Kickstarting Continents - The Acasta Gneiss Complex Part II
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[00:00:00] And we're, we're,
Chris Bolhuis: Hold on. Hold on. Hold on. Hold, hold,
Dr. Jesse Reimink: everybody, get situated, get ready. Producer Watson, are we ready to
go? how did,
Chris Bolhuis: What does Watson say?
Dr. Jesse Reimink: he goes, he's ready to go. No, he's tuckered, man. He's tuckered. We're doing this late night record sesh [00:00:30] here. And, uh, he's like, he's like, dude, it's time for bed. What are we not doing in bed right now? This isn't office time. This is go to
Chris Bolhuis: You are not an early to bed kind of guy though.
Dr. Jesse Reimink: No, that's true. I'm not. Neither are you,
Chris Bolhuis: And you are a very, I know I'm not, but, but you are an early
Dr. Jesse Reimink: you are an early to fall asleep on the couch with Doritos in your hand
Chris Bolhuis: Absolutely.
Dr. Jesse Reimink: Chris doesn't go to bed early, he goes to sleep early, but not to
Chris Bolhuis: Yeah, I do. Best chip ever made. Doritos. there. It's hands down. It's [00:01:00] not even a question.
Dr. Jesse Reimink: So
Chris Bolhuis: Me and processed cheese get along very
Dr. Jesse Reimink: very well. You're just besties.
Chris Bolhuis: I am. We are. We are. We
Dr. Jesse Reimink: good
Chris Bolhuis: Well, hey, Jesse, this is part two of Earth's Oldest Rocks. of the Acasta Gneiss specifically,
Dr. Jesse Reimink: Yeah, this is part de. And, we are This is, this is where Chris, you're going to have your work cut out for you. Get me out of the weeds. Cause we're going to, okay, here's the setting. [00:01:30] We got asked a listener question a while back from Mark, who asked us about the Acasta Gneiss specifically, which sent off alarm bells for me because, yeah, thanks Mark, because this is, this is home turf.
This is, uh, Yeah, this is where I did my PhD, but this kind of got expanded, Chris, into a series of podcast episodes on Earth's oldest rocks that also we've combined with images and are available as an audio book on the Camp Geo mobile app, which is the first link in your show notes where you can go, you can find a ton of free content and [00:02:00] also Geology of Yellowstone, Geology of the Grand Canyon, Geology of the Grand Tetons, and a book on Earth's oldest rocks, which I don't know, Chris, when we're talking about rock specifically, the images do a lot.
The images actually add a lot of value, I think. So go there, you'll get some extra content with images
Chris Bolhuis: of course they do. Like, that's the hope, right? That's, look, that's why I fell in love with geology, actually. I fell in love with geology through imagery and videography. I wasn't in the field, the field sealed the deal, right? [00:02:30] But it is, it's a visual
Dr. Jesse Reimink: It is. And to do it well, I mean, to do it to the podcast, I mean, we do a good job, I think, of explaining these topics in audio, but there's some things you just can't get across in audio. So you can go to our Camp Geo app and get this podcast content with images in the Earth's Oldest Rock chapter.
But the point is, this has expanded into a series on Earth's oldest rocks, kind of because it's home turf for me. And, Chris, our last episode, part one, was basically [00:03:00] the history of the discovery of the Acastanites Complex. the science up until around about 2010, which is when I started my PhD work.
Chris Bolhuis: there was a time, Jesse, when you, would not shut up about the Acasta Gneiss. And so me and Andy and other people that you're
Dr. Jesse Reimink: Mike Agerson, Fre Yeah. Friends of the pod
Chris Bolhuis: Oh my gosh, shut up, Acasta. Okay. We've, we've heard enough.
Dr. Jesse Reimink: is a, this is probably [00:03:30] every PhD student goes through this. I had an extended period of time in the wouldn't shut up about his projects time period, where it's like, dude,
Chris Bolhuis: That's it's understandable, but that doesn't mean we're going to let you get away with it. Okay. I get it, but. But I'm still going to rip on you about it, but Jesse, so that's where we came from setting the stage for the really the history of the Acasta complex. now you have looked into the petrology of rock [00:04:00] samples.
And you've actually come up with kind of a different, uh, how do I say this? Uh, you've framed this maybe in a different tectonic setting, if you will. Is that fair? Like, I mean, you kind of are thinking more along the lines of this Icelandic setting,
where you have like layer upon layer upon layer.
of igneous rocks in, when you, know, when you layer this volume of rocks, the geothermal gradient [00:04:30] comes into play and you have heat and you have pressure and metamorphism then invariably
Dr. Jesse Reimink: Yeah, exactly. does a lot of melting. And so let me just back up just slightly and give kind of perspective. what my PhD contributed as new to the understanding of the Acasta Gneiss complex. So, the time I started, the rocks had been discovered. They had been dated pretty well, and people had mapped them sort of, we had talked about finding these really high strained, flaggy gneisses, the lower strained zones, [00:05:00] which are still gneisses and pretty deformed, but not quite stretched into oblivion.
My contribution, I would say, during my PhD was we had found, kind of by sheer luck, a part of the area that was actually much less deformed and preserved pretty decent rock compositions. The minerals were still sort of recrystallized, but we would believe the chemistry of these rocks. Like, if I took a sample, I would believe that the chemical composition of that rock matched pretty [00:05:30] closely.
The original magma's chemical composition, which means we could do what, you know, quote, unquote, petrology. We could understand the genesis of the rock. Whereas those flaggy
Chris Bolhuis: Hold on. I'm sorry. I just want to back up for the listener. So we understand, what you're saying is the chemical composition of the metamorphic rock very closely matched the chemical composition of the igneous rock, which was the protolith, the parent rock, right? [00:06:00] Right. So the magma cooled and crystallized into the igneous rock.
The igneous rock was tortured into a metamorphic rock, but there was not a dramatic change in chemistry that took
Dr. Jesse Reimink: Exactly right. There wasn't like massive overprinting.
Chris Bolhuis: You have a lot of fluids involved and things like this that are bringing
Dr. Jesse Reimink: different rock types together. Like it's a meaningless number when you're mixing rocks. Whereas we found an area that preserves pretty good rocks. So we could do petrology really on these rocks for the first time. And what we found. For the, especially the oldest rocks.
Chris Bolhuis: [00:06:30] Well, hold on though. Hold on. But I'm sorry. I hate to do this cause I really don't want to interrupt your flow, but you said by luck. What does that mean? You found this by
Dr. Jesse Reimink: Well, it's, you know, it's a combination of luck and just spending time walking around in the rocks. But we, Found an area that preserved, well, what happened is that my PhD supervisor had gone up there on a, uh, yeah, a couple of years before on a field trip with undergrads, like an undergrad mapping, exercise.
They'd gone to the Acasta Gneiss complex. [00:07:00] He'd kind of rocked up to an outcrop. One of his students had gone up and sort of just took a random sample. and brought it back to the lab and they dated it and it had spectacularly preserved zircons that were 4. 02. So he's like, oh wow, we randomly grabbed the oldest rock in the Akasanites complex, you know, we knew that they're around, we just didn't know that this was one of them.
So I went back, building on that, I started in a master's program. project. And we went back, we went up there, we sampled it, we poked around, we looked at the outcrops, we were like, wait, this is actually kind of a [00:07:30] nice package. It's a nicely preserved kind of package of rocks that we could probably do some stuff with. And that led
to a PhD.
Chris Bolhuis: so just to be clear you found the rocks and you didn't Like pick up the rock and know, Oh, we found a rock that had 4. 02 billion year old zircon crystals in it. this meant that you picked up the rocks. You did all of the things to establish the location and the orientation of the rocks and so on that you took them from.
And then they were in the lab. So this was a months long [00:08:00] process. And you're like, Oh my gosh. We found the oldest rocks. We just happened to find them. Right. So then you came back the next year. Right. So just, sorry, I want to, I want to make sure that everyone's following
Dr. Jesse Reimink: this is a great point. And we're going to come back to this point because working in these types of really complicated, multiply deformed, tortured rocks. It requires this iterative process. It requires you to go in the field to collect samples, make a map, come back, date them all.
Do the random ledger chronology in [00:08:30] zircons, then think, okay, wait, my map was wrong there because numbers are telling me that. So I got to go back and rethink it. And I did this three or four years during the course of my PhD, this kind of go up every summer and refine it, refine it, refine it kind of thing.
Chris Bolhuis: So real quick, Jesse, So you said that this was more of an Icelandic setting as opposed to a subduction zone setting. So talk about that. what led you down [00:09:00] the path that these regionally metamorphose rocks didn't have anything to do with subduction
Dr. Jesse Reimink: so in a subduction zone, the magmas that are formed in a subduction zone, think of the Sierra Nevadas, think of Yosemite National Park, those rocks were formed above a subduction zone system. the chemistry of the rocks, the chemistry of the granites, record key signatures that tell you this was formed in a subduction zone system.
In subduction zone magma formation is deep, and it's [00:09:30] wet, because The slab going down brings water down into the mantle that melts really deep and it forms magmas that are deep and wet and you can see various chemical signatures that tell you deep plus wet what we saw when we looked at especially the oldest rocks in the cost of the 4 billion years and the 3.
9 billion year old rocks was not a deep wet signal. We saw a shallow Ciao. dry signal, which is very much more a mantle plume kind of a signal. they match chemical compositions to a really [00:10:00] rare suite of rocks called Icelandites that occur only on really only on Iceland. Um, and so, so the, chemistry just kind of matched the chemical fingerprint.
We talked about this a bunch in our like Yellowstone geology book,
Chris Bolhuis: Yeah, we did, but, but not really in this terminology and you need to, like, you're skipping some steps here in terms of it gives you a shallow, dry signature, if you will, all right, you need to explain, like, what does that mean? What is that signature and how do you recognize[00:10:30]
Dr. Jesse Reimink: Okay. the signature, what the chemical signature is, is it's, it's iron enriched is what we call iron enrichment trend, or some people call it tholietic. You might have heard tholietic trend versus calc alkaline trend. calc alkaline means calcium and the alkali is potassium and sodium. are enriched, whereas the iron enrichment trend, or tholiotic, means there's a lot of iron in these rocks.
So if you compare rocks, so magmas differentiate, we've talked about this, we talked about this in the Camp Geo, chapter, there's some great images [00:11:00] on differentiation, but magmas go from mafic to felsic, they kind of evolve, as they evolve from mafic to felsic, they're increasing the silica content of the rock.
The other elements are changing as well, Iron, Potassium, Sodium. Those are changing as well, but they don't necessarily always change in line with silica. And so in Iceland, in a place like Iceland, we have this, what's called an iron enrichment trend, where iron gets really high, really fast.
And then in subduction zone system, the iron, [00:11:30] kind of stays in line with silica. It kind of drops as silica increases. So the two very different trajectories when you compare iron to silica in these rocks. And the cause, so that's, that's the signal, the cause is everything to do with plagioclase.
Plagioclase, the mineral plagioclase, is stable when magmas are shallow, And don't have a lot of water in them. And so in Iceland, what controls this iron enrichment trend is that the magma, let's say basaltic magma, injects [00:12:00] itself into the crust and sits there and cools down. It's shallow and it's dry.
So plagioclase will be stable. And plagioclase forms and fractionates out. It crystallizes out, which plagioclase removes calcium, aluminum, silica. It removes it out of the magma. And what it doesn't remove is calcium. Iron. And iron gets driven up really fast in the magma itself. Now, we'll compare that to a subduction zone setting, where a magma intrudes really deep and it's [00:12:30] wet.
It's wet and it's deep. That magma, Plagioclase is not stable. So you'll crystallize clinopyroxene and olivine, and the iron will get soaked out of that. It won't end up in the magma, the iron will get drawn out and crystallized down, and then the stuff that erupts on the surface doesn't have a lot of iron in it.
So it's really about plagioclase, whether plagioclase is stable, and shallow dry. Plagioclase is stable and shallow dry, if that makes sense. so it, you know, it, it gets, this gets into like, advanced [00:13:00] level petrology. Yeah, exactly. But, but that's, that's the signal we sort of see that, that makes us think it's an Iceland like, uh, kind of setting.
Chris Bolhuis: So, Iceland can be thought of kind of like a layered cake then, right? Where the composition changes. so what you're saying is, toward the surface, it's more iron enriched. Is that correct? Am I getting you?
Dr. Jesse Reimink: broadly, yes. When you have, I mean, Iceland also erupts a ton of basalt too, so you get a,
Chris Bolhuis: Well, yeah, but this, this, this [00:13:30] is, if you have these different layers, can explain how Iceland has really vastly different kinds of eruptions that, that happens, some violent and some nonviolent, you know, because
Dr. Jesse Reimink: Yep.
So there's two different ways that rocks are, that, felsic rocks are really formed on Iceland. One is by this extreme differentiation, extreme fractionation. The other one is Iceland erupts a ton of basalt, that basalt gets hydrated, water interacts with it, and then it gets buried by later basalt, and it gets buried such that it gets melted.
So the Rhyolites in Iceland are [00:14:00] often formed by that melting of the basalt, as it kind of gets buried and buried and buried, and it's wet, and it's sopping wet, and it gets melted. the Icelandites are formed by this extreme fractionation. So, put a basalt there, and crystallize 80 percent of it, or 90 percent of it, that last 10 or 20 percent is going to be Icelandite composition.
This iron enriched rock, which we see in Acasta. So
at risk of sort of belaboring the point there, like that's what we contributed, I think, in my PhD, was the sort of thinking [00:14:30] about the chemistry of these magmas, because we found this This nice area. At the same time, Annie Bauer, who's now a professor at University of Wisconsin, was doing her PhD with Sam Bowering, actually, on samples from the Acasta Ice Complex.
She came into the field with us, and she was working on the isotope geochemistry, and she started seeing signatures that Acasta, the rocks that we see in Acasta, uh, she was kind of confirming some of these signatures and observing new ones that the 4 billion and the 3. 9 billion year old rocks were actually [00:15:00] formed their source material.
What melted to form those was 4. 3 billion years old. So there's like even older crust that was melted to form the rocks we see today.
Chris Bolhuis: Now, is that a new technique that allows. A researcher to go back to
Dr. Jesse Reimink: it's, so Chris, we talked about this in, oh man, a previous episode about like how the earth, I forget it was, how the earth works or
something like
Chris Bolhuis: we forget, we forget things. Don't we?
Dr. Jesse Reimink: Chris has forgotten more than most of us have learned in our lifetimes. [00:15:30] Um,
Chris Bolhuis: That's true, it's sadly true, uh, it's so depressing.
Dr. Jesse Reimink: But we talked about neodymium. We talked about the extinct neodymium isotope and how it can be like a tracer.
So if you see a lot of this, 142 neodymium or 143 neodymium in the rock, it had to come from something that had a lot of samarium in it. And that's felsic crust, right? So that kind of tells you, did it come from the mantle or from a crustal composition? And so those are the types of [00:16:00] techniques that Annie was, was using to analyze these rocks.
Chris Bolhuis: How long did that process take? Was this like a, uh, she was doing her PhD at the time, so was this like a four year project for, for her? Yeah. Okay. All right. Jesse, you know, it occurs to me that we never, Really set the stage for where Acasta is,
Dr. Jesse Reimink: Oh, yeah.
Chris Bolhuis: You know, we should have done that right at the
Dr. Jesse Reimink: We
Chris Bolhuis: Um, we, just refer to it as a Craton, you know, like, Oh, [00:16:30] okay. It's in the Craton, but be
Dr. Jesse Reimink: Okay. uh, go, if you're in the U.
S., let's go from there. You go to the Montana border Montana, Alberta border there, and, uh, you got to drive, uh, Basically, to drive straight north all the way to the top of Alberta, it's like a 12 hour drive. No, it's more than that. 16 hour drive. Then you hit the Northwest Territories, you get to drive up to Yellowknife.
Yellowknife is where the road ends. There's no real all season road that goes north from Yellowknife, really. There you take a float plane, from Yellowknife about [00:17:00] 200 miles north to the Acasta Ice Complex. And there's a beautiful little beach landing area you land on and, there's a little island that everybody camps on in this Acasta River system.
I mean, it's the Canadian Shield, so there's like, 40 percent water and, uh, you know, 60 percent rock.
Chris Bolhuis: Okay. So to summarize, this is a long ways north, um, it's in the northwest territories and it is not easy to get
to.
Dr. Jesse Reimink: easy. this is why it's not a well studied is because it's so remote. [00:17:30] So it takes a long time to get there.
Chris Bolhuis: Okay. So Jesse, let's do this part of it really quickly, but what are some other, other people maybe have worked
Dr. Jesse Reimink: Yeah. So, so there's a bunch and I'm going to be, you know what, this is my podcast. So
Chris Bolhuis: Yeah. Hey, what, what did you just say? Oh my gosh.
Dr. Jesse Reimink: So I get to say what I want, this
Chris Bolhuis: Oh my gosh. That hurt my heart, Jesse. you just took over right now.
Okay. You
Dr. Jesse Reimink: taking over by, you know, not allowing you to hit the record button in [00:18:00] the new software we
Chris Bolhuis: me get a word in edgewise either. So Holy
Dr. Jesse Reimink: Picking topics that I
Chris Bolhuis: it's time to,
Dr. Jesse Reimink: I just talk and talk and talk
Chris Bolhuis: Um, all right. So one of the research. groups have, they've zeroed in on meteorite impacts as maybe the source of the Acasta Gneiss. Right. What do you
Dr. Jesse Reimink: I, I mean, I think it's, I mean, it's a more complicated model and not necessarily. We don't have direct evidence for meteorite impacts. It could be right, but it's not the simplest explanation for the data we have. And this [00:18:30] comes back to our conversation we had with Mike Akerson about, how science is done.
And, people publish things that end up being wrong. I've published stuff that ends up being wrong. that's fine, you know, these ideas keep getting sort of iterated around and kind of worked on. And so And so meteorite impacts, maybe we need to test it.
I don't think there's evidence for it yet, but it's, it's possible. other people are searching for old rocks and, you know, still kind of debating the age of the rocks. You know, some people would argue that [00:19:00] the Acasta Gneiss complex is actually just 3. 9 billion years old, that the 4 billion year old rocks are.
Not actually four billion years old. They're inheriting stuff. So, there's still debate.
Chris Bolhuis: seem a bit pedantic to you?
Dr. Jesse Reimink: I think it seems a bit pedantic, and I think we really kind of nailed the age. Like, I think we, a really good age for rocks that we know are igneous, and, um, so it's not really, Oh, for
Chris Bolhuis: The Acasta Complex is 4. 019 plus or minus 1. 8 million years [00:19:30] old. Cause you know what, that million years, it matters. So, there we go. It is established because, hey, this is Jesse's podcast, everybody. Okay? Yeah,
Dr. Jesse Reimink: actually.
Chris Bolhuis: no, you're gonna name it the Jesse Reimink podcast with his little sidekick, Chris,
Dr. Jesse Reimink: Yeah.
Chris Bolhuis: his old little
Dr. Jesse Reimink: we could get a little sort of Batman and Robin photo going on for the cover cover art. I like this
Chris Bolhuis: yeah, over my dead body, over my dead [00:20:00] body. All right. So Jesse. No, it's not good stuff. Actually. I'm offended. Um, real quick. I think we need to move on to like, where are we at now? I think we've already established this, but where are we now?
Dr. Jesse Reimink: there's a lot of outstanding questions, here. One of them is like, where are the 4. 2 billion year old rocks? Are they still out there? We have, we talked about the fact that there's this one xenochristic zircon core that's 4. 2 billion years old. So there must've been 4.
2 billion year old rocks there. I don't know if they [00:20:30] still are or not. It's open for debate.
Chris Bolhuis: So in geology, we use the kind of turn of phrase a lot of walking the contact. Is this just a matter of just stumbling upon the right outcrop you think? Or maybe it's, you said there's a lot of water, so you only have access to, certain amount of it. Do you think it's there?
Dr. Jesse Reimink: It's a great question. I don't know. there's a bunch of different colors of gray here and the darkest ones are mafic. We don't know how to date those. It's really hard to date really[00:21:00]
Chris Bolhuis: Okay, all right. We need to tease that out just for like 30 seconds. Why are mafic rocks Difficult to date
Dr. Jesse Reimink: Old ones are really difficult because they just don't have zircon in them. didn't form
Chris Bolhuis: oh, okay. Yeah. Yeah.
Dr. Jesse Reimink: it's basically as simple as
Chris Bolhuis: Are they gonna be more in the lighter bands the zircons then as opposed to the
Dr. Jesse Reimink: exactly. That's exactly right.
So that just shows there's a lot of mafic rocks out there. Some of them might be 4. 2 billion years old. We just [00:21:30] haven't, took the time to try and date them.
The other complexity here is that you look at this image, image number seven, there's four different, five different rock compositions in different ages in that one outcrop.
Chris Bolhuis: your legs in this? I want to see your
Dr. Jesse Reimink: I think I'm on the
Chris Bolhuis: left
Dr. Jesse Reimink: Yeah, that, those are my legs. Those are my, my big boots there. Um, and, uh, so it takes a lot, you have to date almost every rock you come across.
You have to like get zircons out, date the [00:22:00] zircons to figure out the age. And so you just can't date them all. So you kind of end up, I don't know, Chris, I don't know the answer if there is,
Chris Bolhuis: Well, let me, I have a question then this area has been heavily, heavily glaciated.
you studied that the glacial deposits
Dr. Jesse Reimink: have,
Chris Bolhuis: like, because, because you know, they would have, picked up stuff and scoured it and gotten deeper
and then plopped it off
Dr. Jesse Reimink: it's a great idea, Chris. And, we have, there [00:22:30] was a master's student at the University of Alberta who actually looked at esker zircons.
Chris gets the segue award today. Um, because eskers are, I mean, we see some eskers in Michigan, not a lot of eskers, right? Like there's not too
Chris Bolhuis: Now there there are there are clusters of Eskers in Michigan Yes, there and you get them in Minnesota a lot. So an Esker is it's what we call stratified drift For glaciologists, this is, uh, it's a deposit that is [00:23:00] formed by rivers that are running through glaciers at the bottom of glaciers and so on.
And the river in a glacier and in the middle of a glacier and even on top of a glacier has everything that a normal river would have. It has stream banks, it has, you know, a stream bed, it sorts the sediment in every single way. Because it's a water deposit. And then as the glacier melts, it all just kind of slumps together.
And it forms this kind of [00:23:30] sinuous, snake like, meandering river deposit, essentially. And it's just kind of plopped off on top of the land. And, and so they're really, really cool. Uh, you know, if they are very cool, like I'll, Jesse, to me, there's nothing better than going for a long run on top of an esker.
it's spectacular. they make great roads because these back country roads, you know, because they're, they're gravel, [00:24:00] essentially sand and gravel, and they have great drainage. So if you just you know, make a dirt path on top of it, they're awesome for that, for dirt roads.
Dr. Jesse Reimink: you're hitting all the key points here. And They stand out like a sore thumb. and you got to think back to the Laurentide Ice Sheet. The entire region was covered by an ice sheet.
And this ice sheet was retreating. And eskers in this region are spaced every 10 kilometers. You'll have a big esker sort of train, a big esker system. And they're running kind of in this part of the world, they're running from east to west, kind of from where the [00:24:30] center of the Laurentide ice sheet was out to the west is where they're draining.
So we looked at
Chris Bolhuis: Yeah. That's interesting too, Jesse, because eskers we have in Michigan would run north
Dr. Jesse Reimink: Yeah, exactly. So in this part of the Northwest Territories, it was, the ice sheet center was due East, basically.
Chris Bolhuis: So basically what that means everybody is that, the eskers are going to run parallel to the motion of the leading edge of the glacier. And these kinds of ice sheets are so massive that they spread outward from the zone of accumulation. So wherever the ice was the thickest, they [00:25:00] would just kind of ooze outward in all
Dr. Jesse Reimink: And beauty about eskers, because you have a bunch of glacial sediments, you have till, reworked material that is different glaciers. Unsorted, you know, unstraight, whereas, until can be sourced from hundreds of miles away, because it's picked up in the ice and then dumped off. Eskers, the thought is, and there's a bunch of people who've worked on mostly in the diamond community, like people use eskers to trace diamond deposits down, Eskers [00:25:30] kind of, they sample rocks five kilometers by five kilometers upstream from your sample site, or maybe 10 by 10 or something like that.
They're a little bit more localized sort of sampling devices. And so we sampled the Eskers and looked at the zircons in the Eskers. And in some way, kind of mapped out where old rocks are in Acasta. And basically the story is there's not a lot of 4. 0 billion year old rocks out there. There's a decent amount of 3.
7 and there's a bunch of 3. [00:26:00] 4 billion year old rocks in the Acasta ice complex. So the 4 billion year old stuff looks to be fairly restricted. we didn't see a lot of 4 billion year old zircons in the Esker zircons. Let's put it that way.
Chris Bolhuis: Okay. So basically, that's really interesting. Actually, you're saying that if you look at the ratio of the age of the zircons that you find in there, it's going to give you. a pretty good summary of the ages of the rocks that are exposed in the Craton [00:26:30] in the Northwest territories where the Acasta is formed.
That's really, That's interesting. That, that makes a lot of sense, but I never really thought about it before.
Dr. Jesse Reimink: Yeah. So they're, they're actually kind of, I they're not perfect, but they're, decent sort of samplers in that regard. So the other
Chris Bolhuis: So how big of an area are we talking about then in terms of like where this Acasta complex is like, what, what are we referring
Dr. Jesse Reimink: So where everybody has studied basically everybody studied about, uh, including myself, you know, a dozen PhD projects in an area that's about [00:27:00] 30 to 50 square kilometers. The Acasta Gneiss complex is more like 1300 square kilometers.
and most of that's pretty unstudied apart from sort of this esker sampling thing we did. But there's a ton of gneisses that are exposed that nobody's dated. And actually a master student of mine, we're about to publish this work, but a master student, about 250 kilometers north, almost on the Arctic coast, image number nine shows the location of this.
She found some samples [00:27:30] that are 3. 8 billion year old samples and they look just like Acasta. And so there might be a bunch of old crust in this area that we just don't know about, outside of this little 30 square kilometer window that everybody's studied. It's just really hard to explore. yeah, so that's sort of an open question is like, are there more old rocks?
How extensive are they? We, we just don't really know.
Chris Bolhuis: Really interesting. Probably a bigger area than, it's so hard to get to, this is so remote, [00:28:00] you know, which leads me to the last thing that I want to talk about actually is, all right, the Acasta Knight is pretty damn awesome. It's very difficult to get to. so first of all, one, is it getting mined at all for anything?
And two, how do people get their hands? On a piece of Acasta, cause I have mine, you have
Dr. Jesse Reimink: you have yours from Yeah, that's exactly right. I have [00:28:30] mine. so yeah, there are people who've, at least two, who have staked mineral claims on the Acasta. Nice to extract.
Chris Bolhuis: are they looking for?
Dr. Jesse Reimink: They're just getting rocks to sell. And so that answers the second question. Really, that's what they're doing.
They're getting, they'll make necklaces out of it, they'll make little bookends, they'll make coasters, they'll just sell raw slabs of it. and you'll see, if you go to like, whatever, eBay or whatever, whatever you're buying things on, you'll find probably a gaussinized complex samples. And, you know, at the Gem and Mineral [00:29:00] shows, there'll probably be somebody selling them.
So they do get passed around. I've met a couple of these people who have these things.
Chris Bolhuis: they reliable? Ha ha ha!
Dr. Jesse Reimink: you know, that's super nice. one guy I've met, super nice guy, has this mining claim and he's really interested in understanding the sort of chronology because we've shown a bunch of images of how complicated these outcrops are.
So you can't just rock up to an outcrop and Take a sample and say, this is, it would be accurate to say, this is the Acasta Gneissus, but it's inaccurate to say, this is a 4 billion year old rock, [00:29:30] because in one outcrop, there's five different ages of rocks. so,
Chris Bolhuis: a four billion year old rock, Jesse? Ha ha
Dr. Jesse Reimink: a four billion year old rock.
I can show you the publication. So, but I would just say, be a little careful. really hard to tell. You just can't really tell unless you like dated the individual sample, brought it to my lab and like we measured the ages. It's just really hard to tell if that is actually, The oldest rock in the world, or if it's, you know, the piece right next to it, that's actually 3.
[00:30:00] 6 billion years old or 3. 8 billion years old. And so part of it doesn't matter because it's up there. Like it's a part of it
Chris Bolhuis: Yeah, it doesn't matter. It doesn't matter. I mean, I'm happy that I have a four billion year old rock. Do I have a 4. 02 billion year old rock? Oh, I see. I love that. But you know what?
Dr. Jesse Reimink: if you had a,
Chris Bolhuis: damn happy if I had a 3. 4 billion year
Dr. Jesse Reimink: If you had a 3. 6 billion year old rock, you would still have one of the six oldest rocks in the face of the earth that we know of. So [00:30:30] like, is it really that big of a difference? I mean, I don't know
Chris Bolhuis: Exactly. And it, and I'm going to say too, that it is a, an absolutely gorgeous rock. Jesse, you and I love this. We'd love the look of these tortured rocks. You know, my countertops are, are, they're intensely metamorphic. And, I couldn't go with anything else.
You know, I
Dr. Jesse Reimink: roots of the continents, man. It's like so good. The deep tortured roots. It's, it's like, you know, going to Grand Canyon [00:31:00] and you gotta see the deep stuff at the base of it, man. It's like the
Chris Bolhuis: You have to see the Vishnu.
Dr. Jesse Reimink: Vishnu, to the Vishnu. That's, those were shirts we had. That was what our shirts said when on the field, field camp I went to.
It was, to the Vishnu.
Chris Bolhuis: Yeah.
Dr. Jesse Reimink: so funny. Erosion happens, baby. okay, Chris, that's, that's the spiel about the Acasta Dice. That's the end of part two of the spiel.
Chris Bolhuis: Absolutely.
Dr. Jesse Reimink: Peace. [00:31:30]
