Latest / PlanetGeo: The Geology Podcast / So You Think You Know Plate Tectonics? Part 2

Transcript

So You Think You Know Plate Tectonics? Part 2 · PlanetGeo: The Geology Podcast

• 0:03
  SPEAKER_01: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:13
  SPEAKER_00: Hey, how we doing, doc?
• 0:15
  SPEAKER_00: Hey, what's up, Chris?
• 0:16
  SPEAKER_00: What's going on?
• 0:18
  SPEAKER_00: Uh not a whole lot.
• 0:20
  SPEAKER_00: I am ready to roll, but I'm looking at you, and I'm looking I just gotta say today, love is blind, and you're living proof for that.
• 0:32
  SPEAKER_01: You love me and it's blind.
• 0:34
  SPEAKER_00: No, no, no, no, not at all.
• 0:35
  SPEAKER_00: Not at all.
• 0:35
  SPEAKER_00: I'm talking about Tess.
• 0:37
  SPEAKER_00: Um like I don't I don't what it how I don't know how you manage to finagle this situation, but you marry it.
• 0:48
  SPEAKER_01: So back to you criticizing me.
• 0:50
  SPEAKER_01: Uh yeah, I um I'm not sure what to say.
• 0:53
  SPEAKER_01: I don't understand it either.
• 0:54
  SPEAKER_01: I'm not gonna argue with it.
• 0:56
  SPEAKER_00: Somebody's gotta marry up, right?
• 0:57
  SPEAKER_00: So that's right.
• 0:59
  SPEAKER_01: You know, somebody's gonna very rarely would it be an equal.
• 1:01
  SPEAKER_01: That's right.
• 1:02
  SPEAKER_01: That's exactly right.
• 1:03
  SPEAKER_01: Um, so I have a confession to make.
• 1:06
  SPEAKER_01: Uh oh, I have no idea what you're gonna say right now.
• 1:08
  SPEAKER_01: You don't?
• 1:08
  SPEAKER_01: Oh.
• 1:09
  SPEAKER_01: I do not.
• 1:10
  SPEAKER_01: I I confess that I was I was wrong about this whole plate tectonics thing, it turns out.
• 1:17
  SPEAKER_01: Uh it was a well, it was a popular episode.
• 1:20
  SPEAKER_01: Let's put it that way.
• 1:21
  SPEAKER_01: People seem to like it.
• 1:22
  SPEAKER_01: We're continuing on in the same theme here, which is plate tectonics questions.
• 1:28
  SPEAKER_01: Do you know plate tectonics?
• 1:29
  SPEAKER_01: Random thoughts on plate tectonics and the unified plate tectonics.
• 1:35
  SPEAKER_00: You need you're doing a horrible job at this, by the way.
• 1:38
  SPEAKER_00: All right.
• 1:38
  SPEAKER_01: Okay, go for it.
• 1:39
  SPEAKER_00: If first of all, I don't feel like you did a good job of um saying why you were wrong.
• 1:44
  SPEAKER_00: I mean, the backstory has to come into this, you know.
• 1:47
  SPEAKER_00: You fought me hard on this one.
• 1:49
  SPEAKER_00: Like you didn't you did not want to do this, and I was right, and you can't just gloss over and say, Oh, I was wrong, and then just quickly change topic.
• 1:58
  SPEAKER_00: That doesn't work for me.
• 1:59
  SPEAKER_01: I think that's allowed.
• 2:00
  SPEAKER_01: What do you want me to do?
• 2:00
  SPEAKER_01: Get down and bow on my knees and you know, beg your forgiveness or something?
• 2:03
  SPEAKER_00: Heck no, are you kidding me?
• 2:05
  SPEAKER_00: I just I think a little more backstory is appropriate.
• 2:08
  SPEAKER_00: But hey, look, this is a series, and we said that from the outset, and we just kind of broke this up by topic and in terms of like how does plate tectonics unify massive parts of the field of geology, right?
• 2:23
  SPEAKER_00: That's where this came from.
• 2:24
  SPEAKER_00: But it really came from a discussion that I had with my classes, and that they thought they knew plate tectonics, and I'm just thinking, no, you really don't.
• 2:33
  SPEAKER_00: You you know these boundaries and things like this, and you know it at a rudimentary level.
• 2:37
  SPEAKER_00: And so I wrote a bunch of questions.
• 2:40
  SPEAKER_00: These are some of them that we're gonna talk about that we talked about in our last episode, we're gonna talk about today, a few more of them, that to me gets at a, and I think you can agree, right?
• 2:50
  SPEAKER_00: They get at a deeper level of plate tectonics and explaining just really important things in geology.
• 2:58
  SPEAKER_01: Yeah, I think you know, it's um it is a idea or it's a concept or it's a theory that permeates through an entire introductory course.
• 3:07
  SPEAKER_01: I mean, we're recording this Camp Geo thing, which gives us a good opportunity to advertise Camp Geo if you want to learn about geoscience in a very structured way with all the images in a conversational way.
• 3:17
  SPEAKER_01: The link in the show notes, first link right at the top there, will take you to our mobile-friendly conversational textbook that we're calling Camp Geo.
• 3:24
  SPEAKER_01: So go to that, let us know what you think.
• 3:26
  SPEAKER_01: We would love some feedback on that.
• 3:27
  SPEAKER_01: But back to the story of plate tectonics, Chris, is that plate tectonics really permeates this entire field because when I teach the intro to geology, physical geology section, almost every lecture contains something about plate tectonics from glaciers to metamorphic rocks, like we're gonna talk about today, to streams to climate cycling.
• 3:49
  SPEAKER_01: I mean, so it's all there.
• 3:51
  SPEAKER_01: It is the grand unifying theory.
• 3:53
  SPEAKER_01: And there are parts of every little subdiscipline that relate to plate tectonics.
• 3:59
  SPEAKER_01: And that's kind of what we're sort of working through.
• 4:01
  SPEAKER_01: And this is part two out of that sort of series.
• 4:03
  SPEAKER_01: We don't really know how long this is gonna go.
• 4:05
  SPEAKER_01: It could be six, it could be seven, it could be five.
• 4:07
  SPEAKER_01: We don't really know.
• 4:08
  SPEAKER_00: So and the the title of this is this series is well, and you fought me on this too, but it's so you think you know plate tectonics.
• 4:16
  SPEAKER_00: Hey, hey, like all right, this is a good thing.
• 4:18
  SPEAKER_01: Oh, no, no, no.
• 4:19
  SPEAKER_01: Although we're gonna I'm gonna interject here a little bit.
• 4:21
  SPEAKER_01: I think uh this does not mean that I'm not gonna fight you next time you come up with a hairbrand idea.
• 4:26
  SPEAKER_00: This is I don't come up with a lot of hairbrand ideas.
• 4:29
  SPEAKER_00: I'm pretty well thought out, Jesse Ramink.
• 4:31
  SPEAKER_00: I don't I don't deserve that at all.
• 4:33
  SPEAKER_00: But that that's because that was my thought when my students were talking the way they were talking.
• 4:39
  SPEAKER_00: I'm like, oh, so you think you know this?
• 4:41
  SPEAKER_00: Here we go.
• 4:42
  SPEAKER_00: So that's where this comes from.
• 4:44
  SPEAKER_00: Today, we're gonna tackle these three questions.
• 4:47
  SPEAKER_01: Let me interject real quick, Chris, because last time we talked about the questions we kind of went through is how does plate tectonics generate the rock basalt?
• 4:55
  SPEAKER_01: How is andesite produced, and how does plate tectonics explain the formation of granite?
• 5:00
  SPEAKER_01: And those three rocks are igneous rocks, and so those are rocks formed from magma or lava, molten rock crystallized to form a new rock.
• 5:08
  SPEAKER_01: Today we're gonna kind of go in the other direction, other rock types.
• 5:12
  SPEAKER_01: Sorry, go ahead.
• 5:13
  SPEAKER_00: Good on you, Jesse.
• 5:14
  SPEAKER_00: You know, talking about where we came from.
• 5:16
  SPEAKER_00: That's that's good teaching.
• 5:17
  SPEAKER_00: So today we're gonna talk about how plate tectonics relates to and and explains the formation of sedimentary rocks.
• 5:27
  SPEAKER_00: Then we're gonna go into how plate tectonics explains the formation of metamorphic rocks, and then a huge topic that we have to like stay pretty tight on.
• 5:37
  SPEAKER_00: How do Earth's resources, our natural resources, relate to plate tectonics?
• 5:44
  SPEAKER_00: In other words, mineral resources that we get, things like these ore deposits and so on, they form directly because of plate tectonics.
• 5:55
  SPEAKER_00: And we're gonna get into some of the examples of that.
• 5:58
  SPEAKER_00: So those are the three questions.
• 5:59
  SPEAKER_01: And each of these could be a very, very, very long discussion.
• 6:03
  SPEAKER_01: So we're gonna try and keep it to the very high level, you know, the the most important summary.
• 6:08
  SPEAKER_01: So, Chris, where does your mind go when you wrote this question about how does plate tectonics relate to the formation of sedimentary rocks?
• 6:15
  SPEAKER_00: Okay, well, first a little bit of backstory on this.
• 6:18
  SPEAKER_00: Um, hold on, I lost my train of thought there a minute.
• 6:22
  SPEAKER_01: Wow, so oh yeah, so quickly that that was the train barely got moving and it got lost off the tracks.
• 6:29
  SPEAKER_00: It comes and goes.
• 6:31
  SPEAKER_00: It's that was all right.
• 6:34
  SPEAKER_00: I see how this is gonna go.
• 6:35
  SPEAKER_00: Okay, well, before we get into it, I just want to say too that I really don't know the angle you're gonna take.
• 6:42
  SPEAKER_00: And I love that because I think your mind is very interesting, and I I can't wait to like hear your talk about it.
• 6:47
  SPEAKER_01: It's a wild world over here.
• 6:50
  SPEAKER_00: Something.
• 6:51
  SPEAKER_00: And the other thing is too, uh, this first question.
• 6:53
  SPEAKER_00: Now, let's talk specifically about that.
• 6:55
  SPEAKER_00: How plate tectonics explains the formation of sedimentary rocks.
• 7:00
  SPEAKER_00: I remember the first time I saw a question like this, and it made me think.
• 7:06
  SPEAKER_00: Now, here I am, you know, fresh out of college, perhaps, when I first saw this.
• 7:12
  SPEAKER_00: So I, you know, you think you know really what you you got a college degree, right?
• 7:17
  SPEAKER_00: You think you know what you're talking about, and then all of a sudden somebody throws this at you, and I was like, wait a second, I had never thought about that before.
• 7:25
  SPEAKER_00: And it gave me pause to think.
• 7:28
  SPEAKER_00: That stuck with me, that experience, and that's where this question comes from.
• 7:32
  SPEAKER_00: So I I kind of think of my response to this: how does plate tectonics explain the formation of sedimentary rocks?
• 7:40
  SPEAKER_00: There are two very broad forces in geology forces that lift things up and forces that wear things down, kind of like a big belt grinder from above, right?
• 7:54
  SPEAKER_00: And without plate tectonics, Earth would look very different and very a lot less interesting.
• 8:03
  SPEAKER_00: But plate tectonics is that force that lifts things up.
• 8:09
  SPEAKER_00: Weathering and erosion is the force that tears things down, and they're always in opposition.
• 8:14
  SPEAKER_00: And then when one of them stops, then the other one, like you know, if if a plate tectonic event uh you know kind of changes direction or or ceases, you know, that event ends as they all do eventually, then weather and erosion takes over and just like just slowly and you know, meticulously and relentlessly just grinds it all down.
• 8:36
  SPEAKER_00: And so sedimentary rocks when things are lifted up, weathering and erosion is accelerated.
• 8:45
  SPEAKER_00: So the breakdown of rocks mountain, then that's the weathering of them.
• 8:52
  SPEAKER_00: Then they get carried downstream usually, where then they get sorted, and then they get deposited, and then they get lithified, where they get you know cemented and compacted and cemented together.
• 9:07
  SPEAKER_00: That process is directly tied to the uplift that caused it all to start.
• 9:14
  SPEAKER_00: And that uplift is plate tectonics.
• 9:16
  SPEAKER_00: So that's my like main explanation for how sedimentary rocks are related to at least like how the process is accelerated by plate tectonics by uplift.
• 9:28
  SPEAKER_01: Well, that that's kind of uh where I was well hoping and uh maybe expecting you to go with that.
• 9:33
  SPEAKER_01: And and that's a good one.
• 9:34
  SPEAKER_01: I mean, that's like the the key thing is the production of sediment is required to make sedimentary rocks.
• 9:40
  SPEAKER_01: So you gotta have stuff to you gotta have stuff to be broken down, which is mountain ranges, before you can form sedimentary rocks.
• 9:46
  SPEAKER_01: So so I like that.
• 9:48
  SPEAKER_01: Um this will come back to uh when we talk about the sort of planetary aspects of this a little bit, and this is uh like a theme uh that we talked about last week too, is there are sedimentary rocks, you know, on Mars.
• 9:59
  SPEAKER_01: We know that now.
• 10:00
  SPEAKER_01: There's sedimentary rocks on Mars, which is really interesting.
• 10:02
  SPEAKER_01: Ask the question of like, what did Mars look like?
• 10:04
  SPEAKER_01: What did ancient Mars look like?
• 10:06
  SPEAKER_01: Did ancient Mars have plate tectonics, for instance, maybe?
• 10:09
  SPEAKER_01: You know, these are some really interesting questions about other planetary bodies driven by the fact that there are sedimentary rocks that we observe on the surface of Mars.
• 10:19
  SPEAKER_01: We don't know how old they are really, we don't know exactly how they formed, but they are there.
• 10:24
  SPEAKER_01: So I think Chris, I I generally broadly agree completely with that assessment or the what that answer to the question.
• 10:31
  SPEAKER_00: I sense a but coming.
• 10:33
  SPEAKER_01: No, not really.
• 10:34
  SPEAKER_01: No, I think it's uh not a not at all a but.
• 10:36
  SPEAKER_01: I think it's uh a kind of um maybe one step one step further, one step back in a in a weird way.
• 10:42
  SPEAKER_01: So like there's this old idea about sedimentary rocks that relates exactly to what you're saying.
• 10:47
  SPEAKER_01: Let's say we have a sequence of rocks in the rock record uh that starts at the base, and you have a conglomerate where it's all a bunch of what we call lithic class, so little pieces of rock that are in a sedimentary rock, and maybe those pieces of rocks are from a volcanic source.
• 11:05
  SPEAKER_01: So think of if you formed a sediment right off the Andes mountain belt, the Andes are shedding material off into the Pacific Ocean, and you're forming some sediment there, it's gonna be what we call juvenile, tectonically juvenile.
• 11:18
  SPEAKER_01: And as that mountain belt gets eroded down, the rocks are gonna change.
• 11:22
  SPEAKER_01: The sedimentary rocks that are feeding into that will be changed during that process.
• 11:28
  SPEAKER_01: And so there's like you can use the sedimentary rocks to infer the ancient tectonic setting, uh, if that makes sense.
• 11:35
  SPEAKER_01: So you can kind of go deeper and deeper and deeper down into this and understand ancient tectonic settings by looking at the sedimentary rock record, if that makes sense.
• 11:44
  SPEAKER_01: That makes sense.
• 11:44
  SPEAKER_01: That's good, that's good.
• 11:45
  SPEAKER_01: I I agree.
• 11:46
  SPEAKER_01: That kind of leads us really nicely into the next question, which is how does plate tectonics explain the formation of metamorphic rocks now?
• 11:53
  SPEAKER_01: And metamorphic rocks are metamorphosis, it's just taking a rock and changing it into a different rock, usually by high temperature and high pressure, some combination of those two things.
• 12:04
  SPEAKER_01: So, Chris, where does your mind go with metamorphic rocks?
• 12:08
  SPEAKER_00: Okay, my mind with metamorphic rocks, and I want to ask you a question, actually, and this is totally off the cuff.
• 12:15
  SPEAKER_00: What plate tectonic boundaries produce the most metamorphic rocks?
• 12:21
  SPEAKER_00: Specifically.
• 12:23
  SPEAKER_00: Ask me that again.
• 12:24
  SPEAKER_00: All right.
• 12:25
  SPEAKER_00: What plate tectonic boundaries produce the most regionally metamorphosed rocks?
• 12:32
  SPEAKER_01: Uh that would be continental collision zones or tectonic collision zones where you're smashing a piece of a continent into another piece of a continent.
• 12:42
  SPEAKER_01: That's just a a lot of force being basically you've got think India smashing into Asia.
• 12:48
  SPEAKER_01: You got the the force of this entire Indian subcontinent smashing into Asia, and that thing has to stop.
• 12:55
  SPEAKER_01: You know, it's like it's like one of those cruise ships.
• 12:57
  SPEAKER_01: You see a video of like a cruise ship accidentally running into shore, right?
• 13:01
  SPEAKER_01: Like that's a lot of mass that you have to slow down.
• 13:03
  SPEAKER_01: That does a lot of damage.
• 13:04
  SPEAKER_01: Same thing goes in the rock record here.
• 13:06
  SPEAKER_00: Okay.
• 13:06
  SPEAKER_00: So in order for metamorphism, especially regionally metamorphic rocks to form, things like gneiss and schist, right?
• 13:14
  SPEAKER_00: You need to have massive amounts of pressure and very high temperatures.
• 13:20
  SPEAKER_00: So this is something, Jesse, that's not typically covered in an intro-level physical geology class, then, with a continent to continent convergent boundary.
• 13:30
  SPEAKER_00: You know, we generally don't talk a lot about we talk a lot about the pressure, obviously, but we don't talk a lot about the heat because we save that for the basic things like, oh, you have an ocean to continent convergent boundary with a subduction zone, and then you get magma generated from that, right?
• 13:46
  SPEAKER_00: It's often left out of the discussion.
• 13:48
  SPEAKER_00: So how does that happen at a continent-to-continent convergent boundary?
• 13:54
  SPEAKER_01: So the heat basically comes from it's like putting two blankets on the bed at night.
• 14:03
  SPEAKER_01: You basically have a doubly thick, you can think of think of a lithospheric plate.
• 14:09
  SPEAKER_01: In this case, it's a continental lithospheric plate.
• 14:11
  SPEAKER_01: So the crust is about 30 to 70 kilometers deep, and then you have a lithosphere beneath that, a mantle lithosphere that's another 100 to 150 kilometers deep.
• 14:19
  SPEAKER_01: That's a pretty thick blanket.
• 14:20
  SPEAKER_01: All the mantle heat is trying to get out, but it just kind of has to diffuse or conduct through the continental crust.
• 14:28
  SPEAKER_01: If you make that doubly thick, it's adding another blanket onto your bed at night.
• 14:32
  SPEAKER_01: It gets hotter.
• 14:33
  SPEAKER_01: And actually, the continent internally does produce a lot of heat.
• 14:36
  SPEAKER_01: There's a lot of radioactivity, lots of uranium, thorum, and potassium in the continental crust.
• 14:40
  SPEAKER_01: So that radioactive decay.
• 14:41
  SPEAKER_01: So it's like adding not only just a blanket, but a heat blanket, electric heat blanket, and doubling, adding two electric heat blankets on top of each other.
• 14:50
  SPEAKER_01: Uh gets really hot in there.
• 14:52
  SPEAKER_01: That's mostly where the heat comes from.
• 14:54
  SPEAKER_00: Does the pressure play into the heat too or not?
• 14:57
  SPEAKER_01: Not a lot.
• 14:58
  SPEAKER_01: The pressure, like the pressure of collision, there's not a lot of like kinetic force that gets.
• 15:04
  SPEAKER_01: There's a little bit, but there's a little bit of a debate about how much that matters, but it's probably not a big source of heat.
• 15:11
  SPEAKER_00: Yeah.
• 15:11
  SPEAKER_00: And that is, by the way, a very, very common misconception with young geoscience students is the pressure is what causes the heat.
• 15:21
  SPEAKER_00: You know, the pressure is what drives the internal heat engine of the earth and all of that kind of stuff.
• 15:25
  SPEAKER_01: People think about any collisions, and you know, the collisions you think of when we talk about geology is probably like a meteorite collision, which does a lot of melting and vaporizes stuff.
• 15:32
  SPEAKER_01: You know, it's way too slow for that sort of kinetic force to transfer to heat and generate heat.
• 15:38
  SPEAKER_01: It it doesn't not a major player.
• 15:40
  SPEAKER_00: That makes sense.
• 15:41
  SPEAKER_00: Okay.
• 15:41
  SPEAKER_00: So continent to continent convergent boundary generates massive amounts of pressure and a lot of heat, and those are the ingredients that you need to regionally metamorphose rocks that form things like gneiss and schist and phillite, and and then you know, as you get a little bit further away with a little less heat and a little less pressure, rocks like slate, right?
• 16:02
  SPEAKER_01: Yeah, for the most part.
• 16:03
  SPEAKER_01: Yep.
• 16:04
  SPEAKER_00: Okay.
• 16:05
  SPEAKER_00: What about ocean to what about subduction zones?
• 16:10
  SPEAKER_00: Generating massive amounts of metamorphic rocks or not?
• 16:14
  SPEAKER_01: Um, a decent amount, probably not by volume, but they generate some pretty diagnostic ones, uh, some pretty unique ones that are higher pressure and lower temperature.
• 16:24
  SPEAKER_01: Chris, do you have a good analogy for this?
• 16:26
  SPEAKER_01: I I always struggle to find a good analogy for this process in class.
• 16:30
  SPEAKER_01: Do you have a good one that describes this?
• 16:32
  SPEAKER_00: Well, here's the thing is that it's counterintuitive to me, to young students, because be here's why.
• 16:38
  SPEAKER_00: Subduction zone, lots and lots of pressure, right?
• 16:40
  SPEAKER_00: And you also have uh tons of heat because you're literally generating magma along the subduction zone.
• 16:46
  SPEAKER_00: Water is driven off that subducting slab, it rises up into the lithosphere, and well, you have magma, so you have a potent heat source.
• 16:55
  SPEAKER_00: So this is counterintuitive.
• 16:58
  SPEAKER_00: If you were to ask uh younger students what uh you know, A, B, or C, right?
• 17:03
  SPEAKER_00: What generates more regionally metamorphosed rocks?
• 17:07
  SPEAKER_00: Uh ocean to continent subduction, ocean to ocean subduction, or continent to continent, it's gonna be the two subduction answers that are gonna generate the most response.
• 17:17
  SPEAKER_01: Okay, gotcha for sure.
• 17:18
  SPEAKER_00: Does that make sense?
• 17:19
  SPEAKER_01: Like yeah, yeah, that's interesting because there's magmatism, so there's heat.
• 17:22
  SPEAKER_01: They think they say, oh, look, there's lots of lava, magma around, so there's heat, and that does contact metamorphism, or that does a lot of metamorphism just by adding heat to the system.
• 17:32
  SPEAKER_01: I mean, that makes sense, yeah.
• 17:33
  SPEAKER_01: That that absolutely makes sense.
• 17:35
  SPEAKER_01: I mean, you've kind of explained the three processes, the three dominant processes that produce different types of metamorphism.
• 17:44
  SPEAKER_01: So, you know, where my mind goes with the formation of metamorphic rocks is that we have a wide variety of different metamorphic rocks on Earth.
• 17:52
  SPEAKER_01: There are schists, but one schist is not equal to another schist.
• 17:56
  SPEAKER_01: There are different types of schists, schists that formed in different ways.
• 17:59
  SPEAKER_01: And you can kind of think of things like how did a rock get metamorphosed?
• 18:04
  SPEAKER_01: Did it go up in pressure first and then increase in temperature and then cool down by decompressing and cooling down?
• 18:10
  SPEAKER_01: Or did it heat up really fast right away and then go deep and then cool down?
• 18:14
  SPEAKER_01: So there's different like pathways to get to high metamorphic conditions, high temperature, high pressure metamorphic conditions.
• 18:21
  SPEAKER_01: And all of these different settings that we've kind of gone through subduction zones, collisional zones, and extensional environments where the mantle kind of gets really close to the surface in some way, that adds a lot of heat to the system.
• 18:32
  SPEAKER_01: All of those generate different PT pathways, pressure-temperature pathways that a rock can experience, which allows us, again, to sort of say things about ancient tectonic environments by studying these things.
• 18:43
  SPEAKER_00: That's exactly the point I wanted to bring this back around to is that you know, all of these boundaries that we're talking about, continent to continent, these subduction zone boundaries, these are all tectonic things.
• 18:52
  SPEAKER_00: They wouldn't happen if we didn't have plates being moved around on the surface of the earth.
• 18:57
  SPEAKER_00: I mean, we learn these almost, I think, all too often on an island.
• 19:01
  SPEAKER_00: You know, we know that metamorphism happens because you need pressure, you need temperature, and you need chemically active fluids, you know, primarily water, but we don't have any of those if we don't have tectonics going on.
• 19:14
  SPEAKER_00: And so plate tectonics directly ties to the formation and it explains the formation of metamorphic rocks.
• 19:20
  SPEAKER_01: I think a helpful thing that, and I just gave this lecture in class last week, and it's just always such an amazing thing, metamorphic rocks.
• 19:28
  SPEAKER_01: They're just really amazing that you can tell so much information about these things.
• 19:31
  SPEAKER_01: These things that have been cooked to 550, 600 degrees centigrade, they've gone down to 10 or 20 kilometers deep, and we can actually extract information about their path down there.
• 19:41
  SPEAKER_01: It's always amazing to me.
• 19:43
  SPEAKER_01: But it's kind of useful, I think, to help understand how powerful this is.
• 19:46
  SPEAKER_01: It's useful to consider the alternative.
• 19:49
  SPEAKER_01: So take something like Mars, which has what's called a stagnant lid planet or a single lid planet.
• 19:54
  SPEAKER_01: The only way to metamorphose stuff is to move it straight up and down, basically what we call vertical tectonics.
• 20:00
  SPEAKER_01: So there's not horizontal plates running into each other, it's just piling lava on top and burying stuff.
• 20:06
  SPEAKER_01: And by doing that, there's only so many pathways you can get to high pressure and temperature conditions.
• 20:12
  SPEAKER_01: Like you're only going to bury it at a certain rate and heat it up at a certain rate.
• 20:15
  SPEAKER_01: So metamorphism on a planet like Mars, let's say, right now, is pretty boring.
• 20:21
  SPEAKER_01: There's only like one type of metamorphic rock.
• 20:23
  SPEAKER_01: Whereas on Earth we have all types of metamorphic rocks, and it's totally cool.
• 20:28
  SPEAKER_00: And the metamorphism that well, no, the metamorphism that you get on Mars is going to be um, it's non-foliated.
• 20:35
  SPEAKER_00: You know, you you have this kind of like equidimensional stress that's applied due to burial.
• 20:41
  SPEAKER_00: If you imagine going to the beach, you know, and and digging a big hole and climbing in it and then having somebody shove sand around all your body, right?
• 20:49
  SPEAKER_00: That constriction that you feel, that equidimensional pressure applied equally in every single direction, that's what that kind of metamorphism produces.
• 20:58
  SPEAKER_00: And it doesn't lead to the what I think, and I think you agree with me, are these beautifully foliated metamorphic rocks.
• 21:05
  SPEAKER_00: I mean, metamorphic rocks, they're they're some of our favorites, Jesse.
• 21:08
  SPEAKER_00: I mean, we are in love with metamorphic rocks.
• 21:10
  SPEAKER_00: In fact, I'm getting new granite countertops tomorrow that are beautifully metamorphosed rocks.
• 21:16
  SPEAKER_00: I cannot wait.
• 21:18
  SPEAKER_01: Excellent.
• 21:18
  SPEAKER_01: That's a good one.
• 21:19
  SPEAKER_01: That that's a great, you know, summary ending to how plate tectonics explains the formation of metamorphic rocks.
• 21:26
  SPEAKER_01: And the third one we want to get to really is how do Earth's resources, and I think by this we typically mean like mineral resources.
• 21:34
  SPEAKER_01: We're talking about iron uh elements that we care about as society, lithium deposits, gold deposits, things like that.
• 21:42
  SPEAKER_01: How do these resources relate to plate tectonics?
• 21:47
  SPEAKER_00: Well, okay, this is a huge topic, and this could be its own series.
• 21:53
  SPEAKER_00: So we're just gonna we need to keep this, I think, like I think simple.
• 21:57
  SPEAKER_00: I'm gonna throw this back at you.
• 21:59
  SPEAKER_00: What What are some common resources?
• 22:03
  SPEAKER_01: This is a like controversial approach you're taking.
• 22:05
  SPEAKER_01: It's throwing it back to me to keep it simple on this one.
• 22:08
  SPEAKER_01: I feel like that that's risky crowd.
• 22:10
  SPEAKER_00: That's that's that's a dangerous maneuver, but talk about like some common resources that would be that would fit into this conversation.
• 22:19
  SPEAKER_00: Oh, that's okay, yeah, yeah.
• 22:21
  SPEAKER_01: We I okay, I think I can do that without getting too rambly.
• 22:24
  SPEAKER_01: Okay, yeah, yeah.
• 22:24
  SPEAKER_01: Yeah.
• 22:25
  SPEAKER_01: You know, we consider things like iron ore deposits, zinc deposits, gold deposits, silver.
• 22:31
  SPEAKER_01: Uh we took we've talked about lithium, copper, exactly.
• 22:34
  SPEAKER_01: And many of these occur in the same deposits.
• 22:37
  SPEAKER_01: So we have things like iron ore copper gold deposits.
• 22:40
  SPEAKER_01: That's like a a category that often occurs together.
• 22:43
  SPEAKER_01: Rare earth elements often occur together in a deposit type.
• 22:46
  SPEAKER_01: So we have kind of deposit classes, lead zinc, sulfide deposits occur together.
• 22:50
  SPEAKER_01: So those are kind of things we would think about.
• 22:53
  SPEAKER_00: So if I think about one example of how resources like iron, let's say, ties back to plate tectonics.
• 23:00
  SPEAKER_00: I think about something like fractional crystallization.
• 23:03
  SPEAKER_01: Okay.
• 23:04
  SPEAKER_01: Yeah.
• 23:05
  SPEAKER_00: You think about like this magma chamber, right?
• 23:07
  SPEAKER_00: Well, the magma chamber, these uh early minerals are very mafic, which means they're very rich in iron and magnesium.
• 23:16
  SPEAKER_00: So these crystals begin to grow and grow and they get bigger, right?
• 23:20
  SPEAKER_00: Think about building a wall.
• 23:22
  SPEAKER_00: Like that's how these crystals kind of grow.
• 23:25
  SPEAKER_00: And they eventually then begin to sink.
• 23:29
  SPEAKER_00: If if the conditions are right, I should say.
• 23:31
  SPEAKER_00: The the crystals can sink to the bottom of the chamber, which can cause them, because these are early formed crystals, it causes them to concentrate in the bottom of an ancient magma chamber, let's say.
• 23:44
  SPEAKER_00: And that's one of the ways that we can get iron ore.
• 23:49
  SPEAKER_00: But how does that tie back to plate tectonics?
• 23:52
  SPEAKER_00: Well, you don't get the magma chamber if you don't have plate tectonics.
• 23:58
  SPEAKER_00: You don't get the magma chamber.
• 23:59
  SPEAKER_01: I think you're no, and you're my mind's going to a very similar place, just kind of the other end of the of the spectrum there.
• 24:04
  SPEAKER_01: Instead of thinking about the minerals that are crystallizing out of the magma chamber and kind of raining down that contain iron and and sort of source all of these iron, nickel, lead, zinc deposits, chromium deposits are formed this way.
• 24:17
  SPEAKER_01: I was thinking the other end of the spectrum where you end up getting this what we call pegmatite-rich fluids, the last dregs of a magma chamber where you don't have minerals that are uncommon are formed there because the elements that don't fit in the rest of the stuff, in the rest of the minerals, are concentrated in this last very fluid-rich phase, which can crystallize.
• 24:37
  SPEAKER_01: Can I interrupt you a second?
• 24:38
  SPEAKER_01: Absolutely.
• 24:39
  SPEAKER_00: I just want to interrupt you because if you if our listeners want to go back to pegmatites, which I think pegmatites, the formation of pegmatites, what pegmatites are, they're some of our favorite kinds of rocks, Jesse.
• 24:51
  SPEAKER_00: Go back, search through.
• 24:53
  SPEAKER_00: I don't know what we we should probably have that ready at hand, but we don't.
• 24:56
  SPEAKER_00: Go back and find our episode on pegmatite form.
• 24:59
  SPEAKER_01: Yeah, I forgot.
• 25:00
  SPEAKER_01: I actually forgot, Chris, we did one on that as we're describing this.
• 25:03
  SPEAKER_01: We did do one on that.
• 25:04
  SPEAKER_01: So I think you know, where my mind goes with this question is a lot of the economic deposits that we care about, whether it's gold or copper or rare earth elements, a lot of these have to do with fluids.
• 25:18
  SPEAKER_01: And plate tectonics is an amazing way to cycle fluids through the earth, through the solid earth, to get fluids from the ocean that interact with oceanic crust, to bring that down a subduction zone system, flux it through the mantle wedge, and it comes up in magma chambers.
• 25:36
  SPEAKER_01: And a lot of these iron ore, copper, gold, IOCG deposits form right along subduction zone systems, right above the magma chambers that end up forming volcanoes.
• 25:46
  SPEAKER_01: And so it's all of this stuff just gets concentrated because fluids are moving from the mantle all the way through the crust, and they have all the opportunity to soak up those elements like gold and copper.
• 25:57
  SPEAKER_00: That's right.
• 25:57
  SPEAKER_00: I mean, think about a mid-ocean ridge.
• 25:59
  SPEAKER_00: Let's go to the other end of the spectrum, right?
• 26:00
  SPEAKER_00: We talked about subduction zones and magma formation.
• 26:03
  SPEAKER_00: Well, what about mid-ocean ridges?
• 26:04
  SPEAKER_00: At mid-ocean ridges, we have a very potent heat source.
• 26:08
  SPEAKER_00: You know, this theosphere material rising up, partially melting, forming basalt.
• 26:13
  SPEAKER_00: So you have this really you have a potent heat source and you have highly fractured rock, right?
• 26:19
  SPEAKER_00: Combined that now we have hot, salty water that's flowing through because it gets heated by this potent heat source.
• 26:27
  SPEAKER_00: Hot, salty water flowing through highly fractured rock.
• 26:31
  SPEAKER_00: Well, these metals they're very soluble in hot, salty, maybe acidic water.
• 26:40
  SPEAKER_00: These things are they're very, very soluble in those kinds of conditions.
• 26:43
  SPEAKER_00: So you're talking about this material, this fluid that you just described, moving through vast volumes of rock, selectively dissolving these very soluble metals and then precipitating them when the conditions change, therefore concentrating again these kind of ore deposits.
• 27:02
  SPEAKER_01: So something's just coming to me.
• 27:04
  SPEAKER_01: I don't know why this is coming to me, but it's an old story.
• 27:06
  SPEAKER_01: I don't know if I've ever told you this before, Chris.
• 27:08
  SPEAKER_01: But so economic geology is the study of economic deposits, right?
• 27:14
  SPEAKER_01: Like that's what economic geology is.
• 27:15
  SPEAKER_01: And it's really all about fluids.
• 27:17
  SPEAKER_01: It's about understanding how fluids are moving through the Earth's system, and you know, whether it's subduction zone fluids or fluids that are flowing through sedimentary rocks coming out of metamorphosed basement gneisses and flowing into sedimentary rocks and moving elements and then dumping them somewhere, like hit some chemical boundary and dumping them somewhere.
• 27:34
  SPEAKER_01: But I had a roommate who was an economic geologist in um in grad school, and we had another roommate who was a French physicist who knew nothing about rocks.
• 27:44
  SPEAKER_01: And at one point, have I ever told you this story?
• 27:46
  SPEAKER_01: I'm not sure if I have.
• 27:47
  SPEAKER_01: At one point, Xavier, who's the French guy, he goes, Joe, uh, what is economic geology?
• 27:54
  SPEAKER_01: And he said in a French accent, which I'm not going to try and replicate, but what is economic geology?
• 27:58
  SPEAKER_01: Is that just like cheap geology?
• 28:03
  SPEAKER_01: Which I thought was brilliant.
• 28:06
  SPEAKER_01: Just geology, very, very cheap.
• 28:09
  unknown: Yeah.
• 28:10
  SPEAKER_01: That's was he trying to be funny or no?
• 28:12
  SPEAKER_01: You know, he just he was like, what is this term?
• 28:14
  SPEAKER_01: Economic geology.
• 28:16
  SPEAKER_01: Is it just the cheap geology?
• 28:19
  SPEAKER_01: I thought it was great.
• 28:20
  SPEAKER_01: But I mean, yeah, I think we're on the same page.
• 28:22
  SPEAKER_01: And it's all about fluids.
• 28:24
  SPEAKER_01: Fluids build these resources for us, and plate tectonics really controls where the fluids go and how far they go, how deep they go, uh, what kind of fluids there are.
• 28:34
  SPEAKER_00: So yeah, plate tectonics is the mechanism for generating the fluids.
• 28:38
  SPEAKER_00: Yeah.
• 28:38
  SPEAKER_00: And then the fluids do the work, right?
• 28:40
  SPEAKER_00: It's then you get into geochemistry and and then the conditions change and they precipitate them and they're concentrated now.
• 28:46
  SPEAKER_00: Because, you know, at a mid-ocean ridge, all rocks have these metals in it.
• 28:50
  SPEAKER_00: All rocks have gold in it, right?
• 28:52
  SPEAKER_00: I mean, very, very minute time requirement.
• 28:56
  SPEAKER_00: Small percentages of it, but they're there.
• 28:58
  SPEAKER_00: But then if you take these fluids that are hot, they're salty, and sometimes acidic, and they're flowing through the stuff and they selectively dissolve it, they're concentrating it bit by bit by bit, and then making something that's economic.
• 29:11
  SPEAKER_01: That's exactly right.
• 29:12
  SPEAKER_01: And cheap, exactly.
• 29:14
  SPEAKER_01: And that's something that we kind of talked about to bring it full circle.
• 29:17
  SPEAKER_01: And the reason we really put this um Earth's resources and plate tectonics in this particular episode is because we can think about metamorphic rocks and sedimentary rocks in the same way.
• 29:27
  SPEAKER_01: Sedimentary rocks are great density filterers, and so there are gold deposits that form, and there are diamond deposits actually, that form just because those are really dense things, and you need a stream to really filter those and wash away all the light stuff and keep all the dense stuff behind.
• 29:43
  SPEAKER_01: And so sedimentary rocks and plate tectonics actually concentrate some of these things for us too, as do metamorphic rocks.
• 29:51
  SPEAKER_01: Certain melting reactions will concentrate zirconium or lithium or um neodymium in the melt as well.
• 29:58
  SPEAKER_01: So all these processes work to concentrate stuff for us, which is the key to forming resource-rich areas.
• 30:05
  SPEAKER_01: So that was a good one, Chris.
• 30:07
  SPEAKER_01: I think that's is that a wrap?
• 30:08
  SPEAKER_01: Do you do you have I think it's a wrap?
• 30:10
  SPEAKER_00: I I have a thought.
• 30:11
  SPEAKER_00: As you were rambling on, I had a thought there.
• 30:13
  SPEAKER_01: So your mind was was wandering.
• 30:15
  SPEAKER_00: It was it did a little bit.
• 30:16
  SPEAKER_00: Um, I'm like, okay, he's talking again.
• 30:18
  SPEAKER_00: I can think.
• 30:20
  SPEAKER_00: Um here's my thought.
• 30:23
  SPEAKER_01: I why do I do this with you?
• 30:25
  SPEAKER_01: You're you're a bit of an a-hole sometimes, you know that it comes by me naturally.
• 30:31
  SPEAKER_00: So I'm thinking about our next episode.
• 30:34
  SPEAKER_00: Would our listeners be able to answer these questions?
• 30:36
  SPEAKER_00: Like, all right, how does this relate to plate tectonics?
• 30:39
  SPEAKER_00: How does this relate to plate tectonics?
• 30:41
  SPEAKER_00: Like, we should have started the episode with that, I think.
• 30:43
  SPEAKER_00: You know?
• 30:44
  SPEAKER_00: Like, how does plate tectonics relate to the formation of sedimentary rocks?
• 30:48
  SPEAKER_00: Can you answer that right here, right now?
• 30:50
  SPEAKER_00: You know?
• 30:51
  SPEAKER_00: I'm curious about that.
• 30:52
  SPEAKER_00: And I would I would really like feedback from our listeners on this.
• 30:55
  SPEAKER_00: Like, send us an email on this and let us know what you think.
• 30:58
  SPEAKER_00: When you first heard it, did you have an answer ready to go?
• 31:02
  SPEAKER_00: Oh, I see.
• 31:02
  SPEAKER_00: Does that make sense?
• 31:03
  SPEAKER_01: Yeah, okay, yeah, yeah.
• 31:04
  SPEAKER_01: So send us feedback.
• 31:05
  SPEAKER_01: You're asking, send us feedback.
• 31:06
  SPEAKER_01: I'm asking for feedback.
• 31:08
  SPEAKER_01: Yeah, yeah, yeah.
• 31:08
  SPEAKER_01: I like it.
• 31:09
  SPEAKER_01: I like it.
• 31:09
  SPEAKER_01: Yeah, if you thought that, oh, I have an answer to how plate tectonics relates to the formation of sediment trucks, send us that.
• 31:16
  SPEAKER_01: We'll cover it in the beginning of next episode.
• 31:18
  SPEAKER_01: Absolutely.
• 31:19
  SPEAKER_01: At the outset.
• 31:20
  SPEAKER_01: That's a good idea.
• 31:20
  SPEAKER_01: So that's all I had.
• 31:21
  SPEAKER_00: That was just a thought.
• 31:22
  SPEAKER_01: Yeah, send us some feedback.
• 31:23
  SPEAKER_01: We are going to keep working our way through these.
• 31:25
  SPEAKER_01: We might take a few breaks to do some other stuff in between, but we will get through a whole bunch of questions about plate tectonics here over the next couple months.
• 31:32
  SPEAKER_01: We're also going to take a little bit of a break over the holidays and re-release some stuff, but stay tuned.
• 31:37
  SPEAKER_01: We will keep the good content coming here.
• 31:39
  SPEAKER_01: You can follow us on all the social medias.
• 31:41
  SPEAKER_01: We're at Planet Geocast.
• 31:42
  SPEAKER_01: Our website is planetgeocast.com and our email is planetgeocast at gmail.com.
• 31:47
  SPEAKER_01: Check out our Camp Geo, the first links at the bottom if you want to learn about geology in a very structured way with beautiful images.
• 31:56
  SPEAKER_01: Check it out.
• 31:56
  SPEAKER_01: We're constantly updating that stuff.
• 31:58
  SPEAKER_01: Have a great week.
• 31:59
  SPEAKER_01: Cheers.
• 32:00
  SPEAKER_01: Cheers.