1
00:00:03,300 --> 00:00:06,600
This is geology B with all of us
trampled. 

2
00:00:07,600 --> 00:00:10,200
Ever since Alfred Wegener 
proposed the theory of 

3
00:00:10,200 --> 00:00:15,200
continental drift in 1912, we've
been aware that blocks of the 

4
00:00:15,200 --> 00:00:17,900
Earth's lithosphere. 
Are moving with respect to each 

5
00:00:17,900 --> 00:00:22,700
other with the Advent of plate 
tectonics in the 1960s, these 

6
00:00:22,700 --> 00:00:26,200
moving blocks became identified 
with the tectonic plates that 

7
00:00:26,200 --> 00:00:29,100
tile the Earth's surface. 
We now have accurate 

8
00:00:29,100 --> 00:00:32,400
measurements of plate, motion 
speeds, which range from about 

9
00:00:32,400 --> 00:00:36,300
half a centimeter per year to 
about 10 centimeters per year. 

10
00:00:37,400 --> 00:00:41,300
But there is still no General 
consensus as to what makes 

11
00:00:41,300 --> 00:00:45,100
plates move, broadly speaking, 
there are two competing 

12
00:00:45,100 --> 00:00:49,900
explanations in the first, the 
plates ride on top of convection

13
00:00:49,900 --> 00:00:55,300
cells of a vigorously convecting
mantle in the second it is the 

14
00:00:55,300 --> 00:00:59,600
forces acting on plate 
boundaries principally the pull 

15
00:00:59,600 --> 00:01:03,800
of dense lithospheric slabs 
subducting into a less dense, 

16
00:01:03,800 --> 00:01:08,600
mantle that drive the plates. 
That white van hints. 

17
00:01:08,600 --> 00:01:13,600
Bergen is a professor of global 
tectonics and paleogeography at 

18
00:01:13,600 --> 00:01:17,300
the University of Utrecht. 
He has reconstructed the history

19
00:01:17,300 --> 00:01:20,500
of plate motions in various 
locations around the world. 

20
00:01:20,800 --> 00:01:24,100
With the primary goal of using 
this history to understand the 

21
00:01:24,100 --> 00:01:27,600
Dynamics of the mantle. 
And his latest research is 

22
00:01:27,600 --> 00:01:30,600
directed to shedding light on 
the long-standing question. 

23
00:01:30,600 --> 00:01:34,600
As to what drives tectonic 
plates that were even hints. 

24
00:01:34,600 --> 00:01:38,100
Bergen, welcome to geology B. 
It's a pleasure to be here. 

25
00:01:38,700 --> 00:01:42,200
Before we talk about what drives
the motion of tectonic plates. 

26
00:01:42,600 --> 00:01:46,100
I'd like to ask you about your 
plate motion reconstructions? 

27
00:01:46,600 --> 00:01:50,100
Are they Global in nature like 
those of deepmind Willows Group,

28
00:01:50,100 --> 00:01:54,200
which we discussed in an earlier
podcast or rather a regional the

29
00:01:54,200 --> 00:01:58,400
rigor structures that I make are
mostly based on Mountain belts 

30
00:01:58,400 --> 00:02:01,700
and they are there for regional.
So we try to reconstruct the 

31
00:02:01,700 --> 00:02:04,600
plates that we have lost because
they have subducted. 

32
00:02:04,700 --> 00:02:06,700
What regions have you 
reconstruct? 

33
00:02:06,900 --> 00:02:10,600
Did almost all regions that 
disappeared in the last 200 

34
00:02:10,600 --> 00:02:12,700
million years. 
So that is, especially the 

35
00:02:12,700 --> 00:02:17,000
Mediterranean region, the area 
between Arabia Eurasia, the 

36
00:02:17,000 --> 00:02:20,900
Himalaya and Tibet southeast 
Asia and the sucker Pacific 

37
00:02:20,900 --> 00:02:24,300
regions. 
How did you go about performing 

38
00:02:24,300 --> 00:02:27,700
these reconstructions? 
And What observations did you 

39
00:02:27,700 --> 00:02:30,300
use what? 
We try to figure out is the 

40
00:02:30,300 --> 00:02:33,700
paleogeography of plates that 
existed and the plate boundaries

41
00:02:33,700 --> 00:02:36,700
that existed in areas that have 
fully subducted. 

42
00:02:37,200 --> 00:02:40,800
And the rappers that we can use 
for that are now making larger, 

43
00:02:40,800 --> 00:02:44,300
Creationary Mountain belts, and 
with a Grecian room and melts. 

44
00:02:44,300 --> 00:02:48,200
I'm referring to table scrapes 
relics that form the upper few 

45
00:02:48,200 --> 00:02:51,800
kilometers of plates that have 
now subducted and you find them 

46
00:02:51,800 --> 00:02:54,800
in Mountain belts like we have 
in Japan or in New Zealand but 

47
00:02:54,800 --> 00:02:58,000
also the Himalaya or the Alps 
and many of the mountain belts 

48
00:02:58,000 --> 00:03:01,600
are the Mediterranean region are
made of those off scrape relics 

49
00:03:02,300 --> 00:03:05,700
and in those Mountain belts in 
those off scrape relics, we see 

50
00:03:05,700 --> 00:03:08,700
all sorts of rock types. 
And the nature of the rock types

51
00:03:08,700 --> 00:03:11,500
of fossils in the rock types, 
the ages of the Rocks. 

52
00:03:12,000 --> 00:03:15,000
Give us a lot of information 
about what the geographic 

53
00:03:15,000 --> 00:03:17,800
features were that these Rock 
times formed on. 

54
00:03:18,100 --> 00:03:21,800
For instance, we can find 
Barrier Reef type platforms 

55
00:03:21,900 --> 00:03:24,700
carbonate platforms and that 
will probably tell you that 

56
00:03:24,700 --> 00:03:27,000
you've been on large Continental
fragments. 

57
00:03:27,400 --> 00:03:31,200
Whereas if it is a local at all,
like we may find around Hawaii, 

58
00:03:31,400 --> 00:03:33,400
you will get a very different 
geological record. 

59
00:03:33,600 --> 00:03:37,000
So the relics that we find in 
these Mountain belts, Tell us 

60
00:03:37,000 --> 00:03:40,500
the type of rock the age of The 
Rock and the moment that that 

61
00:03:40,500 --> 00:03:44,200
rock arrived at a trench and 
that is the type of data that we

62
00:03:44,200 --> 00:03:47,600
use to let's say to put them 
back on the now, selected 

63
00:03:47,600 --> 00:03:49,600
lithosphere and make 
reconstructions with them. 

64
00:03:49,900 --> 00:03:53,500
That's fascinating. 
So just by identifying the rock 

65
00:03:53,500 --> 00:03:57,600
types in the mountain belts 
which are as you put it off 

66
00:03:57,600 --> 00:04:01,400
scraped relics literally scraped
off the top few kilometers of 

67
00:04:01,400 --> 00:04:05,800
plates when they subducted you 
can infer the extent of those 

68
00:04:05,800 --> 00:04:09,200
subducted plate. 
And when their various parts 

69
00:04:09,200 --> 00:04:11,300
reached, the trench and 
subducted. 

70
00:04:11,800 --> 00:04:16,000
So what we can see in a mountain
belt is what is still there. 

71
00:04:16,700 --> 00:04:20,200
And that probably is the biggest
problem that we have in geology,

72
00:04:20,300 --> 00:04:22,300
geologists can only study, what 
is there? 

73
00:04:22,900 --> 00:04:24,400
Particularly in these Mountain 
belts? 

74
00:04:24,400 --> 00:04:29,200
These are minimum records if 
there was a notion 5000 km wide 

75
00:04:29,300 --> 00:04:33,400
of which no rock ever accreted. 
We will never be able to tell 

76
00:04:33,400 --> 00:04:34,600
that. 
That ocean was there. 

77
00:04:35,000 --> 00:04:38,500
So, as a first starting point, 
For these reconstructions we use

78
00:04:38,500 --> 00:04:41,700
the reconstructions like deeper 
Muller has made did mer and his 

79
00:04:41,700 --> 00:04:44,700
group are the world's leading 
experts in making 

80
00:04:44,700 --> 00:04:48,300
reconstructions of the oceans 
that we do have today. 

81
00:04:48,800 --> 00:04:51,700
Magnetic stripe things in the 
ocean floor and large faults on 

82
00:04:51,700 --> 00:04:53,100
the ocean floor of the fracture 
zones. 

83
00:04:53,100 --> 00:04:57,300
In the ocean floor, they tell us
what the formation history and 

84
00:04:57,300 --> 00:05:00,200
the growth history of these 
ocean basins have been if we go 

85
00:05:00,200 --> 00:05:04,500
back to 150 million years ago, 
only about half of the surface 

86
00:05:04,500 --> 00:05:06,200
of the Earth is covered by 
rocks. 

87
00:05:06,200 --> 00:05:08,700
That we I have today, and the 
other half is lost. 

88
00:05:09,300 --> 00:05:12,800
So, the first thing that we do 
is estimate, using Rico 

89
00:05:12,800 --> 00:05:15,900
structures, like deep, Mars how 
much lithosphere of loss is not 

90
00:05:15,900 --> 00:05:18,300
only the ocean. 
I was lithosphere was lost on 

91
00:05:18,300 --> 00:05:22,400
Witchblade was lost and it tells
us how fast blades were moving 

92
00:05:22,400 --> 00:05:25,000
together and in what direction, 
they were moving together. 

93
00:05:25,200 --> 00:05:28,500
And then on those plates that 
we, let's say pulled back up 

94
00:05:28,500 --> 00:05:31,800
from the mantle, we stick the 
bits and pieces that we find the

95
00:05:31,800 --> 00:05:35,300
mountain belts, systematically 
one-by-one, across the planet. 

96
00:05:35,500 --> 00:05:41,300
And then we get the Sure of 
let's say 90% white void, no 

97
00:05:41,300 --> 00:05:45,100
information and 10% little 
fragments in bits and pieces and

98
00:05:45,100 --> 00:05:48,600
those fragments are little bits 
and pieces, still make for a 

99
00:05:48,600 --> 00:05:51,200
quite an accurate geography, and
because you can have an 

100
00:05:51,200 --> 00:05:53,000
educated. 
Guess what is missing in 

101
00:05:53,000 --> 00:05:56,300
between? 
Is there a way to test these 

102
00:05:56,300 --> 00:05:59,300
reconstructions with 
observations of a different 

103
00:05:59,300 --> 00:06:03,300
nature to make sure that 
consistent there are most 

104
00:06:03,300 --> 00:06:06,200
directly? 
You can see where those plates 

105
00:06:06,200 --> 00:06:08,400
might currently. 
We reside in the Earth's mantle,

106
00:06:08,400 --> 00:06:11,400
we have seismological techniques
and the cat-scans of seismic 

107
00:06:11,400 --> 00:06:15,700
tomography that allows us to see
where we have anomalously, high 

108
00:06:15,700 --> 00:06:19,900
wave, speed, anomalies in the 
mantle, that could be subducting

109
00:06:19,900 --> 00:06:22,400
lithosphere. 
So we can predict whether we 

110
00:06:22,400 --> 00:06:24,900
find subducting lithosphere and 
places. 

111
00:06:24,900 --> 00:06:27,100
Where are we go? 
Structured tells us there is 

112
00:06:27,100 --> 00:06:29,900
subducted lithosphere and 
clearly, if we do that at modern

113
00:06:29,900 --> 00:06:33,600
subduction zones, then it works 
because, you know, that's how we

114
00:06:33,600 --> 00:06:35,700
know that that's abducted 
literature in the first place 

115
00:06:35,700 --> 00:06:38,500
because we can calibrate 
Tomorrow motions, but in 

116
00:06:38,500 --> 00:06:42,300
Mountain belts, like in Iran or 
in the Mediterranean region, we 

117
00:06:42,300 --> 00:06:46,300
see the relics of subduction 
zones that formed and died in 

118
00:06:46,300 --> 00:06:48,500
the geological past in 
locations. 

119
00:06:48,500 --> 00:06:50,500
Far away from the motor mount 
belt. 

120
00:06:50,500 --> 00:06:54,700
And for those reconstructions, 
we can use tomography as a test.

121
00:06:55,300 --> 00:06:59,500
Another independent test to see 
whether we place a deformed Rock

122
00:06:59,500 --> 00:07:02,700
unit that we now have a mountain
belt in the right position on 

123
00:07:02,700 --> 00:07:05,800
the Earth's lithosphere is 
through paleomagnetic data, the 

124
00:07:05,800 --> 00:07:08,900
played, That we have. 
We can place relative to the 

125
00:07:08,900 --> 00:07:12,300
Earth's spin axis by using 
Bailey magnetic data from stable

126
00:07:12,300 --> 00:07:16,100
continents. 
And then we can see whether we 

127
00:07:16,200 --> 00:07:18,900
put the rock units that we have 
in Mountain belts in the right 

128
00:07:18,900 --> 00:07:22,000
position at the right latitude 
and the geological past, that's 

129
00:07:22,000 --> 00:07:25,600
really interesting. 
So you actually don't use the 

130
00:07:25,700 --> 00:07:30,600
seismic tomography or the 
paleomagnetic data as inputs to 

131
00:07:30,600 --> 00:07:34,300
your reconstruction, you just 
use them as tests once you've 

132
00:07:34,300 --> 00:07:38,100
done it using your examination 
of Belts in the other logic that

133
00:07:38,100 --> 00:07:42,800
you described earlier exactly 
what I try to do is predict 

134
00:07:43,000 --> 00:07:47,300
based on the structure of 
mountain belts and based on the 

135
00:07:47,300 --> 00:07:51,000
history of the seafloor, I try 
to predict what unit must have 

136
00:07:51,000 --> 00:07:54,200
been where and with the 
information that we have in 

137
00:07:54,200 --> 00:07:58,000
Mountain belts on fault motions,
plus simple geometry. 

138
00:07:58,000 --> 00:08:01,200
You know, it has to fit if you 
take something as complex as the

139
00:08:01,200 --> 00:08:05,300
Mediterranean region, there are 
so many constraints from so many

140
00:08:05,300 --> 00:08:09,000
different Corners that each 
Eventually may have multiple 

141
00:08:09,000 --> 00:08:11,800
options to interpret, but if you
put them all together, there are

142
00:08:11,800 --> 00:08:14,800
not that many options where you 
can put everything, you know, if

143
00:08:14,800 --> 00:08:17,700
two regions both receive 
sediments, they cannot have been

144
00:08:17,700 --> 00:08:21,000
on top of each other. 
So, by using geometry, we 

145
00:08:21,000 --> 00:08:24,500
normally end up with a 
reconstruction that has limited 

146
00:08:24,500 --> 00:08:28,000
degrees of freedom and then we 
predict Bailey magnetism and in 

147
00:08:28,000 --> 00:08:31,500
some cases like for instance, in
Corsica Sardinia in the 

148
00:08:31,500 --> 00:08:35,600
Cretaceous and the Mediterranean
region Bailey, magnetism told us

149
00:08:35,600 --> 00:08:37,799
they had really a Current 
position for what you 

150
00:08:37,799 --> 00:08:40,500
reconstructed. 
It was permitted by what I knew 

151
00:08:40,500 --> 00:08:43,200
but there was no way to tell 
from the get-go so that is an 

152
00:08:43,208 --> 00:08:47,600
example where we changed it. 
But if it is possible to avoid 

153
00:08:47,600 --> 00:08:51,500
to use Paley magnetism as input 
than I do also because 

154
00:08:51,500 --> 00:08:55,200
paleomagnetism has a much larger
uncertainty than we have 

155
00:08:55,200 --> 00:08:59,200
appreciated in the past. 
The mantle I specifically do not

156
00:08:59,200 --> 00:09:02,700
use as input because it is 
precisely the evolution of the 

157
00:09:02,700 --> 00:09:05,100
mantle and the Dynamics of the 
mantle that I try to 

158
00:09:05,100 --> 00:09:08,500
reconstruct. 
So, I force my reconstructions 

159
00:09:08,500 --> 00:09:12,000
to fit a pattern in the mantle 
that I think should belong to 

160
00:09:12,000 --> 00:09:14,600
it. 
Then I lose my independent 

161
00:09:14,600 --> 00:09:17,100
control on what happened in the 
mantle. 

162
00:09:17,200 --> 00:09:21,200
And if I want to understand how 
the mantle is moving collecting 

163
00:09:21,200 --> 00:09:24,600
or not, and I used more refuse 
input from our reconstructions, 

164
00:09:24,600 --> 00:09:26,700
I inevitably end up in a 
circular reasoning. 

165
00:09:27,400 --> 00:09:31,400
Let's talk about how 
reconstructions can shed light 

166
00:09:31,600 --> 00:09:35,600
on what drives plate motions. 
So can you recap for us? 

167
00:09:35,900 --> 00:09:39,800
What the The two competing 
theories are about what drives 

168
00:09:39,800 --> 00:09:43,000
tectonic plates. 
The two theories are both more 

169
00:09:43,000 --> 00:09:45,600
than 50 years old. 
The first one essentially 

170
00:09:45,600 --> 00:09:48,300
originates from the famous 
Arthur Holmes. 

171
00:09:48,300 --> 00:09:52,100
Who was the first to realize 
that radioactive decay in the 

172
00:09:52,100 --> 00:09:56,700
Earth's mantle must be a heat 
engine and he envisaged run over

173
00:09:56,700 --> 00:10:00,200
boiling pan of milk willaura 
feet with collecting mental, 

174
00:10:00,200 --> 00:10:03,800
trying to lose its heat and he 
supposed that the continental 

175
00:10:03,800 --> 00:10:07,800
drift hypothesis of a gunner at 
I'm, which was lacking a 

176
00:10:07,800 --> 00:10:11,800
mechanism that he supposed that 
the horizontal Flowage as he 

177
00:10:11,800 --> 00:10:16,000
called it would be a driver of 
that horizontal motion of blocks

178
00:10:16,100 --> 00:10:18,400
or whatever they were because 
they didn't really know. 

179
00:10:18,900 --> 00:10:22,500
Then, when plate tectonics 
started to become the Paradigm 

180
00:10:23,100 --> 00:10:27,200
Forsyth in a way that I think, 
is 75, had the perfectly logical

181
00:10:27,200 --> 00:10:31,100
notion that if you have ocean 
floor and that ocean floor cools

182
00:10:31,100 --> 00:10:33,500
and becomes denser than the 
mantle, that it will sink. 

183
00:10:34,100 --> 00:10:38,000
And if it sinks at subduction 
zones is - buoyancy will act as 

184
00:10:38,000 --> 00:10:39,800
a pull force on the Dow going 
plate. 

185
00:10:40,200 --> 00:10:43,800
Apart from that the Aging of 
oceanic lithosphere, also comes 

186
00:10:43,800 --> 00:10:46,600
with the topographic effect that
will give a horizontal Force 

187
00:10:46,600 --> 00:10:50,400
known as Ridge push, which is 
thought to be subordinate to 

188
00:10:50,400 --> 00:10:52,500
slap. 
Ooh, but that suggests that. 

189
00:10:52,500 --> 00:10:55,900
It's the density structure of 
the moving plates rather than 

190
00:10:55,900 --> 00:10:58,200
the boiling of the mantle 
underneath convection in the 

191
00:10:58,200 --> 00:11:00,800
mantle of myth. 
But there's one thing that both 

192
00:11:00,800 --> 00:11:02,900
ideas have in common, or two 
things. 

193
00:11:02,900 --> 00:11:04,500
First of all, they kind of make 
sense. 

194
00:11:05,100 --> 00:11:08,000
And the second is, they were 
both Made when we knew nothing 

195
00:11:08,000 --> 00:11:11,900
of the mantle, we had no direct 
observations of the mantle below

196
00:11:11,900 --> 00:11:14,700
her feet. 
And that is, I think the 

197
00:11:14,700 --> 00:11:18,000
interesting point where we are 
now with all the Decades of 

198
00:11:18,000 --> 00:11:22,200
seismological work, geochemical 
work, the interpretation of the 

199
00:11:22,200 --> 00:11:25,800
geological history of the mantle
that came with the connection of

200
00:11:25,800 --> 00:11:29,800
seismic tomography to records. 
That we see a mountain belts and

201
00:11:29,800 --> 00:11:32,500
we're now coming into the point 
that we cannot only see how 

202
00:11:32,500 --> 00:11:35,400
please move over the surface, 
but also how they move through 

203
00:11:35,400 --> 00:11:38,900
the Earth's mantle and we start 
to see a history below our feet.

204
00:11:38,900 --> 00:11:41,100
We can start to evaluate to what
extent. 

205
00:11:41,100 --> 00:11:45,100
These ideas of pulling slabs and
whirling mantels are actually 

206
00:11:45,100 --> 00:11:49,000
consistent with what we see what
are the observations of the 

207
00:11:49,008 --> 00:11:52,800
mantle the bear on the question 
of plate drivers. 

208
00:11:53,300 --> 00:11:56,800
The first thing that comes to 
mind is seismological images 

209
00:11:56,800 --> 00:12:00,000
that map out where seismic waves
in the mantle are fast and 

210
00:12:00,000 --> 00:12:03,100
whether slow one way of 
explaining fast and slow. 

211
00:12:03,100 --> 00:12:07,100
And that is the way that is most
common is that Is that are 

212
00:12:07,100 --> 00:12:10,500
colder than average will have a 
seismic velocity that is higher 

213
00:12:10,500 --> 00:12:14,300
than average and reaches that 
are halter have slower. 

214
00:12:14,400 --> 00:12:18,100
Seismic waves but seismology is 
also explained that 

215
00:12:18,200 --> 00:12:22,100
compositional, differences or 
water differences may also have 

216
00:12:22,100 --> 00:12:25,200
such effect. 
What we see in the mantle is 

217
00:12:25,200 --> 00:12:30,600
that there are regions that are 
elongated, large bodies of 

218
00:12:30,600 --> 00:12:35,100
anomalously, fast stuff, 
whatever it might be that when 

219
00:12:35,100 --> 00:12:38,600
you compare it to play triggers,
Structures have volumes that go 

220
00:12:38,600 --> 00:12:42,600
inside with a history of 
lithosphere consumption. 

221
00:12:43,400 --> 00:12:48,900
So with seismic tomography, we 
see a current snapshot of where 

222
00:12:48,900 --> 00:12:52,700
the bodies in the mantle are 
that might be slams and the next

223
00:12:52,700 --> 00:12:55,700
step that we took his new 
interpretation step whereby, you

224
00:12:55,700 --> 00:12:58,800
connect the interpreted 
geological history of Seduction 

225
00:12:59,800 --> 00:13:04,700
with those bodies in the mantle,
if you correlate the shallowest 

226
00:13:04,800 --> 00:13:08,600
bodies in the mantle The 
youngest records of Seduction 

227
00:13:09,100 --> 00:13:12,500
and you assume that older 
seduction records tend to 

228
00:13:12,500 --> 00:13:17,500
correlate to deeper slabs deeper
anomalies, then you get a very 

229
00:13:17,500 --> 00:13:21,200
consistent pattern whereby. 
All subduction zones of the last

230
00:13:21,200 --> 00:13:26,200
200 to 250 million years are 
accounted for in the mantle and 

231
00:13:26,200 --> 00:13:29,700
there are no major anomalies 
left unaccounted for. 

232
00:13:30,800 --> 00:13:34,500
On the other hand, the 
geochemists have been working on

233
00:13:34,500 --> 00:13:38,600
the chemical composition of 
volcanic rocks that apparently 

234
00:13:38,800 --> 00:13:41,800
come from different reservoirs. 
In the mantle, there's volcanism

235
00:13:41,800 --> 00:13:44,200
correlated to reaches of 
Seduction for organism 

236
00:13:44,200 --> 00:13:46,800
correlated to regions of 
extension, a mid-ocean ridges 

237
00:13:47,200 --> 00:13:49,300
and their volcanism that is 
intraplate. 

238
00:13:49,300 --> 00:13:52,800
And that is not just intraplate.
But is intraplate a very 

239
00:13:52,800 --> 00:13:55,500
specific regions relative to a 
normally structures in the 

240
00:13:55,508 --> 00:14:00,200
deepest mantle and those 
different volcanic provinces. 

241
00:14:00,700 --> 00:14:02,600
Have different signature 
suggesting that there are 

242
00:14:02,600 --> 00:14:06,200
different reservoirs in the 
mount but also that the mantle 

243
00:14:06,200 --> 00:14:10,100
is much more heterogeneous than 
we would expect from a mantle 

244
00:14:10,100 --> 00:14:13,700
that is very quickly mixing and 
convicting. 

245
00:14:14,000 --> 00:14:17,400
So that is a constraint. 
Then a third constraint that I 

246
00:14:17,400 --> 00:14:20,800
think is very spectacular is 
that there are places in the 

247
00:14:20,800 --> 00:14:25,200
mantle where people in the last 
20, 25 years, I found zircons 

248
00:14:25,400 --> 00:14:29,600
minerals that normally forming 
magmatic rocks and we find 

249
00:14:29,700 --> 00:14:32,200
zircons that are we You're older
than the volcanoes. 

250
00:14:32,200 --> 00:14:36,600
Are the crust the oceanic crust 
on, which they form, in places, 

251
00:14:36,600 --> 00:14:39,200
where they should not be like, 
on the Mid-Atlantic Ridge. 

252
00:14:39,800 --> 00:14:43,700
These are features that are now 
so often observed that we start 

253
00:14:43,700 --> 00:14:47,600
to be able to piece together a 
picture of the mantle directly 

254
00:14:47,600 --> 00:14:51,000
from observations that was not 
available at the time that we 

255
00:14:51,000 --> 00:14:53,600
came up with the ideas of the 
drivers of plate tectonics. 

256
00:14:54,100 --> 00:14:58,300
So there's the seismic 
tomography which is one 

257
00:14:58,300 --> 00:15:03,700
constraint, there's the Geo. 
So chemical signature which we 

258
00:15:03,700 --> 00:15:07,600
get by analyzing the trace 
element and the isotopic 

259
00:15:07,600 --> 00:15:12,800
composition of lavas Source from
the mantle below at mid-ocean 

260
00:15:12,800 --> 00:15:17,900
ridges above subduction zones. 
And at intraplate hot spots, 

261
00:15:18,300 --> 00:15:23,000
which all point to a hydrogen 
are T in the mantle and there is

262
00:15:23,000 --> 00:15:27,700
the presence of crystals of 
zircon crystals, which we know 

263
00:15:28,100 --> 00:15:30,700
really could only a formed in 
the magmatic rock that Than 

264
00:15:30,700 --> 00:15:34,100
crystallised that's coming up 
from the mantle so those three 

265
00:15:34,100 --> 00:15:38,600
things together, our new data 
that tell us about the mantle 

266
00:15:38,600 --> 00:15:41,500
that we didn't have at the time 
that these two competing 

267
00:15:41,500 --> 00:15:43,300
theories were formulated 
initially. 

268
00:15:43,500 --> 00:15:46,400
Yeah, I'm sure there are more, I
think particularly that the 

269
00:15:46,400 --> 00:15:49,200
seismologist and a mineral 
physicists have a few other 

270
00:15:49,200 --> 00:15:52,200
tricks up their sleeve that I 
have yet to learn more about, 

271
00:15:52,300 --> 00:15:56,300
but there are now quite a lot of
observations that will constrain

272
00:15:56,300 --> 00:15:58,200
at least how the Earth is 
operating. 

273
00:15:58,200 --> 00:16:01,800
Now, it doesn't mean that it Is 
always operating that way. 

274
00:16:01,800 --> 00:16:05,600
But I think we can get a better 
idea about to what extent. 

275
00:16:05,600 --> 00:16:08,400
The mantle is vigorously, 
convecting or not. 

276
00:16:09,200 --> 00:16:14,700
So how does all this relate to 
the plate motion reconstructions

277
00:16:14,800 --> 00:16:19,300
that we discussed earlier on the
mental is a geological product 

278
00:16:19,400 --> 00:16:21,500
itself. 
It's the product of a geological

279
00:16:21,500 --> 00:16:24,800
history. 
So if we find zircons in the 

280
00:16:24,800 --> 00:16:28,400
mantle in a location where they 
cannot have formed recently, 

281
00:16:28,400 --> 00:16:31,500
like in the Mid-Atlantic Ridge, 
Would you get them there? 

282
00:16:31,500 --> 00:16:34,100
These are kids that are 3 
billion years old up all the way

283
00:16:34,100 --> 00:16:35,900
until a couple hundred million 
idea. 

284
00:16:35,900 --> 00:16:38,600
Get all those are kids together 
in the first place but you do 

285
00:16:38,600 --> 00:16:41,600
that in the Sandstone. 
That's how you get crystals 

286
00:16:41,600 --> 00:16:44,100
together on a geological 
surface. 

287
00:16:44,900 --> 00:16:48,900
How do you get sand in a mental?
Well, you need to have a 

288
00:16:48,900 --> 00:16:51,800
subduction zone for that. 
Sand doesn't sink through 

289
00:16:51,800 --> 00:16:55,100
mid-ocean ridge into the mantle.
So the plate reconstruction 

290
00:16:55,100 --> 00:16:59,700
should predict, which anomaly 
that we see in tomography when 

291
00:16:59,700 --> 00:17:02,500
that anomaly. 
Could have formed and where but 

292
00:17:02,500 --> 00:17:05,599
we know where the tomography 
tells is not where that thing is

293
00:17:05,599 --> 00:17:11,500
today, and it seems reasonable 
to assume so far that one slabs 

294
00:17:11,500 --> 00:17:15,800
break from lithospheric plates. 
They do not move a lot anymore. 

295
00:17:15,800 --> 00:17:18,700
Horizontally, so the just sing 
vertically. 

296
00:17:19,000 --> 00:17:22,700
So if we have a slab deep in the
mantle somewhere and we want to 

297
00:17:22,700 --> 00:17:25,800
figure out when the last 
opportunity has been to form 

298
00:17:25,800 --> 00:17:28,900
that thing with subduction and 
we need a plate reconstruction 

299
00:17:28,900 --> 00:17:31,300
and we needed to know that 
bladebreakers Action relative to

300
00:17:31,300 --> 00:17:34,500
the Earth's mantle which is not 
straight forward, but there are 

301
00:17:34,500 --> 00:17:38,400
ways to estimate that. 
So there was a paper last year 

302
00:17:38,500 --> 00:17:42,100
of an Australian group led by 
Mariana veto who found something

303
00:17:42,100 --> 00:17:44,700
quite unexpected. 
On the North Pole they found on 

304
00:17:44,700 --> 00:17:48,500
the GAC, origin active Ridge. 
Today, they found a signature of

305
00:17:48,500 --> 00:17:52,500
Seduction in the geochemistry 
and they noted that in the 

306
00:17:52,500 --> 00:17:55,200
mantle below their feet, but at 
a depth of 15 hundred 

307
00:17:55,200 --> 00:17:59,200
kilometers, or so, there is an 
anomaly that suggests that there

308
00:17:59,200 --> 00:18:00,900
has been Seduction on and North 
Pole. 

309
00:18:01,400 --> 00:18:04,000
And if you then take a plate 
reconstruction, the youngest 

310
00:18:04,000 --> 00:18:05,800
subduction zone that was 
reconstructed. 

311
00:18:05,800 --> 00:18:09,700
At that location is something 
like 130 million years old which

312
00:18:09,700 --> 00:18:13,100
suggests that that signature 
survived in the location where 

313
00:18:13,100 --> 00:18:18,800
it Formed still right above that
slab and over 3000 years ago and

314
00:18:18,800 --> 00:18:22,600
we made a similar case with 
rocks that had a magnetic 

315
00:18:22,600 --> 00:18:25,600
signature that we see on New 
Guinea but they've seemed to 

316
00:18:25,608 --> 00:18:27,500
have formed in absence of 
Seduction. 

317
00:18:28,500 --> 00:18:31,700
And we also notice that we start
to find those rocks. 

318
00:18:31,700 --> 00:18:34,700
As soon as are reconstructions 
Dallas, the New Guinea started 

319
00:18:34,700 --> 00:18:38,800
to move over as tobacco-related,
anomaly in the mantle over slab 

320
00:18:38,800 --> 00:18:41,300
on the mantle which formed 
because of interoceanic 

321
00:18:41,300 --> 00:18:44,200
Seduction, 30 million years. 
Prior what? 

322
00:18:44,200 --> 00:18:48,400
That might suggest is that those
anomalies do not move much 

323
00:18:48,400 --> 00:18:51,400
horizontally in the mantle over 
a very long period of time. 

324
00:18:52,000 --> 00:18:54,400
And if that is true, then it 
means that the mantle is moving 

325
00:18:54,400 --> 00:18:57,100
that much, at least not in the 
last time in the 30 million 

326
00:18:57,100 --> 00:19:00,000
years. 
Okay, so let me see if I fully 

327
00:19:00,000 --> 00:19:03,700
understand the logic here. 
So when you have a subduction 

328
00:19:03,700 --> 00:19:09,700
that goes down into the mantle 
and because of a certain amount 

329
00:19:09,700 --> 00:19:14,100
of melting and interaction with 
the mantle that will change the 

330
00:19:14,100 --> 00:19:18,100
chemistry of the mantle to a 
certain extent, which we can 

331
00:19:18,100 --> 00:19:22,100
detect later using our modern 
geochemical techniques. 

332
00:19:22,100 --> 00:19:27,600
So by using your 
reconstructions, we can tell the

333
00:19:27,600 --> 00:19:30,600
history. 
Turi, and the location of pasts 

334
00:19:30,600 --> 00:19:34,300
abductions. 
And what we seem to be finding 

335
00:19:34,300 --> 00:19:37,900
is that the geochemical imprint 
of those paths. 

336
00:19:37,900 --> 00:19:42,600
Abductions has survived through 
geological time in roughly, the 

337
00:19:42,600 --> 00:19:47,000
same locations, where that 
imprint was originally created 

338
00:19:47,000 --> 00:19:49,500
by the subduction itself. 
If I got it right. 

339
00:19:49,500 --> 00:19:51,300
It's better explain than I do. 
But yes. 

340
00:19:52,500 --> 00:19:56,700
So by putting together the 
reconstructions, with the 

341
00:19:56,700 --> 00:20:00,800
modern, Geochemistry and 
tomography. 

342
00:20:01,400 --> 00:20:03,500
We are now beginning to piece 
together. 

343
00:20:03,500 --> 00:20:07,200
A picture. 
That maybe the mantle is really 

344
00:20:07,500 --> 00:20:11,600
pretty still, maybe not stagnant
but really not moving very much.

345
00:20:11,600 --> 00:20:14,300
Is that the conclusion? 
Yeah, that is the conclusion 

346
00:20:14,300 --> 00:20:16,300
that I'm slowly starting to 
draw. 

347
00:20:16,800 --> 00:20:23,600
And so the implications are that
the mantle is not like a boiling

348
00:20:23,700 --> 00:20:27,000
pail of milk with vigorous 
convection cells. 

349
00:20:27,900 --> 00:20:32,700
Therefore plate motions would 
not really be driven because 

350
00:20:32,700 --> 00:20:34,700
there's no convecting sell to 
drive them. 

351
00:20:35,100 --> 00:20:37,500
Yeah. 
That a search may not be a 

352
00:20:37,500 --> 00:20:40,100
shocking conclusion because 
people have argued that blade 

353
00:20:40,100 --> 00:20:42,900
motions themselves can be 
explained by slabs going down, 

354
00:20:43,400 --> 00:20:46,600
but even models that have slabs 
driving. 

355
00:20:46,700 --> 00:20:49,100
The plates, have those same 
slabs. 

356
00:20:49,100 --> 00:20:53,300
Also driving convection. 
So that the mantle itself is 

357
00:20:53,300 --> 00:20:56,300
rigorously convecting from a 
geodynamic point of view is 

358
00:20:56,300 --> 00:20:58,800
still the Paradigm. 
The question is only been, is 

359
00:20:58,800 --> 00:21:01,300
that convection driving it or is
that convection passive? 

360
00:21:01,500 --> 00:21:04,300
And what these observations 
only? 

361
00:21:04,300 --> 00:21:07,400
I think we're only at the start 
of this whole thing with these 

362
00:21:07,400 --> 00:21:10,300
observations seem to suggest is 
that not only are the place 

363
00:21:10,300 --> 00:21:13,800
driving themselves at least in 
the last few Animo years, but 

364
00:21:13,800 --> 00:21:16,800
they're not doing much to the 
mantle underneath the man alone 

365
00:21:16,800 --> 00:21:20,800
needs appears to be a more or 
less sluggish passive body of 

366
00:21:20,800 --> 00:21:23,600
Rock. 
That melts if you decompress it 

367
00:21:23,600 --> 00:21:28,000
or you had some water that will 
certainly move as swirl where 

368
00:21:28,000 --> 00:21:30,700
you move your pedal through the 
washer where your slabs are. 

369
00:21:30,700 --> 00:21:34,100
Moving through the mountain, 
they certainly are starting the 

370
00:21:34,100 --> 00:21:37,200
monthly fee. 
Slab is retreating, which we can

371
00:21:37,200 --> 00:21:40,300
demonstrate happens. 
I'm not last to move around so 

372
00:21:40,300 --> 00:21:44,500
it's not a solid body of rock. 
It can move if somebody pushes 

373
00:21:44,500 --> 00:21:48,600
it but it's on the large scale. 
It seems not to be doing too 

374
00:21:48,600 --> 00:21:51,200
much. 
So in other words the convection

375
00:21:51,600 --> 00:21:56,600
Driven by the radioactive heat 
is not really driving these 

376
00:21:56,600 --> 00:21:59,600
plate motions. 
As Arthur Holmes might have 

377
00:21:59,600 --> 00:22:03,000
suggested originally when you 
proposed the theory, but what 

378
00:22:03,000 --> 00:22:06,000
motions? 
There are would be responsive to

379
00:22:06,300 --> 00:22:09,600
the Dynamics of the plates 
themselves and the forces acting

380
00:22:09,600 --> 00:22:12,900
on the edges. 
Whether it's push or pull, yes, 

381
00:22:13,000 --> 00:22:19,700
and those motions are local and 
on the large scale, minor one or

382
00:22:19,708 --> 00:22:23,100
two orders of magnitude slower. 
Then the plates are moving. 

383
00:22:23,700 --> 00:22:26,300
I don't say that. 
I understand the dynamic 

384
00:22:26,300 --> 00:22:30,100
consequences of that statement. 
I do get a Mattox. 

385
00:22:30,100 --> 00:22:33,400
I tried to piece out how stuff 
moved. 

386
00:22:33,700 --> 00:22:36,600
Not so much wide moved. 
Sure, I'm do that and with 

387
00:22:36,600 --> 00:22:40,800
colleagues and with my research 
I'm either blessed or 

388
00:22:40,900 --> 00:22:44,300
compromised by a very poor 
knowledge of mathematics and 

389
00:22:44,300 --> 00:22:46,700
physics. 
So my limitations tell me that I

390
00:22:46,700 --> 00:22:49,900
can figure out when stuff moved 
and where it moved but not why. 

391
00:22:50,400 --> 00:22:51,800
So from that point Point of 
view. 

392
00:22:51,800 --> 00:22:54,500
I came to this conclusion and I 
think that on the other hand, 

393
00:22:54,500 --> 00:22:57,100
this can be a beautiful 
constraint on trying to figure 

394
00:22:57,100 --> 00:22:59,900
out what is driving things 
because whatever is driving. 

395
00:22:59,900 --> 00:23:03,500
It has to fulfill these 
observations or perhaps we 

396
00:23:03,500 --> 00:23:07,600
misinterpret these observations.
If this is correct, it gives a 

397
00:23:08,200 --> 00:23:12,900
rather unique constraint on the 
workings of the planet that we 

398
00:23:12,900 --> 00:23:15,300
didn't realize before. 
Yeah, it's fascinating. 

399
00:23:15,300 --> 00:23:18,400
I mean, obviously, this is a 
question that's been around for 

400
00:23:18,500 --> 00:23:21,000
many, many decades, and now 
appears this. 

401
00:23:21,300 --> 00:23:24,300
Kind of a new line of evidence 
that might bear on on the 

402
00:23:24,300 --> 00:23:26,700
question of what drives plate 
tectonics. 

403
00:23:27,300 --> 00:23:32,500
So if the mantle is, let's say 
relatively stagnant and the 

404
00:23:32,500 --> 00:23:37,300
driver is the forces acting on 
plate, boundaries, what does 

405
00:23:37,300 --> 00:23:41,600
that tell us about individual 
plate motions that we see in. 

406
00:23:41,600 --> 00:23:45,200
Clit help us understand why some
plates are moving fast and some 

407
00:23:45,200 --> 00:23:50,100
plates are moving slowly. 
It must be all our experiments 

408
00:23:50,100 --> 00:23:53,400
are numerical experiments or 
analog experiments of plate, 

409
00:23:53,400 --> 00:23:56,700
motion sale. 
I have a plate and there's 

410
00:23:56,700 --> 00:24:00,000
something buoyant on that plate 
like a continent and incontinent

411
00:24:00,000 --> 00:24:02,200
hits the trench. 
Then I shoot you see a change in

412
00:24:02,200 --> 00:24:06,000
my plate motion. 
But I'm not sure whether we do 

413
00:24:06,000 --> 00:24:10,700
there, are many places Australia
has collided twice with 

414
00:24:10,700 --> 00:24:14,200
interoceanic subduction zones, 
and slabs attached to it, and 

415
00:24:14,200 --> 00:24:17,800
they're broken off and nothing 
happened in its plate, motion 

416
00:24:17,800 --> 00:24:20,500
history, just happily kept going
and India. 

417
00:24:20,500 --> 00:24:24,200
We see the same thing, India 
still moving northward and the 

418
00:24:24,200 --> 00:24:28,300
last phases of slab, break of 
have barely any effect on plate,

419
00:24:28,300 --> 00:24:31,400
motion Mediterranean region. 
There's been Continental 

420
00:24:31,400 --> 00:24:34,100
subduction for 100 million years
on and off Off. 

421
00:24:34,700 --> 00:24:36,800
We don't really see it in the 
plate motions. 

422
00:24:37,100 --> 00:24:41,300
So even though slab pool must be
the driving factor of plate 

423
00:24:41,300 --> 00:24:45,800
tectonics, as we think the loss 
of slab does not really have the

424
00:24:45,800 --> 00:24:49,100
predicted result. 
So I'm not sure whether we 

425
00:24:49,100 --> 00:24:53,200
understand and to make life even
more difficult, there is a paper

426
00:24:53,200 --> 00:24:55,100
that just came out by Chuck the 
mats. 

427
00:24:55,100 --> 00:24:58,900
And so I got Mercury of who are 
well known for high resolution 

428
00:24:58,900 --> 00:25:02,000
reconstructions of plate, 
motions, we know that India went

429
00:25:02,000 --> 00:25:07,100
super fast 50 million Oh 60 more
years ago up to 150 km from the 

430
00:25:07,100 --> 00:25:10,400
year or even more and then it 
slowed down and everybody has 

431
00:25:10,400 --> 00:25:12,300
always been saying something to 
do with Collision. 

432
00:25:12,600 --> 00:25:15,200
Well, they showed is actually 
that in the time, that it went 

433
00:25:15,200 --> 00:25:17,200
super fast. 
India was speeding up and 

434
00:25:17,200 --> 00:25:21,600
slowing down by fifty to a 
hundred percent of their speed 

435
00:25:21,600 --> 00:25:24,800
in time. 
Scales of 23 million years that 

436
00:25:24,800 --> 00:25:28,900
we really cannot explain and 
these are crazy or high 

437
00:25:28,900 --> 00:25:32,500
resolution records. 
So, as usual, I think that the 

438
00:25:32,500 --> 00:25:35,300
more we learn, the more, More. 
We figure out that we do not 

439
00:25:35,300 --> 00:25:38,900
understand what's going on 
again, if you look at where 

440
00:25:38,900 --> 00:25:41,300
these Concepts came from, they 
make perfect sense. 

441
00:25:41,400 --> 00:25:44,800
But in the light of everything 
we know now there are a couple 

442
00:25:44,800 --> 00:25:48,400
of observations that show that 
it's either incorrect or 

443
00:25:48,500 --> 00:25:53,100
incomplete and we can speculate 
a little bit about what might be

444
00:25:53,100 --> 00:25:55,800
driving it. 
I think it's an exciting time 

445
00:25:55,800 --> 00:25:59,400
and you learn Amex. 
That woman hits buggin. 

446
00:25:59,400 --> 00:26:03,200
Thank you very much. 
You're welcome for more about 

447
00:26:03,200 --> 00:26:06,800
geology b as well as pictures 
and illustrations. 

448
00:26:06,800 --> 00:26:11,400
That support this podcast, you 
can go to geology B.com