This is Java g. B, with all of us trampled, the
mantle makes up 84 percent of the Earth's volume because it's
covered by the plates of the lithosphere information about
its chemical. Composition is hard to come by.
It mostly comes from lavas that we believe are sourced from the
mantle and most of that lies under the ocean which is a
notoriously difficult place from which to obtain samples.
But as we managed to extract more and more mantle sourced
lava samples, some very unexpected patterns in mantle
Composition are emerging. Matt Jackson is a professor of
earth science at the University of California, Santa Barbara,
his research focuses on the isotopic and chemical
composition of lavas erupted at hotspot volcanoes.
Matt Jackson. Welcome to geology B.
Thank you, Oliver. Thanks for having me today.
I just managed to catch you before you embark on a research
vessel for a six-week trip, starting in Guam and heading
down to the South Pacific. Is that to sample seafloor
lovers there. Oh yeah, absolutely.
We have the older portions of couple of long-lived oceanic
hotspots that exhibit some volcanism on the Western
Pacific. These hot spots are very
similar. To the archetypal hotspot the
Hawaiian hotspot. The Hawaiian hotspot has about
80 million years of recorded volcanism and the older portion
of the Hawaiian. Hotspot, of course, is
subducting into the Kamchatka trench that you hot spots that
will be looking at go back to over 100 million years and
therefore we're looking at over 100 million years of continuous
vulcanism of these two hot spots and older portions are now
located the Western Pacific. And subducting into the Marianas
Trench Wrench. So we'll be out there to look at
the older portions of these two long-lived hot spots but there
are quite a few hot spots that erupt lavas above the oceans.
Hawaii being the obvious example you just mentioned but also
Samoa and the Canary Islands and a few others.
Why go to all the trouble to sample, them below the ocean's.
The main issue with volcanoes in Oceanic settings is that very
few of volcanoes actually make it above sea level?
We have on the order of Hundred thousand sea mounts that are a
kilometer high or higher above. The ocean floor, where as we're
dealing with, perhaps hundreds of islands, in Oceanic settings.
So by tackling the submarine volcanoes, we greatly open up
the number of volcanoes that we can explore to better
disentangle the histories of these different hotspots.
Wow, that's a really overwhelming statistic.
I had no idea. Let's return to your upcoming
Voyage, the South Pacific prior surveys have been able to
identify a bunch of hot spot trails.
In fact, I think you told me that it's even referred to as
like, hotspot highway. So how do we know that these are
hot spot. Trails, Oceanic hotspots are
thought to generate age Progressive.
Volcanic Trends. So you have a little schoeneck
plate, that's moving laterally, over an upwelling plume, you
generate a volcano above The upwelling plum but as the plate
moves off that hot spot, another volcano forms in its place.
And that volcano then gets wrapped it off laterally and
another volcano forms in its place and so forth.
You end up generating a nice, linear age, Progressive, Trend
Hawaii. Of course is the classic
example, but we have other examples in the Pacific.
For example, the small one hot spot and McDonald hot spot and
some lesser-known hot spots like the Ergo hot spot now.
Several hot spots in the south Pacific are aligned along the
trend of plate motion. So along the flow line at the
Pacific Plate, so we have the McDonald Hot Spot, the error, go
Hot Spot, perhaps the Rarotonga hot spot in the small hot spot
all aligned. They're all about 1000 to 1200
kilometers apart and because they're aligned Downstream of
the easternmost hotspot. So to the west of the
easternmost hotspots in McDonald, hotspot, you have
McDonald hotspot, sea mounts, that are accumulated.
Relating around the are ago. Region, their Rarotonga region
and the small one region further to the west.
And so, we have these four hot spots in a row that are
generating what we refer to as the hotspot Highway.
Because we have this continuous trail of seamounts that have
been generated by the various hot spots along this Trent.
Well, if we go further to the Western Pacific where these hot
spots, then Trend to, right? So if you look at the Hawaiian,
hotspot, for example, you have this beautiful band, Hawaiian.
Hotspot track at about 50 million years, we have the trend
of the hotspot, goes for approximately East-West to a
closer to a north-south trending.
We call this the a trend and this dominates, the strike of
the Hawaiian hotspot over much of the Cretaceous.
We see similar bends in these hot spots from The Hot Spot
Highway the issue is we have this province with thousands of
sea mounts but very few of them have ever been sampled,
characterized your chemically or HD did.
So it's hard to tell. Well, which of the four hot
spots from The Hot Spot, Highway these various seamounts came
from. So we're going to head out to
that part of the Pacific on our upcoming expedition to sample.
And then later characterize, these various sea mounts to see
if we can disentangle the different hotspots from the
hotspot highway. So just about all these
seamounts, while the seamount, so they're under the water.
So what kind of ocean depth are we talking about here, where
you're going to be sampling? So, the ocean depths in the
Western Pacific at least, Of the trench is around 5,000 meters.
So we'll be getting samples from as deep as 5,000 meters at the
base of these sea mounts. And, in some cases, we might be
going as shallow as 3,000 meters, but we want to be
getting the deepest portions of these volcanoes, the sample, the
deepest to trigger fee and capture the earliest stages of
vulcanism on each of these hotspots.
Of course, as we go further to the west and this Western
Pacific, seamount Province will be getting closer to the trench.
So ocean bathymetry Re deepens where depths go to is, we know
about 11,000 meters, some of the sea mounts that are going into.
The trench will be harder for us to sample, will be spooling out.
A lot of dredge cable to get the deeper portions of these sea
mounts, that are currently gliding into the trench.
That's a fantastic. The amount of water to be
working under. How do you find the right places
to sample? I mean, how do you know you're
not going to just be sampling? Recent sediments that tell you
nothing whatsoever about the lava underneath Eighty to ninety
percent of the ocean floor remains on mapped to any
reasonable degree. So we rely on satellite based or
gravity-based, but them a tree and the gravity base bathymetry
has a resolution of about a kilometer, and I think a
kilometer in many cases is being generous, but it allows us to
see where the big bumps are in the ocean floor.
These bumps are the sea mounts. So what we do with the ship, as
we target specific seamounts and we make high-resolution Maps
using multi-beam Sonar And these high-resolution Maps, allow us
to get much finer, resolution of the seamount in the thema.
Tree, The Contours of the seamount at depth.
And based on this information, we can Target this steepest
portions of the seamount for sampling.
Specifically, the portions that are not only steep but highly
reflective to sonar and the reason we do this is because
surfaces that are reflective to sonar tend to be sediment poor.
So we're more likely looking at Solid Rock surfaces or
Ferromanganese and rind and crusted rocks.
Furthermore, we target the steeper portions of the sea
mounts as well, because sediment and debris, like corals for
example, lots of these seamounts.
We're actually at the surface at one point before erosion and
subsidence. The steeper portions of these
seamounts allow the corals and debris to Slough off, allowing
us to directly sampled. The basaltic Bedrock at the seam
out for the bigger seamounts. We can spend 8 to 10 hours,
trying to get decent Maps. Soooo of the flanks of the
seamount to identify the best dredge targets and then the
dredging itself. So it can also take eight to ten
hours, depending on water depth, of course.
And whether or not the dredge gets stuck on the ocean floor.
So, I'm curious how you got 5 kilometers of cable, strung Out
Below your ship. I mean, presumably their ocean
currents and who knows what moving this thing around.
So you may know where you are from the sonar.
But how do you know where the dredge is going to be?
Do you have a camera down there or something?
We don't have a camera on the dredge cable.
We put a camera on the dredge cable.
It would probably get torn off pretty early on in the dredging
process when we spool out a cable, the dredging process is a
tried and tested technique. I like to refer people to 6 B's
paper from the early 1880s showing our drawing of a dredge
that is not unlike the dredges that we're using.
Now, 140 years later, basically, we spool out cable, 5, 6 7,
Hours worth of 30,000 pound test cable of the we can get the
dredge basket down on the ocean floor.
The issue is we never know exactly where the dredge basket
is because at five kilometers depth, you can have ocean
currents that are moving in a different direction than you
have at the surface and the dredge basket can get pulled off
to a little bit to one side or the other.
So we do is we target the seamount and regions wall above
the Abyssal Plains. And we have a pretty good sense.
Say within several hundred meters of where the dredge
basket actually ends up. Now, you might say well, well,
Matt, I mean this isn't as good as GPS sampling.
Do we have on Ocean Islands or we can record the location of a
rock to better than a meter, and that's true.
Absolutely true. But, on the other hand, the sea
mounts that we're targeting, have never been mapped, they've
never even been sampled. And so, having one sample from
this seamount is incredibly valuable because then we know
its composition. We know it's age, we can figure
ER out how it formed in some cases, all we have is one rock
that comes on board and so making the rock very valuable to
us. Everybody wants a split of The
Rock and sometimes I reflect on this and told the graduate
students who were on the ship. For the first time that that
rock can represent 50 thousand dollars worth of resources.
Because when we're out at Sea, it's about fifty thousand.
Dollars a day to run these ships, the fuels, incredibly
expensive, maintaining the ship, the salary at for the Crew and
the scientist, how big are your samples?
Typically, samples range in size.
The upper end is limited by the opening in the dredge basket.
That's 40 centimeters or so, we can get some pretty sizable
pillow Basalt chunks, and we put burlap sacks, and sometimes find
netting inside of the base of the bags that we can capture the
smaller samples. We drag these dredges on the
seafloor up the sides of these seamounts for hundreds of
meters. It's, um, Cases will go a
kilometer. It takes so long to map a
seamount and it takes so long to lower the dredge basket down
5,000 meters and bring it up. 5,000 meters that we want to
make sure we bring that dredge basket up Plum full of rocks.
So we'll Drag The Dredge basket. And some cases for hundreds of
meters of our km, just to make sure we get rocks in there.
Okay. So you bring these lava samples
back to your lab and you make a number of chemical and isotopic
measurements on them. What Actually, are you trying to
find out about these samples? So two things we want to figure
out the composition of these samples and we want to figure
out their age, so that we can then determine which hotspot,
these samples came from. So each of the hotspots that
I've described as unique geochemical signatures.
So we'll measure the radiogenic Isotopes compositions of the
samples. So for examples radiogenic
strontium, pretty genic neodymium hafnium lead.
Aw. Osmium and so forth.
To really characterize the geochemical Fingerprints of the
samples that we can then say, which hotspot each of these
seamounts came from and by the same token will get age dates on
these samples to then figure out where on the gauge distance
trends of these various hot spots that the particular
seamount relates to. Now for me a big picture
question is why do these different see mouse or hot spots
have different geochemical Prince and it turns out the
geochemical fingerprints can be so good at identifying specific
locations that my former thesis advisor like to joke, that if he
didn't have GPS in someone, put him on a remote desert island
with just a clean lab and a mass spectrometer, he could based on
the composition of the basalt in that Island pinpoint which
island he was on. But what does this geochemistry
then tell us about the composition of the Earth's
interior. Well, it turns out that the
composition of the Earth's interior is highly
heterogeneous, due to a number of processes in one that we
focus on a lot. And this particular Expedition
coming up is the process of subduction.
So oceanic crust and continental crust, or materials derived,
from continental crust, enter the mantle, at subduction zone.
So when two plates collide inevitably, one of the plates,
Was down into the Earth's interior.
And then the big question is, what happens to that plate after
subduction? Well we think that plate goes
down deep into the mantle resides down there for some
period of time and then is conveyed back to the surface
again and upwelling blooms, it partially melts and then we look
at the lavas that hotspots to identify then signatures of what
went down in ancient trenches deep in geologic, time and we
find some key geochemical signatures Jurors that are
associated with different subducted.
Materials that went down into ancient trenches.
So for example, recycle oceanic crust We Believe can generate
radiogenic LED isotope signatures over time and sure
enough some hotspots show. Some really clear.
Where do you genic? Let isotopic compositions,
similarly continental crust or materials, derived from
continental crust that was subducted and deep time, it
should have very radiogenic strontium Isotopes.
And very On ready, Jennifer low 143 144, neodymium isotopic
characteristic, and we see these particular characteristics for
example, in the Samoan hotspot. And in fact, the small and
hotspot has exhibited, these isotopic characteristics based
on preliminary data over a hundred million years of its
history. So one of the reasons actually,
while we're going back to the Western Pacific is because we
think we've picked up the scent of the Samoan hotspot based on
some Legacy. Has obtained. 20 to 40 years
ago? On various Expeditions.
What we see. Is that a small and hotspot has
continuously sampled these recycled continental crust
signatures for this 100 million years of its recorded vulcanism.
So, I can understand that a particular compositional ratios.
If you like of these various Trace elements and Isotopes can
act as a kind of fingerprint or signature.
But do we actually understand the mechanism for example, where
by subduction The oceanic crust results and more radiogenic LED
we know why that is, there are a couple of different proposed
mechanisms and the one that I favor is that oceanic crust.
When it enters the subduction zone, it goes through various
nin, amorphic reactions that result in dehydration and loss
of fluid mobile elements. And we believe that lead is
preferentially lost relative to uranium and Thorium in this
becomes important because uranium And thorium when they
undergo radiogenic Decay, ultimately end up at the various
Regional a isotopes of lead. 208 lead is the result of decay of
232 thorium and 2007. LED and 2006 LED or the result
of radiogenic decay of uranium two different isotopes of
uranium and so when oceanic crust enters a subduction zone
and it loses its lead relative to its uranium you're setting up
the opportunity. To generate an overwhelmingly
large amount of radio genic lead in that downgoing slab after
it's been aged and the mantle for a couple of billion years.
And indeed we see very radiogenic, let isotope ratios
in some hot spot lavas and we have one of the hot spots that
we're going to be targeting. Has exhibited radiogenic led.
Isotope signatures for over 100 million years.
This is sort of remarkable that one hot spot can sample.
Mantle Source composition deep in the mantle for a hundred
million year period. Meanwhile that hotspot are ago
is only 2000 kilometers away from the small and hotspot which
has been sampling. Not ready genic lead but instead
radiogenic strontium and unready genic neodymium for its hundred
million year history. So as you hot spots that are two
thousand kilometers apart the surface and of course, much
closer at the bottom of the mantle, right?
At the base of these clones are only going to be about a
thousand kilometers apart. These two plumes are sampling, G
chemically distinct sources, even though there are thousand
kilometers apart over a hundred million year period, this is
completely remarkable to me and, you know, I still don't have a
satisfying explanation for how this is possible.
It seems like the plume feeding zones for these hotspots should
be overlapping with each other. We should see these two hot
spots, sharing geochemical signatures but they remained
remarkably distinct in spite of being so close together.
Either geographically over this hundred million year period.
They've been active. So what kind of signatures have
we been able to? Identify you mentioned?
We can see if there's a signature from subducted Oceanic
lithosphere and also if we see signs of Continental, crosstalk,
crosstalk, derived materials are there any other signatures that
we can identify and do we know what they represent?
There are signatures in a mantle that are left over from the very
Days of the earth. And it appears that the mantle
domains that have been able to preserve.
These really ancient signatures are the domains that have been
least impacted by mixing with subducted crust of the oceanic
or Continental varieties. And these early formed or
ancient domains are characterized by one very key
signature that a lot of people have focused on and that's high
heels. Liam 3 over helium-4 ratios so
elevated helium-3 over helium-4 is a signature that we associate
with primordial materials in the solar system.
So for example, we know from the Galileo spacecraft that the
atmosphere of Jupiter has a helium-3 over helium-4 ratio,
that is 120 times that which we have in the Earth's atmosphere
and that helium-3 is a primordial isotope of helium
very, very Little of it is made inside of the earth helium for
some portion of that mirrors, interior is primordial, but
helium-4 tends to accumulate in the earth and increase in
abundance because uranium and thorium Decay by Alpha DK.
Those alpha particles are simply helium-4 nuclei and so we end up
generating helium Ford's out of the earth while in these mantle
domains that have recycled Oceanic and continental crust.
Now some new work is I've been coming online recently, Oceanic
lavas with elevated helium-3, you over helium-4 ratios have
these unusual 182, tungsten an anomaly.
So what does this mean 182? Tungsten is the byproduct of 182
hafnium 2K. + 1. E, 2, hafnium loves a very
short-lived radioactive isotope. In fact, it's Half-Life, is only
about nine million years, and so after A handful of half-lives of
occurred. So say 50 or 60 million years
after truster Lucretia and there was essentially no 182 hafnium
left on the planet. So any 182 tungsten or anomalies
that were formed on the earth were formed in the first 50 to
60 million years of Earth's history.
And the fact that we're seeing 182 tungsten anomalies and
modern hotspot. Lavas tells us that this ancient
signature generated in the very Earliest history of the planet
has somehow survived despite mantle convection, and the
chaotic motions of the mantle and the mixing and stirring with
Oceanic and continental plates, that b abducted in the Years.
Interior somehow the signature has survived a for over four and
a half billion years of Earth's history.
The community is still trying to figure out the origin of this
182. Tungsten signature one idea is
the concept of core and treatment so a little bit of the
Earth's core has Eat its way into the base of the mantle and
then Ben and trained and upwelling mantle.
Plumes this raises the possibility of mantle plumes
that are not only sampling subducted oceanic crust and
continental crust but might also be sampling bits of material.
Derived directly from Earth's corn, it remains to be seen
whether or not we're actually dealing with a core signature
and modern hot spots. It may be possible.
The 182 tungsten signature is could be byproducts of of the
early accreted materials from when Earth was forming and this
is a debate that's going to be resolved.
Only with an generation of additional data looking at other
isotope systems that are sensitive to Coral formation or
to terrestrial accretion. Do we see evidence of subducted,
continental crust and oceanic crust.
So to speak polluting the mantle and generating These
heterogeneous mantel domains over the entire history of the
earth. It appears that there are two
distinct stages of subduction of material nurse interior.
It looks like oceanic crust began subducting several billion
years ago but doesn't look like continental crust, began
subducting, until more recently, perhaps the late neoproterozoic
and we've been looking at the geochemical distribution of
hotspot lavas. Has in the Earth's interior and
it sure seems to be consistent with this kind of picture.
If we can see that Continental across, 70 seem to subduct from
the late neoproterozoic. I guess about 650 million years
onwards which is actually something that was mentioned by
Peter k word in his podcast on the origin of plate tectonics.
And in fact some people take that as evidence that plate
tectonics didn't start to this latest that.
But do we see the signature of To Oceanic lithosphere in the
mantle before that time. So fortunately wish he hadn't
caught spots and this islands and seamounts resulting from
these hotspots. Really only give us records that
go back is old as the oceanic crust they're sitting on.
So it's really about 200 million years, but if we want to look at
longer term records, we can turn to kimberlite vulcanism.
Let me just interject here to say that in kimberlite,
volcanism rocks from the mantle called kimberlites.
Are brought to the surface in small, but powerful eruptions in
Continental settings. But all we see is that the
enriched mental signatures that we associate with subducted
continental crust, really only starts to appear in the
Mesozoic, and there's no signature whatsoever in the
kimberlite record, for subducted continental crust, prior to the
last couple of hundred million years that this is really
interesting, and I think it's consistent with very recent
subduction of continental crust. I have continental crust is only
been subducted in the last 650 million years, then you wouldn't
expect to see continent across signatures really showing up,
until after 650 million years. Then you might be saying, Matt,
why is it that we have this four hundred million year lag between
the first Abduction of Continental cross that about 650
million years and then the appearance of recycled
continental crust and kimberlites at about 200 million
years, and I think that's just based on the amount of time, I'm
it takes for subducted material to make its way down into the
Earth's interior, where it then resides for some period of time
and then it's in trained and brought to the surface and
mantle plumes. I think that that cycle is
probably going to be a few hundred million years.
What's really interesting to me is how subducted continental
crust really shows. I've really narrow geographic
distribution in the Earth's interior.
So what can we say about the spatial distribution of these
magical signatures? Let's start with the larger
scales, the most Gia chemically enriched signatures that we
often associate with subducted continental crust.
Materials tend to be focused in the southern hemisphere, the 11
hot squats with the most geochemical and Rich signatures
it, which specifically had the lowest 143 144 neodymium that we
associate with subducted continental crust materials,
these hot spots are all located in the southern hemisphere.
Up to the equator. Why do we have continental
crust? Signatures isolated in the
southern hemisphere, some early work suggested that it may have
something to do with gondwana, because gondwana, and then
Pangaea were assembled primarily in the southern hemisphere, see
it a lot of Continental collisions and subduction going
on in the southern hemisphere that could deliver.
A lot of subducted continental crust into the southern
hemisphere, the problem with this model ever since it was
first suggested in 1984, was the, it doesn't explain why?
We don't have subducted continental crust in the
northern hemisphere When the continents were located in the
Northern Hemisphere and subducting in the Northern
Hemisphere and the archean way before the Assembly of gondwana
and Pangaea. And this is where we're making
the link to the initiation of continental crust, subduction
being in the late, New York proterozoic.
And so, it's only in the late neoproterozoic when Cardinal
cross was able to first start making its way to the Earth's
deep interior. In the continents were located
in the southern hemisphere before the late neoproterozoic.
We don't have any evidence from the geologic record of
Continental crustal rocks. Making it to ultra high pressure
conditions cotton look Russell rocks, were just not going deep,
yet the thermal history and the conditions of the Earth's
interior, including rheology of slabs, didn't seem to be
conducive to transporting, buoyant continental crust.
Deep enough into the mantle work, could undergo the
necessary. Is changes for a console across
to them being negatively buoyant and continue on into the Earth's
deep interior. So we have starting the late
neoproterozoic and not before are these conditions where
continental crust can subduct for the first time and the
continents are also located in the southern hemisphere.
This is perfect alignment of conditions, in a couple of
previous podcasts such as the one with Barbara Romantic Poets.
And with Alan McNamara, we talked about another very large
Gail feature in the mantle, which occurs below southern
Africa and below the South Pacific, where the mantle
seismic wave speed is lower than average, the so-called large low
Shear velocity provinces do these affect the distribution
and chemical signatures of hot spots.
We've known since 1988 that all the Cucumber clean, Rich hot
spots with these recycle content, La Crosse.
Signatures are geographically Associated or lie above these.
All those PPS. I don't have a great answer for
why this is the focus of recycled continental crust
signature is over the OLS VPS. I mean have a lot to do with
just how mantle convection is set up around the lsv piece.
We know, for example that the location of subduction zones,
Auntie correlates with the ls V PS today and for the last couple
of hundred million years at least so that can be interpreted
as, you know, subduction zones represent regions of downwelling
in the mantle Oh, and then the return flow occurs over the L SV
P. So you have mantle up willing or
the lfpp. So in this type of as large
system where you have downwelling at the subduction
zones and upwelling over, the all is Fifi's.
So dr. Connor La Crosse is going to be
drawn into the LSP peas and tend to accumulate their over
geologic time. So then it's perhaps not
surprising that. We see continental crust
signature showing up at hot spots that are located above the
LSD PCP. Let's talk a bit about my little
Hatchet identities that we see on smaller scales and I'm
reminded of the recent podcasts about the Icelandic eruption of
2021. With that Marshal, we're over
the space of just a couple of months, the chemistry of the
lava which is thought to have come from the mantle varied
quite dramatically and the speculation.
Was that a new batch of magma? With a different composition?
May have been injected into the source region there.
So does this tell us something about mantle heterogeneity on
meter or kilometer scale I was lucky to be living in Iceland
this last year and had a great time with Ed Marshall in the
field and observing this eruption the rapid change in
geochemistry of the eruption completely changed the way that
I view ocean, volcanism and specifically the dramatic change
in geochemistry of this eruption over just a few months.
Was remarkable. It went from a relatively Chia,
chemically depleted signature to a more enriched signature.
And this tells me that the volcano is being fed by a couple
of different magma chambers that are being sourced by different
mantle Source compositions, and that these mantle sources must
be relatively close to be contributing melt to magma
Chambers beneath the same volcano.
So on one hand, we have the very largest scale.
Geochemical anomalies. The mantle that seemed To
spanned an entire hemispheres. But on a shorter length, scales,
we seem to have juxtaposition of different mantle domains, with
distinct, you comical signatures that are close enough together
to be able to Source a single volcano with distinct signatures
over the course of a single relatively short-lived.
Eruption before this eruption, I had convinced myself that I
could sample a lava from a lava flow and that that was going to
tell. Tell me about the isotopic
composition of that eruption. But when, when Iceland we have
an eruption that went on for just a few months and the flows
that came out of that single eruption and the entire range of
isotope compositions that have been sampled by all the
volcanoes. Along the entire Rican, this
peninsula and Iceland for the last 10,000 years.
And one, eruption, what about on even smaller scales like meter
or centimeter? Xena list can show relatively
dramatic isotope heterogeneity at shortlink scale, one
xenoliths from the Samoan, hotspot each green, the sample
tended to show, pretty different drawn, IAM and neodymium
isotope, signatures, relative to other grains in this sample.
In fact, the isotopic variability in this 3, cm
xenoliths spanned 1/4 of the total variability of strontium
isotopes that we have identified in the earth's.
Oceanic mantle One sample 3 cm wide is sampling. 25 percent of
the variability a quarter to the variability that we have
identified in the oceanic mantle across all the world's
motion-based. So it's sort of mind-boggling
that we zoom in on one sample and the isotopic complexity
literally explodes. Wow, in light of all these
mantle compositional variations that you've just described both
temporally as as The Total Transformation of the eruption
in Iceland over. Couple of months and spatially
down to centimeter scale than the Zenith.
Is the whole notion of a geochemical signature for RC
Mount or its parent hotspot, still a valid idea.
Oh yes, absolutely. The Icelandic eruption tells us
that a single eruption just samples, a wider range of
compositions than we knew before.
But all of the lavas that have come out of this 20:21 Icelandic
eruption are all still very clearly Icelandic.
What's surprising? Though is that we're sampling
this incredible range of compositions in just 60 days in
the case of the small ones analyst.
What we're trying to do is get it, the smallest length, scales
of spatial variability. So these analysts are still very
much Samoan and composition. The important observation is
that. That range of strontium isotope
composition is that we? Observe in Samoa is observe it.
Very, very small length scale. I also want to emphasize that a
lot of the topics that I've discussed here are Cutting Edge
there, so new that they're all in the review process.
For example, the hotspot Highway story, where we tracing Samoa
and the cook austral hotspots, back to 100 million years.
This is a story that's in review in nature.
Icelandic eruption worked is also in review in nature and the
late neoproterozoic subduction of continental crust, being
responsible to the southern hemisphere isotope enrichment.
This is also in review Matt Jackson.
Thank you very much. And good luck with your upcoming
Voyage. Thank you.
Oliver, thanks for having me today. for more about geology b,
as well as pictures and illustrations, that support this
podcast, you can go to geology B.com