Heat flow, temperature, and electrical conductivity of the crust and upper mantle in the U.S.S.R.

Tectonophysics - Elsevier Publishing Company, Amsterdam Printed in The Netherlands

HEAT FLOW, TEMPERATURE, AND ELECTRICAL CONDUCTIVITY OF THE CRUST AND UPPER MANTLE INTHE U.S.S.R. E.A. ~U~I~~~VA and I.S. FELDMAN The Institute of the Earth’s Physics, Academy of Sciences of the U.S.S.R., Moscow (U.S.S.R.) (Received April 15, lS?oj

SUiWR’L4RY

A review of new heat flow values for regions of the U.S.S.R. is given. The temperature values corresponding from 0.5 to 2.0 HFU and the different

to the different

heat flow values

thickness of the continental crust which are observed for the U.S.S.R. territory are constructed. The reliability of the magnetotellurie investigations for some regions of the U.S.S.R. territory is discussed. Using the laboratory data on the energy activations and electrical conductivity of olivinites for temperature range of 500°-1,200* C the models of electrical conductivity distributions in the upper mantle are constructed on the basis of temperature curves on the conditions that divines predominate in the composition of the mantle and they contain IO-I% fayalites. In the regions of the south Caspian depression as well as the Hungarian trough, as evidenced by the data of magnetotelluric investigation, an anomalously conducting layer (about 20 km thick) is traced in the upper mantle at the depth of 40-60 km. The presence of this layer may be related to the partial melting of the matter of the upper mantle.

INTRODUC TION

The temperature distribution within the earth’s mantle still remains one of the most difficult problems of solid earth physics to be solved. The relevant parameters are: data on heat generation at different depths, heat transfer coefficier& heat flow, and the position of boundaries between different physical properties. Using the equations for heat transfer and the above data it is possible to calculate a temperature distribution for the earth which does not harmonize with some other geophysical data, for instance with the pattern of seismic waves velocities. There are, however, many uncertainties in the calculation of the earth’s temperature distribution based on the earth’s thermal history, which lead to great ambiguity in the result. This ambiguity can be reduced by using some new independent data. During the last several years the researchers attention has been devoted to the correlation of temperature with the electrical conductivity, because the electrical properties of the earth’s deep interior are very sensitive to temperature variations. In this paper, Tec~~~ophysies, 10 (1910) 245-281

245

an attempt has been made to correlate heat flow data with the results of magnetotelluric investigations in several distinct tectonic zones within the U.S.S.R., as well as temperature and electrical conductivity distribution for some petrographic models of the crust and the mantle.

NEW HEAT FLOW DATA IN THE U.S.S.H.

During the last two years a group from the Institute of Earth Physics, Academy of Sciences, U.S.S.R., has made simultaneous investigations of thermal and electrical features within both stable and mobile zones of the crust. The areas studied were the Kolsky Peninsula of the Baltic Shield, the junction of the Ukrainian and Belorussian massifs, the Black Sea and Caspian Sea depressions, the mountains of mid-Asia, the Baikal rift system, the Kurile Islands, and the Arctic regions. A map of all heat flow data in the U.S.S.R. is given in Fig. 1. Exact positions and figures are listed in Table I, II. Among the areas studied the Kolsky region of the Baltic Shield and the transitional area from the Ukrainian crystalline shield to the Belorussian crystalline massif are typical of relatively stable zones. In a previous paper we have reported rather low values of heat flow of approximately 0.7-0.9 HFU for the areas of outcrop of the Pechenegskaya series of rocks and the Monchegorsky pluton in the Kolsky Peninsula (Lubimova, 1968). Now results are added for Khibinskaya synclinal region, Lovozersky pluton and Kandalakshiskaya anticlinal zone (see Fig. 1). The profile of flow values in the vicinity of line Z-Z’ is given in Fig.2. The highest heat flow of 0.95-1.10 HFU was observed in the Khibinskaya synclinal zone. In the other three zones - Lovozero, Pechenega and Monchegorsk - the heat flow is below 0.9 HFU. All the low values of heat flow so far obtained, fully harmonize with the generally accepted heat conditions of Precambrian plates (Smirnov, 1968). Let us consider the southern parts of the European zone: the results of measurement in the region of Ante Caucasus, the mountains of the Great Caucasus, Crimea and several points in the Black Sea are in Fig. 1, 3 and 4. Twenty-five points in the Black Sea are distributed very unevenly. Single points in the central part of the Black Sea show heat flow less than 1 HFU (Fig. 3). In the coastal zone of the Caucasus heat flow values are still lower (Fig. l), but heat floiv increases in the seismic region towards Yalta, where heat flow equals 1.4-1.6 (point A in Fig.1 and 3) through the bottom of the Black Sea at a depth of about 1,000 m. Increasing heat flow is revealed over a magnetic anomaly (point B in Fig. 1) which follows the deep trench in the south-east part of the Black Sea, descending to the upper mantle. In the region of Alpine Cenozoic folding of the Caucasus, heat flow increases in the geanticline of the Great Caucasus and decreases in the region of marginal depressions such as Indolo-Cuban and Tesko-Caapian ones. The maximum of heat flow in the region of Great Caucasus is 3.4 HFU, including Cenozoic volcanic regions such as Casbec Mountain and the minera waters outcrop. A high positive anomaly is apparent in the region of the Stavropoleky dome with a mean value of 2.05 HFU (Fig. 4). This anomaly seems to have a deep origin, and its southern part is united 246

Tectonophysics,

10 (1970) 245-281

-

..-

8

I i

Tectonophysics,

10 (1970)245-281

247

'rABLE I Heat flow data from marine stations

---

Latitude

Longitude

40°24' 42O25' 42O30' 42O33' 42'=30' 42O24' 50053 50°42' 50044' 50031 50'=36' 50003' 83OlO' 83='10' 83“lO' 83“lO' 83OlO 83OlO' 83010' 83O20' 54057' 53055' 52O12' 51°36' 52='15' 51“38' 51“58' 39042' 39043' 39043' 39042' 39042' 39042' 85“53' 86O2l' 86“29' 86O32' 86“36' 86“35' 86O35' 86“34' 86O36' 86O39' 86O31' 86000' 86001' 86O22' 86“27' 87O47' 88*50' 88O50'

77005' 77004' 77004' 77004' 77O18' 77019' 155='12' 154“58' 155OO6' 155='21' 155011' 154O38' 120010' 118='40' 118OlO' 118“OO' 117040' 116O40' 116='20' 116OlO' 109053' 109“08' 105053' 104035' 105049' 104013' 105044' 51003' 50='24' 50°36' 50051' 50041' 51O16' 158O26' 158O16' 155039' 153O78' 152039' 153O24' 153O24' 154007' 152O58' 153='36' 155031' 154055' 16OO48' 161O33' 162“25' 154049' 156OO7' 155O56'

248

ydT/dz (Y/km) 34

43 117 23 69 22 100 112 105 108 105 150 13 120 115 35 70 145 150 170 100 187 142 120 126 112 154 52 127 72 79 61 48 62 63 51 72 94 60 68 71 68 106 70 115 68 70 69 77 58 52

h (10e3cal./cm sec.%)

g 2 (Cal./ cm .sec)

25 24 21 50 22 25 19 17 19 22 18 23 24 24.5 25 25.5 23.5 21.5 21 22 -

0.85 1.03 2.46 1.15 1.52 0.55 1.9 1.9 1.9 2.4 1.9 3.3 0.3 2.9 2.9 0.9 1.6 3.0 3.2 3.7 1.6 1.3 1.6 1.7 1.7 2.6 2.0 1.2 2.3 1.34 2.28 1.0 0.90 1.70 1.72 1.48 1.94 2.44 1.68 1.83 1.88 1.83 2.56 1.96 2.66 1.97 2.03 2.00 2.08 1.56 1.42

23.4 18.4 18.2 18.9 16.1 18.1 27.4 27.4 29.0 27.0 26.0 28.0 27.0 26.5 27.0 24.2 28.0 24.2 29.0 29.0 29.0 27.0 27.5 27.5

Tectonophysics, 10 (1970)245-281

TABLE

I (continued)

Latitude

Longitude

89O13’ 89O36’ 43“23’ 43’=22’ 41044’ 42OO8’ 43O58’ 43054’ 43051’ 43“46’ 43=‘38’ 43=‘38’ 41053’ 43O18’ 42O48’ 42O35’ 43O28’ 41=‘38 42O2.3’ 42OO.2’ 42009’

146OO ’ 144049’ 39050’ 39050’ 41°32’ 41029’ 38O19’ 38=‘25’ 38=‘25’ 38O16’ 38”26’ 36O28’ 40°28’ 34OO2’ 37O38’ 34OO2’ 31°23’ 29O38’ 41O22’ 42O22’ 41O26.6’

ydT/dz (“C/km)

X (10m3cal. /cm.sec

cl 2 (Cal. /cm . set)

.“C)

25.2 25.2 22.2 18.7 26.0 22.4 -

82 $3) (15.3) 44.0 40.0

-

2.06 (2.12) (0.34) 0.28 1.1 0.9 1.38 1.18 1.70 1.20 1.21 0.6 0.9 1.1 1.3 0.9 1.0 0.9 0.48 2.56 0.91

20 20 20 20 20 20 20 27 25 43

38 45 60 65 45 50 45 176 225 212

q; HFU

3-

2-

1-x

-4______--r--------

.?. 1

.

3 400

0 a

WXJ

Up0

800

b

_t

j

a

.

'2qoo J

2@00 km c

f-1 Fig. 2. Profile of heat flow values in the vicinity of line II-I. a = region of Precambrian Baltic Shield; b = Russian Plateau and a contact between Bellorussian Massif &d Ukrainian Shield; c= zone of Ukrainian Shield. 1 = Pechenga region; 2 = Lovozero - Monchegozsk region; 3 = Kandalaksha region; 4 = Khibinskaja synclinal zone; 5 = Belorussian Massif, Pripjatskaya valley; and 6 = Ukrainian Shield. Tectonophysics,

10 (1970) 245-281

249

_. HFU

tl

0 3

WFU

6

6 *4

2

1 i

. 600

4001

!

km

0

I

800

950

’

0 fl .ib.i_

t

Lb./_

d

km

J

Fig, 3. Profile of heat flow values in the vicinity of lineZZ’-ZZ. 1 = region of Ukrainian Shield; 2 = margin of Russian Plateau; 3 = Crimean hydrothermal anomaly in ~ar~h~ut; 4s hydro~ermal Novoselovs~ya point; 5 = Hercynian part of Scythian Plateau; 6 P axis of the Crimean Alpine folding zone; 7 = valley of the Black Sea; and 8 P its axis. Fig. 4. Profile of heat flow values in the vicinity of lineZZZ’-ZZZ. a = region of Cenozoic volcanoes; b = region of intermountain valley; c = Great Caucasus geanticline zone; d a Scyphian Plateau, Stavzopolsky rising; b ’ = axis of intermountains valley; and c’= axis of the geanticfine zone of Caucasus.

q; HFlJ 3-

t

O-

IV’-

km

IV

Fig. 5. Profile of heat flow values in the vicinity of lineZV’-ZV for Middle Asia. 1 t Pri~sh~nt valley; 2 = ax&t of mountain zone; 3 = mountain zone; 4 = Ferganskaya basin; and 5 = its axis.. 250

Tectonophysfcs, 10 (1970) 245-281

TABLE

II

Heat flow data from

land stations

Latitude N

Longitude E

Depth of boreholes (m)

Time equilibrium (in months unless otherwise stated)

Heat flow q(cal./cm2*

50033’ 50009’ 49O56’ 50018’ 49001’ 50003’ 49033’ 49*24’ 49025 49”18’ 49024’ 49O22’ 49O24’ 49O23’ 49005’ 49005’ 49O12’ 49023’ 49011’ 49013’ 49013’ 49*12’ 49OO8’ 49008’ 49004’ 49004’ 49004’ 49004’ 48O57’ 48O57’ 48=‘52’ 49013’ 49012’ 49004’ 48O41’ 48O57’ 48O25’ 48”08’ 52O16’ 52‘=‘15’ 52O16’ 52“16’ 52OlO’ 52007’ 52*18’ 5Z028’ 52OOO’ 51049’ 45O32’ 45034’ 45033’ 45010’ 45015’

24O56’ 24“Zl’ 24O57’ 24002’ 25O25’ 23O18’ 23O38’ 23“45’ 23“50’ 23O55’ 23O49’ 23059’ 23959’ 24=‘00’ 24*25’ 24*25’ 23“51’ 25O15’ 23O43’ 23O40’ 23O40’ 23091 23O55’ 23*55’ 24OO3’ 23059’ 23O59’ 23‘=59’ 24OO3’ 24004’ 24Oll’ 23”35’ 23O34’ 23O33’ 22051 22021’ 22O42’ 22O54’ 30017’ 30°16’ 30011’ 30=‘18’ 30040’ 30“38’ 30003fi 29*05’ 29O16’ 29OO5’ 41012’ 41019’ 41Q27’ 42O56t 42”54’

2,380 2,075 1,400 1,960 2,200 1,150 1,400 2,520 I. ,250 2,550 1,400 1,130 1,400 1,900 1,700 1,800 750 1,400 2,300 300 2,531 2,537 2,520 1,900 2,000 2.800 2;100 3,000 1,800 2,600 2,550 2,300 2,050 3,800 1,350 1,442 1,600 1,900 -500 -500 -500 -500 -500 -500 -500 --500 -500 -500 1,125 1,150 1,150 681 650

18 8

1.05 1.30 0.95 1.29 1.,04 1.36 1.27 1.04 1.19 0.90 1.18 1.18 1.08 1.14 0.80 0.90 1.05

36 .l 12 33 1 2 1 0.5 3.6 10 3 4 6 18 6 6 5 12 9 0.5 1 0.5 1.0 24 2 3 Il 12 0.7 0.5 22 2 17 60 48

1 1 2 1 1

year, 5 months year years, 7 months year year

1.03 0.87 0.97 1.10 0.95 0.96 1.10 1.20 1.17 1.28 1.22 1.07 1.30 1.25 1.55 2.00 2.20 2.30 2.30 1.23 1.40 1.24 1.01 1.03 1.05 1.44 0.92 0.73 0.78 2.1 2.1 2.0 1.5 1.7

set)

TABLE

II(continued)

Latitude Longitude N I:

45017 44008' 44004 43055' 43055' 45005' 44C49' 44049' 44='48' 44050' 44048' 460371 46Yxi' 45049' 44051 44O56'

43005 42051' 42054' 42043' 42043' 38OO5' 38015 38Q1.5' 38053' 38049' 38058' 39017' 40°27' 40“28' 41°18' 41006'

45050' 44O32' 46O37' 46"28' 46"25' 46O19' 46O22' 46O14' 44043' 44044' 44O38' 44040'

42“55' 41053' 38O27' 38O38' 39'=20' 38O57 39030' 39009' 40003' 41°12' 40°48' 40025'

45O52' 45033' 46W6' 45“52' 46OO9' 46OOO' 45O46' 45054' 45018' 44045' 45035'

41'18' 41*2?' 3B030' 39033' 38044' 39005' 3tf"38' 39*06' 39037' 38055' 38OO5'

45O20' 44049' 44044' 44019' 44044' 44003' 45010' 45015' 45050'

37O58' 44OO8' 44'21' 44059' 45O21' 42='56' 43030' 42055' 42O55'

252

Depth of boreholes (m)

Time equilibrium Heat flow 2 finmonths unless q(caI./cm 'see) otherwisestated) _~__

565 787 425 398 375 700 1,200 825 2,050 1,975 1,145 1,440 1.830 21560 1,072 2,530 735 1,090 2,025 2,220 2,270 2,240 1,910 2,400 2,120 2,658 2,600 2;750 2,780 1,265 2,700 2,730 1,105 1,767 2,684 1,900 2,000 2,080 3,200 3,400 2,450 2,650 1,924 2,100 3,000 1,100 2,050 1,495 1,400 1,680 2,600 2,300

5 1 year

3 years 5.5 5 11

8 9 1 year,10 months 1 year, 1 month >6 months >S months 2years >6 months >6 months >6 months 61days >6months 3 years >6 months 3 years >6 months 3 years >6 months 3 years 30 days A6 months 56 months 16 months >6 months 16 months 4 >6 months >6 months >6 months 56 days ;6 months >6 months 5 1.5 years 11 2 years T6 months b6 months 50days b6 months 15 0.6 1

1.6 1.8 2.1 1.6 1.2 1.1 1.2 1.3 1.3 1.2 1.4 1.66 1.28 1.70 2.85 1.80 2.36 2.97 1.68 1.28 1.57 1.54 1.57 1.44 1.36 1.49 1.56 1.26 1.41 1.36 1.55 1.6 1.93 1.54 1.95 1.81 1.69 1.46 1.75 1.60 1.07 0.98 1.12 1.15 2.02 1.97 2.02 1.57 2.14 1.55 1.85 1.67

10 (1970)245-281 Tectonophysics,

TABLE

II (continued)

Latitude N

Longitude E

45050’ 45035’ 45034’ 45034’ 45034’ 45034’ 45034’ 45015’ 45015’ 45015’ 45015’ 45O25’ 45O25’ 45O25’ 45O25’ 45005’ 45005’ 44050’ 44050’ 44050’ 44050’ 44045’ 44030’ 44010’ 43*12’ 42O48’ 42O24’ 41°24’ 41°18’ 41005’ 40035’ 40037’ 40037’ 40’=08’ 39054’ 40014’ 40015’ 40019’ 4OQ56’ 41°56’ 41006’ 40°26’ 40047’ 44015’ 44015’ 44O26’ 46O17’ 46=‘35” 46OlO’ 46=‘00’ 45040’ 45015’

42O55’ 41055’ 41019’ 41019’ 41OlQ’ 41019’ 41019’ 42OO5’ 42OO5’ 42OlO’ 42“lO’ 41040’ 41040’ 41040’ 41040’ 41050’ 41050’ 41015’ 41015’ 41015’ 41015’ 41055’ 42O50’ 43040’ 77“02’ 75013’ 78“Ol’ 6Q”01’ 69008’ 69OOO’ 69052 70*08 70°08’ 70037’ 71°18’ 71028’ 71°42’ 72O21’ 72O34’ 72O45’ 72”22r 71057’ 71°32’ 41055’ 41055’ 39010’ 39035’ 3Q055’ 3Q010’ 39005’ 39O37’ 39045’

Tectonophysics,

Depth of boreholes (m)

960 640 1,160 1,080 1,030 1,120 2,800 880 1,050 1,000 810 480 760 760 760 2,050 720 1,000 1,020 1,100 800 440 2,040 1,150 >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO 121,000 >l,OOO >l,OOO >l,OOO >l,OOO >l,OOO > 1,000 1,560 1,360 2,500 2,500

.1,500 2,500 2,500 2,500 2,500

10 (1970) 245-281

Time equilibrium (in months unless otherwise stated)

Heat flow 2 q(cal./ cm v set)

2.0 1.5 1.0 1.1 1.1 4.4 1.0 5.7 1.5 1.3 2.2 7.1 2 2 65 20 1.5 2 2.5 1 0.5 8 1.5 1.0 46 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months >6 months 26 months >6 months >S months >6 months >6 months >6 months 1 month 1 month 1 month 1 month 1 month 1 month 1 month 1 month 1 month

2.20 2.07 1.41 1.55 1.48 2.02 1.58 2.75 1.95 2.12 2.18 2.54 2.06 2.22 2.56 1.73 2.41 2.20 2.38 2.46 2.20 2.65 1.95 1.94 1.1 1.2 1.8 0.62 1.33 1.39 2.07 2.04 1.34

1.56 1.31 1.07 1.33 1.00 2.05 1.92 1.05 1.08 1.02 1.42 1.40 1.75 1.35

253

TABLE II(continued) ~ -__-.-~-~____ Latitude Longitude Depth of boreholes N E (m) ~-------.~44045' 44040' 45O32' 45034' 45033' 44054 45010' 45015' 45017' 44008' 44404' 43055' 43055' 45005' 44049' 44049' 44O48' 440501 44*48' 45030' 44O24' 45000' 45000' 45010' 19015' 50012 50"38' 48“02' 47055' 47055' 48“02' 49“48' 4Y"48' 48050' 49005' 48O44' 48O22' 5OO20' 42020" 46O18' 45053'

41015' 410051 4101.2' 41019 41027' 43055 42"56' 42O54' 43*05 42051' 42054' 42O43' 42“43' 38OO5' 38O15' 38°15' 38='53' 38049' 38"58' 35005' 34O12' 34Oliv 34010' 35030' 34020' 34030' 36"32' 33"20' 33“20' 33“20' 33“20' 30007' 30°06' 29059' 30057' 30015' 22"45' 24"OO' 23='20' 34='38' 34057'

45046 46O48' 45044' 45039' 45"38' 45O36'

34015' 34“16' 34005' 33037' 33OO6' 33O42'

45033'

33043'

45030'

33050'

254

. ..~ _~^_.________ Y,OUU

3,000 1,125 1,150 1,150 2,525 681 650 565 787 425 398 375 700 1,200 825 2,050 1,975 1,145 1;500 2,000 2,000 2,000 1,900 1,500 2,425 817 740 1,260 1,425 363 140 112 135 140 183 700 500 350 1,900 600 500 1,000 2,400 3,200 1,950 2,400 2,500 1,200 I 1,800 1,100

Time equilibrium (inmonths unless otherwisestated)

Heat flow 2 q(cal./cm .set)

1 month 1 month >l year

1.65 2.15 2.1 2.1 2.0 1.8 1.5 1.7 1.6 1.8 2.1 1.6 1.2 1.1 1.2 1.3 1.3 1.2 1.4

1 year

>2 years 1 year lyear 1 year 5 1 year 3 years 5.5 5 11 7 8 9 22 13 0.5 year 1 year 1 year 1 year 9 0.5 0.5 3 0.5 year 0.5 year 1.5 9 2 years 2 years 4.5 years 1 year 5.5 1 year 1 year 1 year 320 days 30 days 12 days 55 days 30 days 10 days 33 days 12 days 30 days 20days

Tectono~y~ic~,

-- _.---- __._ -_

:i:‘oj 1.0

ii!*) 1.4 1.1 1.4 0.74 0.69 0.71 0.93 0.60 (0.6) 0.64 0.63 0.69 2.6 (I.21 (0.7) 1.0 1.2 1.0 1.4 1.3 1.3 1.7 1.7 1.8 1.9 1.8 2.5

10 (1970) 245-281

TABLE

II (continued)

Latitude N

Longitude E

Depth of boreholes (m)

Time equilibrium (in months unless otherwise stated)

Heat flow 2 q(ca1. /cm . set)

45031’ 45O28’ 45O28’

2,000 1,300 2,670 2,200

15 18 42 90

1.7 1.4 1.7

45O28’

34003’ 33031’ 32O32’ 32O57’

45O26’ 45O23’ 45OO6’ 45OO8’ 45007’ 45OO6’

34045’ 33010’ 35’=27’ 35039’ 35033’ 35053’

2,700

60 days

45004’

35049’

45004’ 44054’

35033’ 35015’

45000’

33040’

45037’

32“58’

45034’ 69”17’ 69O17’ 69O17’ 69OOl’ 69OOl’ 69OOl’

33000’ 30011’ 30011’ 30011’ 30011’ 30011’ 30011’

Tectonophysics,

1,560 1,200 1,200 1,100 2,400 1,500 1,900 I 2,000 2,000 600 740 900 I 1,100 1,100 1,260 1,100 535 771 622 531 470 355

10 (1970)

245-281

2’0 12 19 10 12

days days days days days days days days days

180 days 180 days 30 days 90 days 1,300 days 1,087 days 21 days 2.5 9 4 12.5 1.3

1.7 1.3 1.4 0.8 1.7 1.3 1.3 1.5 1.3 1.3 1.3 1.2 1.2 1.0 1.3 2.0 2.0 2.0 0.7 0.88 0.76 0.79 0.87 0.84

255

with the field of heat flow values corresponding to the geanticline of the Great Caucasus. The deep origin of this anomaly is confirmed by high seismicity and a large positive isostatic anomaly as well as high positive gradients of neotectonic movements. Thus heat flow data confirm the idea that the Stavropolsky dome seems to be an example of tectonic activation in the Alpine orogenesis. The investigations of unstable zones of this crust were carried out in mountains of mid-Asia within the areas of contrast giving tectonic conditions (Fig. 5). Background heat flow values in the Ferganskaya depression with its thick sedimentary cover vary from 1.0 to 1.56 HFU (Fig. 2), except for the localities Supetau, Adrasman and Nephtebad, on the edge of the geanticline where heat flow is 2.07, 2.05 and 2.04 HFU, respectively. In the Pritashkentskyaya foothills depression the heat flow in the three localities Shreder, Aktepe and Yangiul is 0.73, 1.38 and 1.40 HFU respectively (see Table I). In the Kuraminskaya anticline adjoining this depression heat flow was determined in a well in the Altin-Topkan deposit situated on the slope of Kuraminski Mountain. The temperature at a depth of 700 m is 22.4OC. Correlation of thermograms for these 4 wells Shreder, Aktepe, Yangiul, Altin-Topkan indicates the existence of a mountain province. The temperature in the foothills at 700 m depth is 16°-1’70 higher than that in the mountains. This indicates the crustal cooling associated with a high heat conductivity of local rocks and with climatic conditions in the mountains. In the foothills the 40° isotherm corresponds to depths of 300-400 m below sea level and in Altin-Topkan Mountains to a depth equal to 600 m. However, in the Kuraminskaya geanticline heat flow is 58% more, due to higher heat conductivity, than in the foothill depression. Thus we may suppose a horizontal gradient of temperature and heat flow between rock and foothill areas in this region of mid-Asia. The cooling effect of the deposition process that has taken place in the Ferganskaya valley at a rate of 0.1 mm/year gives a correction of 4% to 6% and the background value for Fergana becomes 1.20 + 10% HFU, which corresponds to the statistical estimate for intermountai% and neotectonic depressions (Smirnov, 1968). In addition, the anomalously high heat flows in Supetau, Adrasman and Nephtebad show local distortions of the background of the heat field under the influence of anticlinal domes, oil fields and possibly of pressing structures because of the friction during the clay diapir’s intrusion. Some measurements at the depths of 309-500 m were made by the oceanographic method of heat flow measurement through the bottom of Issik-Kule Lake in high mountains of the centre of the mid-Asia region of the U.S.S.R. The heat flow running from north to south is varied at depths 670-580 m in the following manner: 0.8, 1.1, 2.2, 2.0 and 0.55. Values of 2.5 and 2.0 are characteristic of the deepest central part of the lake (see Fig. l), and were obtained by repeated measurements in 1968 and 1969. Irregular temperature and heat flow distribution in mid-Asia and a block-storage structure of the crust, especially in the Pritashkentski region, are possible physical reasons for accumulation of thermo-e1asti.c stresses in this area. The stresses can be‘considered as one of the prerequisites for seismic energy release. Stresses are estimated from a formula for two joined blocks of different substances: 256

Tectonophysics, 10 (1970)245-281

El E2 ha! AT (r= El +E2 -61E2-d2El where G1e2 = Poisson’s ratios, and Ao = difference between coefficients of thermal expansion of the two materials (substances). Supposing the joined rocks in the Pritashkentiski area to be either limestones and granodiorites, or limestones and tuffs of quartz porphyrites we should take respectively: El = 7.45.105kg/cm2; E2 = 3.99.105 kg/cm2; AT = 200-300° C; and Acr = 8.10-6 degree-l, and obtain: a = 400-1000 kg/cm2. At a de th of 8-12 km the ultimate strength of limestone rocks oKWl,200 kg/cm B. Consequently thermo-elastic tensions at these levels could cause seismic activity. A chain of high heat flows has been obtained in the southern depression of the Caspian Sea at depths of 60~7?0 m amounting to 1.6 to 2.4 HFU which is probably associated with much volcanism (Fig.1) and partial melting in the upper mantle. Magnetotelluric investigations for this region will be discussed below. From the investigations of heat flow in the Arctic regions within the area of rift-formation over the Nansen Cordillera it was concluded that a mean value of this heat flow is 3.0 f 0.2 HFU (Lubimova et al., 1969) see Fig. 6. This fully corresponds to mobility and dynamics of the crust in this zone and to its high seismicity and volcanism. Linearity of magnetic anomalies near the Nansen Cordillera is in the same relation to the high heat flow as on other mid-oceanic ridges,

4;

HFU

.

Arctic

.

Fig. 6. Profile of heat’ flow values in the vicinity of line VI’-VI for ridges. a I Lomonosov Ridge zone; b = valley; c = Nansen Cordillera zone,

Tectonophysics,

10 (1970) 245-281

257

The correlations of heat flow values in mobile zones with locations of magnetic anomalies and magnetotelluric elements have indicated that such a simultaneous interpretation may result in disclosing deep melting areas, especially for volcanic regions. A few recent measurements have been made in a mobile zone of the crust in the Kuril Islands within the area of the north and middle islands of Paramushir and Atlasova
157” 7l

156=

157”

1.

49’ 154”

155”

a”

49” 158O

f==J~gj-g/=qp1 123

4

5

6

7

8

9

Fig.?. Values of heat flow in the Kurile Islands. Legend. 1 = Heat flow station and heat flow value. 2 = Volcanoes. 3 = Active volcanoes. 4 = Inner volcanic arc of the Kurile Island arc. 5 = Inside non-v&ear&! arc. 6 = Latest inner part of the Kurile Island arc. 7 - Sea of Okhotsk plate. 8 = Modern western Kamchatskaja Platform. 9 = Active faults. 258

Tectonophysics, 10 (1870) 245-281

q; HFU

Fig. 8. Profile of heat flow values in the vicinity of line V’-\J for Baikal rift zone: a = Trkutskaya Plateau; b = Baikal rift zone.

high value of 3.30 IIFU ai station 12 may be attributed to a young active fracture zone, Considering the effect of underwater volcanism the maximum heat flow on the profile across the Kurile Islands is expected to occur in the South-Kuril deep water depression. Magnetotelluric investigations accomplished in volcanic zones of Kamchatka give evidence of occurrence of melting at depths of 40-60 km (Copytenko et al., 1967). Fig. 8 shows the heat flow profile on the line V’- V, which crosses different tectonic zones of the Irkutskaya Plateau (a) and the Baikal rift zone (b). A high and remarkably non-uniform heat flow is apparent in the Baikal rift region, with a moderate and uniform heat flow in the Irkutskaya Plateau. The general heat flow distribution in various regions in the U.S.S.R. is in accordance with the normal distribution. Comparison of the results by means of Student’s t-criterion reveals significant differences between different regions.

Let us calculate the values of heat flow and temperature, on the basis of the generation of heat and the thermal conductivity coefficient for various types of the crust, In all the variants the thickness of the crust is assumed to be 34 km. The thickness of the upper sedimentary layer is set at 2 km, with a generation of heat equal to that of the granite layer, and a thermal conductivity (h) of 0.003 cal. /cm tiOC*sec. For this sedimentary layer the temperature dependence of the thermal conductivities and volume capacity of the granitic and basaltic layers is taken into consideration, and

‘I’ABIX III Dependenceof heat flow values g on the thickness h (km)

0

2

q (HJW

0.47

0.56 0.65 ______~_.._~~

4

of the granitic

layer

1:

6

8

10

12

14

16

0.74

0.83

0.92

1.1

1.2

1.29

18 1.38 ----~--~

20 1.47

for the peridot&? and pyrolitic layer account is also taken of the effect of pressure on A. Assuming a peridotite mantle with a minimum heat generation of 0.22*10-14 cal,/cm3. set, the dependence of heat flow on the thickness of the granitic layer is shown in Table III. As can be seen from the table, the flow of heat varies from 0.5 to 1.5 with increase of i%from 0 to 20 km and is almost linearly dependent upon the thickness of the granitic layer, q = 0.47 + 0.05 /2HFU. This is almost fully consistent with the experimentally found relationship in the Cordillera (Roy et. al., 1998). In the case of higher rate of heat generation in the u per mantle, complying with the pyrolytic composition (H = 1.2 10 -1801. /cm2. set), the flow of heat responds in a considerably lower extent to the thickness of the granitic l

HFU q bc

12

20 37 MnsuCb(1064)

1.1

11 37 r&is&I(~)

12 1.1

20 c=d=25

0.7

07 a5

I.

0

~

I

50

I

L.

*

I

loo

I

I1

a

d

16 c=d*25 TO cud=25 8 c=d=2!5 2 c-d=26

L

l!mkm

Fig. 9. Temperature curves for the different heat flow values of generation of heat in the mantle and curst. b = granitic layer (O-20 km); c = basaltic layer (U-34 km);and d 5 unifon radio-active layer (400 km j.

layer and the position of the Conrad boundary. Hence, with a low content of radioactive elements in a peridotite mantle, the variations of the thickness of the granitic layer should control the fluctuations in heat flow, which does not, however, exceed the mean value, I.5 HFU, for a maximum possible thickness of the continuous granitic layer of 20 km. With a high generation of heat in the mantle to a depth of 400 km, complying with the pyrolytic composition, the heat flow is increased from 1.68 to 2.13 HFU. In Fig. 9 are given the temperature curves for different thicknesses of granitic layer (b = O-20 km), basaltic layer (c = 12-34 km) with the uniform radioactive layer (d = 400 km) of upper mantle consisted from peridotites, dunites or with a non-uniform radioactive layer corresponding to a variant by Masuda, 1964. The curves of Fig. 9 correspond to different heat flow values from 0.5 to 2.0 HFU and thicknesses of the continental crust which are observed within the U.S.S.R.

TE~PE~TUR~

AND ELECTRICAL

CO~UCTIVITY

Now consider the relationship between temperature and electrical conductivity. Hughes (1955) obtained experimentally aE/ap = 4.8, - 10-6 eV/bar for peridotites with E = 2.7 eVat temperatures from 1,063P to 1,21O*C and pressures from 0 to 8.5 bar; This corresponds to 1.26 times increase in the activation energy E between 0 and 420 km. The conductivity of electronic semiconductors both impurity and intrinsic, is known to increase with pressure. This has been shown experimentally (Bradley and Jamil, 1962, 1964; Vereshchagin et al., 1962) and is in agreement with some theoretical assessments (Rikitake, 1952; Runcorn and Tozer, 1955; Tozer, 1959). For both mechanisms an increase in conductivity is connected with a decrease of activation energy (Fig. 10). The effect of pressure on electrical conductivity within the intrinsic conductivity zone has received the least study. From the ion crystal theory it follows that defect producing energy increases with pressure. A relative change of this energy (E/EO) may be estimated from the variation of compressibility, using an expression for the energy of the ionic crystal lattice (Magnitsky, 1965). Theoretical and experimental data now available show a notable effect of pressure on electrical conductivity beginning from a depth of about 200 km. At lesser depths conductivity distribution is governed mainly by temperature. According to the most popular view, the upper mantle has a peridotitic composition and its olivine portion makes up over 50% of the content (Magnitsky, 19651 Ringwood, 1966). Olivine is-a solid solution of fayalite (Fe2Si04) and forsterite fMgzSi04). The latter constitutes not less than 80 and more likely 9Osbof the mantle olivines (Fujisawa, 1968; Ringwood, 1968). Of the other components the majority are minerals of the pyroxene and garnet group rich in magnesium and iron. Comparison of electrical conductivity,for individual petrographic groups or rocks indicates that olivinites possess greater conductivity than other possible components of the upper mantle. Taking into account the prevalence of olivine, we can Consider the mantle conducti~ty to be determined by that of olivine.

Tectonophysics, 10 (19’79)245-281

261

E,ev

0.3

0

5

10

15

20

25

P kg/cm2x

30

35

40

45

50

55

lo3

Fig. 10. Dependence of activation energy upon pressure in the zone of impurity conductivity according to data of various authors. 1 - juvite; 2 P trachytoid ijolite; 3 = fayalite; 4 = fayalite; 5 0 fayalitt+sp: structure; 6 i: olivine (10.4% fayalite); 7 P olivine (17.5% fayalite); 8 = pyroxenite; and 9 I amphibolite.

An important result of investigating olivine conductivity is the fact that fayalite conductivity greatly exceeds (by hundreds of thousands times) that of forsterite at ambient temperature (Hamilton, 1965). The nature of their conductivities is different: it is impurity ionic for forsteritic and electronic semiconductor for fayalite (probably-intrinsic electronic semiconductor). This is confirmed by directly examining charge carrier sign by measuring the thermal e.m.f. in olivine samples (Bradley and Jomil, 1954). At low temperatures olivine’s conductivity is determined by fayalite despite its low content. As the temperature rises from 700 to l,OOO°C and above, the conductivity becomes mainly intrinsic ionic and becomes dependent on the basic olivine structure i.e. on forsterite. It is not equal, however, to pure forsterite conductivity because the fayalite diluted in olivine solid solution changes energetic proportions in the crystal structure. Currently the conductivity parameters of olivine are being studied rather completely at various proportions of fayalite and forsterite at moderate temperatures, i.e. in zones with impurity and intrinsic semiconductor types of conductivity. The same parameters for intrinsic ionic orou ly investigated. Hughes (1955) reported ;;;$t;;;~t~; I”;. ;;;; 3. ,,*, E. = 2.7 eV; Runcorn and Tozer (1955) have found for olivines E = 3.0 eV; Ore&kin (1965) calculated E = 2.2 eV for forsterite. We have carried out with AL Bondarenko some experiments on the investigation of electrical conductivity of olivine-containing rocks at temperatures of 100°-1,200° C in a free atmosphere. Fig. 11 shows the results of the experiments, As can be seen on the histograms in Fig. 12 one may distinguish zones having close Eg and 00 parameters with some 262

Tectonophysics, 10 (1970)245-281

-6

-8

Fig. 11. Dependence of electrical conductivity of olivine upon temperatur The hatched area is the region of experimental curves for olivinites. Different hatching patterns are used to indicate zones, in which the portions of the curves log o = f(l/T) have close parameters, 00 and EO, given in Table III. --- zone of impurity conductivity Groups I, II and III, Group IV zone of intrinsic conductivity Group V I Group VI i Inflexion points. Dashed line represents the extrapolation of the zone of intrinsic conductivity to high-temperature regions. X= experimental points for peridotite at atmospheric pressure, obtained by Hughes, 1955. Solid lines indicate the results of study of synthetic olivines. 1 = forsterite, 100% (Ore&!&, 1965). 2 = olivine, 10% fayalite, 23 kbars (Bradley and Jamil, 1964) 3 = forsterite, lOO%, 23 kbars ~ 4 = olivine, 10% fayalite 5 = olivine, X7.556fayalite 3 (Hamilton, 1965) 6 = olivine, 50% fayalite, 23 kbars (Bradley and Jamil, 1964) 7 = fayalite, IOU%, 23 kbars 8 = fayalite, lOO%, spine1 phase 7 (Bradley and Jamil, 1964)

Tectonophysics, 10 (1970}245-281

263

Fig. 12. Histograms of distribution olivinites at different temperatures.

of EO (in A) and 00 (in B) of

temperature ranges. The values of Eg and 00 parameters are given in Table III. Fig. 11 illustrates similar results of experimental measurements of the conductivity of synthetic olivines (Bradley and Jamil, 1964; Hamilton, 1965). In Fig. 11 the curves for olivine containing l-179 of fayalite fit well within the area of the first three curve groups. The conductivity parameters of syn etic oliT$res from 100° C up to 300-5OO’Jc (E = 0, 7-0, 75 eV; 00 = 10’ Y-lo-3Q -cm-l) are in good agreement with the second group parameters and evidently correspond to impurityionic conductivity, as do those of the first group. Over the range 3Q@-5OOOC tq 75%900° C synthetic olivine has E = O.ibO.95 eV and a0 = loo-10’2 0 -cm, conforming to the third group. According to Bradley and Jamil, (1964) this group exhibits semiconductor Conductivity. The fourth and fifth groups are apparently pertinent to a zone of olivine intrinsic conductivity as evidenced by inflection points on curves of Fig. 11, high values of activation energy and conservation of conductivity mechanism up to the temperatures nearing l,200° C. It is not yet clear why there are two groups instead of one. Experimental curves for some samples have inflection points at temperatures from 900 to 1,200° C. The conductivity parameters of these samples give no clearly defined values of E and 00 above the ‘nfler-tion points but only the intervals: E = 3,2-3,8 eV, oQ = IOl~lOlg Q -1. cm-l. These parameters characterize to a greater extent the alteration processes within a sample than intrinsic ionic conductivity of olivines. 264

Tectonophyeice, 10 (1970) 245-281

One can assume four processes of electrical conductivity in minerals of the upper mantle: ionic (impurity and intrinsic) and semiconductor types of conductivity (impurity and intrinsic). Thus:

U =

CUiexp

(-2)

=Olexp

62)

+a2exp

(2)

+03exp (-z)+o4exp(-

2:)

where al, El are parameters for impurity ionic conductivity 02E2 are parameters for intrinsic ionic conductivity, ~3 E3 are parameters for impurity electronic semiconductivity and a4 E4 are parameters for intrinsic semiconductivity. Electrical conductivity of deeper zones of the upper mantle should be considered on the basis of hypothetical concepts of the physical nature of these zones. The most notable feature of the mantle structure is the existence of the so-called transient zone, or the “C”-layer (400-900 km) where seismic wave propagation and density are abnormal. The nature of this zone seems to be associated with a series of stepwise mineralogical transformations and a more dense packing of the crystal lattices (Magnitsky, 1965; Ringwood, 1966, 1968). Mineralogical transformation can run in two modes - polymorphic or by decomposition. For minerals of the olivine group the transition from an olivine rhombic structure to a cubic spine1 structure was obtained experimentally for fayalite (Akimoto et al., 1967) and forsterite (Ringwood, 1966; Akimoto and Yoshiaki, 1966). Experiments have also shown a stepwise conductivity increase by two orders of magnitude during olivine spine1 transition in Fe3SiO4 and Ni2SiO4 (Akimoto and Fujisawa, 1965). A similar pattern is to be expected for transition in forsterite due to analogous alterations of crystal structure. Experiments with pyroxene have two possible results: either they decompose into olivine plus stishovite at a pressure slightly below that of the olivine-spine1 transition in forsterite (Sclar and Carrison, 1964), or they decompose into spine1 plus stishovite at pressures somewhat over that of the transition in forsterite (Ringwood and Major, 1966). Thus both olivines and pyroxenes are transformed into a spine1 modification of olivines in a rather narrow range of thermodynamic conditions. Hence transformations taking place within the mantle in this range are accompanied by a notable increase in electrical conductivity. Analysis of experimental data of mineralogical transitions has shown that a step-wise increase in conductivity should be expected at a depth between 350 and 450 km. Anderson (1965), Press (1965), Archambeau et al. (1967) and Barr (1967), analyzing seismic data, suggested the .possibility of two sharp variations of velocity of seismic waves at the depths of 400 and 700 km, which found support in recent examinations of velocity distribution of the mantle (Anderson, 1967). A density model having two sharp changes is also consistent with the available geophysical data (Press, 1966). An important feature of the phase state of the upper mantle is the possible existence of melting zones. An analysis of the experimental study of electrical conductivity during the melting process (Khitarov and Sluzky, 1962) leads to the following.conclusions. Electrical conductivity of the

Tectonophysics, 10 (1970) 245-281

265

system rises sharply by 100-1,000 times with melting and afterwards it increases with temperature slightly. Samples examined during various melting stages show that such abrupt increase in conductivity depends upon the stage at which the liquid begins to envelop solid particles forming a transparent film structure. It is evident that in this case the volumetric conductivity of the system under study is mainly determined by the higher conductivity of the liquid phase. Thus at the depths where ultimate liquid phase concentration is reached in the course of melting, one should expect an abnormal rise of electrical conductivity. Investigation of silicates after quenching at the moment of melting indicated that their conductivity in the vitreous state can greatly exceed the conductivity of the same silicates having a crystal structure (Eitel, 1962). This can be attributed to the freezing of the defects formed during the melting process. If a substance is becoming amorphous in the low velocity layer, the conductivity of this layer may be above “normal” at this depth. Accordingtothis view, 2% volume increase of amorphous phase is enough for a 6% decrease in seismic velocity. If the amorphous phase conductivity is close to that of the melt, under the conditions of volumetric connection of conducting component, the conductivity in a zone of low velocity layer may be 5 to 10 times more than in crystalline rocks under the same conditions.

ELECTRICAL CONDUCTIVITY WITHIN THE MANTLE ING TO ELEC’l?ROMAGNETIC DATA

OF THE EARTH ACCORD-

The theory of electromagnetic induction permits use of magnetic fluctuations of various periods in the natural geomagnetic field for investigation of electrical conductivity at depths in the earth. Until recently the electrical conductivity of the upper mantle had been determined on the basis of three component spectra of geomagnetic fluctuations. Measurements were made with the aid of the potential distribution method which provided a generalized data average for the earth as a whole. According to these data the 3 layer of the upper mantle of the earth is considered to be electrically almost uniform and to have high resistivity down to depths measured in hundreds of kilometres (Fig. 13). The separation of the potential of geomagnetic fluctuations into internal and external parts can be made through the analysis’of various types of geomagnetic fluctuations (Sq, Sd, Dst, SSG , etc.). This analysis is carried out either for the earth as a whole or for separate local areas of the earth’s surface, depending on the type of fluctuation involved. The most convenient for spherical harmonic analysis are solar daily (Sq) magnetic variations. Such analysis has been conducted by many authors for different intervals of time. The parameters of the Lamb model calculated on the basis of these data vary over wide ranges. It has been found that the th’ckness of the nonconducting layer varies om 100 to 800 km for the P2f harmonic and from 0 to 500 km for the P3Y harmonic, that is, the results obtained are too sparse. The use of higher harmonics, P$ and Pii& for calculations of conductivity is hampered by scattering of data. The discrepancy between the results obtained by analysis of cyclic fluctuations (both Sq and longer period), depending on the season of obser266

Tectonophysics,

10 (1970) 245-281

30 km

Fig. 13. Distribution of conductivity within the earth’s mantle. Curves v = f(U) calculated by: 1 = RikUke (1969); 2 = Lahiri and Price (1939) (model d); 3 = McDonald (1957); 4 = Yukutake (1959); 5 = Eckardt et al. (1953); 6 = Lahiri and Price (1939) (model ef. The values of conductivity corresponding to the effective penetration depth of geomagnetic fluctuations: a = Chapman (1910), S fluctuations; b = Hasegawa (19361, Sq fhmtuations c = Chapman and Price (193 8 f, fist fluctuation; d = Yukutake (1968), bays; e = Yukutake (1968), effect of solar flare; f = Benkova (1941), Sq fluctuations. Hatched areas of o and H refer to determinations made by various authors; I = according to data of analysis of bay-shaped Sq and 1Dstfluctuations.

vations and on the point selected for analysis, has also been pointed out (Matsushita and Maeda, 1965; Kulieva, 1966). In particular, the thickness of the nonconducting layer as measured from the coastal points has been found to be strongly overestimated. According to calculations based on the analysis of aperiodic fluctuations, the parameters of conductivity within the mantle vary signifiTectonaphysics,10 (1970)245-281

267

cantly from point to point (Rotanova, 1966), from 100 up to 1,000 km, but the validity of these fluctuations is highly doubtful. Fig. 13 shows the curves of electrical conductivity for the mantle obtained by different methods. The hatched regions in the figure are those within which the values of conductivity are simultaneously consistent with several independent data of the analysis of geomagnetic fluctuations. Two features are characteristic of all the patterns involved: (1) rather sharp (probably, even stepwise) increase of conductivity at a depth of several hundred kilometres under a sufficiently high-resistance overlying layer; and (2) gradual increase of conductivity in the lower mantle. Considerable discrepancies between available geomagnetic data do not allow us to judge at present the path of the curve of conductivity in the interior of the earth with more confidence than is possible from the limits of the hatched regions, The sections falling in these limits will be called here normal geoelectrical sections.

SOME MODELS OF THE UPPER ~NTLE AND THEORETICAL DEEP ~GN~TOTELLURI~ ~NVESTr~T~~N

CURVES OF A

Currently the main method for studying the electrical conductivity of the earth’s deep interior i@ magnetotelluric investigation. The development of the magnetotelluricYapproach and geomagnetic depth-sounding method opened up new possibilities for investigating the electrical properties of the upper mantle and for locating anomalies. The application of these methods is beset with difficulties arising due to the interference of nonuniformities of the sedimentary thickness. Some of the anomalous magnetic variations, for example, the one in northern Germany (Kremser, 1962; Kertz, 1964) may be caused by surface dlsturbantes and may be associated with the currents induced in the conducting sedimentary jacket (Vanyan, 1968). A substant~l error is possible due to the presence of rises over the high-resistance floor. Nevertheless, by making use of this method we have succeeded in obtaining a series of sufficiently reliable results attesting to the variability of the geoelectrical section of the upper mantle. Interpretation of experimental conductivity curves is made by their comparison with theoretical curves. On the basis of up-to-date knowledge, the electrical conductivity of the upper mantle is believed to increase sharply at a definite depth determined from the asymptotic formulae for K-type three-layer section. In this case downward branches of the curves and H-line (asymptotic line). However, analysing the theoretical curves Of conductivity within the earth we came to the conclusion that none of them shows a distinct point of rapid increase, except the version with melting. Therefore there is a need to calculate theoretical curves from magnetotelluric investigations capable of reflecting a smooth rise of conductivity with depth, An attempt to perform such calculations was made by Vanyan and Zabolotnaya (1968) for the simplified model of the upper mantle. We will use the new laboratory data and a more real petrological model of the upper mantle. Fig. 14 shows the electrical conductivity versus depth for various temperature distributions. These curves are calculated assuming a faya268

Tectonophysics,

10 (1970) 245-281

log

c

ohm-’

cm-’

Fig. 14. Models of depth distribution of electrical ~ondu~ti~ty within the earth’s mantle. Solid line.= 10% fayalite; and dashed line = 17% fayalite. f,8 = Precambrian shields and ancient plateaus; 2,P = Paleozoic plateaus; 3,10 = Regions of Cenozoic folding or activation; 4,11 = oceanic troughs; 5 = Cenozoic folded mountain structures; 6 = eugeosynclines, island arcs, rifts; and 7 = pattern with existence of 5% of molten phase at depth 70 km.

lite content of 10% and 17%. The parameters used in the calculations are given in Table IV. They correspond to the results of a study of synthetic olivines within a low temperature area (Bradley and Jamil, 1962, 1964; Hamilton, 1965). The parameters of specific conductivity were taken from our data, and the dependence E = f(p) was reported by Hughes (1955). For olivine in the spine1 form we used the results for fayalite (Akimoto and Fujisawa, 1965). As may be seen from Fig. 14, in the beginning the conductivity increases with temperature and depth under the influence of pressure;then it stops to increase until the start of the C-layer where it increases again. The points of the conductivity maximum on the curve for tectonically active areas reflect the assumption of melting zones at a definite depth. The level of the geoelectrical boundary of the C-layer was tentatively accepted as the balance curve for olivine-spine1 transition in forsterite. Tectonophysics, 10 (1970)

245-281

269

Temperature range (“C)

100-500 500-750 700-~1,500-2,000)

100-300 300-900 999-(1,500-2,000)

1,509--2,000

Percentage of fayalite

10

17

II320

Laboratory data on the electrical

~-

intrinsicsemiconductor

semiconductor intrinsic-ionic

-

semiconductor intrinsic-ionic

-

Type of conductivity

lo1

0.37 5 *

8 * 10-l 5 9 lo3

10-2

0.70 0.90 1.8 9 .

6 . 10;; 8 . 5 . IO3 10

(ohmM1.cm-l)

W) 0.75 0.91 1.8

00

EO

-4.6

* lo6

l

-6 -3.5 * 10-6 -3.5 1o_6 4.8 * 10

-3.5 * lo6 -3.5 * 1o-6 4.8 * 10-6

(eV/ bar}

swap

conductivity of olivinites and rocks containing olivines

olivines with spinei structure, convalent bond _.___ .-..__

solid solution of fayalite and forsterite in olivine structure, ionic bond

Crystalline structure

By virtue of the positive slope of the balance curve in the therm~ynamic coordinates the depth of transition increases with temperature. Comparing the curves obtained, one can see that maximum variations of electrical conductivity should be observed at 50-100 km depths where they reach five orders of magnitude. The curves approach each other rapidly at large depths. The major growth of conductivity within the upper f+ ohm to4

log -7

-6

-5

d

-4

ohm' cm’ -3

-2

-1

1

Fig. 15. Theoretical curves of geomagnetic depth-sounding and corresponding distributions of electrical conductivity. Numbers of curves represent various tectonic zones (f,2, and 3 are denoted in Fig. 14). 4 = Cenozoic folded mountain structures. 5 = eugeosynclines, isIand arcs, rifts. Dashed lines represent curves calculated for the same sections of the mantle at different values of total longitudinal conductivity of sedimentary thickness. Line H = 420 km. Jt corresponds to asymptotic form of geomagnetic depth-sounding_curves for the case: 00 - 420 km < 10-5 to 1Ue7 n-lecm-l. CT> 420 km > 10e2 to 10m3 QW1.cm-l.

Tectonophysics, 10 (1970)245-251

271

mantle occurs at depths of 50-150 km and then it increases only slightly. The main feature of the curves of magnetotelluric investigation is the non-coincidence of high downward branches with the so-called H-line (at an angle of 63O). In this instance, as Vanyan and Zabolotnaya (1968) mentioned, the H value obtained from the formulae valid for K-type section at p3 = 0, is a conditional value depending on a model type. We also have plotted theoretical magnetotelluric curves for the models with a smooth increase in conductivity. Fig. 15 illustrates some results of the calculations. Let us formulate the principal conclusions based on the analysis of our theoretical magnetotelluric curves: (1) The right-side downward branches of the curves for all conductivity distributions discussed have no portions corresponding to H-line over the whole period. (2) The range of periods where the magnetotelluric curve contains information about the C-layer exceeds the limits of diurnal variations and this does not depend on the C-layer conductivity. (3) The mutual positions of electrical conductivity curves are regular (conforming to an established rule) in accordance with the regular arrangement of temperature curves for different areas in the earth. The relationship between downward branches of magnetotelluric curves is also regular. These branches may be approximated by straight lines with adequate accuracy, (4) The position of downward branches is determined by the character of conductivity rise within the upper mantle and does not depend on the conductivity of sedimentary stratum (S) for S 5 40,000m1. At larger S-values, downward branches become nearer to the H-line and thus bear no information regarding the mantle conductivity. (5) The observed regularities support the principle of calculating parametric formulae permitting the interpretation of the magnetotelluric curves by means of models with smoothly increasing conductivity within the upper mantle. SOME RESULTS OF MAGNETOTELLURIC INVESTIGATIONS Let us now go on to consider the results of magnetotelluric investigations carried out in the following regions: Kamchatka, Baikal Lake, the south Caspian depression, Turkmenia, and the Vilyuy syneclise. These results will be compared with similar data pertaining to the Hungarian trough, the Rhine graben and western North America. As an example of the interpreted curves obtained by magnetotelluric investigations we will consider the curves of conductivity in a longitudinal direction typical for the south Caspian depression (Berdichvsky et al., 1969; Gokhberg et al., 1969). They are well organieed and have an extended descending branch which belongs to the layer at a depth of 40-80 km at the margin of the depression (Fig. 16). At the points on the periphery of the depression in the direction of the Kopet Dag and Caucasus Mountains these curves correspond to the conducting layer which subsides to a depth of 100 km and may be connected with the distortion effect of basin boundary. Upon transition to the Kara-Kum Plateau the conducting layer disappears. Hence, the transition from the plateau to the geosyncline is 272

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10 (1970) 245-281

p ohm

r

A

,

10

I

fisec

100

0

10

Fig. 16. Magnetotelluric curves in a longitudinal direction for the south Caspian depression. The hatched lines correspond to H-lines, i.e. falling curves (p-T) for the section containing the high conductivity layer, the top of which is at a depth of 40-60 km. accompanied by a change in the geoelectrical sections of the upper mantle. An analogous pattern has been established for the Hungarian trough (Peaus, 196’7; Adam and Vero, 1968). Thus, in the regions of the south Caspian depression and the Hungarian trough, as evidenced by the data of magnetotelluric investigation an anomalous conducting layer (about 20 km thick) is traced in the upper mantle at a depth of 40-60 km. The contours of the spreading of this layer have been obtained, which indicates that this layer may be related to the zones of recent settling of the Alpine erogenic belt of Eurasia. According to the above analysis the presence of this layer may be related to the partial melting of the substance of the upper mantle. This is in agreement with the increased geothermal activity and Oligocene-Quaternary volcanism of the region under consideration. Thus, the data now available indicate a close similarity between geological and geophysical characteristics of the south Caspian and Hungarian depressions. (Fig. 17, 18). The volcanism provides direct data on melting processes occurring within the mantle. The present formations (QuaternaryOligocene) in the Hungarian depression have been thoroughly studied. Such a study in the south Caspian depression is complicated due to the outcropping of possible volcanic products which were introduced when the depression was sinking. Tectonophysics, 10 (1970) 245-281

273

caspm

10 0

100

sea

Balkers

km

c

10 20

I

30

1

1

” 1

”

*

40

50 60 kml A Wlngarian

dep_essIon

Carpathians

10 Y

20-v

7”

“I”

30-v

Y

40-

v

y

SO-”

*

*

y

Fig. 17. A. Schematic cross-section of the earth’s crust and upper mantle in the region of the south Caspian depression. B. Schematic cross-section of the Hung&i&nBasin region of the upper mantle.

Legend. I = ~eogeRe-Tertiary sediments. 2 = Mesozoic sediments. 3 = Paleozoic sediments. 4 = “Granitic” layer. 5 = “Basaltic” layer. 6 = Deep faults. 7 = Anomalous conducting layer based on magnetotelkic data.

Hkm

Hkm

Fig. 18. Histograms of positions of higb conductivity layer for regions of Fig. 17. 274

Twtonophysics,

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However, the development of magnetic anomalies in the peripheral zones of both depressions enables one to suppose that formations with basic volcanics are also widely developed in the south Caspian depression within the stratum of Pliocene-Quaternary sediments. The history of volcanism in the Hungarian depression can be divided into two stages: geosynclinal proper and erogenic. In the first stage the volcanism was confined to the internal Karpatski volcanic belt, which probably represented a typical island arc during accumulation of flysch. The magma of that period is related to the Pacific type characteristic of the present island arcs. The second stage of volcanism corresponds to effusion of Atlantic basalts related to the Pannon termination. In this stage the volcanism is covering the interior of the depression, concentrating in regions with the most intensive differential movements of crustal blocks. Considering the intensive activity of thermal and carbonate springs we may assume that basaltic volcanism continued up to the Pleistocene. Probably in this case we observe only the first phase of a new stage which can be correlated with the termination of geosynclinal development in this part of the Alpine erogenic belt. The fundamental possibility of the use of bay-shaped disturbances for the purpose of geomagnetic depth-sounding has been pointed out in a number of papers (Vanyan and Kharin, 196’7). Determination of impedances for various periods permits the stratified distribution in conductivity within the earth to be surveyed at the point of observation. The impedance curves plotted for several points along the profile across Baikal (eastern Siberia) point to the depth of the top of the conducting mantle from 180 km on the plateau to 80 km under the Baikal rift system (Vanyan and Kharin, 1967). As we reported earlier, the observed pattern is in good agreement with the heat flow anomaly (varying within the range of 1.6-3.4 HFU) (Lubimova, 1969). The observations carried out recently in the region of the Baikal rift system testify to the possibility of development of two anomalously conducting layers within the earth’s crust and on the boundary between the crust and the mantle (Bulmasov et al., 1968; Pospeyev et al., 1969). The location of the two layers in the section serves for the delineation of the tapered crust-mantle structure characteristic to the recent rift systems (Fig. 19). For comparison, the figure also shows the seismic section across the Rhine graben. An interesting correlation between the zones of increased electrical conductivity and those of decreased seismic wave velocities is observed. By comparing the results obtained in the regions of Baikal and the Vilyuy syneclise, which lies along the northeastern continuation of the Baikal rift, we may suggest that there exists a genetic relation between these two regions. A conducting layer (p = 1 a ) several kilometres thick has been detected within the crust at a depth of 15-20 km in the region of the Vilyuy syneclise. Area1 studies make it possible to trace its extent in the region of observations (Berdichevsky et al., 1969). An analysis of the currently available geological and geophysical data pertaining to this region shows that the detected layer is associated with the phenomena of dehydration of metamorphic rocks which took place in the course of active rearrangement of the earth’s crust. Tectonophysics, 10 (1970) M5-281

275

0

50 km

0

50 km

Rhine

10 30 50

B

Baikal

km’

Fig, 19. Comparison of geophysical sections across the Rhine graben and Baikal rift. A. Seismic section across the Rhine graben Ratched areas are zones of decreased velocities (Mueller et al., 1967). B. Geoelectrical section across the Baikal rift. Hatched areas are zones low resistivities.

The m~netotelluric ~vesti~ti_~s. and geomagnetic dep~-soundi~ investi~tions carried out in Kamchatka (Klyuchi station) enabled detection of a highly conducting layer at a depth of about 50 km (Co~ite~o et al., 1968). Its thickness ranges from 10 to 30 km and its resistivity is equal to several ohm-metres. This layer is traced by using the data provided by magnetotelluric investigations as well as by magnetovariational sounding. The interpretation of these results may be that the magma accumulation zone in the region of recent active volcanism is located at a depth of 50-60 km and its thickness is about 20 km. The distribution of the seismic wave velocities V and Vs points to the lowering of these velocities beginning from the bor iier line of the MohoroviEiC discontinuity (Moho) over a distance of 80-110 km. The absorption of seismic waves has a maximum at depths of 40-60 km. The effect of screening of the seismic waves travel&&gfrom distant earthquakes also lends support to the existence of the reduced viscosity at a depth of 5Q-60 km under the Klyuchi group of volcanoes. The mean annual number of earthquakes and the energy per earthquake decreases at a depth of 30-40 km and increases at a depth of W-80 km (Averyanova, 1966). The reduction of the number of earthquakes is indicative of either the absence of stresses or the decreased viscosity at the same level of stresses. The decrease of the energy of earthquakes is perhaps associated with the process of creep and hence the reduction of strength. 276

Tectonophysics, 10 (1970)245-281

According to the distribution of earthquake foci across the strike of island arcs the aseismic zones are observed at depths of 29-30 km and 80-100 km. Thus, the total sum of the available data, including geoelectrical and geothermal information, indicate that the concentration of the liquid magmatic phase is occurring at a depth of 40-100 km under the volcanic zone of the Kuril-Kamchatka arc. It should be noted that the high conductivity layer in the region of recent volcanism of western North America is observed at the same depth interval (Caner and Cannon, 1967).

CONCLUSION

The available data attest to the existence of a correlation between geoelectrical parameters and geothermal activity of separate regions, Serious difficulties are, however, encountered in the determination of temperatures directly by the use of electrical conductivity data, For depths exceeding 400 km we do not know the exact parameters of the relationship E = f( P, T). At such a depth there occurs the rearrangement of the crystalline structure of minerals. A large volume of work has been accomplished with the aid of various geoelectrical methods in various regions, but only a small part of results can be considered reliable. These results demonstrate that it is possible to discover a localized anomalously conducting layer, at depths from 20 to 100 km, associated with the process of melting or dehydration. The determination of the electrical parameters of deeper horizons is at present a problem in which much remains unclear. For example, note should be taken of the question of the distorting effect of horizontal geoelectrical nonuniformities, and also of the necessity to extend our conceptions of the structure of external sources, We may suppose that the electrical conductivity of the mantle depends on olivine in which the content of fayalite ranges from 10% to 20%. The parameters of the relation o = f’(P, 7’) for olivines are known, From the data on magnetic variations as well as the information provided by the geomagnetic depth-sounding method it is known that the conductivity to a depth of 400 km is lower than 10-4 or 10-5 51-I *cm-l. The data available do not allow us to finalize these figures or to make any judgement about the pattern of conductivity in this depth range. If the effect of pressure is disregarded, which would be valid for a depth of 100 km or so, then the temperature cannot exceed 700-l,OOO°C under these conditions. Further calculation of temperature at greater depths reduces to a consideration of the effect of pressure, which compensates, in the case of the intrinsic-ionic mechanism, the increase of electrical conductivity at the expense of temperature rise. The range of maximum temperature is l,OOO-1,300°C. According to the available data on heat flow, generation of heat, and thermal conductivity, the temperature at a depth of 400 km cannot be less than 1,500°C. The inconsistency between the thermal method and the geoelectrical method is especially evident in the regions of recent volcanism, where a conducting layer is observed in the upper mantle according to the data furnished by magnetotelluric investigations Tectonophysics, 10 (1970) 245-281

277

and geomagnetic depth-sounding. The minimum on the sounding curves which is related to this layer and the second ascending branch once more demonstrate that the conductivity below this layer, i.e., at depths of 60-100 km, should be comparable with the conductivity of the crystalline part of the earth s crust, that is, equal to 10-6 or 10-Y 52-I.cm-I (see also Schmucker, 1970). In this event the temperature at these depths should not be higher than 600-‘?OO°C. Calculations of temperatures and the very fact of existence of melts in the mantle provide temperatures twice as high as these estimates. The incompatibility of these figures makes it very difficult at present to answer the questions concerning the interrelation between temperatures and electrical conductivity within the earth. The causes resnonsible for this contradiction remain unknown and are matters for future solution. first of all, to finalize the paraIn further work it will be necessary, meters of the relationship (T = f (P, T) for compounds which are thought, of the according to modern conceptions, to enter into the composition mantle. REFERENCES Adam, A., 1968. A felso kopeny elektromos jolvezeto zetegeneh osszefuggese a nagytektonikaval. Geofiz. Koslemen, 17 (l-2): 52-54. Adam, A., 1968. tuber die Informationen der elektromagnetischen Messungen in Ungarn. Geofiz. Koslemen., 17 (l-2): 23-38. Adam, A. and Vera, J., 1968. Magnetotelluric deep soundings in Hungary. Deta Geoda&, Geophys. Montan. Acad. Sci. Hungary, 3 (l-2):129-149. Akimoto, S. and Fujisawa, H., 1965. Demonstration of the electrical conductivity jump produced by the olivine spine1 transition. J. Geophys. Res., 70 (4): 443-449. Atimoto, S. and Fujisawa, II., 1966. Olivine-spine1 transition in the system Mg2Si04-Fe2SiO~.at 866 O. Earth Planetary Sci. Letters, I(4): 237-240. A,;imoto, S. and Yoshi 1, I., 1966. High-pressure synthesis of Mg2Si04 spinel. Earth Planetary Sci. Letters, l(5): 358-359. Akimoto, S., Komsda, E. and Kushiro I., 1967. Effect of pressure on the melting of olivine and spine1 polymorph of Fe2Si04. J. Geophys. Res., 72(2): 6’79-686 Anderson, D.L., 1965. Structure and composition of the earth’s mantle. In: C.H. Ahrens, K. Rankhama, and SK. Runcorn (Editors). Physics and Chemistry of the Earth. Pergamon, London.6: I-129. Anderson, D.L., 1967. Latest information from seismic observations. In; T.F. Gaskell (Editor), The Earth’s Mantle. Academic Press, London and New York, pp. 335-420. Arch&beau, C.B., Flin, E.A. and Lambert, D.G., 1967. Fine structure of the upper mantle from seismic observations (Abstr.). Trans. Am. Geophys. Union, 48 (1):201. Barr, K.G., 1967. Upper mantle structure in Canada from seismic observations using chemical explosions. Can. J. Earth Sci., 4(5):961-975. Benjkova, N.P., 1941. Quiescent solar diurnal variations of the earth’s magnetism. Gidrometeorologicheskoye Isd., Mrrscow 74 pp. (in Russian). Berdichevski, M.N., 1968. Electrical prospecting by the method of magneto-telluric profiling. Nedra. Moscow, 255 pp. (in Russian). Berdichevski, M.N., Vanjan, L.L., Gokhberg, MB., Dubrobski, V .G. and Fajnberg, E.B., 1967. Recent results in connection with dep-h ~~etotellu~c investigations. Dokl. Akad. Nauk, S.S.S.R,, 177(3):564-566. Berdichevski, N.M., Borisova, V.P., Vanjan, L.I., Feldman, IS. and Yakovlev, I.A., 1969. Electric conductivity anomalies within the earth’s crust in Yakutiya. Izv. Akad. Nauk S.S.S.R., Ser. Fiz. Zemli, 1969 (10): 43-49. 278

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F., 1965. Speculations on the earth’s thermal history. Bull. Geol. Sot. Am., 76 (2): 133-154. Bradley, R.S. and Jamil, A.E., 1962. Electrical conductivity of fayalite and spinel. Nature, 193(4819). conductivity of olivine at high Bradley, R.S. and Jamil, A.E., 1964. The electrical temperatures and pressures. Geochim. Cosmochim. Acta, 28(1)X669-1677. Bulmasov, A.P., Gornostajev, V.P., Mandelboum, N.M., Pospeev, V.P. and Savinski, K.A., 1968. Deep magnetotelluric sounding in the Baikal region. In: A. Florensov (Editor), Baikal Rift Zone. Nauka, MOSCOW, pp. 140-147 (in Russian). Cagniard, L., Basic theory of the magnetotelluric method of geophysical prospecting. Geophysics. lB(3): 605-635. Canner, B. and Cannon, W.H., 1965. Geomagnetic depth-sounding and correlation with other geophysical data in western North America. Nature, 207(5000):927-928 Chapman, S., 1919. The solar and lunar diurnal variations of terrestrial magnetism. Phil. Trans. Roy. Sot. London, Ser. A, 218: 1-118. Chapman, S. and Price, A. T., 1930. The electric and magnetic state of the interior of the earth as inferred from terrestrial magnetic variations. Phil. Trans. Roy. Sot. London, Ser. A, 229: 427-460. Copyitenko, U.A., Gorshkov, Ad. S., Gorshkova, T.A., Feldman, I.S. and Feldman, T.A., 1967. Magnetotelluric sounding in the village Kljuchi of the Kamchatka region. Izv. Akad. Nauk., Ser. Fiz. Zemli, 1967 (9): 66-72 (in Russian). Eckhardt, D., Larner, K. and Madden, T., 1963. Long-period magnetic fluctuation and mantle electrical conductivity estimates. J. Geophys. Res., 68(3). Eital, V., 1962. Physical Chemistry of Silicates. Foreign Literature Publishing‘ House, Moscow,l055 pp. (in Russian). Elsasser, W.M., 1950. The earth’s interior and geomagnetism. Rev. Mod. Phys., 22(l): l-35. England, A.W., Simmons, G. and Strangway, D., 1968. Electrical conductivity of the moon. J. Geophys. Res., 73(10):3219-3226. Flathe, H., 1967. The determination of the electrical resistivity of the crust within the region of the Rhine graben. Abhandl. Geol. Landesamtes Baden-Wiirttemberg, 6(1967) 97-106. Fujisawa, H., 1968. Temperature and discontinuities in the transition layer within the earth’s mantle: geophysical application of the olivine-spine1 transition in the Mg2Si04-Fe2Si04 system. J. Geophys. Res., 75(10):3281-3294. Gokhberg, M.B., Dubrovski, V.G. and Nepesov, K., 1968. The results of the use of magnetic storms for deep sounding in Turkmenia. Izv. Akad. Nauk, S.S.S.R., Ser. Gepfiz., 1968 (12) 96-97. Hamilton, R.M., 1965. Temperature variation at constant pressures of the electrical conductivity of periclase and olivine. J. Geophys. Res., 70(22r5679-5692. Hasegawa, M., 1936. Representation of the field of diurnal variations of terrestrial magnetism on quiet days by the method of graphical integration. Proc. Imp. Acad. Tokyo, 12: 225-228. Hughes, H., 1955. The pressure effect on the electrical conductivity of peridot. J. Geophys. Res., 60(2): 187-191. Kertz, W., 1964. The conductivity anomaly in upper mantle found in Europe. J. Geomagnetism Geoelectric., 15(4): 185-192. Kremser, G.: 1962. Ergebnlsse erdmagnetischer Tiefensondierung in der Umgebung von Giittingen. 2. Geophys., 28: l-10. Kitarov, N.I. and Sluzki, A.B., 1965. The impact of pressure upon the melting temperature of albite and basalt (according to the data of electric conductivity measurements). Geochemistry, 12: 1395-1403 (in Russian). Kulieva, R.N., 1966. The electric conductivity within the earth from the data on the annual geomagnetic variations. Geomagnet. Aeronomy, 1966 (2): 370-374 (in Russi:m). Lachenbruch, A., 1968. Preliminary geothermal model of the Sierra Nevada. J. Geophys. Res., 73(22): 6977-6989. Lahiru, B.N. and Price, A.T., 1939. Electromagnetic induction in non-uniform conductors and determination of the conductivity of the earth from terrestrial magnetic variations. Phil. Trans. Roy. Sot., London, Ser. A, 237: 509-540. Tectonophysics,

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Lidyard, .A., 1362. Crystals Ionic Conductivity. Foreign Literature Publishers, MOSCOW,222pp. Lubimova, E.A., 1968. Thermal studies of the Earth and the Moon. Nauka, Moscow, 27; pp. ~~atsushita~ S. and iMaeda, H., 1965. On the geomagnetic solar quiet daily variation field during the IGY. J. Geovhvs. Res., 70 (2): 2535-2558. IMacDonald, G.J.;., 1965. Geophysical deduction from observations of heat flow. ln: W.H.K. Lee (Editor), Terrestrial Heat Flow, Geophys. Monograph, 8: 191-210. Magnitsky, V.A., 1965. The Internal Structure and Physics of the Earth. Nedra, Moscow, 378 pp. Masuda, A., 1965. Geothermal and petrogenic implications of the distributional relationship between thorium and uranium. Tectonophysics, 2(l): 69-82. McDonald, K.L., 195%. Penetration of the geomagnetic secular field through a mantle with variable conductivity. J. Geophys. Res., 62(l): 117-141. Mueller, S., Peterschmitt, E., Fuchs, K. and Ansorge, J., 196’7. The rift structure of the crust and upper mantle beneath the Rhinegraben. Abhandl. Geol. Landesamtes, Haden-Wiirttemberg, 6: 108-113. Oreshkin, P.T., 1965. Electric Conductivity of Refractory materials. Isdatelstvo Metallurgic, Moscow, 153 pp. (in Russian). Parkhomenko, E.I., 1965. Electrical Properties of Rocks. Nauka, Moscow, 163 pp. (in Russl~~. Pospeev, V.P., Mikhalevski, V.N. and Gornostajev, V.P., 1969. The results of izsing magnetotelluric methods in the regions of East Siberia and Far East. Magnetotelluric techniques in studying the structures of the earth’s crust and upper mantle. Nauka, Moscow, 4: 139-149 (in Russian). Praus, O., 1967. Study of the electrical conductivity of the earth on the territory of Czechoslovakia. Studia Geophys. Geodact, 3: 373-381. Press, F., 1966. Seismological information and advances. Advances in Earth Science, London, pp. 247-286. Rncitake, T., 1952. Electrical conductivity and temperature in the earth. Bull. Earthquake Res., Inst. Tokyo Univ., 30: 13-24. Rikitake, T., 1968. Electromagnetism and Internal Structure of the Earth. Elsevier, Amsterdam, 308 pp. Ringwood, A.E., 1966. NIineralogy of the mantle. Advances in Earth Science, London, pp. 357-399. Ringwood, A.E., 1968. Phase tr~sformations and the constitution of the mantle. Phys. Earth Planetary Interiors, 3: 109-156. Ringwood, A.E. and Major, A., 1966. Some hi&pressure transformations in olivines and pyroxenes. J. Geoph. Res., 71(18): 4448-4449. Roteanova, N.M., 1966. Mapping of a chart of the conductivity and the thickness of a non-conductive layer from geomagnetic data. Geomagnet. Aeronomy, 6 (1): 121-125 (in Russian). Roy, R.F., Blackwell, D.D. and Birch, F., 1968. Heat generation of plutonic rocks and continental heat flow provinces. Earth Planetary Sdi. Letters, 5(l): l-12. Runcorn, SK. and Tozer, D.C., 1955. The electrical conductivity of olivine at high temperatures and pressures. Ann. Geophys., 11: 98-102. Schmucker, U., 1964. Anomalies of geomagnetic variations in the south-western United States. J. Geomagnetism Geoelec., 15(4): 193-221. Schmucker, U., 1970. Anomalies of Geomagnetic Variations in the Southwestern United States. University of Californta Press, Berkeley, Calif. Selar, C.B., Carrison, L.C. and Schwarts, C-M., 1964. High-pressure reactian of clino-enstatite to forsterite plus stishavite. J. Geophys. Res., 69(2): 325-330. Smirnov, Ja.B., 1968. Relationship of thermal field with the structure and development of the earth’s crust and upper mantle. Geotectonics, 6: 6-25 (in Russian). Tozer, D.C., 1959. The Electrical Properties of the earth interior. In: L.H. Ahrens, K. Rankama and S.K. Runcorn (Editors), Physics and Chemistry of the Earth. Pergamon, London, 3: 414-436. Vacquier, V., Sclater, J.G. and Corry, C.E., 1967. Studies of the thermal state of the earth, Zlst. Heat Flow, Eastern Pacific. Bull. Earthquake Res. Inst. Univ. Tokyo, 45(2): 375-393. 280

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Vanyan, L.L., 1966. Electromagnetic investigations of geothermal conditions in the upper mantle. Byul. Mosk. Obshehestva Ispytatelei Prirody, Otd. Geol., 41(3): 141-142 (in Russian). Vanyan, L.L. and Kharin, E.P., 1967. Deep magnetic-variation sounding in the Baikal region. In: Regional Geophysical Investigations in Siberia. Nauka, Novosibirsk, pp. 184-193 (in Russian). Vanyan, L.L. and Zabolotnaya, N.A., 1968. On typical theoretic curves of deep electromagnetic soundary. Izv. Akad. Nauk, S.S.S.R., Geofiz. Ser., 1968(l): 63-70 (in Russian). Vereshchagin, L.F., Semerchan, A.A., Popova, S.V. and Kusin, N.N., 1962. Variation of electric conductivity of some semiconductors at pressures up to 300,000 kg/cm2. Dokl. Akad. Nauk S.S.S.R., 145(-i): 757-761 (in Russian). Volarovich, M.P., Parkhomenko, E.I. and Bondarenko, A.I., 1966. Study of electric resistance of main, ultramain and alkali rocks and mineral at high pressures and temperatures. Dokl. Inst. Geofiz. 37(204): 168-179 (in Russian). Yukutake, T., 1959. Attenuation of geomagnetic secular variation the conducting mantle of the earth. Bull. Earthquake Res., Inst. Tokyo Univ., 37: 13-22. Zharkov, 1’.N., 1958. .In the electric conductivity and temperature of the earth’s shell. (in Russian). Izv. Akad. Nauk, S.S.S.R., Ser. Geofiz., 1958 (4)‘ 458-470

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