Full text of DOI:10.1007/BF02900610

R
are induced by plate drift, and propose a simpler but more
self-consistent global motion mechanism. This model is a
The Earth’s inner core devia-
tion to plate movement
4
-stroke-cycle model, Spherical Coupling Model (SCM).
1 A global dynamic model based on crust-mantle-
core coupling
1
HUANG Dinghua , WU Jinping , DUAN Yichun ,
1
2
1
1
1
GUO Hao , ZHANG Heng , YAO Lingqing ,
The sketch of the working hypothesis is as follows
(fig. 1):
1
ZHANG Fan , LI Bin , WANG Junhui & YIN Hongfu
1
1
1
1
. The Faculty of Earth Science, China University of Geosciences, Wu-
han 430074, China;
. The Ministry of Land and Resources of China, Beijing 100035, China
2
Correspondence should be addressed to Huang Dinghua (e-mail:
dhuang@cus.edu.cn)
Abstract Under the premise of the Earth’s layer struc-
ture and mass distribution, the solid inner core cannot be
stable in the center of the sphere. Thus, the deviation of the
inner core is towards the sphere’s center and the liquid outer
core must have asymmetrical thermal convection. Based on
the two suggestions, a concise and self-consistent global mo-
tion model can be built. The model consists of the following
cycle: an asymmetrical thermal convection structure in the
outer core led by the dislocation of the inner coreėthe plume
is in special upwell position because of differential activation
ėthe formation and split of lithosphereėthe split plates
drift and assemble in a new location, the mass of which
causes the inner core to deviate towards this direction again
ėthe new asymmetry is formed. As this circulation contin-
ues, a definite and periodical motion emerges/forms. Its
nonlinear features result in the Earth’s motion with simple
mechanisms but complex behavior. Ultraterrestrial events
may disturb or even interrupt this movement but would not
significantly affect the cycle.
Fig. 1. Interior structure of the Earth. a, Lithosphere (solid); b, as-
thenosphere (melt); c, mantle (solid); d, outer-core (liquid); e, inner-core
(
solid) here it is off-centred to the south; f, activated plume; g, shattered
and newborn lithospheric plates; h, potential plume; i, aggregating
plates.
If the solid inner-core is off-centered for some reason,
the thermal convection in the liquid outer-core, on the side
nearer to the deviated inner-core, will strengthen substan-
tially because of the thinner convection layer. Thus, the
bottom half of mantle will cauterize more violently than
other parts. Then a new (supper-) plume from the “baked
side” will be activated and upwell to the base of litho-
sphere. The lithosphere will heat and tear, while new crust
forms. The neonatal crust and the torn lithospheric plates
will drift to a new location in the opposite hemisphere,
collisions and subduction processes accompany this. Due
to these processes, the mass of the hemisphere will in-
crease gradually. After the hemisphere outweighs the op-
posite hemisphere, the inner-core will attract backwards
across the Earth’s center; then new plume(s) will activate
again in a similar procedure, tear up the integrated plates
and drive them away.
Keywords: inner-core’s deviation, plate novement, mantle convec-
tion, new model of global movement.
It has been a geoscience controversy for almost a
century how the Earth’s engine drives the lithosphere to
[
1ü6]
move
. Morgan, Sleep, Anderson, Larson, Stein and
Hoffman et al. proposed, with new evidence from geology,
geochemistry and geophysics, that the plate motion is
mainly triggered by the upwelling of a mantle plume
[
7ü15]
originating from the Core-Mantle boundary
(CMB).
But it is still a puzzle what and how a plume, fixed pro-
tractedly in Earth’s spheroidal coordinates, originates,
upwells intensifies and then decays. Is the distribution of
an active plume destined or random? Moreover, the cau-
sality between the inner-core and the plate motion remains
unclear, though the outer-core is regarded as the heat
[
16ü19]
source of the mantle plume
. In other words, in the
The variable changes in the global motion can be
shown in fig. 2.
models, the inner-core is excrescent and the outer-core
does not necessarily have to be liquid for plate movement.
Thus, we speculate the currently adopted concept that
lithospherical plates are only pushed to-and-fro passively.
Considering the change of state in the Earth’s inner
spheres and thermo-convection in the outer-core, we hy-
pothesize that inner-core’s deviation and mass migration
First, the deviation of the inner-core can be induced
by any of the following factors: (1) The primordial in-
ner-core does not have to be in the center of the Earth; (2)
the material distribution in the interior of the Earth could
be modulated asymmetrically during deep thermal proc-
esses; (3) the impact of an asteroid; (4) the possibilities of
Chinese Science Bulletin Vol. 46 No. 19 October 2001
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PAPER
ejections of the moon from the Earth; (5) the unbalance of
mass distribution between two hemispheres caused by
plate movement as well as by plume upwelling. Secondly,
the 4-stroke Earth engine shown in fig. 2 may start at any
step of the strokes without any preferred condition. The
characteristics make it more possible for the core, mantle
and crust couple to form a perfect and self-contained dy-
namic system. It is obvious that plate convergence, ac-
cording to the model, would induce another plate diver-
gence, or vice versa. This suggests that lithospheric plate
movements can be predicted qualitatively because they
can periodically repeat.
between the equivalent barycentres of them shown in fig.
3. Obviously, the change of mass distribution between two
hemispheres can disturb the stability of the solid in-
ner-core within the liquid outer-core. According to New-
ton’s law and Stocks theorem, we can get the motion
equation of the inner-core:
2
d x
§
¨
©
m m
1
m m
2
·
¸
¸
¹
ic
ic
¨
, (1)
mic
F ꢀF c f ꢀ
ꢁ
ꢀ4ʌ a Kv
0
2
2
2
dt
r
r2
1
§
m m
1
m m ·
2 ic
ic
where F f ¨ꢀ
¸ is the sum of gravita-
ꢁ
¨
2
2
¸
r
r2
©
1
¹
tion between two hemispheres (except for inner-core) and
the inner-core, it is also the driving force of the deviation
activation of
Deviation of
mantle plume
inner-core
of the inner-core. F c 4 ʌ a Kv is the viscous damping
0
0
of the motion induced by the outer-core’s viscosity, a is
the radius of the inner-core, f is gravitational constant, K
is the coefficient of viscosity of the outer-core,
Plate union
Torn & Reborn
of lithosphere
dx / dt is the motion velocity of the inner-core, m
and r have the same meaning as in fig. 3.
In the state of equilibrium, from eq. (1), we get
1
,
v
m
to new locus
2
, mic, r
1
2
Fig. 2. Procedure of the inter-coupled global motion.
r
m2
1
Compared with the plume model (in our hypothesis),
SCM takes into account two additional factors: the devia-
tion of the inner core and the migration of global mass
distribution. These two factors should not be neglected on
geological timescale. The two additional factors and the
confirmed factorüüplume upwelling, will be sufficed to
maintain the lithosphere moving periodically and end-
lessly. The upwelling plume is the driving mechenism to
lithospheric movement; the convergence-divergence of
lithospherical plates directs the inner-core’s deviation; the
deviation of the inner-core determines where the plume(s)
will activate. The only question is: can plate movement
cause the deviation of the inner-core and can the deviation
of the inner-core activate the plume?
.
(2)
r2
m1
Then and only then
m1 m2
,
r
r2
, the inner-core will
1
keep its position in the center of the Earth, or it will in-
evitably be off-centered. In certainty, because the plume
upwelling and plate movement are induced by the in-
ner-core’s deviation, sometimes the value of m
2
larger than that of m and sometimes not. Allow the in-
1
has to be
ner-core to migrate between the two hemispheres. When
the inner-core deviates, F Ą, according to eq. (1), can only
make the motion of the inner-core slow down, but it can-
not stop the migration of the inner core to its new equilib-
rium position. Thus the lithospheric plate movement
and/or plume upwelling could cause the deviation of the
inner-core.
It must be emphasized that the deviation is distinct
from but can be coupled by the differential rotational of
the inner core induced by the magnetic coupling
The solid inner-core is suspended within the liquid
outer-core, the crust and the mantle will affect the in-
ner-core (only) by gravitation. To illustrate this, a
1-dimensional motive coordinate system was set up,
showing the Earth divided into two hemispheres (fig. 3).
[
24ü26]
.
Respectively, the two motions within the inner core are
influenced by different causes and are characterized by
different timescales.
[
9]
Larson et al. suggest that the heat, from the melt
iron in the outer-core, penetrates CMB and is absorbed by
Fig. 3. Sketch of the gravation between the two hemispheres and the
inner core. a, Inner-core; b, outer-core; m
hemisphere except for inner-core; mic, equivalent barycentre of in-
ner-core; m , equivalent barycentre of the other hemisphere except for
inner-core, r , barycentric distance between inner-core and a hemisphere;
, barycentric distance between inner-core and the other hemisphere; x,
1
, equivalent barycentre of a
silicate rocks in the bottom of mantle within 100ü200 km
above the boundary. Having accumulated enough heat
energy, the rocks will over-heat and become much lighter.
This will traverse the mantle and terminate at the base of
the lithosphere as a hotspot. This process will improve the
efficiency of the heat conduction between the core and the
mantle in the hemisphere which is closer to the inner-core.
Especially, when there is thermal-convection in the liquid
outer-core, a little deviation of the inner-core can give rise
2
1
r
2
the symmetric axis of the Earth’s mass.
The single axis x is the symmetric axis of the Earth’s
mass and towable with the mass change between the two
hemispheres. The gravitation between two hemispheres
and the inner-core can be simplified as the interaction
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Chinese Science Bulletin Vol. 46 No. 19 October 2001

R
to changes in heat conduction, because Reynords number
4
process of Pangea’s cauterizing, splitting, breaking up and
drifting soon after the congregation of it occurred.
Ra gk'Td (d is the thickness of the convection layer),
After this congregation event, driven by the SCM
mechanism, the centroid of the Earthüthe inner-coreü
the Earth’s thermal center continued their migration proc-
esses sequentially. This can be confirmed through the
global mantle plume motion and plate distribution’s varia-
tion: in the mid-Cretaceous, an excessive large-scale sea
4
i.e. R vd . That is to say, the lesser the R
a
is, the
a
stronger the thermal convection will be. Thus, when the
inner-core deviates towards one hemisphere, the mantle
bottom in this hemisphere is more intensively cauterized,
causing a plume raise and thrust into the base of litho-
sphere, then the lithosphere may be torn up and pushed
[
9]
basaltic eruption occurred in the sea floor of Atlantic ,
which showed the trend of the mantle plume’s migration
westward (fig. 4(c)). This is because in the upper period of
Pangea’s aggregation, continental lithospheric plates fo-
cused mainly on the west side of it. Thus, after splitting
Pangea again, the mantle plume beneath Siberia pushed
most of the split plates westward, which led to the west-
ward deviation of the inner-core. As fig. 4(c) illustrates,
the mantle plume motion in Cretaceous split the Atlantic,
causing most continental plates drifting eastward again.
1 2
away. This will overturn the ratio m Ήm to dampen the
heat of the mantle plume in this side, while a new plume
in opposite side is in gestation. Thus, the deviation of the
inner-core can control the evolution of the plume.
In summary, there is certainly a coupling mechanism
in the 4-stroke motion, a global motion like this is more
reasonable. Therefore, it is called the 4-stroke-cycle
model Spherical Coupling Model and this global motion,
Spherical Coupling Motion. They both can be abbreviated
to SCM.
[
27]
While the modern mantle plume distribution pattern
fig. 4(d)) centered on South Africa indicates that the
(
2 The drift of Pangea and migration of mantle plume:
trace of inner-core’s deviation
global heat center has migrated from west to east again,
which should be the continuation of the plates’ eastward
migration led by the mantle plume motion in upper Cre-
taceous. According to this, we can qualitatively conclude
the migration trace of the inner-core since Carboniferous
may be from the Southern Hemisphere of modern geo-
graphy pattern (the corresponding mantle plume motion
centers in the high latitude area in the Southern Hemi-
sphere) to the Northern Hemisphere (the corresponding
mantle plume motion center migrated beneath the Siberia
plate with it), then deviated toward southwest, and finally
formed a rather active supermantle plume group in the sea
Supercontinents, the recondite events in the geologi-
cal history, may have occurred more than once. Their
occurrence needs an assemblage center of plates which is
hard to interpret by the existing mantle convection or the
mantle plume model. While, SCM can present a qualita-
tive interpretation to it, i.e. the motion of mantle plume(s)
controlled by the inner-core’s deviation, should be hemi-
spheric (differential function takes hemisphere as a spatial
scale). Therefore, during peak periods of its motion, the
mantle plume motion of one hemisphere would be more
intense than that of the other (hemisphere). Thus, the hot-
ter hemisphere could push massive (neonatal and split)
lithospheric plates to the other hemisphere, which leads to
their convergence and finally the formation of supercon-
tinent. Taking Pangea in the transition period of Pa-
[9]
floor of the Atlantic Ocean in mid-Cretaceous . Hence-
forth, the inner-core migrated from west to southeast
again, causing the Earth’s heat center migrated beneath
South Africa nowadays. However, the result of these man-
tle plume motion and the plates motion has not changed
the condition that the Earth’s centroid mainly has rested in
the Northern Hemisphere since Pangea’s assemblage and
split. Since there is a lag between the mantle plume’s mo-
tion center’s migration, together with analysis according
to eq. (1), the deviation of the inner-core was actually
surge to-and-fro around the Earth’s centroid. So, today’s
inner-core should approach the Earth’s centroid, i.e. mi-
grating toward the Northern Hemisphere (fig. 4(d)).
[
28ü30]
leo-Mesozoic
layer coupling process as follows (fig. 4 and refer to fig.
): from about 300 Ma and before, the mass of litho-
as an example, we can deduce the then
1
spheric plates concentrated more in the Southern Hemi-
sphere (fig. 4(a)). The position of the inner-core deviated
accordingly, which led to gradual formation of the South-
ern Hemisphere’s heat center, and the activation of mantle
plume motion. The later cauterized and separated Gand-
wana, which congregated in the Southern Hemisphere,
pushed the cracked plates to the Northern Hemisphere,
and in the transition of Paleo-Mesozoic, caused the largest
supercontinental aggregation in the geological history (fig.
3
Discussion
From the inner-core to the lithosphere, Earth’s inte-
rior structure possesses a symmetrical solid-liquid-solid-
melt-solid pattern (30ü32) shown as fig. 1. Within the
components of the structure, the lithosphere and the in-
ner-core play the protagonists in the operation of SCM;
the mantle is the heat passage and momentum source; the
liquid outer-core and the melt asthenosphere provide
braced framing for the deviation of the inner-core and
4(b)). The large-scale basaltic activation occurring in Si-
beria about 250 Ma was the result of new activities of the
mantle plumes within the Northern Hemisphere, which
was led by the deviation of the inner-core towards the
Northern Hemisphere in the late period of the congrega-
tion of lithospheric plates, thus triggering the motion
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PAPER
Fig. 4. Position of mantle plumes and Migration path of inner-core. (a) The position of mantle plumes in 306 Ma; (b) The position of man-
tle plumes in 237 Ma; (c) The position of mantle plumes in 69 Ma; Where the ellipses show the positions of mantle plumes. (d) the position
of inner-core from 306 Ma to the present. Where the circles show the positions of inner core, the arc-arrows show migration paths of in-
ner-core. 1, The position of inner-core in 306 Ma; 2, the position of inner-core in 237 Ma; 3, the position of inner-core in 69 Ma; 4, the posi-
tion of inner-core at recent (base map after Scotese, 1997).
movement of the lithosphere, respectively. Thus, to the
earth’s present components, the Earth’s movement, which
is in progress relied upon SCM, needs no more extrinsic
complements and lacks none of intrinsic components.
With respect of this, SCM makes the Earth as a self- con-
tained and self-consistent global dynamic system.
As an integrate and self-consistent global dynamical
system, SCM also provides a kind of movement style
which is the simplest but the most effective according to
the Earth’s present structure and physical condition. Its
feedback mechanism, self-organization and self-stability
feature maintain plates’ or even between core-mantle’s
movement and evolution for a long time, and illustrate
various complex but definite behavior, i.e. plates’ peri-
odical change direction movement, Pangea’s periodical
assemblage and split, the migration of mantle plumes, etc.
What is more, as to the geomagnetism field’s production
and maintenance, the influence factors in the global
change process and its control style, and such puzzles, the
existing coupling relationship between these layers may
suggest us to relate them with the above special deep
background and seek more reasonable interpretations.
Compared with the existing theoretical model, SCM
has predictable stages or periodicity and self-consistent
physically. From the formation of the solid inner-core to
the ultimate solidification of the liquid outer-core, this
layer coupling movement including plate movement con-
tinues depending on the Earth’s layer structure and inner
energies. Factors outside the Earth can disturb or interrupt
this process, but cannot alter its lasting motion law. All
these convinced us that the Earth is a perfect machine
produced according to nature’s simplest principle; the
layer coupling and the plates’ movement triggered by it
Based on the mantle convection and the mantle
plume model, together with the consideration of probabil-
ity of the deviation of the inner-core and the plates drift
effects, this note indicates a global dynamical model
ground on the layer coupling process. This model includes
the reasonable parts of the original mantle thermal con-
vection model and the mantle plume model, at the same
time, it overcomes their partial existing difficultyüü
besides the interpretation about the problem of Pangea in
the last section, as to the problem of how the mantle
plume produces, intensify and decay, SCM can give a
qualitative interpretation or even forecast by the influence
of the inner-core’s deviation and lithospheric plates’ as-
semblage and split. Thus, like plate movements, the evo-
lution of mantle plumes is an essential part in the layer
coupling process. Its production, intensification and de-
cline therefore have a reasonable foundation in geophysics:
From this, the mantle plume must exist relative to the
fixed Earth coordinate in a certain period, but at other
[
9ü14,27]
times, as mentioned above
, its position and quantity
would vary accordingly and cause the plate movement.
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R
mafic potassic magmas; key to plume-lithosphere interactions and
continental flood-basalt genesis, Earth Planet. Sci. Lett., 1996,
carry out just like this.
Acknowledgements We thank Prof. R. Mason for conducive discus-
sion. We also thank Kimberly Le for revising this note. This work was
supposed by the National Natural Science Foundation of China (Grant
No. 49632070) and the Ministry of Land and Resources of China.
1
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(Received March 27, 2001)
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