20000106 by girlbanks

VIEWS: 2 PAGES: 10

									Vol. 7 No. 1
Mar. 2000
Earth Science Frontiers (China University of Geosciences, Beijing)
2000 ^ 3 n
A NEW MODEL OF THE EARTH'S
ISOSTASY IN GEOPHYSICS
AND GEOTECTON ICS
Konstantin F. Tyapkin
(The National Mining University of Ukraine, Dniepropetrovsk, Ukraine, 320027)
+ffl*H&-9:P312	1005 - 2321(2000)01 "0069 - 10
0 Introduction
The form of our planet (geoid) is very close to the equilibrium figure of rotating liquid of
equal mass (spheroid), included in different envelopes of the Earth. The spheroid or theoretical
geoid is near to or differs only a little from a sphere, and is characterized by the compression co¬
efficient of the Earth, e = 1/298.25, depending on the angular speed and internal distribution
of masses in the Earth.
The hypothesis on the equilibrium state of the Earth (isostasy) was first presented in the
middle of the XIX century as a result of studying the form of our planet by using geodesist
methods. The essence of the hypothesis was described by Lustich( 1967)^1 and others. Here
let us consider only the main points, which are necessary for our further exposition.
Initially, according to the dominated ideas about the"swimming"of the crust in the mag¬
ma, the study on equilibrium condition of the Earth was substituted by the study on equilibrium
condition of the crust. However, it did not take into account the equilibrium of the whole crust
but only of the lithosphere. In the latter case the underlying magma was considered as the hy¬
pothetical asthenosphere. Under the isostatic equilibrium it is understood the condition of the
crust (lithosphere) lying on the substratum as if it was swimming according to the
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2000,7(1)
Archimedean law (Lustich, 1967)"'. One consequence of such a preposition is the equality of
pressure due to the above-lying masses on a surface in substratum named the surface of compen¬
sation. The main (but not the only) method to study the isostatic state of the crust was and
rests the gravitational one. In the process of the development of the conception of isostasy for
the qualitative appreciation of the equilibrium state, researchers used different physical and geo¬
logical models (Airy, 1855r2j; Pratt, 1860)[3]. The models are based upon the preposition that
the distribution of masses in the crust and its equilibrium are determined only by the topography
of the Earth's surface.
Recently Golizdra( 1972)"^has developed the conception of isostasy of the plain regions
from the equilibrium state of the crust by using not only topographic masses but also the hetero¬
geneity in the upper parts of the crust as compensation factors. In a platform region the latter
factor is of decisive importance. In particular, Golizdra (1972)[4] has shown that in the condi¬
tion of the smooth topography of the Ukrainian shield, the surface heterogeneity of the upper
part of the crust produces significant amplitudes of changes in gravitational field, and the condi¬
tion of the crust in general is close to isostatic state. Therefore the topographic masses may not
be the only factor determining the isostatic state of the crust, and may not be considered as the
main one; as it will be shown later. Many attempts were made to use the conception of isostasy
as the base for geotectonic hypothesis of the Earth's development. The detailed review of the
early prepositions was made by Lustich (1967)"^. Now it is possible to state the following:
notwithstanding the apparently natural interconnection between the redistribution of masses in
the lithosphere and tectonics, the concrete role of isostatic forces in the formation of tectonic
structures is not established. The contemporaneous movement of the crust observed now in dif¬
ferent regions tends to reach the equilibrium state at the Earth's surface.
The conception under consideration of the isostasy of the crust (lithosphere) regards the
rotational regime of the Earth as constant and the corresponding figure of equilibrium as un¬
changeable. It was some of the developments of the conceptions of isostasy reflected the state of
knowledge on the Earth's structure at that time. Now a lot of data has been accumulated and
the conclusions from them contradicts to the main points of the conception under consideration.
The necessity for their revision is clear. So let us review some of them.
First thesis according to the contemporary ideas about the structure of the Earth, it is not
logic to substitute the equilibrium state of the earth by the equilibrium state of the crust. It is
an arbitrary separation of one part of the planet from the rest parts of it, which in fact are
closely connected. In order to study the equilibrium state of the Earth, it has to be considered
as a single system.
The acceptance of the first thesis leads to the adoption of the second one. When some par¬
ticular geodetic problems were solved in limited territories or specific locations of particular geo¬
logical structure, the neglect of the change of the rotational regime of the Earth was in some
measure founded. But by studying the equilibrium state of the planet as a whole determined by
the rotational regime (the situation of its axis of rotation, angular speed and so on), it is not ad¬
missible not to take into account of the change of this regime. As the conservation of the equi¬
librium state of the planet, corresponding to its constantly changing rotational regime is possible
only by some redistribution of masses in it(tectonics), so this thesis must be attributed to the
Earth's tectogenesis.
1 A new model of isostasy
I^et us introduce the concept of equilibrium state of the Earth as a whole and giving it the
name of geoisostasy. It must correspond to such a condition of the Earth which it should take if
70
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2000, 7(1)
the substratum composing it in each envelope became liquid and did not mix. In that case our
planet could be characterized by an aggregate of level surfaces being a system of spheroids with
constantly diminishing coefficients
1
of compression, in the formation
of which have taken part in the
masses of all the Earth, including
the hydrosphere and the atmo¬
sphere. For practical purposes of
essential importance is the
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spheroid closely with the geoid
(Tyapkin, 1984)^.
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Let us consider the conditions
for attaining to the geoisosuisy.
As the first condition of the
Earth's equilibrium, equivalent to
the Pascal' s law, used in classical
models of isostasy of the crust (lithosphere) with the parameter e being small, we can take, the
weights of the sectors cut by the equal central solid angles A/3 (Fig. la). Quantitatively this
condition corresponds to the integral expression(Makarenko, 1983)^.
a(r)g(r)2dr - const
jo
where a (r)—the law of the density's change in the limits of the sector of the Earth; g
(r) acceleration of free fall at the points in the sector on the distance r from the centre of the
earth.
b
Fig. 1 To the determination of the model of geoisostasy
SI
1. The geoid; 2. The spheroid
■»
aa
(i)
The expression(l)can be given in form of three integrals
I\ + Ii + h = const
(2)
I\ = A^2 V(r)g(r)r2dr
I2 ~ A/3 f V(r)g(r)r2dr,
^1
where
cr(r)g(r)r2dr.
h-
Rt
Ri—the internal radius of the mantle, Re—its external radius. Based on the belief that the
external nucleus is in quasi-liquid state (Fig. la), the quantity I\ may be considered as con¬
stant. By solving the problem about the equilibrium state of the mantle one can neglect the val¬
ues of the integral 13, characterizing the atmospheric pressure on the earth's surface because it
is very small comparing to ^.Then the equation (1) takes the form.
= const
f V(r)g(r)r2dr
Jr.
aa
(3)
At the second condition for attaining the geoisostasy it is necessary that the potential in ev¬
ery point on the Earth is equal to its theoretical value corresponding to the introduced determi¬
nation of geoisostasy. The implementation of this condition is convenient to check on the
Earth's surface and instead of the values of potential to use the marks of the geoid (Rg) and
spheroid (Rs). The difference between the marks (f) can be taken as a criterion for the Earth'
s equilibrium (Fig. lb). In particular, according to the introduced determination of geoisostasy
the geoid may be considered to be in a state of equilibrium if it does not differ from the reference
ellipsoid; i.e. when the following equation is fulfilled
(4)
r = Rg - Rs = 0
— 71
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2000,7(1)
In fact, if the geoid were made of liquid; i. e. the interconnection between its solid parts
becomes feeble, it would take the figure of equilibrium and that is the spheroid. But as there
are some deviations of the geoid from the spheroid caused by heterogeneity of the Earth's struc¬
ture, there must be some stresses trying to equalize these heterogeneity, to bring them in corre¬
spondence with the figure of equilibrium. The law of distribution of the stresses will be deter¬
mined by the function of the geoid's deviations from the corresponding spheroid.
Based on the variation principle of minimal action, Klushin^ has demonstrated that for
rather large sectors of the earth the local changes of their radii have to be accompanied by verti¬
cal redistribution of density. The physical law regulating the redistribution of density in the
Earth's sectors, cut down by solid angles A{2 is the law of conservation of the angular momen-
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180°
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180°
270°
90°
Fig,2 The map of geoid's heights
(Wagner, 1977181)
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Contour interval 10 m
turn. In its expression enters the fourth degree of the distance of masses from the center of the
planet. So the most important are the values of masses for the geospheres removed from the
center with more than 0.8 of the earth's radius. In particular the moment of the earth's mo¬
mentum is nearly on a half determined by the masses in the interval of depths from 0 to 700~
1 000 km corresponding to the tectonosphere.
In order to understand the contemporaneous state of the Earth's equilibrium, let us take a
look at the map of the geoid's heights (Fig. 2). Judged by relatively small deviations of the
geoid from the corresponding spheroid (( ~ 160 + 78)m), the conclusion that the earth is essen¬
tially equalized is confirmed. A complete absence of correlation of the geoid's heights with the
situation of the continents and the oceans is observed. And this means that topographic masses
not be taken to determine the isostatic state of the Earth.
can
72
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2000,7(1)
2 The problem of isostasy in applied geophysics
In applied geophysics the classical models of isostasy of the crust (lithosphere) can be used
at least in two aspects: (l)to calculate the so-called isostatic anomalies of gravitational field,
which are in some measure the criteria for the appreciation of the state of equilibrium of the
crust; (2) to simulate vertical sections of the upper layers of the crust on the evidence of the data
of deep seismic soundings and gravity as additional conditions limiting the ambiguity of solution
of the inverse problem.
The calculation of isostatic anomalies of gravitational field has some sense for solving
geodetic problems. But their use in applied geophysics is more than doubtful. The isostatic
anomalies calculated with the models of Airy(1855)'2' and Pratt(1860are practically the
same. But it is the nature of isostatic compensation that is the object of investigations by solving
the most of the problems with the aid of gravity prospecting.
Artemjev^9 "analyzed the isostatic anomalies of gravity field of the southern parts of the
USSR for determination of the nature of isostatic compensation of the crust in the limits of
structures with different geological history. He analyzed two groups of compensating factors:
the change of the Earth's thickness and the influence of the crust's and undercrust's density
heterogeneity.
In his work the author came to the conclusion that the structures with different geological
history have different models of isostatic compensation. For our aims it is important to stress
that Artemjev (1984)^ has put under doubt the assertion about a direct interconnection be¬
tween the disturbances of isostasy of the crust, and contemporaneous tectonic activity of some
regions. He affirmed, in particular, that the ideas about the existence of some large distur¬
bances of isostatic equilibrium in the regions of contemporaneous mountain formation are in
many cases erroneous, as being based on the interpretation of isostatic gravity anomalies ob¬
tained with the aid of isostatic models coinciding badly with the existing data concerning the
density heterogeneity of the crust and the undercrust layer. We find this affirmation to be very
important. It can be used as a base for solving the problem about the advisability of calculating
and following use in applied geophysics of the maps of gravity anomalies in isostatic reduction.
If the anomalies calculated with the aid of the most simple isostatic models can not be used for
explaining the equilibrium state of some parts of the crust under study, two approaches are pos¬
sible: either to make the isostatical models more complex or to make the combined interpreta¬
tion of gravitational field taking into account all the existing geological and geophysical data
without introducing previously isostatic reductions.
Theoretically both approaches are of equal value. But as not all the regions are studied with
the same measures, some lack sufficient data for using more complex isostatic models. So the
second approach is preferable; i. e. the combined interpretation of geological and geophysical da¬
ta for the regions (or profiles) where the data are sufficient. However, in this case the con¬
struction of the maps of isostatic anomalies for the whole territories loses its sense.
The classical isostatic models are used for taking into account the weights of the columns
with the same base X and vertical thickness from the surface of the Earth (h) till the accepted
depth of compensation (M). The expression for it has the form
const,
CM
ff(z)g(z)dz =
h
(5)
where o(z)—the density of the column of rocks,#(2)—gravity acceleration in the inter¬
val from h to M. Practically, neglecting the change of AgCr) in this interval the weights of
— 73 —
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2000, 7(1)
the columns are substituted by their masses
M
a(z)dz = const
The expression (6) is used to estimate the trustworthiness of vertical sections of the crust
and upper mantle on data of gravity and seismic observations. For our aims it is important to
notice that the choice of either of surfaces of compensation (the foot of the crust, the top of the
asthenosphere or any conditional more profound boundary) presupposes automatically the ab¬
sence of any heterogeneity in the mantle below this surface. The known results of interpretation
of regional anomalies testify to the contrary.
In accordance with the new proposed model of geoisostasy, the equations (5) and (6) have
to be correct under the condition that a surface of compensation is taken the boundary nucleus-
mantle. In all the other cases these equations can be considered as only approximate ones.
The above stated can give the impression that by bringing the surface of compensation to
the lower boundary of the mantle we shall miss a simple and convenient criterion to control the
trustworthiness of the construction of vertical sections of the crust and upper mantle according
to geophysical data. But it is the case. The expression (5) and (6) can not be used practically
as a criterion, because with any arbitrary chosen surface of compensation they can be fulfilled
only approximately, and the degree of approaching depends on an unknown anomalous distribu¬
tion of masses in the Earth and so can not be given beforehand.
A direct substitution of the criterion discussed earlier in the new model of the Earth' s
isostasy is, regretfully, impossible to propose now. As an indirect substitute can use the values
of anomalies of the heights of the geoid £ for the calculation of anomalous distribution of
inside the earth and its consequent comparison with the distribution of masses found by the data
of other geophysical methods.
In the literature there are some successful attempts to use the values (of potential anoma-
lies)alone or in combination with other components of gravitational field for interpreting region¬
al anomalies. The experience of such investigations is still limited but it is clear that the inde¬
pendent use of anomalies £ opens a prospect for obtaining the independent distribution of
anomalous masses inside the Earth.
(6)
masses
3 Geoisostasy in geotectonics
The new rotational hypothesis of structure formation(Tyapkin, 1998)[10] is based upon the
conception of geoisostasy. The essence of it is in the following.
The form of the Earth and the distribution of masses inside it correspond in the first ap¬
proach to its rotational regime. The interaction of the Earth with the physical fields surround¬
ing it changes the rotational regime and in particular leads to a change of the spacial position of
the Earth in relation to its axis of rotation. The established equilibrium is broken. Some stress¬
es appear to reestablish the equilibrium corresponding to the new rotational regime. Under the
influence of these stresses a redistribution of masses occurs, which minimize these stresses, as
well as the formation of structures and related geological processes in the upper envelope of the
Earth called the tectonosphere.
In the formation of the structures two groups of tectonic processes take part. The process¬
es of the first group appear under the influence of discharge of planetary stresses in the upper
envelopes of the Earth and are seen essentially in the displacements of large blocks of these en¬
velopes, the new spacial situation of which generally satisfies the new figure of equilibrium. So
the regional compensation is attained. The processes of the second group are closely related to
74
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2000,7(1)
those of the first one and in some sense are reactions on them. This group can be attributed to
the exogene processes of denudation-sedimentation type as well as the endogenic ones.
It is important to underline that
both groups of tectonic processes
taking part in structure formation oc¬
cur under the influence of geoisostatic
forces trying to keep the planet to equi¬
librium and the source of energy for
tectogenesis of the earth is its interac¬
tion with the surrounding physical
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fields.
T
As we have taken the deviations
of the geoid from the spheroid for the
criterion of the Earth' s equilibrium,
we have to notice such a regularity
(Fig.2): on the map of the heights of
the geoid there are two pairs of nega¬
tive and positive anomalies with the
amplitude values of the geoid's heights
of -100 m and + 78 m. Their spacial
situation is such that in the first ap¬
proach it corresponds to the deviations
of the heights of the geoid with the ho¬
mogeneous upper envelopes from the heights of the spheroid of the same weight(Fig. 3)as a re¬
sult of reorientation of the Earth in relation to its axis of rotation(Tyapkin, 1998)'10^. The cor¬
respondence of regular deviations of the geoid's surface from the spheroid's can serve a good
confirmation of the conclusion that the reorientation of the earth in relation to its axis of rota¬
tion can be considered as one of the main factors determining the regularity of tectonic deforma¬
tions of the Earth's ellipsoid.
From these considerations it is clear that the direction of geological development of the up¬
per envelopes of the Earth, and in particular of the tectonosphere, has to be such that this" in¬
creases" the weight of the region with negative values of the heights of the geoid and" decreases"
that of the regions with positive values of them. Let us consider some possible physical and geo¬
logical processes, the participation of which from our point of view is the most probable for at¬
taining geoisostasy.
The increase in weight of some regions of the earth can be resulted from the following pro¬
cesses: the elevation of the blocks of the Earth's crust leading to the elevation of the height of
the Earth' s surface, covering with ice of some parts of this surface, filling the submerged parts
of the geoid with water, the" impregnation" of the granite envelope with more dense basaltoids
and hyperbasites(dyke-formation), formation of traps (platobasalts), displacements of the Mo-
ho-discontinuity(M) upwards as a result of phase transition between type basal and eclogite.
The discharge of some regions of the Earth originates from the following processes: the
sinking of blocks of the Earth's crust leading to some decrease of the geoid's marks; the de¬
nudation of projectioning blocks of the Earth' s crust and the melding of ice on them formed in
the previous epochs; the filling of the upper parts of the Earth's crust with light magmatic for¬
mations of acid composition; the displacement of the boundary downwards as a result of phase
transition of the matter in the mantle between basalt and eclogite.
The main particularity of these and some other processes leading to the equilibrium state of
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Fig. 3 The schema of deviation of the geoid from the
spheroid as a result of reorientation of the earth in
relation to its axis of rotation
75
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2000,7(1)
the Earth is the close interaction of most of them. I^t us take a look at it with some examples.
Example 1. The formation of the structures of geosynclinal type from the positions of the
new rotational hypothesis of structure formation looks in such a way (Tyapkin, 1998). In the e¬
poch of tectonic activation the discharge
of planetary stresses appearing as a result
of reorientation of the earth in the rela-
\ . \|
tion to its axis of rotation leads, as it was
demonstrated, to such relative displace¬
ment of the blocks of the earth' s crust
(Fig. 4) when the new condition of equi¬
librium is roughly satisfied. The compen¬
sation of a further displacement of the
blocks in the same direction is made in
the limits of the elevated block by the
processes of denudation, and of the sink¬
ing one by the accumulation of sediments.
In addition the equilibrium of the sinking
block is attained as well by a layer of wa-
X
. V,
1
Fig. 4 The schema of formation of the structures of
geosynclinal type on the boundary of two groups of blocks
1—the block of the basement! 2—the ophiolite formation; 3—the ter and magmatic formations of basic and
layer of water and terrigenous sediments; 4—horizontal stresses in
the crust
ultra-basic composition (ophiolite forma¬
tion) . The redistribution of masses in the
upper parts of the crust disturbs the attained pressure in the region of its lower boundary. It
may serve as a cause of phase transformation of the matter of the type basalt eclogite on the
boundary crust-mantle, regulating the situation of the Moho discontinuity.
Example 2. The formation of the Earth' s crust of oceanic type occurs evidently on a
schema very close to that described in the example 1. The oceans are the merged blocks of the
crust filled with water. The lowering of the level surface produced by the sinking of these
blocks is partly compensated by the mass of the water and the rest-by more dense magmatic for¬
mation of mainly basic composition.
The mechanism of genesis of magmatic melding in the inner parts has been described
(Tyapkin, 1998), and the main factor regulating the fissure effusions of magmas is their striv¬
ing for attaining the geoisostasy. As a result, the basalt fields in the oceans and their underlying
basement is saturated with dykes and sills.
The described geological processes lead to a change in physical parameters of the upper part
of the Earth's crust of the oceans and, in particular, of the speed of propagation in them of e¬
lastic waves giving some reasons to geophysicists to single out such parts of the crust in a special
type. Let us note that the absence of correlation of the geoid's heights (Fig. 2) with the situa¬
tion of the continents and the oceans puts under doubt the sharp differences of geological partic¬
ularities of the crust, actively used now in the conception of plate tectonics. It looks more likely
that the contemporaneous situation of the continents and the oceans is one of the possible com¬
binations of lowered and merged blocks of the crust that was many times changed in the tecton¬
ic history of the Earth(Tyapkin, 1998).
Example 3. Judging from particularities of geological structure of trap provinces( Makaren-
do, 1984 et al), there are areas of typical "oceanic" crust without water cover. So the schemas
of their formation must be identical. The main factor favorable to the formation of lava covers
and dyke "roots" on the oceans and continents is the smoothing of anomalous/lowered/level
surfaces of the geoid. One of the confirmations of such ideas may be the known facts of exis¬
tence of united basalt fields on the continents and the oceans.
— 76 —
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2000,7(1)
Example 4. I^et us consider the influence of the processes of covering with ice on the equi¬
librium state of the Earth. The covering with ice of some parts of the crust is provoked mainly
by the climatic conditions and is not connected directly with the geological processes in the
Earth. But the covering with ice increases the weight of corresponding blocks of the Earth's
crust; the pressure on the boundary crust-mantle changes, that may quite be the purpose of
transformation of the matter type basalt and eclogite. And the result of these processes, if they
take place, is the displacement of the Moho discontinuity leading to an equilibrium of blocks
covered with ice. It is not possible to exclude some sinking (squeezing) of some blocks of the
Earth's surface covered with ice although we do not dispose of facts confirming this process.
The same should be said about the influence of the ice's melding which from the positions of
geoisostasy is analogous to the process of denudation.
The reaction on it may quite be the deep transformation of matter of the type basalt and
clogite or similar phenomena equalizing the isostatic state of the Earth.
These examples of formation of tectonic structures and transformation of the matter inside
the crust and upper mantle under the influence of the processes regulated by isostatic forces
show us a very close interconnection of these processes.
The relative contribution of each of them in the formation of different geological structures
is not equal. Nevertheless, it does not give a reason by studying isostasy to take any of these
processes or its appearance on the Earth's surface as the only factor regulating the isostatic state
of the Earth(topographic masses, the layers of the Earth's crust, the ice charge etc).
In conclusion, it is appropriate to pose a questions why was it impossible to use the classi¬
cal variant of isostasy to elucidate the tectogenesis of the Earth. Therefore the proposed model of
geoisostasy is the base of the new rotational hypothesis of structure formation permitting to ex¬
plain many known geological regularities. Perhaps the answer to this question has to be looked
for in different approaches to solve the problem of the Earth's isostasy and its tectogenesis. In
particular, the use of isostasy in traditional tectonic conceptions is hindered by the idea of un¬
changeable figure of the Earth's equilibrium, which the isostatic forces have to bring to. So by
attaining the isostasy the process of deformation of the geoid has to stop and the interval forces
of the Earth taken as the source of energy for the tectogenesis can not bring it out of the condi¬
tion of equilibrium.
References:
[ 1 ] Lustich E N. Isostasy and Isostasical Hypophesis (in Russian)[Mj. Moscow; Izd. ANUSSR, 1967.90.
[2]	Airy G B. On the contribution of the effect of the attraction of mountain masses [J ]. Royal Soc London, Philos
Trans, 1855,145:101-104.
[3]	Pratt F H.On the deflection of the plumb line in India, caused by the attraction of the Himalaya mountains and of the
elevated regions beyond, and its modification by the compensation effect of a deficiency of matter below the mountain
mass[J].Royal Sbr London, Philos Trans, 1860,149:745-778.
[4]	Golizdra G YA. About the isostatic equilibrium of the earth's crust of the Ukrainian shield [J ]. Hseecmust AH.
<Pu3um 3eMAu(in Russian), Moscow, 1972,10:44—45.
[5]	Tyapkin K F.A new isostatic model of the Earth[j].&o/Aysir Trans (Budapest), 1984,30(1): 3—10.
[6]	Makarendo G F. Basalt Fields of the Earth (in Russian) [M]. Moscow: Nedra, 1983.148.
[7]	Klushin J G. The interaction of tectonical movements and magmatism of the earth on the base of variation principle of
minimal action(in Russian) [R]. Reports of Leningrad University. Leningrad, 1963,46(2):33—50.
[8]	Wagner C A, Lerch F 1, Brownd I E, et al. Improvement in the geopotential derived from satelite and surface data
(GEM 7 and 8)[J]. Geophysical Res, 1977,82(5):901~904.
[9]	Artemjev M E. Isostatic com[>ensation of orogene regions (in Russian) [R]. Theses of Report. XXVII International
Geological Congress, Moscow, 1984(4) • 19—21.
[ 10 j Tyapkin K F. The Physics of the Earth (in Russian)[Mj. Kiev; Visisha Shkova, 1998.312.
e-
— 77 —
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2000.7(1)
A NEW MODEL OF THE EARTH'S ISOSTASY
IN GEOPHYSICS AND GEOTECTONICS
Konstantin F. Tyapkin
(The National Mining University of Ukraine, Dniepropetrovsk 320027.Ukraine)
Abstract'.Some classical models of isostasy are discussed. It has shown that they can be used
neither for appreciation of equilibrium state of the earth, nor for the explanation of tectogene-
sis. A new model of isostasy is introduced corresponding to a certain rotational regime of the
earth. As a criterion of the earth' s equilibrium is taken the deviation of the geoid from the
spheroid. The earth is considered to be balanced in points where this deviation is approaching to
zero. The difference of the marks between the geoid and the spheroid is determined by the di¬
rection of geological processes in upper envelopes of the earth. The proposed model of geoisosta-
sy is the base of the new rotational hypothesis of structure formation in the crust.
Key wordsigeoisostasy; new model; geophysics; geotectonics; rotational hypothesis of structure
formation
CLC number:P312 Document code: A Article 1D:1005-2321(2000)01-0069-10
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