day island arcs like we see in the Pacific 97 00:06:06,920 --> 00:06:10,840 Ocean like in the Solomons or in Fiji, whatever. 98 00:06:11,360 --> 00:06:15,520 And so if we see an arc association, let's say in 99 00:06:15,520 --> 00:06:18,920 Ireland, and we see the same arc association in Newfoundland and 100 00:06:18,920 --> 00:06:24,440 they have very similar ages and their faunas in the associated 101 00:06:24,440 --> 00:06:27,880 sedimentary rocks and everything else is very similar, then the 102 00:06:27,880 --> 00:06:29,960 correlation is a valid way to go. 103 00:06:30,560 --> 00:06:34,360 I understand that we see evidence of extension that took 104 00:06:34,360 --> 00:06:36,840 place in association with this collision. 105 00:06:36,840 --> 00:06:39,000 Can you talk a bit about that? Yes. 106 00:06:39,000 --> 00:06:43,080 So during the opening of the the up this ocean, we noticed that 107 00:06:43,080 --> 00:06:46,800 there was hyperextension, which means that the continents were 108 00:06:46,800 --> 00:06:50,760 rifting apart without producing a lot of magnetism and going 109 00:06:50,760 --> 00:06:53,840 into spreading very rapidly. And so during this 110 00:06:53,840 --> 00:06:57,440 hyperextension eventually you bring the litospheric mantle to 111 00:06:57,440 --> 00:07:01,840 the service on the ocean floor. We can see that today off the 112 00:07:01,840 --> 00:07:06,160 coast of Spain and Portugal and also maybe off the coast of 113 00:07:06,160 --> 00:07:09,120 Ireland. And so these rocks are preserved 114 00:07:09,240 --> 00:07:13,680 and they are very similar bows in the British Isles and in 115 00:07:13,680 --> 00:07:15,840 Newfoundland and in the rest of New England. 116 00:07:16,120 --> 00:07:19,160 So we see an association of ultra mafic rocks and sediments 117 00:07:19,160 --> 00:07:22,080 that were deposited very close to the Laurentian margin. 118 00:07:22,200 --> 00:07:25,640 These rocks, we call them Ocean Continent Transitional rocks and 119 00:07:25,640 --> 00:07:28,280 we have dated them. So we know that they formed very 120 00:07:28,280 --> 00:07:31,240 early on in the history of the opening of the upatus. 121 00:07:31,320 --> 00:07:34,320 We know for sure that they were not an interoceanic terrain or 122 00:07:34,320 --> 00:07:36,240 whatever. They must have formed during the 123 00:07:36,240 --> 00:07:39,360 rifting period, and the fact that these rocks are very 124 00:07:39,360 --> 00:07:43,640 similar is another link between the processes that took place 125 00:07:44,120 --> 00:07:46,480 during the opening of the Yaputis Ocean. 126 00:07:46,560 --> 00:07:51,400 The ocean that existed in the early Paleozoic and then was 127 00:07:51,400 --> 00:07:55,680 basically closed and then eventually another ocean was 128 00:07:55,680 --> 00:07:58,800 closed after the arrival of Avalonia. 129 00:07:59,440 --> 00:08:03,000 It was called the Rheic Ocean. But these linkages are important 130 00:08:03,120 --> 00:08:07,120 to us to correlate and see whether the processes are very 131 00:08:07,120 --> 00:08:09,840 similar. So this is one of the arguments 132 00:08:09,920 --> 00:08:12,360 we have used. I also understand that we see a 133 00:08:12,360 --> 00:08:16,800 particular kind of mafic igneous rock called a bonnenite. 134 00:08:17,200 --> 00:08:19,640 Is that something that is correlated on either side as 135 00:08:19,640 --> 00:08:20,840 well? Yes. 136 00:08:20,840 --> 00:08:24,840 So Bonnenites are very rare, especially in the Appalachian 137 00:08:24,840 --> 00:08:29,560 Caledonian origin, but they are relatively common in this first 138 00:08:29,560 --> 00:08:32,200 terrain that arrived at the Laurentian margin. 139 00:08:32,280 --> 00:08:35,159 You can trace these bonanites from New England all the way 140 00:08:35,159 --> 00:08:38,039 into Norway. So that suggests a common 141 00:08:38,039 --> 00:08:40,640 origin. And bonanites are a high 142 00:08:40,640 --> 00:08:46,240 magnesium, high silica and highly depleted in high field 143 00:08:46,240 --> 00:08:50,960 strength elements such as titanium, and they formed under 144 00:08:50,960 --> 00:08:54,200 specific tectonic conditions. And so the fact that these rocks 145 00:08:54,200 --> 00:08:57,400 are very common in this particular terrain, which we can 146 00:08:57,400 --> 00:09:00,840 trace all the way along the length of the origin, is another 147 00:09:00,880 --> 00:09:03,240 argument that these rocks are related. 148 00:09:03,840 --> 00:09:07,840 You mentioned provenance, so how is the provenance on either side 149 00:09:07,840 --> 00:09:11,040 of the Atlantic related? We studied the sediments which 150 00:09:11,040 --> 00:09:15,000 are associated with the rocks involved in these collisional 151 00:09:15,000 --> 00:09:17,440 events. And so we're looking at fossils 152 00:09:17,440 --> 00:09:21,160 and you know already for a long time that these fossils are very 153 00:09:21,160 --> 00:09:23,120 similar along the length of the origin. 154 00:09:23,520 --> 00:09:26,320 So rocks that form close to orange have a very different 155 00:09:26,320 --> 00:09:30,440 faunas than the rocks that come from other continents like 156 00:09:30,440 --> 00:09:34,560 Baltica or Conduana. And so we also look at things 157 00:09:34,560 --> 00:09:37,920 like the trial zircons. So we dated the trial zircons 158 00:09:37,920 --> 00:09:42,520 with uranium lead methods and they tell us what the hint lead 159 00:09:42,520 --> 00:09:45,280 is, where these rocks are coming from and the rocks that are 160 00:09:45,280 --> 00:09:49,680 eroding and then the Tritus is basically being transported by 161 00:09:49,680 --> 00:09:54,240 rivers to the continental margin and then deposited in sediments. 162 00:09:54,680 --> 00:09:57,720 So they tell us these rocks are now a locked in us and they have 163 00:09:57,720 --> 00:09:59,880 been through the mangle, they have been deformed, the 164 00:09:59,880 --> 00:10:04,520 metamorphos, but they still allow us to determine what the 165 00:10:04,520 --> 00:10:05,920 hinterland, what the source rock are. 166 00:10:06,200 --> 00:10:11,160 So we can separate rocks that were having a Laurentian source 167 00:10:11,160 --> 00:10:13,880 from rocks that had a Ghunwanan source, because the hinterlands 168 00:10:13,880 --> 00:10:15,880 are very different. They have very different 169 00:10:16,320 --> 00:10:20,080 basements and very different histories prior to the 170 00:10:20,160 --> 00:10:24,720 Appalachian Caledonian origin. Is it the trace element 171 00:10:24,960 --> 00:10:26,960 signatures that are different? It's the ages. 172 00:10:26,960 --> 00:10:31,600 So for instance, Gondwana is characterized by many 173 00:10:31,600 --> 00:10:36,200 Neoprotozoic activities. Neoprotozoic is the time period 174 00:10:36,200 --> 00:10:40,360 between 1 billion and about 550,000,000 years ago. 175 00:10:40,840 --> 00:10:45,360 And so this event is very rare or absent in North America, but 176 00:10:45,360 --> 00:10:48,720 it's very common in Gondwana. So if you see a lot of these 177 00:10:48,720 --> 00:10:52,680 Neoprotozoic zircon showing up in your sediments, that will be 178 00:10:52,680 --> 00:10:54,840 an argument to say, well, these rocks didn't form close to 179 00:10:54,840 --> 00:10:56,840 Laurentia, but they come from Gondwana. 180 00:10:57,280 --> 00:10:59,080 So this is the kind of things we're looking at. 181 00:10:59,280 --> 00:11:02,120 So other things is like for instance, 2 billion year old 182 00:11:02,120 --> 00:11:05,600 rocks, we call them the Burnian. They are very common for 183 00:11:05,600 --> 00:11:08,080 Gondwana, but they are not common in Laurentia. 184 00:11:08,200 --> 00:11:11,480 So it's a kind of different age groups that show up in these 185 00:11:11,480 --> 00:11:14,160 sediments that are typical for whatever they come from. 186 00:11:14,680 --> 00:11:18,320 You also mentioned that Ophelites were abducted in the 187 00:11:18,320 --> 00:11:21,040 Appalachians. Can you tell us about those? 188 00:11:21,240 --> 00:11:26,440 Yes, some of the best ophelites preserved in the world occur in 189 00:11:26,440 --> 00:11:29,520 the Canadian Appalachians, especially so in Newfoundland 190 00:11:29,520 --> 00:11:31,000 and to a lesser extent in Quebec. 191 00:11:31,680 --> 00:11:36,240 And these ophelites were very important in the acceptance and 192 00:11:36,240 --> 00:11:39,720 the development of plate tectonic models for the origin 193 00:11:39,720 --> 00:11:42,480 of the Appalachian Caledonian origin, which is one of the 194 00:11:42,680 --> 00:11:44,600 longest studied origins in the world. 195 00:11:45,080 --> 00:11:46,920 Are these offrelites in good condition? 196 00:11:46,920 --> 00:11:48,200 Then? Can we actually see the 197 00:11:48,200 --> 00:11:51,040 structures associated with them and say something about the 198 00:11:51,040 --> 00:11:55,080 processes that took place? Yes, some of the offrelites 199 00:11:55,080 --> 00:11:58,600 preserved in the western part of Newfoundland are extremely well 200 00:11:58,600 --> 00:12:00,120 preserved. One of them is the Bay of 201 00:12:00,120 --> 00:12:04,280 Islands Offrelite, very famous. It's very big and it's lying on 202 00:12:04,280 --> 00:12:07,880 top of the Paleozoic laryngian margin. 203 00:12:08,120 --> 00:12:11,720 So the whole process associated with the formation of the 204 00:12:11,720 --> 00:12:16,120 ophelite and it's emplacement onto the margin is relatively 205 00:12:16,120 --> 00:12:19,600 well preserved and all kinds of things are very important for 206 00:12:19,600 --> 00:12:23,720 understanding how these ophelites formed and how they 207 00:12:23,720 --> 00:12:26,840 were in place are in part preserved in these ophelites. 208 00:12:26,840 --> 00:12:29,440 For instance, the metamorphic souls. 209 00:12:29,880 --> 00:12:33,840 So this is a soul of rocks that were glued to the base of the 210 00:12:33,840 --> 00:12:37,560 ophelite are well preserved. And so they basically demanded 211 00:12:37,560 --> 00:12:40,480 that these rocks were in place while they were still very hot. 212 00:12:41,240 --> 00:12:43,920 And so they were metamorphosed in the rocks that were accreted 213 00:12:43,920 --> 00:12:47,360 to it at the base, and hence these rocks were metamorphosed. 214 00:12:47,480 --> 00:12:50,200 Hence the word thermal soul, terminal, aureal. 215 00:12:50,680 --> 00:12:53,840 And you can see the thermal, aureal and metamorphic soul in 216 00:12:53,840 --> 00:12:56,920 Newfoundland Ophelites. Yes, very much on several of 217 00:12:56,920 --> 00:12:58,360 them. These souls are very well 218 00:12:58,360 --> 00:13:02,120 preserved and have been studied early on and very very important 219 00:13:02,280 --> 00:13:07,200 in developing the ideas people had on how these Ovid lines were 220 00:13:07,200 --> 00:13:09,640 in place. Where the Appalachians 221 00:13:09,680 --> 00:13:13,320 originally formed as the Himalayas scale mountain range 222 00:13:13,680 --> 00:13:17,800 and then are the rocks on the surface today the exhumed mid 223 00:13:17,800 --> 00:13:19,520 crustal roots of those mountains. 224 00:13:19,520 --> 00:13:22,400 No, the Appalachians didn't. Only the parts of the 225 00:13:22,400 --> 00:13:25,000 Calavanides did in the Scandinavian Calavanides where 226 00:13:25,320 --> 00:13:29,640 Baltica was in the thrusting Laurentia for a very long time. 227 00:13:29,960 --> 00:13:34,040 But the Appalachians only in a few segments, may have been in 228 00:13:34,040 --> 00:13:37,160 like the Himalayas, like in southern New England where we 229 00:13:37,160 --> 00:13:41,280 have evidence that there was a long lived high standing 230 00:13:41,280 --> 00:13:44,520 tectonic plateau like in Tibet. But in the rest of the 231 00:13:44,520 --> 00:13:47,640 Appalachians, anywhere in northern New England and in 232 00:13:47,640 --> 00:13:50,840 Newfoundland and in the rest of the Canadian Appalachians, the 233 00:13:50,880 --> 00:13:54,160 origin was not like the Himalayas, It was more like what 234 00:13:54,160 --> 00:13:58,040 you would see today in Iran along strike of the Himalayas. 235 00:13:58,200 --> 00:14:01,240 So these are rocks were much lower grade we see here rocks 236 00:14:01,240 --> 00:14:04,440 volcanic and sedimentary rocks of relatively low metamorphic 237 00:14:04,440 --> 00:14:09,840 grade preserved and the reasons between this variation may be 238 00:14:09,840 --> 00:14:12,160 due to the obliquity of the convergence. 239 00:14:12,400 --> 00:14:16,080 It's more oblique to the north and the undertrusting in 240 00:14:16,080 --> 00:14:20,440 southern New England by first Avalonia and then by Africa 241 00:14:20,720 --> 00:14:23,040 during the closure of the Riyadh Ocean. 242 00:14:23,040 --> 00:14:26,640 So that undertrusting was very long lived in the New England. 243 00:14:26,640 --> 00:14:30,240 So I hang pushing up the overlying crust to high levels 244 00:14:30,480 --> 00:14:34,280 and kept it in place for quite a long time, about 70 million 245 00:14:34,280 --> 00:14:37,600 years. So this was Avalonia and 246 00:14:37,600 --> 00:14:41,360 Gondwana under thrusting, similar to the way the Indian 247 00:14:41,360 --> 00:14:43,440 plate is now under thrusting under Tibet. 248 00:14:43,560 --> 00:14:45,960 Exactly. So the Indian plate has been 249 00:14:46,000 --> 00:14:50,000 under thrusting underneath Tibet and Eurasia because Tibet forms 250 00:14:50,000 --> 00:14:52,280 part of the Eurasia for about 50 million years. 251 00:14:52,280 --> 00:14:58,640 So India is a sick continental plate, very buoyant and it has 252 00:14:58,640 --> 00:15:02,960 been pushed underneath Eurasia. So you get double crust. 253 00:15:02,960 --> 00:15:05,040 So you have relatively light crust. 254 00:15:05,040 --> 00:15:08,120 It's the same process. If you have a plank of wood and 255 00:15:08,120 --> 00:15:11,120 you put another plank of it, the amount of wood that will come 256 00:15:11,120 --> 00:15:14,200 out of the water will be higher that that is basically the 257 00:15:14,200 --> 00:15:17,440 principle of isosceles and that happened in Tibet because you 258 00:15:17,440 --> 00:15:20,640 stuff something of low density in the knees Eurasia. 259 00:15:21,320 --> 00:15:25,400 The highest point along the Appalachians today is just over 260 00:15:25,400 --> 00:15:29,480 2000 meters high. Is the present day topography 261 00:15:29,480 --> 00:15:32,440 what's left of the topography that was generated by the 262 00:15:32,440 --> 00:15:34,480 orogenies that formed the Appalachians? 263 00:15:34,480 --> 00:15:39,840 Generally no, because after the Appalachian orogeny was finished 264 00:15:39,840 --> 00:15:43,120 there was about 200 million years of denudation until the 265 00:15:43,120 --> 00:15:48,040 opening of the Atlantic Ocean and so the origin must have been 266 00:15:48,320 --> 00:15:52,360 eroded back to sea level. So the present day topography is 267 00:15:52,360 --> 00:15:56,560 largely due to the processes it first associated with the 268 00:15:56,560 --> 00:15:58,720 rifting and opening of the Atlantic Ocean. 269 00:15:59,320 --> 00:16:02,640 So you get wrist shoulders and magnetism that happened, the 270 00:16:03,160 --> 00:16:06,480 Central Atlantic magnetic province basically pushing up 271 00:16:06,480 --> 00:16:09,840 part of the overlying crust, so forming topography. 272 00:16:10,200 --> 00:16:15,000 And then subsequently during the recent history in the last 6070 273 00:16:15,000 --> 00:16:20,360 thousand years till about 10,000 years ago, we had ice ages and 274 00:16:20,360 --> 00:16:23,840 ice ages were basically loading the underlying crust. 275 00:16:23,840 --> 00:16:27,080 And when the ice disappeared, the crust started to rebound. 276 00:16:27,640 --> 00:16:32,040 So producing topography and the amount of erosion hasn't had 277 00:16:32,040 --> 00:16:35,160 enough time to completely erode this origin back to sea level. 278 00:16:35,160 --> 00:16:39,360 So that's why we see all the various topography in the 279 00:16:39,360 --> 00:16:42,840 Appalachian origin. So do the hills of the present 280 00:16:42,840 --> 00:16:45,720 day Appalachian Mountains actually correspond to the 281 00:16:45,720 --> 00:16:49,360 location of the original accretion and orogenies that 282 00:16:49,360 --> 00:16:52,760 took place? And if so, is that to do with 283 00:16:52,760 --> 00:16:56,720 structural inheritance, in which later stresses are accommodated 284 00:16:56,720 --> 00:16:59,880 by movement along form of faults and orogenies where the rocks 285 00:16:59,880 --> 00:17:03,400 are actually weaker? Reactivation of faults during 286 00:17:03,480 --> 00:17:05,800 subsequent drifting? Most likely, yes. 287 00:17:05,920 --> 00:17:10,240 But the hills have no relationship to where those 288 00:17:10,240 --> 00:17:15,640 falls are, so the topography is to a large extent not related to 289 00:17:15,640 --> 00:17:17,880 where these reactivated falls are. 290 00:17:18,520 --> 00:17:21,280 But yeah, reactivation of the falls during the opening of the 291 00:17:21,280 --> 00:17:25,319 Atlantic most likely occurred. But not exactly where the 292 00:17:25,319 --> 00:17:27,680 Appalachians are today. Like along the seaboard for 293 00:17:27,680 --> 00:17:29,400 example, but not in the hinterland. 294 00:17:29,400 --> 00:17:32,080 Of course, the main rifting event took place along the 295 00:17:32,080 --> 00:17:35,720 eastern seaboard, but also further back into the hinterland 296 00:17:35,720 --> 00:17:40,360 of the Origin to some extent. The amount of motion on these 297 00:17:40,360 --> 00:17:43,960 faults is not very well defined and the ones on the eastern 298 00:17:43,960 --> 00:17:46,520 seaboard are largely buried beneath sea level. 299 00:17:46,520 --> 00:17:49,360 So we don't really know exactly what happened to these faults, 300 00:17:49,360 --> 00:17:54,880 but it's not a coincidence that new oceans form along existing 301 00:17:55,000 --> 00:17:57,440 zones of weakness. It's a well known relationship. 302 00:17:57,440 --> 00:17:59,960 We've seen that in many other origins as well. 303 00:18:00,360 --> 00:18:03,160 Because these rocks are relatively weak, they have major 304 00:18:03,160 --> 00:18:07,680 faults that may continue all the way to the lidosphere, and so if 305 00:18:07,680 --> 00:18:10,160 you start rifting it, those songs of weakness are going to 306 00:18:10,160 --> 00:18:11,880 be reused. Nature is like that. 307 00:18:11,880 --> 00:18:13,200 It always takes the easiest way out. 308 00:18:13,720 --> 00:18:16,600 But that's not directly responsible for the Appalachian 309 00:18:16,600 --> 00:18:18,600 Mountains that we have today, then no. 310 00:18:18,840 --> 00:18:22,800 But yeah, I mean, the rifting we can see, for instance, if you go 311 00:18:22,800 --> 00:18:25,600 to the most western boundary of the Appalachians, you can see a 312 00:18:25,600 --> 00:18:28,920 huge topographic difference between the North Shore of 313 00:18:28,920 --> 00:18:31,920 Quebec and Labrador and the Appalachians. 314 00:18:31,920 --> 00:18:35,840 And that's may have something to do with the rifting episode that 315 00:18:35,840 --> 00:18:39,240 opened up the Atlantic Ocean, parts of Arctic Canada. 316 00:18:39,240 --> 00:18:42,280 For instance, in Baffin Island they have relatively high 317 00:18:42,280 --> 00:18:47,400 standing mountains, which are probably related to magnetism 318 00:18:47,400 --> 00:18:50,680 that was associated with the opening of the Atlantic Ocean. 319 00:18:51,360 --> 00:18:54,680 So the structures we see today then will consequent on much 320 00:18:54,680 --> 00:18:59,240 later events, and some of those later events took place and had 321 00:18:59,240 --> 00:19:03,480 an effect right there because of the adjacent rifting that took 322 00:19:03,480 --> 00:19:07,080 place, which was indeed affected by inheritance. 323 00:19:08,200 --> 00:19:12,280 As I mentioned, the Appalachians are over 2000 miles long. 324 00:19:13,080 --> 00:19:16,400 Are there any analogues of such a long collisional mountain belt 325 00:19:16,400 --> 00:19:19,680 anywhere else on earth? Well, the one comes to my mind 326 00:19:19,680 --> 00:19:24,120 is the Central Asian originic belt in Eastern Asia, which runs 327 00:19:24,120 --> 00:19:30,880 from Siberia and Kazakhstan through Mongolia and northern 328 00:19:30,880 --> 00:19:33,240 China all the way to the Pacific Ocean. 329 00:19:33,760 --> 00:19:37,160 I mean, it's this extremely long mountain belt and also extremely 330 00:19:37,160 --> 00:19:42,840 wide and probably the longest accretionary origin in the sense 331 00:19:42,840 --> 00:19:47,680 that it's an origin where many pieces were accreted to the 332 00:19:47,680 --> 00:19:51,840 Siberian Craton coming from the South and forming a long lived 333 00:19:51,840 --> 00:19:54,560 origin. And that mountain belt is much 334 00:19:54,560 --> 00:19:56,840 bigger than the Appalachian and the Caledonians together. 335 00:19:57,960 --> 00:20:00,320 You're still working on the Appalachians. 336 00:20:00,440 --> 00:20:03,200 In fact, you're setting off for a Newfoundland field trip later 337 00:20:03,200 --> 00:20:06,240 today. What questions are you tackling 338 00:20:06,240 --> 00:20:08,840 now? So we know the, OR at least we 339 00:20:08,840 --> 00:20:11,880 think we know the general tectonic framework, what 340 00:20:11,880 --> 00:20:15,960 happened, but we want to know the details of the processes, so 341 00:20:16,440 --> 00:20:21,280 how these rocks were exhumed and then starting eroding, because 342 00:20:21,280 --> 00:20:23,520 as soon as they come to the surface, they will start 343 00:20:23,520 --> 00:20:26,240 eroding. We want to check that by looking 344 00:20:26,240 --> 00:20:30,080 at the syntectonic, the sedimentary basins that formed 345 00:20:30,360 --> 00:20:33,160 during those processes. So we want to see the unroofing 346 00:20:33,160 --> 00:20:36,480 history and that will tell us about the processes that were 347 00:20:36,560 --> 00:20:40,720 responsible for the burial and then the subsequent exhumation 348 00:20:41,000 --> 00:20:43,680 of these rocks. So we're looking at the 349 00:20:43,680 --> 00:20:46,760 sedimentary bases and we sampling rocks through the 350 00:20:46,760 --> 00:20:51,360 systedographic record and we will dating the minerals that 351 00:20:51,360 --> 00:20:55,600 can be dated by uranium lead methods, minerals such as 352 00:20:55,600 --> 00:20:59,080 rutile, titanite, monacide, appetite. 353 00:20:59,640 --> 00:21:05,640 And so each of these minerals has a closure temperature and 354 00:21:05,640 --> 00:21:08,480 formed at specific metamorphic conditions. 355 00:21:08,640 --> 00:21:12,600 And so we can try to reconstruct the processes that were 356 00:21:12,600 --> 00:21:14,760 associated with that exclamation. 357 00:21:15,440 --> 00:21:18,440 And actually that's a very exciting and very promising new 358 00:21:18,440 --> 00:21:21,120 line of research. Hopefully we will be able to 359 00:21:21,120 --> 00:21:22,960 present this data in the near future. 360 00:21:23,640 --> 00:21:28,800 So this is generating what people refer to as the time 361 00:21:29,000 --> 00:21:32,960 pressure temperature kind of loops in that temperature 362 00:21:32,960 --> 00:21:34,880 pressure space. Yes, exactly. 363 00:21:34,880 --> 00:21:38,200 So we can determine approximately when the rocks are 364 00:21:38,200 --> 00:21:41,680 buried to the maximum depth if we are lucky and maximum 365 00:21:41,680 --> 00:21:44,200 temperature. But then we want to know is when 366 00:21:44,200 --> 00:21:46,680 these rocks, how they got back. So that's basically part of the 367 00:21:46,680 --> 00:21:50,920 PDT loops, as we say, the pressure, temperature, time and 368 00:21:50,920 --> 00:21:53,200 that tells us something about the processes that were 369 00:21:53,200 --> 00:21:56,920 associated with that, whether the rocks were heated up during 370 00:21:56,920 --> 00:22:01,920 this process or they remained refrigerated. 371 00:22:02,440 --> 00:22:04,920 The results that we have so far are very interesting. 372 00:22:04,920 --> 00:22:09,360 I'm very excited about it. You've spent almost all of your 373 00:22:09,360 --> 00:22:11,560 long research career on the Appalachians. 374 00:22:12,040 --> 00:22:14,720 What made you interested in them initially? 375 00:22:14,760 --> 00:22:18,720 That's serendipity. I came to Canada in 1980 to do 376 00:22:18,720 --> 00:22:23,600 my PhD and I did my PhD in Appalachian rocks. 377 00:22:23,680 --> 00:22:27,520 So I got very interested in those rocks and then I was hired 378 00:22:27,640 --> 00:22:31,040 rapidly after the finishing my PhD by the Geological Survey of 379 00:22:31,040 --> 00:22:33,680 Canada. And in their wisdom, the 380 00:22:33,680 --> 00:22:37,480 Geological Survey gave me the task to basically figure out the 381 00:22:37,480 --> 00:22:40,200 Appalachian origin. They gave me a lot of freedom 382 00:22:40,800 --> 00:22:43,360 and I used that. And I was basically driven by 383 00:22:43,360 --> 00:22:47,280 curiosity how these various rocks correlate. 384 00:22:47,680 --> 00:22:51,640 And so it's like in any terrain, the relationships between rocks 385 00:22:51,640 --> 00:22:54,640 are also the most important and they can only be preserved in 386 00:22:54,640 --> 00:22:58,640 some places. So if rocks in Quebec give you 387 00:22:58,960 --> 00:23:02,600 very good relationships, then they may explain relationships 388 00:23:02,600 --> 00:23:04,720 in Newfoundland as well. Those kind of arguments. 389 00:23:04,840 --> 00:23:07,200 And that's why I kept working in it. 390 00:23:07,200 --> 00:23:09,840 And it's a fascinating origin. It's one of the longest studied 391 00:23:09,840 --> 00:23:12,960 origins, but still there's lots of questions to be answered. 392 00:23:13,240 --> 00:23:17,560 Such as? The most important outstanding 393 00:23:17,560 --> 00:23:21,640 tectonic questions concerns the origin of the various terrains 394 00:23:21,640 --> 00:23:25,440 that became isolated in the Yaputis and Rheic oceans. 395 00:23:25,960 --> 00:23:31,200 Terrains like Gonderia, Avalonia and Maguma which became. 396 00:23:31,520 --> 00:23:34,520 Sequentially accreted to. Laurentia, the evidence. 397 00:23:34,520 --> 00:23:37,160 For these. Accretions is preserved in the 398 00:23:37,160 --> 00:23:41,560 Salinic, Acadian, and Neoacadian origenes. 399 00:23:42,040 --> 00:23:46,760 Which occurred between 4:30 and. 360 million years. 400 00:23:46,760 --> 00:23:50,400 Ago these. Questions concerned where these 401 00:23:50,400 --> 00:23:54,960 strains formed, why did they depart and became isolated from 402 00:23:54,960 --> 00:23:57,480 the source continent, and how did they? 403 00:23:57,480 --> 00:23:59,600 Travel. Across the oceans towards 404 00:23:59,600 --> 00:24:02,880 Laurentia and exactly what happened during their odysseys. 405 00:24:03,240 --> 00:24:06,720 And what kind of evidence might help us answer these questions? 406 00:24:06,840 --> 00:24:09,960 Providence studies, pedimagnetism and tectonic. 407 00:24:09,960 --> 00:24:13,040 Reconstructions. This may help answer other 408 00:24:13,040 --> 00:24:16,080 outstanding questions such as why subduction? 409 00:24:16,080 --> 00:24:19,480 Started or was. Ongoing coevenly at several 410 00:24:19,480 --> 00:24:21,760 places in the Yaputas and Rig oceans. 411 00:24:23,000 --> 00:24:26,040 And then, of course, all these lines of evidence will help us 412 00:24:26,040 --> 00:24:29,400 to understand how these oceans. Exactly closed. 413 00:24:29,840 --> 00:24:34,320 And eventually how the supercontinent Pangaea formed. 414 00:24:35,480 --> 00:24:37,680 Keith Van Staal, thank you very much. 415 00:24:37,880 --> 00:24:40,160 You're welcome, Oliver of us, a pleasure, Thanks. 416 00:24:41,680 --> 00:24:44,360 To see pictures and illustrations that support this 417 00:24:44,360 --> 00:24:49,640 podcast, go to geologybytes.com, where you'll also find a subject 418 00:24:49,640 --> 00:24:51,560 matter index of all the episodes. 419 00:24:52,000 --> 00:24:55,360 There you can also give me feedback which I welcome, as 420 00:24:55,360 --> 00:24:58,400 well as sign up to get my emails about new episodes.