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The investigation of elastig and absorption properties of rocks at high pressures and temperatures
Tectonophysics - Elsevier Publishing Company, Amsterdam Printed in The Netherlands
THE ~ESTIGATT~N OF ELASTIC AND ABSORPTION PROPERTIES ROCKS AT HIGH PRRSSURES AND TEMPERATURES
211
OF
M.P. VOLAROVICH Institute of Earth Physics, Academy of Sciences, Moscow (U.S.S.R.) (Reeetved April 10, 1964)
SUMMARY
The
task of i~ve~~i~~io~s of the physical properties of rocks is briefly given in connection with the problem of the structure df the earth’s crust and upper mantle structure. The results of the measurements at the pressures to 4 kbar, the velocities of elastic waves and absorption ratios af igneous and metamorphic rock spe$lmens are described. The results of investigations of electrical properties of rocks are considered at the pressures to 50 kbar at high temperatures. Certain general conclusions of the experimental data obtained are made. INTRODUCTION
As is known during the fnternatlonal Geophysical Year 1957-1958, vast investigatioss were carried out in the domain of earth physics that led to a number of important and interesting conclusions. In recent years problems of earth physics have attracted great attention in connection with cosmic investigations. Science comes close to the stu&y of the physic6 of planets, but the study of the planets’ structures, and the physical processes in them, requires the basis of knowledge of the earth’s structure and the properties of the earth’s matter. However, knowledge of the structure, and particulariy of the compound of various fayers of our planet, is still too schematic and approximate. It should be added also that in many branches of geophysics further advances have become rather difficult without laboratory data concerning the physical properties of the matter of the earth’s inner layers, obtained under the thermodynamic conditions e&sting in the earth’s interior. A number of papers (Volarovich, I960a, 19Qa,b) indicate what types of matter must be ~vestigated, and under which pressures and temperatures and by which methods, for the purpose of studying the earth’s crust, mantle, and core. For studying the earth‘s crust and the uppermost manSle, the properties of rocks and minerals must be investigated at temperatures of hundreds of degrees under pressure intervals from atmospheric to 5-16 kbar, i.e., for depths down to 15-50 km. For the consideration of problems connected with deeper layers of the earth’s mantle, the properties of elements and simple chemical compounds must be studied at pressures of tens and hundreds of thousands bars, at temperatures of 1,CiOO’C and over. Finally,
2 12
II 1’ i c)I.:\ROV~C‘I:
for studying the earth’s core such experiments should be made at pressurc,s of millions of bars, at temperatures of several thousand degrees. The latt~~r conditions cannot yet be realized in the laboratory. Problems of the upper mantle and the earth’s crust are closely connected, and they must be studied Jointly. The processes occurring below the Moho discontinuity influence the phenomena in the earth’s crust in a certain way. At present these problems arc of perhaps the greatest interest. Superdeep holes (down to lsi-18 km), which will be bored sooner or later, will permit us to find out exactly which rocks constitute the foot of the earth’s crust and lie below the Moho discontinuity. Therefore, in interpreting field geophysical data. we cannot speak now of abstract “granite” and “basalt ” layers of the earth’s crust. For instance, when using the data of seismology and deep seismic sounding we must try to specify the types of rocks constituting different layers of a certain area, as distinguished by seismological methods. It seems that clarity may soon be brought into the discussion as to whether deep seismic boundaries in the earth’s crust are due to variations in the chemical compounds of the rocks, or only to variations in the mineral contents of the rocks, and in particular to polymorphic transformations (Afanassiev, 1960, 1962). In connection with the above, in the laboratory dealing with high pressures of the section on physical properties of rocks at the Institute of Earth Physics, Academy of Sciences, U.S.S.R., a complex of methods has been elaborated for the investigation of the properties of rocks in various pressure ranges. Physical-mechanical properties, velocities of elastic longitudinal and transverse waves, modules of elasticity, compressibility, Poisson ratio, and strength and absorption of elastic waves are being studied for specimens of rocks of considerable sizes at pressures up to 5-10 kbar. The investigations on electrical properties, electro-resistance and permittivity for small specimens of rocks can be made under pressures of 50 kbar at temperatures of up to 400 OC.
VELOCITIES
OF ELASTIC WAVES OF ROCK SPECIMENS
A number of general conclusions can be made by means of a systematization of considerable experimental material, based on the velocities of elastic waves in rocks under high pressures (Volarovich, 1960a,b,c; 1962a,b,c; Volarovich and Balashov, 1957; Volarovich and Bayuk, 1960). The velocities of elastic waves under atmospheric pressure in rocks of one type depend firstly on their bulk weight, and hence porosity, as well as on their mineral-petrographic peculiarities. For all rocks, a sharp increase in the velocity of both longitudinal and transverse waves is observed when the pressure reaches up to 1.4 kbar. With a further increase in pressure, velocities become much slower. The increase in velocities is connected with the increase in number and area of contacts between the grains of minerals. This is due to the closing of microfractures under pressure, and the partial closing of volume pores, which is more intensive when the initial porosity of the rock is greater. The determination of the volume change of rocks under pressure (Volarovich et al., 1959) establishes that under a pressure of 5 kbar, 10-30 % of the volume of pores is closed. It can be accepted that firstly th% flat pores, i.e., microfractures, are closed. Tectonophysics,
2 (2/s) (1965) 211-217
ROCK PROPERTIES AT HIGH PRESSURES
AND TEMPERATURES
213
In the earth’s crust rocks can be in a non-uniform, three-axial stress state. Experiments made by means of a specially developed technique (Volarovich et al., 1963) showed that under a confining pressure of 1-Z kbar, simultaneous uniaxial stress causes an additional rise in the velocity of longitudinal waves. At higher confining pressures of up to 10 kbar, the uriaxial stress does not have any additional effect. Heating rock specimens to 200-250’ C causes only a slight decrease in the velocity of elastic waves (Birch, 1960, 1961; Volarovich and Gurvich, 1957; Iida and Kumazawu, 1959). Therefore, the wave velocities in the crustal rocks increase, mainly due to the rise in pressure, to depths down to 10-15 km. At great depths the influence of temperature in the opposite direction leads to a decrease in the velocity rate of elastic waves, and can even lead to a decrease in velocity. At present a considerable amount of data is available on the velocities of elastic waves at high pressures, of up to 4 kbar for igneous rocks. In this respect sedimentary and metamorphic rocks have been studied less. The investigated igneous rocks (more than 50 specimens of different rocks) can be divided into the following principal groups: peridotites and piroxenites, gabbro and diabases, basalt, and granites. Fig.1 gives the generalized data on the velocities of longitudinal and transverse waves as a function of pressure. It can be seen that the regions of rocks of various types are distributed quite regularly. It should be added that within the gabbro region the studied curves of diabases, diorites and amphibolites also fall. In particular, this includes the diabase that we studied together with Fan-vey-tzin (1961) and V(km/sec)
I
norite 7 not-he
“P 6
4
pWXr)
Fig.1. The areas occupied by acid, basic and ultrabasic rocks on the graph of dependence of elastic wave velocities (v) on the pressure (p). 1 = granite; 2 = gabbro; 3 = ultrabasics. Tectonophysics, 2(2/3) (1965) 211-217
Volarovich and Fan-uey-tzin (1962), and the curve for the d&base pribram that was obtained by Czechoslovakian scientists by means of our high pressure shows equipment (Pros et al., 1962). The study of two norite specimens that one of them - a fine-graincd specimen with a density of 3.25 g ,‘cm:’ falls to the regionof ultra-basic rocks, and the other - a coarse-grained specimen with a density of 3.01 g/cm3 - falls in the gabbro region. Comparing the regions of longitudinal velocities in Fig.1 with the results obtained by Birch (1960, 1961). Jdanov and Rezanov (1962) and Rezanov (1962). we can conclude that in general they coincide, though, according to Birch. this region is somewhat broader for hyperbasits and narrower for gabbro and diabases. Birch’s granite region is also narrower, and is shifted somewhat upward in respect to the granite region in Fig.1. As to gneisses and granite-gneisses, according to our data the region of longitudinal waves for these metamorphic rocks is still broader than for granites, and almost completely coincides with the granite region. It is clear, from the examtnation of transverse velocities as a function of pressure in Fig.1, that for these wave6, the regions of different rock types overlap each other to some extent. This is connected with the fact that ultrabasic and basic rocks have a rather high Poisson ratio; it ranges from 0.2-0.3 at atmospheric pressure, changing slightly and most often increasing with the rise in pressure. A number of specimens of granites and granitegneisses has the Poisson ratio of 0.1-0.2 (in accordance with the small figure of this value for quartz 0.07). increasing at high pressures up to 0.15-0.18.
ABSORPTIOI\: COEFFICIEM‘S
OF ELASTIC WAVES OF ROCK SPECIMENS
In connection with the begirming application of the dynamic peeulEarttles of seismic waves far the interpretation of field ob@ervaHons, Levy& and the author (Vc&rovlch et al., 1961; Levyktn, 19a} studied the absor#fon eoefficients of elastic waves at high pressures in specimens of rocks, using a specially developed technique of multiple reflections at ultrasonic freqwrnctes (Valarovich, lQ60). In Fig.2 the data for the &sorption coefficient of longitudinal waves tip as a function of pressure are given for some rocks. It is evident that the absorption coefficient of dtitferent rocks varies at atmospheric pressure in wider ranges than the velocities of elaetic waves, name& from 0.03-0.05 crna for gabbro, and to 0.12-0.14 cm-’ for some granites and gneisses. With the rise in pressure it decreases, this decrease being relatively somewhat larger than the growth of elastic waves with preseure. The absorption coefficient of transverse waves i.n racks is l.%? tfmes greater than that of lo~itudinal waves. It changes with pressure approximately as ap .
ELEUTRICAL
PROPERTIEs
OF ROCK SWCIMENS
It is Meresting to compare the diGa on elastic properties of rocks at hfgh pressures and temperatures with the electrical. propertfes of the rocks. The investigations on the electrical properties of rocks carried out togett?er with ParIchomenIco and Bondarenko (Volarovich and Bondarenko, 1960, 1941; Parkhomenko and Bondarenko, 1960) at pressure of sever&l thousand bars,
ROCK PROPERTIES
AT HIGH PRESSURES
3
2
Fig.2. The absorption coefficient as a function of pressure (E).
AND TEMPERATURES
215
p War)
((u) of longitudinal waves of rock specimens
IOn
Qnpcm lo’o
d -===---_~~ 0
5
10
15
20
25
Fig.3, The electrical resistance at various temperatures. Tectonophysics,
30
pd Ml-1
(p) of basalt as a function of pressure
2 (Z/3) (1965) 211-217
(J$
appeared to be applicable to a pressure range of up to 50 kbar. It is being established that the permittivity for dry rock specimens at pressures of 50 kbar increases by tenths of a per cent. With the increase in temperature (Bondarenko, 1963), the permittivity begins to grow in the range from 30@-500a c. According to the data that we obtained with Parkhomenko and Bondaretiko, the electrical resistance at direct current in the indicated pressure range decreases by tenths of a per cent and for some rocks several times (Fig.3). For certain igneous rocks at pressures of 10-15 kbar the minimum of electrical resistance is obtained, after which it again rises, exceeding the initial value at 40-50 kbar. However, as can be seen from Fig.3, the heating greatly diminishes the resistance of rocks (10~1,000 times and over). Hence the influence of pressure on the electrical properties of rocks in comparison with temperature is somewhat opposite to that observed for the elastic properties of rocks. In general, the electrical properties of basic and ultrabasic rocks are close at both atmospheric and high pressures. Therefore, the method of deep electrical sounding (D.E.S.) can fail to indicate the Moho boundary (Tikhonov et al., 1961). Meanwhile, the strong temperature influence on the electrical properties of rocks will permit the estimation of the temperature at different depths in the earth’s upper mantle, during the interpretation of D.E .S. data. The results of the experiments for the elastic properties of rocks described above show that the seismic boundaries in the earth’s crust can be accounted for by the more or less abrupt change in the chemical compounds of rocks, and by the fact that the upper part of the mantle seems to consist of ultrabasic rocks.
REFERENCES Afanassiev, G.D., 1960. L’ interpretation pdtrographique des don&es geophysiques sur la structure de l’bcorce terrestre. Bul.Soc.CZol.France, 7 (2): 801-820. Afanassiev, G.D., 1962. Additional information on the structure of the earth’s structure according to the geophysical data from the positions of petrography. Izv.Akad. Nauk S.S.S.R., Ser.Geol., 1962 (10): 3-18 (in Russian). Birch, F., 1960. The velocity of compressional waves in rocks to 10 kbar.1. J. Geophys. Res., 65 (4): 1083-1102. Birch, F., 1961. The velocity of compressional waves in rocks to 10 kbar.2. J. Geophys. Res., 66 (7): 2194-2224. Bondarenko, A.T., 1963. The investigation of temperatural dependence on dielectrical permeability and angle tangent of dielectrical losses of rocks at different frequencies. Izv.Akad.Nauk S.S.S.R., Ser.Geofiz., 1963 (3): 455-463 (in Russian). Fan-vey-tzin, 1961. Dynamical impulse method of the determination of elastic parameters of rock samples at high pressures. Izv.Akad.Nauk S.S.S.R., Ser. Geofie., 1961 (10): 1538-1543 (in Russian). Iida, K. and Kumazawu, M., 1959. Measurements of elastic waves in volcanic rocks at high temperatures by means of ultrasonic impulse transmission. J. Earth Sci., Nagoya Univ., 7 (1): 49+4. Jdanov, V.V. and Rezanov, I.A., 1962. On the state and tasks of the study of the physical properties of rocks at high pressure and temperature. Izv.Akad.Nauk S.S.S.R., Ser. Geol., 1962 (11): 75-83 (in Russian). Levykin, AI., 1962. Damping of ultrasonic waves in rock samples of different frequencies, Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1962 (3): 389-391 (in Russian).
Tectonophysics,
2 (2/3) (1965) 211-217
ROCK PROPERTIES
AT HIGH PRESSURES
AND TEMPERATURES
217
Parkhomenko, E.I. and Bondarenko, A.T., 1960. Influence of one-sided pressure on electric resistance of rocks. Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1960 (2): 326-332 (in Russian). Pros, Z., VanEk, J. and Klima, K., 1962. The velocity of elastic waves in diabas and greylvacke under pressures up to 4 kbar. Studia Geophys. Geodaet., Ceskoslov. Akad. Ved, 1962 (6): 347-368. Rezanov, I.A.,.1962. On the structure of the earth’s crust in platform areas. Byul. Mask. Obshchestva Ispytatelei Prirody, Otd.Geol., 37: 2542 (in Russian). Tikhonov, A.N., Lipskaya, N.V., Deniskin, N.A., Nikiforova, N.N. and Lomakina, Z.D., 1961. On electromagnetic sounding of the deep layers of the earth. Dokl. Akad. Nauk S.S.S.R., 140 (3): 587490 (in Russian). Volarovich, M.P., 196Oa. Problems of Tectonophysics. Gosgeoltekhizdat, Moscow (in Russian). Volarovich, M.P., 196Ob. Geology and geophysics. Izv.Akad.Nauk S.S.S.R., 1960 (4): 13-21 (in Russian). Volarovich, M.P., 196Oc. Erforschung elastischer Gesteinseigenschaften bei hohem Druck. Freiberger Forschungsh., C, 81: 231-242. Volarovich, M.P., 1962a. Experimental investigations of deep processes. Izv.Altad. Nauk S.S.S.R., 1962: B%i3 (in Russian). Volarovich, M.P., 19621~. Seminar on the physical properties of rocks at high pressures. Izv.Akad.Nauk S.S.S.R. 19Gi (8): ll’i-120 (in Russian). Volarovich, M.P., 1962~. Physical properties of rocks at high pressures. Tr. Inst. Fizi. Zemli, Akad. Nauk S.S.S.R., 1962 (23): 7-18 (in Russian). of elastic wavs velocities Volarovich, M.P. and Balashov, D.B., 1937. Investigation in rock samples at the pressure to 5,000 kg/cm’. Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1937. (3): 319-330 (in Russian). Volarovich, M.P., Balashov, D.B. and Pavlo~radsky, V.A., 1959. Investigation of compressibility of igneous rocks at the pressures to 5000 kg/cm’. Izv .Akad. 1959 (5): 693-702 (in Russian). Nauk S.S.S.R., Ser. Geofiz., Volarovich, M.P., Balashov, D.B., Tomashevskaya, I.S. and Pavlogradsky, V.A., 19G3. Investigation of elastic wave velocities in rock samples with joint influence of comprehensive pressure and uniaxial compression. Dokl. Akad.Nauk S.S.S.R., 149 (3): 583-555 (in Russian). pressure to Volarovich, M.P., and Bayuk, E.I., 1960. Influence of comprehensive 4,000 kg/cm2 on elastic properties of rock samples. Dokl.Akad.Nauk S.S.S.R., 135 (1): 65-G8 (in Russian). of ultra-sounds to Volarovich, M.P., Bayuk, E.I. and Levykin, A.I., 1961. Application matter study. Collected Papers, 1961 (13): 55+1. Volarovich, M.P. and Bondarenko, A.T., 1960. Investigation of electrical resistance in rock samples at comprehensive pressure to 1,000 kg/cm’. Izv. Akad.Nauk 1960 (7): 946-953 (in Russian). S.S.S.R., Ser. Geofiz., Volarovich, M.P., Tarassov, O.A. and Bondarenko, A.T., 1961. Investigation of dielectrical permeability of rock samples at an atmospheric pressure, one-sided and comprehensive pressures to >,OOO kg/cm’. Izv. Akad.Nauk S.S.S.R., Ser.Geofiz., 1961 (7): 1004-1008. Volarovich, M.P. and Fan-vey-tzin, 1962. Investigation of elastic properties of roclis by statical and dynamical methods at high comprehensive pressures. Tr. Inst. Fiziki Zemli, Akad. Nauk S.S.S.R., 1962 (23): 19-24 (in Russian). Volarovich. M.P. and Gurvich, AS., 1957. Investigation of d.ynamical modulus of elasticity of rocks in dependence on the temierature. fzv. Akad. Nauk S.S.S.R., Ser. Geofiz., 195’7 (4): 417425 (in Russian). Volarovich, M.P., Levykin, A.I. and Sizov, V.P., 1960. Investigation of elastic waves damping in rock samples. Izv. Akad. Nauk S.S.S.R., Ser. Geofiz., 1960 (8): 1198-1203 (in Russian).
Tectonophysics,
2 (2/3)
(1965)
211-217
THE ~ESTIGATT~N OF ELASTIC AND ABSORPTION PROPERTIES ROCKS AT HIGH PRRSSURES AND TEMPERATURES
211
OF
M.P. VOLAROVICH Institute of Earth Physics, Academy of Sciences, Moscow (U.S.S.R.) (Reeetved April 10, 1964)
SUMMARY
The
task of i~ve~~i~~io~s of the physical properties of rocks is briefly given in connection with the problem of the structure df the earth’s crust and upper mantle structure. The results of the measurements at the pressures to 4 kbar, the velocities of elastic waves and absorption ratios af igneous and metamorphic rock spe$lmens are described. The results of investigations of electrical properties of rocks are considered at the pressures to 50 kbar at high temperatures. Certain general conclusions of the experimental data obtained are made. INTRODUCTION
As is known during the fnternatlonal Geophysical Year 1957-1958, vast investigatioss were carried out in the domain of earth physics that led to a number of important and interesting conclusions. In recent years problems of earth physics have attracted great attention in connection with cosmic investigations. Science comes close to the stu&y of the physic6 of planets, but the study of the planets’ structures, and the physical processes in them, requires the basis of knowledge of the earth’s structure and the properties of the earth’s matter. However, knowledge of the structure, and particulariy of the compound of various fayers of our planet, is still too schematic and approximate. It should be added also that in many branches of geophysics further advances have become rather difficult without laboratory data concerning the physical properties of the matter of the earth’s inner layers, obtained under the thermodynamic conditions e&sting in the earth’s interior. A number of papers (Volarovich, I960a, 19Qa,b) indicate what types of matter must be ~vestigated, and under which pressures and temperatures and by which methods, for the purpose of studying the earth’s crust, mantle, and core. For studying the earth‘s crust and the uppermost manSle, the properties of rocks and minerals must be investigated at temperatures of hundreds of degrees under pressure intervals from atmospheric to 5-16 kbar, i.e., for depths down to 15-50 km. For the consideration of problems connected with deeper layers of the earth’s mantle, the properties of elements and simple chemical compounds must be studied at pressures of tens and hundreds of thousands bars, at temperatures of 1,CiOO’C and over. Finally,
2 12
II 1’ i c)I.:\ROV~C‘I:
for studying the earth’s core such experiments should be made at pressurc,s of millions of bars, at temperatures of several thousand degrees. The latt~~r conditions cannot yet be realized in the laboratory. Problems of the upper mantle and the earth’s crust are closely connected, and they must be studied Jointly. The processes occurring below the Moho discontinuity influence the phenomena in the earth’s crust in a certain way. At present these problems arc of perhaps the greatest interest. Superdeep holes (down to lsi-18 km), which will be bored sooner or later, will permit us to find out exactly which rocks constitute the foot of the earth’s crust and lie below the Moho discontinuity. Therefore, in interpreting field geophysical data. we cannot speak now of abstract “granite” and “basalt ” layers of the earth’s crust. For instance, when using the data of seismology and deep seismic sounding we must try to specify the types of rocks constituting different layers of a certain area, as distinguished by seismological methods. It seems that clarity may soon be brought into the discussion as to whether deep seismic boundaries in the earth’s crust are due to variations in the chemical compounds of the rocks, or only to variations in the mineral contents of the rocks, and in particular to polymorphic transformations (Afanassiev, 1960, 1962). In connection with the above, in the laboratory dealing with high pressures of the section on physical properties of rocks at the Institute of Earth Physics, Academy of Sciences, U.S.S.R., a complex of methods has been elaborated for the investigation of the properties of rocks in various pressure ranges. Physical-mechanical properties, velocities of elastic longitudinal and transverse waves, modules of elasticity, compressibility, Poisson ratio, and strength and absorption of elastic waves are being studied for specimens of rocks of considerable sizes at pressures up to 5-10 kbar. The investigations on electrical properties, electro-resistance and permittivity for small specimens of rocks can be made under pressures of 50 kbar at temperatures of up to 400 OC.
VELOCITIES
OF ELASTIC WAVES OF ROCK SPECIMENS
A number of general conclusions can be made by means of a systematization of considerable experimental material, based on the velocities of elastic waves in rocks under high pressures (Volarovich, 1960a,b,c; 1962a,b,c; Volarovich and Balashov, 1957; Volarovich and Bayuk, 1960). The velocities of elastic waves under atmospheric pressure in rocks of one type depend firstly on their bulk weight, and hence porosity, as well as on their mineral-petrographic peculiarities. For all rocks, a sharp increase in the velocity of both longitudinal and transverse waves is observed when the pressure reaches up to 1.4 kbar. With a further increase in pressure, velocities become much slower. The increase in velocities is connected with the increase in number and area of contacts between the grains of minerals. This is due to the closing of microfractures under pressure, and the partial closing of volume pores, which is more intensive when the initial porosity of the rock is greater. The determination of the volume change of rocks under pressure (Volarovich et al., 1959) establishes that under a pressure of 5 kbar, 10-30 % of the volume of pores is closed. It can be accepted that firstly th% flat pores, i.e., microfractures, are closed. Tectonophysics,
2 (2/s) (1965) 211-217
ROCK PROPERTIES AT HIGH PRESSURES
AND TEMPERATURES
213
In the earth’s crust rocks can be in a non-uniform, three-axial stress state. Experiments made by means of a specially developed technique (Volarovich et al., 1963) showed that under a confining pressure of 1-Z kbar, simultaneous uniaxial stress causes an additional rise in the velocity of longitudinal waves. At higher confining pressures of up to 10 kbar, the uriaxial stress does not have any additional effect. Heating rock specimens to 200-250’ C causes only a slight decrease in the velocity of elastic waves (Birch, 1960, 1961; Volarovich and Gurvich, 1957; Iida and Kumazawu, 1959). Therefore, the wave velocities in the crustal rocks increase, mainly due to the rise in pressure, to depths down to 10-15 km. At great depths the influence of temperature in the opposite direction leads to a decrease in the velocity rate of elastic waves, and can even lead to a decrease in velocity. At present a considerable amount of data is available on the velocities of elastic waves at high pressures, of up to 4 kbar for igneous rocks. In this respect sedimentary and metamorphic rocks have been studied less. The investigated igneous rocks (more than 50 specimens of different rocks) can be divided into the following principal groups: peridotites and piroxenites, gabbro and diabases, basalt, and granites. Fig.1 gives the generalized data on the velocities of longitudinal and transverse waves as a function of pressure. It can be seen that the regions of rocks of various types are distributed quite regularly. It should be added that within the gabbro region the studied curves of diabases, diorites and amphibolites also fall. In particular, this includes the diabase that we studied together with Fan-vey-tzin (1961) and V(km/sec)
I
norite 7 not-he
“P 6
4
pWXr)
Fig.1. The areas occupied by acid, basic and ultrabasic rocks on the graph of dependence of elastic wave velocities (v) on the pressure (p). 1 = granite; 2 = gabbro; 3 = ultrabasics. Tectonophysics, 2(2/3) (1965) 211-217
Volarovich and Fan-uey-tzin (1962), and the curve for the d&base pribram that was obtained by Czechoslovakian scientists by means of our high pressure shows equipment (Pros et al., 1962). The study of two norite specimens that one of them - a fine-graincd specimen with a density of 3.25 g ,‘cm:’ falls to the regionof ultra-basic rocks, and the other - a coarse-grained specimen with a density of 3.01 g/cm3 - falls in the gabbro region. Comparing the regions of longitudinal velocities in Fig.1 with the results obtained by Birch (1960, 1961). Jdanov and Rezanov (1962) and Rezanov (1962). we can conclude that in general they coincide, though, according to Birch. this region is somewhat broader for hyperbasits and narrower for gabbro and diabases. Birch’s granite region is also narrower, and is shifted somewhat upward in respect to the granite region in Fig.1. As to gneisses and granite-gneisses, according to our data the region of longitudinal waves for these metamorphic rocks is still broader than for granites, and almost completely coincides with the granite region. It is clear, from the examtnation of transverse velocities as a function of pressure in Fig.1, that for these wave6, the regions of different rock types overlap each other to some extent. This is connected with the fact that ultrabasic and basic rocks have a rather high Poisson ratio; it ranges from 0.2-0.3 at atmospheric pressure, changing slightly and most often increasing with the rise in pressure. A number of specimens of granites and granitegneisses has the Poisson ratio of 0.1-0.2 (in accordance with the small figure of this value for quartz 0.07). increasing at high pressures up to 0.15-0.18.
ABSORPTIOI\: COEFFICIEM‘S
OF ELASTIC WAVES OF ROCK SPECIMENS
In connection with the begirming application of the dynamic peeulEarttles of seismic waves far the interpretation of field ob@ervaHons, Levy& and the author (Vc&rovlch et al., 1961; Levyktn, 19a} studied the absor#fon eoefficients of elastic waves at high pressures in specimens of rocks, using a specially developed technique of multiple reflections at ultrasonic freqwrnctes (Valarovich, lQ60). In Fig.2 the data for the &sorption coefficient of longitudinal waves tip as a function of pressure are given for some rocks. It is evident that the absorption coefficient of dtitferent rocks varies at atmospheric pressure in wider ranges than the velocities of elaetic waves, name& from 0.03-0.05 crna for gabbro, and to 0.12-0.14 cm-’ for some granites and gneisses. With the rise in pressure it decreases, this decrease being relatively somewhat larger than the growth of elastic waves with preseure. The absorption coefficient of transverse waves i.n racks is l.%? tfmes greater than that of lo~itudinal waves. It changes with pressure approximately as ap .
ELEUTRICAL
PROPERTIEs
OF ROCK SWCIMENS
It is Meresting to compare the diGa on elastic properties of rocks at hfgh pressures and temperatures with the electrical. propertfes of the rocks. The investigations on the electrical properties of rocks carried out togett?er with ParIchomenIco and Bondarenko (Volarovich and Bondarenko, 1960, 1941; Parkhomenko and Bondarenko, 1960) at pressure of sever&l thousand bars,
ROCK PROPERTIES
AT HIGH PRESSURES
3
2
Fig.2. The absorption coefficient as a function of pressure (E).
AND TEMPERATURES
215
p War)
((u) of longitudinal waves of rock specimens
IOn
Qnpcm lo’o
d -===---_~~ 0
5
10
15
20
25
Fig.3, The electrical resistance at various temperatures. Tectonophysics,
30
pd Ml-1
(p) of basalt as a function of pressure
2 (Z/3) (1965) 211-217
(J$
appeared to be applicable to a pressure range of up to 50 kbar. It is being established that the permittivity for dry rock specimens at pressures of 50 kbar increases by tenths of a per cent. With the increase in temperature (Bondarenko, 1963), the permittivity begins to grow in the range from 30@-500a c. According to the data that we obtained with Parkhomenko and Bondaretiko, the electrical resistance at direct current in the indicated pressure range decreases by tenths of a per cent and for some rocks several times (Fig.3). For certain igneous rocks at pressures of 10-15 kbar the minimum of electrical resistance is obtained, after which it again rises, exceeding the initial value at 40-50 kbar. However, as can be seen from Fig.3, the heating greatly diminishes the resistance of rocks (10~1,000 times and over). Hence the influence of pressure on the electrical properties of rocks in comparison with temperature is somewhat opposite to that observed for the elastic properties of rocks. In general, the electrical properties of basic and ultrabasic rocks are close at both atmospheric and high pressures. Therefore, the method of deep electrical sounding (D.E.S.) can fail to indicate the Moho boundary (Tikhonov et al., 1961). Meanwhile, the strong temperature influence on the electrical properties of rocks will permit the estimation of the temperature at different depths in the earth’s upper mantle, during the interpretation of D.E .S. data. The results of the experiments for the elastic properties of rocks described above show that the seismic boundaries in the earth’s crust can be accounted for by the more or less abrupt change in the chemical compounds of rocks, and by the fact that the upper part of the mantle seems to consist of ultrabasic rocks.
REFERENCES Afanassiev, G.D., 1960. L’ interpretation pdtrographique des don&es geophysiques sur la structure de l’bcorce terrestre. Bul.Soc.CZol.France, 7 (2): 801-820. Afanassiev, G.D., 1962. Additional information on the structure of the earth’s structure according to the geophysical data from the positions of petrography. Izv.Akad. Nauk S.S.S.R., Ser.Geol., 1962 (10): 3-18 (in Russian). Birch, F., 1960. The velocity of compressional waves in rocks to 10 kbar.1. J. Geophys. Res., 65 (4): 1083-1102. Birch, F., 1961. The velocity of compressional waves in rocks to 10 kbar.2. J. Geophys. Res., 66 (7): 2194-2224. Bondarenko, A.T., 1963. The investigation of temperatural dependence on dielectrical permeability and angle tangent of dielectrical losses of rocks at different frequencies. Izv.Akad.Nauk S.S.S.R., Ser.Geofiz., 1963 (3): 455-463 (in Russian). Fan-vey-tzin, 1961. Dynamical impulse method of the determination of elastic parameters of rock samples at high pressures. Izv.Akad.Nauk S.S.S.R., Ser. Geofie., 1961 (10): 1538-1543 (in Russian). Iida, K. and Kumazawu, M., 1959. Measurements of elastic waves in volcanic rocks at high temperatures by means of ultrasonic impulse transmission. J. Earth Sci., Nagoya Univ., 7 (1): 49+4. Jdanov, V.V. and Rezanov, I.A., 1962. On the state and tasks of the study of the physical properties of rocks at high pressure and temperature. Izv.Akad.Nauk S.S.S.R., Ser. Geol., 1962 (11): 75-83 (in Russian). Levykin, AI., 1962. Damping of ultrasonic waves in rock samples of different frequencies, Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1962 (3): 389-391 (in Russian).
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Parkhomenko, E.I. and Bondarenko, A.T., 1960. Influence of one-sided pressure on electric resistance of rocks. Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1960 (2): 326-332 (in Russian). Pros, Z., VanEk, J. and Klima, K., 1962. The velocity of elastic waves in diabas and greylvacke under pressures up to 4 kbar. Studia Geophys. Geodaet., Ceskoslov. Akad. Ved, 1962 (6): 347-368. Rezanov, I.A.,.1962. On the structure of the earth’s crust in platform areas. Byul. Mask. Obshchestva Ispytatelei Prirody, Otd.Geol., 37: 2542 (in Russian). Tikhonov, A.N., Lipskaya, N.V., Deniskin, N.A., Nikiforova, N.N. and Lomakina, Z.D., 1961. On electromagnetic sounding of the deep layers of the earth. Dokl. Akad. Nauk S.S.S.R., 140 (3): 587490 (in Russian). Volarovich, M.P., 196Oa. Problems of Tectonophysics. Gosgeoltekhizdat, Moscow (in Russian). Volarovich, M.P., 196Ob. Geology and geophysics. Izv.Akad.Nauk S.S.S.R., 1960 (4): 13-21 (in Russian). Volarovich, M.P., 196Oc. Erforschung elastischer Gesteinseigenschaften bei hohem Druck. Freiberger Forschungsh., C, 81: 231-242. Volarovich, M.P., 1962a. Experimental investigations of deep processes. Izv.Altad. Nauk S.S.S.R., 1962: B%i3 (in Russian). Volarovich, M.P., 19621~. Seminar on the physical properties of rocks at high pressures. Izv.Akad.Nauk S.S.S.R. 19Gi (8): ll’i-120 (in Russian). Volarovich, M.P., 1962~. Physical properties of rocks at high pressures. Tr. Inst. Fizi. Zemli, Akad. Nauk S.S.S.R., 1962 (23): 7-18 (in Russian). of elastic wavs velocities Volarovich, M.P. and Balashov, D.B., 1937. Investigation in rock samples at the pressure to 5,000 kg/cm’. Izv.Akad.Nauk S.S.S.R., Ser. Geofiz., 1937. (3): 319-330 (in Russian). Volarovich, M.P., Balashov, D.B. and Pavlo~radsky, V.A., 1959. Investigation of compressibility of igneous rocks at the pressures to 5000 kg/cm’. Izv .Akad. 1959 (5): 693-702 (in Russian). Nauk S.S.S.R., Ser. Geofiz., Volarovich, M.P., Balashov, D.B., Tomashevskaya, I.S. and Pavlogradsky, V.A., 19G3. Investigation of elastic wave velocities in rock samples with joint influence of comprehensive pressure and uniaxial compression. Dokl. Akad.Nauk S.S.S.R., 149 (3): 583-555 (in Russian). pressure to Volarovich, M.P., and Bayuk, E.I., 1960. Influence of comprehensive 4,000 kg/cm2 on elastic properties of rock samples. Dokl.Akad.Nauk S.S.S.R., 135 (1): 65-G8 (in Russian). of ultra-sounds to Volarovich, M.P., Bayuk, E.I. and Levykin, A.I., 1961. Application matter study. Collected Papers, 1961 (13): 55+1. Volarovich, M.P. and Bondarenko, A.T., 1960. Investigation of electrical resistance in rock samples at comprehensive pressure to 1,000 kg/cm’. Izv. Akad.Nauk 1960 (7): 946-953 (in Russian). S.S.S.R., Ser. Geofiz., Volarovich, M.P., Tarassov, O.A. and Bondarenko, A.T., 1961. Investigation of dielectrical permeability of rock samples at an atmospheric pressure, one-sided and comprehensive pressures to >,OOO kg/cm’. Izv. Akad.Nauk S.S.S.R., Ser.Geofiz., 1961 (7): 1004-1008. Volarovich, M.P. and Fan-vey-tzin, 1962. Investigation of elastic properties of roclis by statical and dynamical methods at high comprehensive pressures. Tr. Inst. Fiziki Zemli, Akad. Nauk S.S.S.R., 1962 (23): 19-24 (in Russian). Volarovich. M.P. and Gurvich, AS., 1957. Investigation of d.ynamical modulus of elasticity of rocks in dependence on the temierature. fzv. Akad. Nauk S.S.S.R., Ser. Geofiz., 195’7 (4): 417425 (in Russian). Volarovich, M.P., Levykin, A.I. and Sizov, V.P., 1960. Investigation of elastic waves damping in rock samples. Izv. Akad. Nauk S.S.S.R., Ser. Geofiz., 1960 (8): 1198-1203 (in Russian).
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