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This is Java g. 
B, with all of us trampled, the 

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mantle makes up 84 percent of 
the Earth's volume because it's 

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covered by the plates of the 
lithosphere information about 

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its chemical. 
Composition is hard to come by. 

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It mostly comes from lavas that 
we believe are sourced from the 

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mantle and most of that lies 
under the ocean which is a 

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notoriously difficult place from
which to obtain samples. 

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But as we managed to extract 
more and more mantle sourced 

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lava samples, some very 
unexpected patterns in mantle 

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Composition are emerging. 
Matt Jackson is a professor of 

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earth science at the University 
of California, Santa Barbara, 

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his research focuses on the 
isotopic and chemical 

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composition of lavas erupted at 
hotspot volcanoes. 

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Matt Jackson. 
Welcome to geology B. 

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Thank you, Oliver. 
Thanks for having me today. 

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I just managed to catch you 
before you embark on a research 

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vessel for a six-week trip, 
starting in Guam and heading 

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down to the South Pacific. 
Is that to sample seafloor 

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lovers there. 
Oh yeah, absolutely. 

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We have the older portions of 
couple of long-lived oceanic 

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hotspots that exhibit some 
volcanism on the Western 

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Pacific. 
These hot spots are very 

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similar. 
To the archetypal hotspot the 

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Hawaiian hotspot. 
The Hawaiian hotspot has about 

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80 million years of recorded 
volcanism and the older portion 

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of the Hawaiian. 
Hotspot, of course, is 

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subducting into the Kamchatka 
trench that you hot spots that 

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will be looking at go back to 
over 100 million years and 

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therefore we're looking at over 
100 million years of continuous 

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vulcanism of these two hot spots
and older portions are now 

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located the Western Pacific. 
And subducting into the Marianas

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Trench Wrench. 
So we'll be out there to look at

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the older portions of these two 
long-lived hot spots but there 

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are quite a few hot spots that 
erupt lavas above the oceans. 

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Hawaii being the obvious example
you just mentioned but also 

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Samoa and the Canary Islands and
a few others. 

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Why go to all the trouble to 
sample, them below the ocean's. 

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The main issue with volcanoes in
Oceanic settings is that very 

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few of volcanoes actually make 
it above sea level? 

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We have on the order of Hundred 
thousand sea mounts that are a 

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kilometer high or higher above. 
The ocean floor, where as we're 

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dealing with, perhaps hundreds 
of islands, in Oceanic settings.

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So by tackling the submarine 
volcanoes, we greatly open up 

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the number of volcanoes that we 
can explore to better 

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disentangle the histories of 
these different hotspots. 

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Wow, that's a really 
overwhelming statistic. 

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I had no idea. 
Let's return to your upcoming 

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Voyage, the South Pacific prior 
surveys have been able to 

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identify a bunch of hot spot 
trails. 

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In fact, I think you told me 
that it's even referred to as 

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like, hotspot highway. 
So how do we know that these are

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hot spot. 
Trails, Oceanic hotspots are 

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thought to generate age 
Progressive. 

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Volcanic Trends. 
So you have a little schoeneck 

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plate, that's moving laterally, 
over an upwelling plume, you 

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generate a volcano above The 
upwelling plum but as the plate 

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moves off that hot spot, another
volcano forms in its place. 

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And that volcano then gets 
wrapped it off laterally and 

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another volcano forms in its 
place and so forth. 

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You end up generating a nice, 
linear age, Progressive, Trend 

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Hawaii. 
Of course is the classic 

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example, but we have other 
examples in the Pacific. 

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For example, the small one hot 
spot and McDonald hot spot and 

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some lesser-known hot spots like
the Ergo hot spot now. 

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Several hot spots in the south 
Pacific are aligned along the 

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trend of plate motion. 
So along the flow line at the 

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Pacific Plate, so we have the 
McDonald Hot Spot, the error, go

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Hot Spot, perhaps the Rarotonga 
hot spot in the small hot spot 

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all aligned. 
They're all about 1000 to 1200 

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kilometers apart and because 
they're aligned Downstream of 

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the easternmost hotspot. 
So to the west of the 

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easternmost hotspots in 
McDonald, hotspot, you have 

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McDonald hotspot, sea mounts, 
that are accumulated. 

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Relating around the are ago. 
Region, their Rarotonga region 

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and the small one region further
to the west. 

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And so, we have these four hot 
spots in a row that are 

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generating what we refer to as 
the hotspot Highway. 

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Because we have this continuous 
trail of seamounts that have 

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been generated by the various 
hot spots along this Trent. 

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Well, if we go further to the 
Western Pacific where these hot 

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spots, then Trend to, right? 
So if you look at the Hawaiian, 

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hotspot, for example, you have 
this beautiful band, Hawaiian. 

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Hotspot track at about 50 
million years, we have the trend

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of the hotspot, goes for 
approximately East-West to a 

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closer to a north-south 
trending. 

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We call this the a trend and 
this dominates, the strike of 

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the Hawaiian hotspot over much 
of the Cretaceous. 

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We see similar bends in these 
hot spots from The Hot Spot 

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Highway the issue is we have 
this province with thousands of 

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sea mounts but very few of them 
have ever been sampled, 

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characterized your chemically or
HD did. 

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So it's hard to tell. 
Well, which of the four hot 

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spots from The Hot Spot, Highway
these various seamounts came 

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from. 
So we're going to head out to 

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that part of the Pacific on our 
upcoming expedition to sample. 

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And then later characterize, 
these various sea mounts to see 

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if we can disentangle the 
different hotspots from the 

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hotspot highway. 
So just about all these 

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seamounts, while the seamount, 
so they're under the water. 

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So what kind of ocean depth are 
we talking about here, where 

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you're going to be sampling? 
So, the ocean depths in the 

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Western Pacific at least, Of the
trench is around 5,000 meters. 

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So we'll be getting samples from
as deep as 5,000 meters at the 

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base of these sea mounts. 
And, in some cases, we might be 

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going as shallow as 3,000 
meters, but we want to be 

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getting the deepest portions of 
these volcanoes, the sample, the

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deepest to trigger fee and 
capture the earliest stages of 

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vulcanism on each of these 
hotspots. 

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Of course, as we go further to 
the west and this Western 

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Pacific, seamount Province will 
be getting closer to the trench.

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So ocean bathymetry Re deepens 
where depths go to is, we know 

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about 11,000 meters, some of the
sea mounts that are going into. 

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The trench will be harder for us
to sample, will be spooling out.

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A lot of dredge cable to get the
deeper portions of these sea 

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mounts, that are currently 
gliding into the trench. 

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That's a fantastic. 
The amount of water to be 

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working under. 
How do you find the right places

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to sample? 
I mean, how do you know you're 

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not going to just be sampling? 
Recent sediments that tell you 

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nothing whatsoever about the 
lava underneath Eighty to ninety

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percent of the ocean floor 
remains on mapped to any 

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reasonable degree. 
So we rely on satellite based or

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gravity-based, but them a tree 
and the gravity base bathymetry 

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has a resolution of about a 
kilometer, and I think a 

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kilometer in many cases is being
generous, but it allows us to 

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see where the big bumps are in 
the ocean floor. 

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These bumps are the sea mounts. 
So what we do with the ship, as 

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we target specific seamounts and
we make high-resolution Maps 

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using multi-beam Sonar And these
high-resolution Maps, allow us 

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to get much finer, resolution of
the seamount in the thema. 

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Tree, The Contours of the 
seamount at depth. 

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And based on this information, 
we can Target this steepest 

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portions of the seamount for 
sampling. 

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Specifically, the portions that 
are not only steep but highly 

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reflective to sonar and the 
reason we do this is because 

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surfaces that are reflective to 
sonar tend to be sediment poor. 

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So we're more likely looking at 
Solid Rock surfaces or 

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Ferromanganese and rind and 
crusted rocks. 

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Furthermore, we target the 
steeper portions of the sea 

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mounts as well, because sediment
and debris, like corals for 

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example, lots of these 
seamounts. 

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We're actually at the surface at
one point before erosion and 

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subsidence. 
The steeper portions of these 

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seamounts allow the corals and 
debris to Slough off, allowing 

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us to directly sampled. 
The basaltic Bedrock at the seam

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out for the bigger seamounts. 
We can spend 8 to 10 hours, 

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trying to get decent Maps. 
Soooo of the flanks of the 

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seamount to identify the best 
dredge targets and then the 

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dredging itself. 
So it can also take eight to ten

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hours, depending on water depth,
of course. 

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And whether or not the dredge 
gets stuck on the ocean floor. 

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So, I'm curious how you got 5 
kilometers of cable, strung Out 

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Below your ship. 
I mean, presumably their ocean 

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currents and who knows what 
moving this thing around. 

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So you may know where you are 
from the sonar. 

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But how do you know where the 
dredge is going to be? 

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Do you have a camera down there 
or something? 

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We don't have a camera on the 
dredge cable. 

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We put a camera on the dredge 
cable. 

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It would probably get torn off 
pretty early on in the dredging 

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process when we spool out a 
cable, the dredging process is a

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tried and tested technique. 
I like to refer people to 6 B's 

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paper from the early 1880s 
showing our drawing of a dredge 

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that is not unlike the dredges 
that we're using. 

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Now, 140 years later, basically,
we spool out cable, 5, 6 7, 

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Hours worth of 30,000 pound test
cable of the we can get the 

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dredge basket down on the ocean 
floor. 

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The issue is we never know 
exactly where the dredge basket 

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is because at five kilometers 
depth, you can have ocean 

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currents that are moving in a 
different direction than you 

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have at the surface and the 
dredge basket can get pulled off

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to a little bit to one side or 
the other. 

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So we do is we target the 
seamount and regions wall above 

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the Abyssal Plains. 
And we have a pretty good sense.

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Say within several hundred 
meters of where the dredge 

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basket actually ends up. 
Now, you might say well, well, 

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Matt, I mean this isn't as good 
as GPS sampling. 

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Do we have on Ocean Islands or 
we can record the location of a 

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rock to better than a meter, and
that's true. 

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Absolutely true. 
But, on the other hand, the sea 

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mounts that we're targeting, 
have never been mapped, they've 

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never even been sampled. 
And so, having one sample from 

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this seamount is incredibly 
valuable because then we know 

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its composition. 
We know it's age, we can figure 

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ER out how it formed in some 
cases, all we have is one rock 

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that comes on board and so 
making the rock very valuable to

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us. 
Everybody wants a split of The 

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Rock and sometimes I reflect on 
this and told the graduate 

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students who were on the ship. 
For the first time that that 

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rock can represent 50 thousand 
dollars worth of resources. 

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Because when we're out at Sea, 
it's about fifty thousand. 

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Dollars a day to run these 
ships, the fuels, incredibly 

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expensive, maintaining the ship,
the salary at for the Crew and 

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the scientist, how big are your 
samples? 

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Typically, samples range in 
size. 

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The upper end is limited by the 
opening in the dredge basket. 

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That's 40 centimeters or so, we 
can get some pretty sizable 

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pillow Basalt chunks, and we put
burlap sacks, and sometimes find

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netting inside of the base of 
the bags that we can capture the

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smaller samples. 
We drag these dredges on the 

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seafloor up the sides of these 
seamounts for hundreds of 

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meters. 
It's, um, Cases will go a 

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kilometer. 
It takes so long to map a 

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seamount and it takes so long to
lower the dredge basket down 

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5,000 meters and bring it up. 
5,000 meters that we want to 

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make sure we bring that dredge 
basket up Plum full of rocks. 

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So we'll Drag The Dredge basket.
And some cases for hundreds of 

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meters of our km, just to make 
sure we get rocks in there. 

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Okay. 
So you bring these lava samples 

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back to your lab and you make a 
number of chemical and isotopic 

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measurements on them. 
What Actually, are you trying to

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find out about these samples? 
So two things we want to figure 

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out the composition of these 
samples and we want to figure 

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out their age, so that we can 
then determine which hotspot, 

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these samples came from. 
So each of the hotspots that 

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I've described as unique 
geochemical signatures. 

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So we'll measure the radiogenic 
Isotopes compositions of the 

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samples. 
So for examples radiogenic 

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strontium, pretty genic 
neodymium hafnium lead. 

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Aw. 
Osmium and so forth. 

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To really characterize the 
geochemical Fingerprints of the 

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00:12:26,200 --> 00:12:28,800
samples that we can then say, 
which hotspot each of these 

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seamounts came from and by the 
same token will get age dates on

224
00:12:32,600 --> 00:12:37,500
these samples to then figure out
where on the gauge distance 

225
00:12:37,500 --> 00:12:40,300
trends of these various hot 
spots that the particular 

226
00:12:40,300 --> 00:12:44,800
seamount relates to. 
Now for me a big picture 

227
00:12:44,800 --> 00:12:49,300
question is why do these 
different see mouse or hot spots

228
00:12:49,300 --> 00:12:54,400
have different geochemical 
Prince and it turns out the 

229
00:12:54,400 --> 00:12:58,700
geochemical fingerprints can be 
so good at identifying specific 

230
00:12:58,700 --> 00:13:03,000
locations that my former thesis 
advisor like to joke, that if he

231
00:13:03,000 --> 00:13:07,500
didn't have GPS in someone, put 
him on a remote desert island 

232
00:13:07,600 --> 00:13:13,200
with just a clean lab and a mass
spectrometer, he could based on 

233
00:13:13,200 --> 00:13:16,300
the composition of the basalt in
that Island pinpoint which 

234
00:13:16,300 --> 00:13:19,600
island he was on. 
But what does this geochemistry 

235
00:13:19,600 --> 00:13:22,400
then tell us about the 
composition of the Earth's 

236
00:13:22,400 --> 00:13:24,900
interior. 
Well, it turns out that the 

237
00:13:24,900 --> 00:13:28,100
composition of the Earth's 
interior is highly 

238
00:13:28,100 --> 00:13:32,200
heterogeneous, due to a number 
of processes in one that we 

239
00:13:32,200 --> 00:13:35,000
focus on a lot. 
And this particular Expedition 

240
00:13:35,000 --> 00:13:38,700
coming up is the process of 
subduction. 

241
00:13:39,100 --> 00:13:44,700
So oceanic crust and continental
crust, or materials derived, 

242
00:13:44,700 --> 00:13:48,700
from continental crust, enter 
the mantle, at subduction zone. 

243
00:13:48,700 --> 00:13:52,000
So when two plates collide 
inevitably, one of the plates, 

244
00:13:52,200 --> 00:13:54,200
Was down into the Earth's 
interior. 

245
00:13:54,300 --> 00:13:58,000
And then the big question is, 
what happens to that plate after

246
00:13:58,000 --> 00:14:00,000
subduction? 
Well we think that plate goes 

247
00:14:00,000 --> 00:14:03,400
down deep into the mantle 
resides down there for some 

248
00:14:03,400 --> 00:14:06,600
period of time and then is 
conveyed back to the surface 

249
00:14:06,600 --> 00:14:11,200
again and upwelling blooms, it 
partially melts and then we look

250
00:14:11,200 --> 00:14:16,400
at the lavas that hotspots to 
identify then signatures of what

251
00:14:16,400 --> 00:14:20,200
went down in ancient trenches 
deep in geologic, time and we 

252
00:14:20,200 --> 00:14:22,800
find some key geochemical 
signatures Jurors that are 

253
00:14:22,800 --> 00:14:25,600
associated with different 
subducted. 

254
00:14:25,600 --> 00:14:28,200
Materials that went down into 
ancient trenches. 

255
00:14:28,200 --> 00:14:32,700
So for example, recycle oceanic 
crust We Believe can generate 

256
00:14:32,700 --> 00:14:36,100
radiogenic LED isotope 
signatures over time and sure 

257
00:14:36,100 --> 00:14:39,000
enough some hotspots show. 
Some really clear. 

258
00:14:39,000 --> 00:14:41,500
Where do you genic? 
Let isotopic compositions, 

259
00:14:41,700 --> 00:14:44,700
similarly continental crust or 
materials, derived from 

260
00:14:44,700 --> 00:14:47,600
continental crust that was 
subducted and deep time, it 

261
00:14:47,600 --> 00:14:51,300
should have very radiogenic 
strontium Isotopes. 

262
00:14:51,300 --> 00:14:56,900
And very On ready, Jennifer low 
143 144, neodymium isotopic 

263
00:14:56,900 --> 00:15:00,400
characteristic, and we see these
particular characteristics for 

264
00:15:00,400 --> 00:15:04,200
example, in the Samoan hotspot. 
And in fact, the small and 

265
00:15:04,200 --> 00:15:08,200
hotspot has exhibited, these 
isotopic characteristics based 

266
00:15:08,200 --> 00:15:12,100
on preliminary data over a 
hundred million years of its 

267
00:15:12,100 --> 00:15:14,000
history. 
So one of the reasons actually, 

268
00:15:14,000 --> 00:15:17,200
while we're going back to the 
Western Pacific is because we 

269
00:15:17,200 --> 00:15:20,500
think we've picked up the scent 
of the Samoan hotspot based on 

270
00:15:20,500 --> 00:15:24,600
some Legacy. 
Has obtained. 20 to 40 years 

271
00:15:24,600 --> 00:15:26,300
ago? 
On various Expeditions. 

272
00:15:26,600 --> 00:15:29,100
What we see. 
Is that a small and hotspot has 

273
00:15:29,100 --> 00:15:33,100
continuously sampled these 
recycled continental crust 

274
00:15:33,100 --> 00:15:38,100
signatures for this 100 million 
years of its recorded vulcanism.

275
00:15:38,800 --> 00:15:41,900
So, I can understand that a 
particular compositional ratios.

276
00:15:41,900 --> 00:15:45,100
If you like of these various 
Trace elements and Isotopes can 

277
00:15:45,100 --> 00:15:47,700
act as a kind of fingerprint or 
signature. 

278
00:15:48,000 --> 00:15:51,000
But do we actually understand 
the mechanism for example, where

279
00:15:51,000 --> 00:15:54,600
by subduction The oceanic crust 
results and more radiogenic LED 

280
00:15:54,600 --> 00:15:57,900
we know why that is, there are a
couple of different proposed 

281
00:15:57,900 --> 00:16:02,300
mechanisms and the one that I 
favor is that oceanic crust. 

282
00:16:02,300 --> 00:16:05,800
When it enters the subduction 
zone, it goes through various 

283
00:16:05,800 --> 00:16:10,400
nin, amorphic reactions that 
result in dehydration and loss 

284
00:16:10,400 --> 00:16:15,100
of fluid mobile elements. 
And we believe that lead is 

285
00:16:15,100 --> 00:16:19,100
preferentially lost relative to 
uranium and Thorium in this 

286
00:16:19,100 --> 00:16:23,900
becomes important because 
uranium And thorium when they 

287
00:16:23,900 --> 00:16:28,500
undergo radiogenic Decay, 
ultimately end up at the various

288
00:16:28,500 --> 00:16:33,100
Regional a isotopes of lead. 208
lead is the result of decay of 

289
00:16:33,300 --> 00:16:38,400
232 thorium and 2007. 
LED and 2006 LED or the result 

290
00:16:38,400 --> 00:16:41,800
of radiogenic decay of uranium 
two different isotopes of 

291
00:16:41,800 --> 00:16:46,100
uranium and so when oceanic 
crust enters a subduction zone 

292
00:16:46,200 --> 00:16:50,600
and it loses its lead relative 
to its uranium you're setting up

293
00:16:50,600 --> 00:16:54,300
the opportunity. 
To generate an overwhelmingly 

294
00:16:54,300 --> 00:16:59,900
large amount of radio genic lead
in that downgoing slab after 

295
00:16:59,900 --> 00:17:03,500
it's been aged and the mantle 
for a couple of billion years. 

296
00:17:03,800 --> 00:17:08,000
And indeed we see very 
radiogenic, let isotope ratios 

297
00:17:08,000 --> 00:17:11,000
in some hot spot lavas and we 
have one of the hot spots that 

298
00:17:11,000 --> 00:17:13,500
we're going to be targeting. 
Has exhibited radiogenic led. 

299
00:17:13,500 --> 00:17:17,099
Isotope signatures for over 100 
million years. 

300
00:17:17,099 --> 00:17:21,000
This is sort of remarkable that 
one hot spot can sample. 

301
00:17:22,099 --> 00:17:25,599
Mantle Source composition deep 
in the mantle for a hundred 

302
00:17:25,599 --> 00:17:29,300
million year period. 
Meanwhile that hotspot are ago 

303
00:17:29,300 --> 00:17:33,000
is only 2000 kilometers away 
from the small and hotspot which

304
00:17:33,000 --> 00:17:36,500
has been sampling. 
Not ready genic lead but instead

305
00:17:36,500 --> 00:17:40,500
radiogenic strontium and unready
genic neodymium for its hundred 

306
00:17:40,500 --> 00:17:42,800
million year history. 
So as you hot spots that are two

307
00:17:42,800 --> 00:17:45,900
thousand kilometers apart the 
surface and of course, much 

308
00:17:45,900 --> 00:17:47,800
closer at the bottom of the 
mantle, right? 

309
00:17:47,800 --> 00:17:49,800
At the base of these clones are 
only going to be about a 

310
00:17:49,800 --> 00:17:55,300
thousand kilometers apart. 
These two plumes are sampling, G

311
00:17:55,300 --> 00:17:58,800
chemically distinct sources, 
even though there are thousand 

312
00:17:58,800 --> 00:18:02,900
kilometers apart over a hundred 
million year period, this is 

313
00:18:02,900 --> 00:18:06,300
completely remarkable to me and,
you know, I still don't have a 

314
00:18:06,300 --> 00:18:09,200
satisfying explanation for how 
this is possible. 

315
00:18:09,200 --> 00:18:12,800
It seems like the plume feeding 
zones for these hotspots should 

316
00:18:12,800 --> 00:18:15,500
be overlapping with each other. 
We should see these two hot 

317
00:18:15,500 --> 00:18:18,500
spots, sharing geochemical 
signatures but they remained 

318
00:18:18,500 --> 00:18:22,000
remarkably distinct in spite of 
being so close together. 

319
00:18:22,100 --> 00:18:25,100
Either geographically over this 
hundred million year period. 

320
00:18:25,100 --> 00:18:29,000
They've been active. 
So what kind of signatures have 

321
00:18:29,000 --> 00:18:31,000
we been able to? 
Identify you mentioned? 

322
00:18:31,100 --> 00:18:35,800
We can see if there's a 
signature from subducted Oceanic

323
00:18:35,800 --> 00:18:40,300
lithosphere and also if we see 
signs of Continental, crosstalk,

324
00:18:40,300 --> 00:18:44,300
crosstalk, derived materials are
there any other signatures that 

325
00:18:44,300 --> 00:18:47,100
we can identify and do we know 
what they represent? 

326
00:18:47,300 --> 00:18:51,800
There are signatures in a mantle
that are left over from the very

327
00:18:52,200 --> 00:18:56,000
Days of the earth. 
And it appears that the mantle 

328
00:18:56,000 --> 00:18:58,000
domains that have been able to 
preserve. 

329
00:18:58,000 --> 00:19:02,300
These really ancient signatures 
are the domains that have been 

330
00:19:02,700 --> 00:19:08,700
least impacted by mixing with 
subducted crust of the oceanic 

331
00:19:08,700 --> 00:19:13,500
or Continental varieties. 
And these early formed or 

332
00:19:13,500 --> 00:19:18,200
ancient domains are 
characterized by one very key 

333
00:19:18,200 --> 00:19:21,600
signature that a lot of people 
have focused on and that's high 

334
00:19:21,600 --> 00:19:25,700
heels. 
Liam 3 over helium-4 ratios so 

335
00:19:26,100 --> 00:19:30,700
elevated helium-3 over helium-4 
is a signature that we associate

336
00:19:30,700 --> 00:19:33,900
with primordial materials in the
solar system. 

337
00:19:33,900 --> 00:19:38,100
So for example, we know from the
Galileo spacecraft that the 

338
00:19:38,100 --> 00:19:41,800
atmosphere of Jupiter has a 
helium-3 over helium-4 ratio, 

339
00:19:42,000 --> 00:19:46,200
that is 120 times that which we 
have in the Earth's atmosphere 

340
00:19:46,600 --> 00:19:51,000
and that helium-3 is a 
primordial isotope of helium 

341
00:19:51,100 --> 00:19:54,700
very, very Little of it is made 
inside of the earth helium for 

342
00:19:54,700 --> 00:19:57,800
some portion of that mirrors, 
interior is primordial, but 

343
00:19:57,800 --> 00:20:02,800
helium-4 tends to accumulate in 
the earth and increase in 

344
00:20:02,800 --> 00:20:07,800
abundance because uranium and 
thorium Decay by Alpha DK. 

345
00:20:07,800 --> 00:20:12,400
Those alpha particles are simply
helium-4 nuclei and so we end up

346
00:20:12,400 --> 00:20:16,100
generating helium Ford's out of 
the earth while in these mantle 

347
00:20:16,100 --> 00:20:19,300
domains that have recycled 
Oceanic and continental crust. 

348
00:20:19,900 --> 00:20:24,900
Now some new work is I've been 
coming online recently, Oceanic 

349
00:20:24,900 --> 00:20:29,200
lavas with elevated helium-3, 
you over helium-4 ratios have 

350
00:20:29,200 --> 00:20:34,100
these unusual 182, tungsten an 
anomaly. 

351
00:20:34,100 --> 00:20:39,800
So what does this mean 182? 
Tungsten is the byproduct of 182

352
00:20:39,800 --> 00:20:44,300
hafnium 2K. + 1. 
E, 2, hafnium loves a very 

353
00:20:44,300 --> 00:20:48,700
short-lived radioactive isotope.
In fact, it's Half-Life, is only

354
00:20:48,700 --> 00:20:54,200
about nine million years, and so
after A handful of half-lives of

355
00:20:54,200 --> 00:20:57,000
occurred. 
So say 50 or 60 million years 

356
00:20:57,000 --> 00:21:01,200
after truster Lucretia and there
was essentially no 182 hafnium 

357
00:21:01,200 --> 00:21:04,700
left on the planet. 
So any 182 tungsten or anomalies

358
00:21:04,700 --> 00:21:08,500
that were formed on the earth 
were formed in the first 50 to 

359
00:21:08,500 --> 00:21:10,300
60 million years of Earth's 
history. 

360
00:21:10,600 --> 00:21:15,200
And the fact that we're seeing 
182 tungsten anomalies and 

361
00:21:15,200 --> 00:21:19,700
modern hotspot. 
Lavas tells us that this ancient

362
00:21:19,700 --> 00:21:23,400
signature generated in the very 
Earliest history of the planet 

363
00:21:23,400 --> 00:21:27,900
has somehow survived despite 
mantle convection, and the 

364
00:21:27,900 --> 00:21:31,300
chaotic motions of the mantle 
and the mixing and stirring with

365
00:21:31,300 --> 00:21:34,600
Oceanic and continental plates, 
that b abducted in the Years. 

366
00:21:34,600 --> 00:21:38,000
Interior somehow the signature 
has survived a for over four and

367
00:21:38,000 --> 00:21:39,700
a half billion years of Earth's 
history. 

368
00:21:40,400 --> 00:21:43,200
The community is still trying to
figure out the origin of this 

369
00:21:43,200 --> 00:21:46,800
182. 
Tungsten signature one idea is 

370
00:21:46,800 --> 00:21:50,700
the concept of core and 
treatment so a little bit of the

371
00:21:50,700 --> 00:21:54,300
Earth's core has Eat its way 
into the base of the mantle and 

372
00:21:54,300 --> 00:21:57,000
then Ben and trained and 
upwelling mantle. 

373
00:21:57,000 --> 00:22:00,400
Plumes this raises the 
possibility of mantle plumes 

374
00:22:00,400 --> 00:22:03,400
that are not only sampling 
subducted oceanic crust and 

375
00:22:03,400 --> 00:22:07,600
continental crust but might also
be sampling bits of material. 

376
00:22:07,600 --> 00:22:11,700
Derived directly from Earth's 
corn, it remains to be seen 

377
00:22:11,700 --> 00:22:14,500
whether or not we're actually 
dealing with a core signature 

378
00:22:14,500 --> 00:22:17,700
and modern hot spots. 
It may be possible. 

379
00:22:17,700 --> 00:22:22,700
The 182 tungsten signature is 
could be byproducts of of the 

380
00:22:22,700 --> 00:22:27,000
early accreted materials from 
when Earth was forming and this 

381
00:22:27,000 --> 00:22:29,900
is a debate that's going to be 
resolved. 

382
00:22:29,900 --> 00:22:33,400
Only with an generation of 
additional data looking at other

383
00:22:33,400 --> 00:22:38,400
isotope systems that are 
sensitive to Coral formation or 

384
00:22:38,400 --> 00:22:44,400
to terrestrial accretion. 
Do we see evidence of subducted,

385
00:22:44,400 --> 00:22:47,700
continental crust and oceanic 
crust. 

386
00:22:47,900 --> 00:22:52,500
So to speak polluting the mantle
and generating These 

387
00:22:52,500 --> 00:22:56,900
heterogeneous mantel domains 
over the entire history of the 

388
00:22:56,900 --> 00:23:00,100
earth. 
It appears that there are two 

389
00:23:00,100 --> 00:23:05,500
distinct stages of subduction of
material nurse interior. 

390
00:23:05,500 --> 00:23:08,500
It looks like oceanic crust 
began subducting several billion

391
00:23:08,500 --> 00:23:11,400
years ago but doesn't look like 
continental crust, began 

392
00:23:11,400 --> 00:23:15,500
subducting, until more recently,
perhaps the late neoproterozoic 

393
00:23:15,700 --> 00:23:20,800
and we've been looking at the 
geochemical distribution of 

394
00:23:20,800 --> 00:23:23,700
hotspot lavas. 
Has in the Earth's interior and 

395
00:23:23,900 --> 00:23:27,400
it sure seems to be consistent 
with this kind of picture. 

396
00:23:28,200 --> 00:23:32,100
If we can see that Continental 
across, 70 seem to subduct from 

397
00:23:32,100 --> 00:23:34,900
the late neoproterozoic. 
I guess about 650 million years 

398
00:23:34,900 --> 00:23:38,300
onwards which is actually 
something that was mentioned by 

399
00:23:38,300 --> 00:23:42,100
Peter k word in his podcast on 
the origin of plate tectonics. 

400
00:23:42,100 --> 00:23:45,900
And in fact some people take 
that as evidence that plate 

401
00:23:45,900 --> 00:23:48,200
tectonics didn't start to this 
latest that. 

402
00:23:48,600 --> 00:23:54,000
But do we see the signature of 
To Oceanic lithosphere in the 

403
00:23:54,000 --> 00:23:58,100
mantle before that time. 
So fortunately wish he hadn't 

404
00:23:58,100 --> 00:24:01,300
caught spots and this islands 
and seamounts resulting from 

405
00:24:01,300 --> 00:24:04,200
these hotspots. 
Really only give us records that

406
00:24:04,200 --> 00:24:07,600
go back is old as the oceanic 
crust they're sitting on. 

407
00:24:08,000 --> 00:24:11,600
So it's really about 200 million
years, but if we want to look at

408
00:24:11,700 --> 00:24:15,100
longer term records, we can turn
to kimberlite vulcanism. 

409
00:24:15,200 --> 00:24:18,200
Let me just interject here to 
say that in kimberlite, 

410
00:24:18,200 --> 00:24:21,800
volcanism rocks from the mantle 
called kimberlites. 

411
00:24:22,000 --> 00:24:25,700
Are brought to the surface in 
small, but powerful eruptions in

412
00:24:25,700 --> 00:24:29,300
Continental settings. 
But all we see is that the 

413
00:24:29,300 --> 00:24:33,000
enriched mental signatures that 
we associate with subducted 

414
00:24:33,000 --> 00:24:36,700
continental crust, really only 
starts to appear in the 

415
00:24:36,708 --> 00:24:40,900
Mesozoic, and there's no 
signature whatsoever in the 

416
00:24:40,900 --> 00:24:44,600
kimberlite record, for subducted
continental crust, prior to the 

417
00:24:44,600 --> 00:24:47,200
last couple of hundred million 
years that this is really 

418
00:24:47,200 --> 00:24:50,100
interesting, and I think it's 
consistent with very recent 

419
00:24:50,100 --> 00:24:53,800
subduction of continental crust.
I have continental crust is only

420
00:24:53,800 --> 00:24:58,300
been subducted in the last 650 
million years, then you wouldn't

421
00:24:58,300 --> 00:25:01,100
expect to see continent across 
signatures really showing up, 

422
00:25:01,100 --> 00:25:05,200
until after 650 million years. 
Then you might be saying, Matt, 

423
00:25:05,300 --> 00:25:09,300
why is it that we have this four
hundred million year lag between

424
00:25:09,600 --> 00:25:12,500
the first Abduction of 
Continental cross that about 650

425
00:25:12,500 --> 00:25:16,100
million years and then the 
appearance of recycled 

426
00:25:16,100 --> 00:25:18,700
continental crust and 
kimberlites at about 200 million

427
00:25:18,700 --> 00:25:22,000
years, and I think that's just 
based on the amount of time, I'm

428
00:25:22,008 --> 00:25:25,500
it takes for subducted material 
to make its way down into the 

429
00:25:25,500 --> 00:25:29,200
Earth's interior, where it then 
resides for some period of time 

430
00:25:29,200 --> 00:25:31,600
and then it's in trained and 
brought to the surface and 

431
00:25:31,600 --> 00:25:33,600
mantle plumes. 
I think that that cycle is 

432
00:25:33,600 --> 00:25:36,100
probably going to be a few 
hundred million years. 

433
00:25:36,400 --> 00:25:40,000
What's really interesting to me 
is how subducted continental 

434
00:25:40,000 --> 00:25:43,800
crust really shows. 
I've really narrow geographic 

435
00:25:43,900 --> 00:25:45,900
distribution in the Earth's 
interior. 

436
00:25:46,700 --> 00:25:50,500
So what can we say about the 
spatial distribution of these 

437
00:25:50,500 --> 00:25:53,600
magical signatures? 
Let's start with the larger 

438
00:25:53,600 --> 00:25:58,400
scales, the most Gia chemically 
enriched signatures that we 

439
00:25:58,400 --> 00:26:01,500
often associate with subducted 
continental crust. 

440
00:26:01,500 --> 00:26:06,900
Materials tend to be focused in 
the southern hemisphere, the 11 

441
00:26:07,100 --> 00:26:10,400
hot squats with the most 
geochemical and Rich signatures 

442
00:26:10,700 --> 00:26:15,800
it, which specifically had the 
lowest 143 144 neodymium that we

443
00:26:15,800 --> 00:26:18,500
associate with subducted 
continental crust materials, 

444
00:26:18,900 --> 00:26:21,700
these hot spots are all located 
in the southern hemisphere. 

445
00:26:21,900 --> 00:26:25,300
Up to the equator. 
Why do we have continental 

446
00:26:25,300 --> 00:26:27,500
crust? 
Signatures isolated in the 

447
00:26:27,500 --> 00:26:31,000
southern hemisphere, some early 
work suggested that it may have 

448
00:26:31,000 --> 00:26:33,500
something to do with gondwana, 
because gondwana, and then 

449
00:26:33,500 --> 00:26:36,800
Pangaea were assembled primarily
in the southern hemisphere, see 

450
00:26:36,800 --> 00:26:40,300
it a lot of Continental 
collisions and subduction going 

451
00:26:40,300 --> 00:26:42,000
on in the southern hemisphere 
that could deliver. 

452
00:26:42,000 --> 00:26:44,700
A lot of subducted continental 
crust into the southern 

453
00:26:44,700 --> 00:26:47,600
hemisphere, the problem with 
this model ever since it was 

454
00:26:47,600 --> 00:26:51,800
first suggested in 1984, was 
the, it doesn't explain why? 

455
00:26:52,000 --> 00:26:54,500
We don't have subducted 
continental crust in the 

456
00:26:54,500 --> 00:26:58,200
northern hemisphere When the 
continents were located in the 

457
00:26:58,200 --> 00:27:00,500
Northern Hemisphere and 
subducting in the Northern 

458
00:27:00,500 --> 00:27:04,500
Hemisphere and the archean way 
before the Assembly of gondwana 

459
00:27:04,500 --> 00:27:07,400
and Pangaea. 
And this is where we're making 

460
00:27:07,400 --> 00:27:11,100
the link to the initiation of 
continental crust, subduction 

461
00:27:11,100 --> 00:27:12,900
being in the late, New York 
proterozoic. 

462
00:27:13,100 --> 00:27:17,400
And so, it's only in the late 
neoproterozoic when Cardinal 

463
00:27:17,400 --> 00:27:20,400
cross was able to first start 
making its way to the Earth's 

464
00:27:20,400 --> 00:27:23,300
deep interior. 
In the continents were located 

465
00:27:23,300 --> 00:27:26,300
in the southern hemisphere 
before the late neoproterozoic. 

466
00:27:26,400 --> 00:27:28,600
We don't have any evidence from 
the geologic record of 

467
00:27:28,600 --> 00:27:32,400
Continental crustal rocks. 
Making it to ultra high pressure

468
00:27:32,400 --> 00:27:35,900
conditions cotton look Russell 
rocks, were just not going deep,

469
00:27:35,900 --> 00:27:40,000
yet the thermal history and the 
conditions of the Earth's 

470
00:27:40,000 --> 00:27:44,300
interior, including rheology of 
slabs, didn't seem to be 

471
00:27:44,300 --> 00:27:48,200
conducive to transporting, 
buoyant continental crust. 

472
00:27:48,300 --> 00:27:51,100
Deep enough into the mantle 
work, could undergo the 

473
00:27:51,100 --> 00:27:53,700
necessary. 
Is changes for a console across 

474
00:27:53,700 --> 00:27:57,100
to them being negatively buoyant
and continue on into the Earth's

475
00:27:57,100 --> 00:28:00,100
deep interior. 
So we have starting the late 

476
00:28:00,100 --> 00:28:04,400
neoproterozoic and not before 
are these conditions where 

477
00:28:04,500 --> 00:28:07,000
continental crust can subduct 
for the first time and the 

478
00:28:07,008 --> 00:28:09,600
continents are also located in 
the southern hemisphere. 

479
00:28:09,600 --> 00:28:12,900
This is perfect alignment of 
conditions, in a couple of 

480
00:28:12,900 --> 00:28:16,600
previous podcasts such as the 
one with Barbara Romantic Poets.

481
00:28:16,700 --> 00:28:21,800
And with Alan McNamara, we 
talked about another very large 

482
00:28:21,900 --> 00:28:25,500
Gail feature in the mantle, 
which occurs below southern 

483
00:28:25,500 --> 00:28:28,100
Africa and below the South 
Pacific, where the mantle 

484
00:28:28,100 --> 00:28:33,600
seismic wave speed is lower than
average, the so-called large low

485
00:28:33,600 --> 00:28:38,000
Shear velocity provinces do 
these affect the distribution 

486
00:28:38,000 --> 00:28:40,300
and chemical signatures of hot 
spots. 

487
00:28:40,900 --> 00:28:44,900
We've known since 1988 that all 
the Cucumber clean, Rich hot 

488
00:28:44,900 --> 00:28:47,300
spots with these recycle 
content, La Crosse. 

489
00:28:47,300 --> 00:28:51,800
Signatures are geographically 
Associated or lie above these. 

490
00:28:52,000 --> 00:28:54,900
All those PPS. 
I don't have a great answer for 

491
00:28:54,900 --> 00:28:58,100
why this is the focus of 
recycled continental crust 

492
00:28:58,100 --> 00:29:01,600
signature is over the OLS VPS. 
I mean have a lot to do with 

493
00:29:01,600 --> 00:29:05,900
just how mantle convection is 
set up around the lsv piece. 

494
00:29:06,100 --> 00:29:09,800
We know, for example that the 
location of subduction zones, 

495
00:29:10,100 --> 00:29:14,400
Auntie correlates with the ls V 
PS today and for the last couple

496
00:29:14,400 --> 00:29:17,700
of hundred million years at 
least so that can be interpreted

497
00:29:17,700 --> 00:29:21,200
as, you know, subduction zones 
represent regions of downwelling

498
00:29:21,200 --> 00:29:25,800
in the mantle Oh, and then the 
return flow occurs over the L SV

499
00:29:25,800 --> 00:29:27,800
P. 
So you have mantle up willing or

500
00:29:27,800 --> 00:29:30,800
the lfpp. 
So in this type of as large 

501
00:29:30,800 --> 00:29:32,800
system where you have 
downwelling at the subduction 

502
00:29:32,800 --> 00:29:35,100
zones and upwelling over, the 
all is Fifi's. 

503
00:29:35,300 --> 00:29:37,200
So dr. 
Connor La Crosse is going to be 

504
00:29:37,200 --> 00:29:42,300
drawn into the LSP peas and tend
to accumulate their over 

505
00:29:42,300 --> 00:29:44,500
geologic time. 
So then it's perhaps not 

506
00:29:44,500 --> 00:29:46,900
surprising that. 
We see continental crust 

507
00:29:46,900 --> 00:29:51,000
signature showing up at hot 
spots that are located above the

508
00:29:51,000 --> 00:29:54,100
LSD PCP. 
Let's talk a bit about my little

509
00:29:54,100 --> 00:29:58,300
Hatchet identities that we see 
on smaller scales and I'm 

510
00:29:58,300 --> 00:30:01,600
reminded of the recent podcasts 
about the Icelandic eruption of 

511
00:30:01,600 --> 00:30:05,400
2021. 
With that Marshal, we're over 

512
00:30:05,400 --> 00:30:08,700
the space of just a couple of 
months, the chemistry of the 

513
00:30:08,700 --> 00:30:12,400
lava which is thought to have 
come from the mantle varied 

514
00:30:12,400 --> 00:30:15,500
quite dramatically and the 
speculation. 

515
00:30:15,500 --> 00:30:19,200
Was that a new batch of magma? 
With a different composition? 

516
00:30:19,200 --> 00:30:21,800
May have been injected into the 
source region there. 

517
00:30:22,600 --> 00:30:26,400
So does this tell us something 
about mantle heterogeneity on 

518
00:30:26,400 --> 00:30:31,000
meter or kilometer scale I was 
lucky to be living in Iceland 

519
00:30:31,000 --> 00:30:34,600
this last year and had a great 
time with Ed Marshall in the 

520
00:30:34,600 --> 00:30:39,000
field and observing this 
eruption the rapid change in 

521
00:30:39,000 --> 00:30:43,200
geochemistry of the eruption 
completely changed the way that 

522
00:30:43,200 --> 00:30:48,300
I view ocean, volcanism and 
specifically the dramatic change

523
00:30:48,300 --> 00:30:52,200
in geochemistry of this eruption
over just a few months. 

524
00:30:52,400 --> 00:30:55,200
Was remarkable. 
It went from a relatively Chia, 

525
00:30:55,200 --> 00:30:58,400
chemically depleted signature to
a more enriched signature. 

526
00:30:58,700 --> 00:31:02,900
And this tells me that the 
volcano is being fed by a couple

527
00:31:02,900 --> 00:31:06,800
of different magma chambers that
are being sourced by different 

528
00:31:06,800 --> 00:31:10,300
mantle Source compositions, and 
that these mantle sources must 

529
00:31:10,300 --> 00:31:14,400
be relatively close to be 
contributing melt to magma 

530
00:31:14,400 --> 00:31:16,700
Chambers beneath the same 
volcano. 

531
00:31:16,700 --> 00:31:20,100
So on one hand, we have the very
largest scale. 

532
00:31:20,100 --> 00:31:22,400
Geochemical anomalies. 
The mantle that seemed To 

533
00:31:22,400 --> 00:31:26,300
spanned an entire hemispheres. 
But on a shorter length, scales,

534
00:31:26,400 --> 00:31:31,000
we seem to have juxtaposition of
different mantle domains, with 

535
00:31:31,000 --> 00:31:35,000
distinct, you comical signatures
that are close enough together 

536
00:31:35,200 --> 00:31:40,900
to be able to Source a single 
volcano with distinct signatures

537
00:31:40,900 --> 00:31:43,600
over the course of a single 
relatively short-lived. 

538
00:31:43,600 --> 00:31:48,100
Eruption before this eruption, I
had convinced myself that I 

539
00:31:48,108 --> 00:31:52,100
could sample a lava from a lava 
flow and that that was going to 

540
00:31:52,100 --> 00:31:54,000
tell. 
Tell me about the isotopic 

541
00:31:54,000 --> 00:31:57,600
composition of that eruption. 
But when, when Iceland we have 

542
00:31:57,600 --> 00:32:01,600
an eruption that went on for 
just a few months and the flows 

543
00:32:01,600 --> 00:32:06,200
that came out of that single 
eruption and the entire range of

544
00:32:06,200 --> 00:32:10,000
isotope compositions that have 
been sampled by all the 

545
00:32:10,000 --> 00:32:12,500
volcanoes. 
Along the entire Rican, this 

546
00:32:12,500 --> 00:32:15,600
peninsula and Iceland for the 
last 10,000 years. 

547
00:32:15,900 --> 00:32:20,500
And one, eruption, what about on
even smaller scales like meter 

548
00:32:20,500 --> 00:32:24,600
or centimeter? 
Xena list can show relatively 

549
00:32:24,600 --> 00:32:28,000
dramatic isotope heterogeneity 
at shortlink scale, one 

550
00:32:28,000 --> 00:32:32,300
xenoliths from the Samoan, 
hotspot each green, the sample 

551
00:32:32,300 --> 00:32:35,400
tended to show, pretty different
drawn, IAM and neodymium 

552
00:32:35,400 --> 00:32:38,600
isotope, signatures, relative to
other grains in this sample. 

553
00:32:38,600 --> 00:32:43,100
In fact, the isotopic 
variability in this 3, cm 

554
00:32:43,100 --> 00:32:47,600
xenoliths spanned 1/4 of the 
total variability of strontium 

555
00:32:47,600 --> 00:32:50,600
isotopes that we have identified
in the earth's. 

556
00:32:50,600 --> 00:32:56,100
Oceanic mantle One sample 3 cm 
wide is sampling. 25 percent of 

557
00:32:56,108 --> 00:32:58,400
the variability a quarter to the
variability that we have 

558
00:32:58,400 --> 00:33:02,400
identified in the oceanic mantle
across all the world's 

559
00:33:02,400 --> 00:33:04,600
motion-based. 
So it's sort of mind-boggling 

560
00:33:04,600 --> 00:33:09,100
that we zoom in on one sample 
and the isotopic complexity 

561
00:33:09,200 --> 00:33:13,500
literally explodes. 
Wow, in light of all these 

562
00:33:13,500 --> 00:33:17,400
mantle compositional variations 
that you've just described both 

563
00:33:17,400 --> 00:33:21,000
temporally as as The Total 
Transformation of the eruption 

564
00:33:21,000 --> 00:33:24,100
in Iceland over. 
Couple of months and spatially 

565
00:33:24,100 --> 00:33:26,300
down to centimeter scale than 
the Zenith. 

566
00:33:26,700 --> 00:33:30,000
Is the whole notion of a 
geochemical signature for RC 

567
00:33:30,000 --> 00:33:33,600
Mount or its parent hotspot, 
still a valid idea. 

568
00:33:34,000 --> 00:33:37,100
Oh yes, absolutely. 
The Icelandic eruption tells us 

569
00:33:37,100 --> 00:33:40,500
that a single eruption just 
samples, a wider range of 

570
00:33:40,500 --> 00:33:42,600
compositions than we knew 
before. 

571
00:33:42,600 --> 00:33:47,300
But all of the lavas that have 
come out of this 20:21 Icelandic

572
00:33:47,300 --> 00:33:50,800
eruption are all still very 
clearly Icelandic. 

573
00:33:50,800 --> 00:33:53,500
What's surprising? 
Though is that we're sampling 

574
00:33:53,500 --> 00:33:57,300
this incredible range of 
compositions in just 60 days in 

575
00:33:57,300 --> 00:34:00,100
the case of the small ones 
analyst. 

576
00:34:00,300 --> 00:34:02,700
What we're trying to do is get 
it, the smallest length, scales 

577
00:34:02,700 --> 00:34:06,300
of spatial variability. 
So these analysts are still very

578
00:34:06,300 --> 00:34:09,900
much Samoan and composition. 
The important observation is 

579
00:34:09,900 --> 00:34:12,100
that. 
That range of strontium isotope 

580
00:34:12,100 --> 00:34:15,000
composition is that we? 
Observe in Samoa is observe it. 

581
00:34:15,000 --> 00:34:20,199
Very, very small length scale. 
I also want to emphasize that a 

582
00:34:20,207 --> 00:34:23,800
lot of the topics that I've 
discussed here are Cutting Edge 

583
00:34:23,800 --> 00:34:26,500
there, so new that they're all 
in the review process. 

584
00:34:26,500 --> 00:34:30,400
For example, the hotspot Highway
story, where we tracing Samoa 

585
00:34:30,400 --> 00:34:33,900
and the cook austral hotspots, 
back to 100 million years. 

586
00:34:34,100 --> 00:34:37,199
This is a story that's in review
in nature. 

587
00:34:37,300 --> 00:34:41,600
Icelandic eruption worked is 
also in review in nature and the

588
00:34:41,600 --> 00:34:44,500
late neoproterozoic subduction 
of continental crust, being 

589
00:34:44,500 --> 00:34:47,300
responsible to the southern 
hemisphere isotope enrichment. 

590
00:34:47,300 --> 00:34:51,100
This is also in review Matt 
Jackson. 

591
00:34:51,300 --> 00:34:54,500
Thank you very much. 
And good luck with your upcoming

592
00:34:54,500 --> 00:34:55,900
Voyage. 
Thank you. 

593
00:34:55,900 --> 00:35:00,300
Oliver, thanks for having me 
today. for more about geology b,

594
00:35:00,400 --> 00:35:03,800
as well as pictures and 
illustrations, that support this

595
00:35:03,800 --> 00:35:07,400
podcast, you can go to geology 
B.com