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Positive heat flow anomaly in the Carpathian basin
D A T A ANDM E T H O D REVIEWS ANDRESEARCH N O T E S Geothermics
(i973) - VOL. 2, N o . 2
Positive Heat Flow Anomaly in the Carpathian Basin T. I~OLDIZSAR *
ABSTRACT Intensive geothermal investigations in the central Hungarian Tertiary sedimentary basin show uniform high temperature gradients between 45 and 70"C/kin. New temperature measurements between 3000-5800 m depth confirm previous values between 400-2000 meters. Sixteen heat flow measurements showed values between 2.0 and 3.3 Itcal/cm~s (84 and 138 mW/m 2 respectively). Sporadic measurements outside the Carpathian basin have shown invariably average or low heat flow and low temperature gradients. The investigation of the crustal structure in Hungary along 5 profiles indicates the depth of the Moho as being between 24.5 and 30.4 kin. Comparing the isobaths of the Moho with the temperature gradient map there is an evident relation between high temperature gradients, the consequent high heat flow and the elevated position of the Moho. Areas with high heat flow are found where the Moho is 24.5-26 km deep. The Carpathian basin can be compared with the Black Sea depression where the Moho is 20 km deep. An interesting geothermal similarity exists between the Carpathian basin and the marginal basins of the western Pacific. The Okhotsk, Iapan, Shikoku, Parace-Vela basins have a high mean heat flow above 2 !tcal/cm 'e s. In the southwestern Pacific, the Fiji plateau and the Lan basin are also characterized by high heat flow. The Japan and Okhotsk seas may represent a subsidence similar to the Carpathian basin, caused by the uplift of the surrounding mountain ranges e.g., Kurili island arc.
Introduction G e o t h e r m a l i n v e s t i g a t i o n s in H u n g a r y s t a r t e d in 1952. S y s t e m a t i c c o l l e c t i o n of t e m p e r a t u r e m e a s u r e m e n t s m a d e in d e e p m i n e s a n d e x p l o r a t i o n b o r e h o l e s , f u r t h e r m e a s u r e m e n t a n d c o r r e c t i o n of t h e t e m p e r a t u r e o f o u t f l o w i n g h o t w a t e r wells m a d e it p o s s i b l e to e s t a b l i s h t h e d i s t r i b u t i o n o f t h e t e m p e r a t u r e g r a d i e n t s in t h e H u n g a r i a n b a s i n . S y s tematical arrangement of the great amount of temperature data, by dropping those values which were obviously incorrect, showed that temperature gradients everywhere w e r e b e t w e e n 45 a n d 7 o ° C / k m a v e r a g i n g a b o u t 5 6 ° C / k i n for t h e tvhole c o u n t r y . (BOLDIZSAR 1958 a, 1958 b). I n o r d e r to i n v e s t i g a t e t h i s n e w a n d i n t e r e s t i n g geothermal phenomenon the author established a geothermal l a b o r a t o r y in t h e T e c h n i c a l U n i v e r s i t y o f S o p r o n w h e r e c o n d u c t i v i t y m e a s u r e m e n t s w e r e m a d e . T h e first m e a s u r e d h e a t flow v a l u e , w h i c h w a s t h e first m e a s u r e m e n t o n t h e European continent, showed a value more than twice as h i g h as t h e w o r l d a v e r a g e r e g a r d e d in t h e m i d d l e fifties to b e as h i g h as 1.2 ! t e a l / e r a 2 s. (]~OLDIZSAR1965, BOLDIZSAR t959). F o l l o w i n g m e a s u r e m e n t s c o n f i r m e d t h a t in t h e w h o l e t e r r i t o r y o f H u n g a r y , w i t h o u t e x c e p t i o n , t h e h e a t flow is a b o u t 2.o-3. 4 I t c a l / c m 2 s (84-138 m W / m 2 ) . I n t h e N E p a r t of t h e b a s i n , o u t s i d e of H u n g a r y , S o v i e t m e a s u r e m e n t s s h o w e d t h e s a m e e l e v a t e d h e a t flow as in t h e c e n t r a l p a r t
* Technical University, H-3515 Miskolc-Egyetemvfiros, Hungary.
of t h e b a s i n (LUBIMOVA 1966) a n d m e a s u r e m e n t s in t h e n o r t h e r n p a r t o f t h e L i t t l e H u n g a r i a n P l a i n (CERMAK 1967) also c o n f i r m e d m y p r e v i o u s o p i n i o n t h a t t h e p o s i t i v e geothermal anomaly occupies the whole territory within the C a r p a t h i a n a r c (BOLDIZSAR I964b). M e a s u r e m e n t s p u b l i s h e d u p to n o w a r e s h o w n in T a b l e t. TABLE 1. - - Heat ~low values in the Carpathian basin. Place Zob~k Nagylengyel Hosszuhet~ny Banska Stiavnica Hajduszoboszl6 Bakonya Szentendre Edeldny Zalush Malacky L~ib Kol~rovo Ptruksa Stretava-5 Stretava-7
Longitude east
Latitude north
Heat flow !tcal/cm 2 s
Author
46°11 ' 46°46 ' 46010 , 48°27 ' 47026 , 46°05 ' 47041 , 48018 , 22042 ' 17°00 ' 16057' 18001, 22004 , 22°03 ' 22004 '
18014' 16'45" 18022, I8'>5Y
3.31 1.9-2.0
BOLDIZSAR ~,
2.49
~>
2.66
~>
21°23"
2.2-2.6
~>
18o05' 19°05 ' 20"46' 48°24' 48027 , 48023 , 47o56 ' 48029 , 48°37 ' 48036 ,
2.46 2.01 3.1 2.60 1.57
>> >> >> LUBIMOVA CERMAK
2.22 2.32
, ,>
2.45 2.70 2.70
~> >> ,
S i n c e h e a t flow v a l u e s a n d t e m p e r a t u r e g r a d i e n t s w e r e obtained from rocks relatively near the surface, generally b e t w e e n 3OO-lOOO m f o r h e a t flow a n d IOO-200o in f o r temperature gradients, it has always been an open question as to t h e r e l a t i o n b e t w e e n n e a r s u r f a c e h e a t flow a n d t h e i n t e r n a l h e a t of t h e e a r t h .
Geothermal exploration I n t h e m e a n t i m e e x p l o i t a t i o n of t h e g e o t h e r m a l potentialities of the Hungarian positive geothermal anomaly r e s u l t e d in t h e d r i l l i n g of 80 wells of a b o u t 2ooo-25oo m d e p t h b e t w e e n 1965 a n d 1972 a n d a c c u r a t e r o c k t e m p e r atures were obtained by measuring the temperature of the h o t w a t e r a t t h e d e p t h of t h e a q u i f e r . D e e p e x p l o r a t i o n o f oil a n d g a s wells b e t w e e n 30o0 a n d 6ooo m g a v e r o c k temperatures by measuring the temperature of the fluid d u r i n g f l o w - r a t e m e a s u r e m e n t s b y m e a n s of a J o h n s o n tester. Fluid temperature measurements are far superior to t h o s e of b o t t o m t e m p e r a t u r e r e c o r d s , as f a r as r o c k t e m p e r a t u r e s a r e c o n c e r n e d , b e c a u s e in d e e p b o r e h o l e s t h e d i s t u r b a n c e o f t h e t e m p e r a t u r e field b y m u d c i r c u l a t i o n is a p p r e c i a b l e a n d in m o s t c a s e s t h e r m a l e q u i l i b r i u m is n e v e r a t t a i n e d . T h a t is w h y b o t t o m t e m p e r a t u r e r e c o r d s o n t h e s a m e p e t r o l e u m or g e o t h e r m a l field g i v e s c a t t e r e d 61
g r a d i e n t values, while fluid t e m p e r a t u r e d a t a are c o n s i s t e n t a n d even small local t e m p e r a t u r e variations can be evaluated by the latter method. T e m p e r a t u r e g r a d i e n t m a p s h a v e been published since ~96o a n d revised yearly using new reliable d a t a f u r n i s h e d b y m o r e r e c e n t m e a s u r e m e n t s , which also enabled d r o p p i n g old values of d o u b t f u l accuracy. More t h a n ~ooo d a t a h a v e been i n v e s t i g a t e d a n d the r e c e n t g e o t h e r m a l m a p (Figure 2) c o n t a i n s only 567 grad i e n t values. All values b e t w e e n ~oo a n d 400 m d e p t h from the surface were d r o p p e d , whereas in I96o several values b e t w e e n 6o-too m existed on t h e m a p . T h e d e p t h of the average t e m p e r a t u r e m e a s u r e m e n t s has increased from 420 m to zo5o m during ~2 years of i n v e s t i g a t i o n . The t e m p e r a t u r e g r a d i e n t s have b e c o m e more a c c u r a t e a n d v e r y few d o u b t f u l d a t a exist where reliable t e m p e r a t u r e m e a s u r e m e n t s are not available. In Figure ~ a n d Table ~ gradients are d i s t r i b u t e d over t h r e e territories. I
Table ~ shows t h a t w i t h i n each region t h e average t e m p e r a t u r e g r a d i e n t decreases as t h e d e p t h increases. Only two g r a d i e n t s f r o m 18 values c o n t r a d i c t this t e n d e n c y . The cause of this decreasing t e n d e n c y is regarded to be '~s follows :
- - deeper strata are more compact and have higher conductivity values; - - lower gradient values are obtained in those areas where the basin is deeper; consequently the heat flow is diminished owing to rl~e pattern of the bottom of the basin (BoLmzsag 1964a). TABLE 2, - - Distribution o/ temperature gradients according to region and depth, in Hungary. Transdanubia I Depth interval m
400-1000 1000-1500 1500-2000 200%2500 2500-3000 more than 3000 Total or average
Transdanubia, west of ~he Danube, including the Mid-Hungarian Mountains. II -Inter-Danube-Tisa lowland, including the eastern part of the Mid-Hungarian Mountains. I I I - Transtisian lowland east of the Tisza river. -
A l t h o u g h this d i s t r i b u t i o n is p u r e l y g e o g r a p h i c a l , Table 2 shows a n i n t e r e s t i n g e a s t w a r d increase of t h e t e m p e r a t u r e g r a d i e n t f r o m I to I I I .
Inter Danube-Tiscia I.I
Number Average Numbei' of temp. of values gradient values "C/kin
Transtisian III
Average Number Average temp. of temp. gradient values gradient c'C/km "C/kin
34 31 37 30 14 13
51.57 48,64 48,10 48.74 44,51 46,43
83 34 50 18 3 1
55.79 53.11 49,93 48.20 50.60 45,20
95 44 46 25 3 6
56.60 56.60 55.1) 50.35 49.40 47,71
159
48,00
189
50.47
219
52.56
567
50,34
For Hungary
/
, I I
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47 °
o 1
77°
18 ~
t9 °
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20 °
Fro. 1, - - Pattern o[ the base o[ the Paleo-Mesozoic lormations in Hungary. Contours in position o[ boreholes deeper than 3000 meters,
62
21 ° metres"
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sea level,
Black circles,
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l@--_\ \ " ~ I ~ " ~ _ ) S.~0Contour lines of the ~L_~~ ,-, t~q temperature --]\t 5~3 ~ ) ---~s~ ~67~,2~ f ~ . k . ; ~c gradientin'C/km ~./t~[ \~ f~," ~A ,-~ "'*~'5"~.x..i-.. " ~~5-0 \) ~o,1 ~ Miocene and older ' "Ill ~ \ ~ ~ ~ J Z,/" !0/~ .,r 60 :b - ' I outcrops, volcanics
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. 21 °
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FIG. 2. - - G e o t h e r m a l gradient m a p o/ Hungary. G r a d i e n t values represent an average b e t w e e n the sur/ace and the b o t t o m ot the basin (1000-3000 m).
V'
F r o m this it follows t h a t t h e high t e m p e r a t u r e gradients o b s e r v e d in the C a r p a t h i a n basin are n o t related to a near surface p h e n o m e n o n , b u t t h a t t h e elevated rock t e m p e r a t u r e s really exist down to t h e b o t t o m of the basin. In the last few years oil and gas p r o s p e c t i n g wells reached 3ooo - 58oo m. Very a c c u r a t e rock t e m p e r a t u r e m e a s u r e m e n t s (Table 3) i n d i c a t e d elevated values and only slightly lower average t e m p e r a t u r e gradients. Since these boreholes are s i t u a t e d in the d e e p e s t p a r t of the basin (Figure I) these gradients can b e regarded as m i n i m a l values, w h e r e the h e a t flow is also a t m i n i m u m . I n these <, g r a b e n s , of t h e basin, Pliocene and Pleistocene sedim e n t s are 4000 - 50o0 m thick, which m e a n s an average speed of deposition a m o u n t i n g to 0.5-0.6 r a m / y e a r over 8 million years. Since t h e subsidence of t h e b o t t o m of the basin centres is still continuing, it is clear t h a t this sinking process has d i m i n i s h e d t h e t e m p e r a t u r e increase a n d the h e a t flow. Accordingly t h e deep regional h e a t flow m u s t be slightly higher t h a n values related to b o t h grabens. There are regions where t h e m o v e m e n t of w a t e r und e r g r o u n d d i s t u r b s t h e t e m p e r a t u r e field. In t h e Middle H u n g a r i a n Mountains t h e m o v e m e n t of deep k a r s t w a t e r transfers h e a t in a lateral direction a n d diminishes h e a t flow considerably, I n some places this effect can b e felt down to 600 m. On t h e o t h e r h a n d in the Tisza valley of the Great H u n g a r i a n Plain t h e vertical p e r m e a b i l i t y of Pleistocene sands a n d gravels is high enough to allow vertical m o v e m e n t of t h e w a t e r T h e r e exists a circulation
T.xr;J.r. 3. - - Rock temperatures and gradients measured in boreholes over 300) 7": deep
Borehole
Depth m
T e m p e r - Temp. " Average ature gradient °C/km "C °C/km
I - Transdanubian Bajcsa-I B6s~rk~iny-1 Budafa-I Budafa-VI
3590.0 4474.0 4071.0 4067.0 4060.0 3208.0 3220.6 3220.0 3120.0 3076.0 3125.0 3392.0 3440.0
Budafa-500 Budafa-501 Budafa-III Budafa-502 Szentgy6r~yv~l~v-5 Fels6szentm~4rton-1 III-
180.0 126.0 183.0 214.0 219.0 165.0 154.4 163.0 159.0 160.0 149.5 154.4 158.0
47.2 48.1 42.2 50.0 51.3 48.1 44.5 47.2 47.4 48.4 44.2 42.3 42.7
47.3
42.5
Inter-Danube-Tiscia
Algy6-21
3209.6 156.0 I I I - Transtisian
45.2
Filbi~insebestydn-3 Kondoros-1
2980.0 (1t 3177.0 3118.0 3775.0 3175.0 3020.0 5750.0
46.6 48.5 49.5 50.3 47.8 47.4
Szarvas-DNy-1 Hddmez6vflrhely-I
50.65
150.0 165.5 165.5 170.5 162.8 154.0 217.0 (21
49.03
(1) Depth of the borehole 3600 m. (2) No thermal equilibrium. Probable value 272°C.
63
p a t t e r n , w h e r e w a t e r slowly goes u p in t h e m i d d l e of t h e area a n d cold w a t e r i n t a k e is p r e s e n t o n t h e p e r i p h e r y . I n t h e region of Tiszak6cske, near t h e surface, in 50 m deep boreholes g r a d i e n t s u p to i 5 o ~ C / k m were m e a s u r e d , whereas on t h e p e r i p h e r y o n l y i 6 - 2 o ° C / k m were o b s e r v e d in a n area where t h e n o r m a l g r a d i e n t is a b o u t 5 o ° C / k m (BoLmZSAR 1967). A deep b o r e h o l e of 16oo m showed t h a t u n d e r 4oo m t h e a n o m a l y d i s a p p e a r e d . B o t h t y p e s of anom a l y areas h a v e b e e n left o u t in t h e c o n s t r u c t i o n of t h e geothermal map. T h e rock t e m p e r a t u r e in deep boreholes shows a s l i g h t decrease in t h e a v e r a g e g r a d i e n t , as a f u n c t i o n of d e p t h . This is t h e c o n s e q u e n c e of t h e increasing c o n d u c t i v i t y of t h e more c o m p a c t e d s e d i m e n t s in d e e p e r regions. Conseq u e n t l y t h e a v e r a g e g r a d i e n t s a n d t h e h e a t flow m e a s u r e d a n d c o m p u t e d below 4oo m c a n be used w i t h confidence for e s t a b l i s h i n g h e a t flow c o m i n g from g r e a t e r d e p t h , from u n d e r t h e b o t t o m of t h e b a s i n . T h e region from w h i c h t h e h e a t flow rises is a t least 6-8 k m deep. T a b l e i lists t h e m e a s u r e d h e a t flow values in t h e C a r p a t h i a n b a s i n . T h e e a s t w a r d increase of t e m p e r a t u r e g r a d i e n t s shows t h a t deep h e a t flow s h o u l d also increase t o w a r d s t h e east. T h e r e are h i g h g r a d i e n t a n d h e a t flow v a l u e s in t h o s e places w h e r e t h e b o t t o m rock is e i t h e r on t h e surface (Zob&k-Hosszuhet~ny) or near t h e surface ( s o u t h e a s t T r a n s d a n u b i a w h e r e t h e M e s o z o i c - b o t t o m is uplifted). T h e s e values are considered to d i m i n i s h d o w n w a r d s , b e i n g caused b y t h e t o p o g r a p h i c effect of t h e Meso-Pateozoic b o t t o m w h i c h h a s a good t h e r m a l c o n d u c t i v i t y . Figure 3 i l l u s t r a t e s t h e h e a t flow m e a s u r e d a t t h e surface a n d
t h e regional h e a t flow" a t 6-8 k m d e p t h ( n u m b e r s in brackets). C o m p a r i n g F i g u r e 3 w i t h t h e i s o b a t h m a p of t h e Moho, d r a w n up along 6 profiles (Figure 4), it seems t h a t t h e high t e m p e r a t u r e g r a d i e n t a n d high h e a t flow region across t h e m i d d l e p a r t of H u n g a r y coincides with a n ele v a t e d Moho area with d e p t h values of 24.5 2fi km, whereas in o t h e r p a r t s of t h e c o u n t r y t h e Moho goes down to 28-30 k m (MITuCH, POSGAV 1972 ). I t seems t h a t the t o p o g r a p h y of t h e Moho acts in t h e same m a n n e r on t h e h e a t flow as t h e t o p o g r a p h y of t h e Meso-Paleozoic basem e n t . T h a t m e a n s a b e t t e r crustal a n d s u b c r u s t a l conduct i v i t y u n d e r t h e Paleozoic a n d m e t a m o r p h i c rocks of t h e bottom. T h e C a r p a t h i a n b a s i n s u b s i d e d in t h e Miocene whereas t h e a d j a c e n t Dinarids, t h e C a r p a t h i a n arc a n d t h e eastern Alps were uplifted. T h e subsidence c o n t i n u e d in t h e Pliocene a n d Pleistocene. T h e slow- plastic flow of rocks from u n d e r t h e C a r p a t h i a n b a s i n t o w a r d s t h e u p l i f t e d zone was needed to s u p p o r t t h e b u i l d i n g u p a n d t h i c k e n i n g of t h e crust under the mountain system. M a g n e t o t e l l u r i c m e a s u r e m e n t s a l o n g specific profiles in t h e H u n g a r i a n b a s i n i m p l y t h a t t h e d e p t h of t h e good c o n d u c t i n g layer is b e t w e e n 55-ioo kin, a v e r a g i n g 7o k m whereas in t h e Baltic a n d U k r a i n i a n shield region of t h e S o v i e t U n i o n it is more t h a n 20o k m deep (ADAM I97O ). T h e h i g h position of t h i s layer is t h e c o n s e q u e n c e of t h e high e n v i r o n m e n t t e m p e r a t u r e a t 5o-Ioo k m w h i c h causes t h e rock to flow. T h i s ,, flow ,, is a very slow plastic: flow of high t e m p e r a t u r e rock m a t e r i a l . I t can be b e t t e r t e r m e d
,1
--
?~ ~ 1 t [2.3] (X"
7/
/
I
t'
a Yl
o 20 ~-. ~--..,.j--" 17 °
18 °
k 79 °
I, 20 °
Fro. 3. - - Heat /low map o/ Hungary. 64
2t °
40 k ~
as a high t e m p e r a t u r e c o n t i n u o u s mass creep of high t e m p e r a t u r e a n d high pressure rocks. F r o m t h e e l e v a t e d position of t h e Moho a n d t h e good c o n d u c t i n g layer i t c a n b e safely c o n c l u d e d t h a t t h e regional high t e m p e r a t u r e gradient, a n d c o n s e q u e n t h i g h h e a t flow, e x t e n d from near surface (6-8 k m deep) d o w n to a t least 8 o - m o km, t h r o u g h t h e Moho-level d o w n to t h e good c o n d u c t i n g layer. Similar basins w i t h high heat flow a n d i n t e r m e d i a t e c r u s t t h i c k n e s s are s i t u a t e d in t h e s o u t h e r n p a r t of t h e Black Sea, in t h e J a p a n a n d O k h o t s k seas. T h e Moho in t h e Black Sea basin is 2o-3o k m deep, in t h e J a p a n Sea a b o u t 25 km, in the O k h o t s k Sea 2o-3o k m . These basins can be considered as depressions in t h e process of b e i n g filled up, while in t h e C a r p a t h i a n b a s i n this process is n e a r l y complete. H i g h h e a t flow in t h e Fiji p l a t e a u a n d Lau basin, in t h e S h i k o k u a n d P a r e c a Vela basins (ScLaTER ~972), c a n n o t be correlated to these basins m e n t i o n e d before, since t h e y are b o r d e r e d b y oceanic t r e n c h e s a n d are a p a r t of t h e Circumpacific s y s t e m . T h e c h a r a c t e r i s t i c s a n d origin of t h e h e a t source w h i c h is o b v i o u s l y s i t u a t e d u n d e r t h e high c o n d u c t i v i t y layer, below a b o u t IOO km, are n o t k n o w n a n d it is difficult to give an e x p l a n a t i o n of such. Theories of worldwide conv e c t i o n c u r r e n t s are no longer in fashion a n d I do n o t consider it necessary to r e p e a t m y negation of t h e i n c o r r e c t usage of this h y d r a u l i c engineering t e r m in geophysics for t h e high t e m p e r a t u r e c o n t i n u o u s mass creep of m a n t l e rock t a k i n g place a t d e p t h . I consider this peculiar m a n t l e m o v e m e n t in t h e low v e l o c i t y region responsible for causing uplift a n d subsidence a t t h e same t i m e in various places of t h e globe. U p l i f t a n d subsidence are interconnected b y t h e same process emerging from t h e same cause.
T h e t h i c k n e s s a n d mass of t h e conti,Jental c r u s t are regulated b y t h e isostatic b a l a n c e in such a way t h a t t h e b o t t o m a n d t h e c r u s t of t h e oceans are sinking w h e n new c o n t i n e n t a l c r u s t is b e i n g created (BOLDrZSaR ~959). On t h e c o n t r a r y , if t h e c o n t i n e n t a l c r u s t is b e i n g a n n i h i l a t e d , immersed or a s s i m i l a t e d into t h e mantle, which I do not believe to be t h e general situation, t h e b o t t o m of a c e r t a i n oceanic region reacts w i t h a n a p p r o p r i a t e uplift, Geological o b s e r v a t i o n s s t r o n g l y s u p p o r t t h e view t h a t t h e r e is a growing of t h e c o n t i n e n t a l c r u s t or a t least t h e quasi c o n s t a n c y of it. In t h e l a t t e r case t h e e v o l u t i o n oI t h e c o n t i n e n t a l c r u s t does not m e a n an increase in size a n d mass, b u t only its cyclic r e w o r k i n g c o n n e c t e d w i t h u p h e a v a l a n d subsidence of various p o r t i o n s a t different times. F o r m o u n t a i n b u i l d i n g t h e underflow of m a n t l e material is needed and, on t h e c o n t r a r y , subsidence of c o n t L nental c r u s t should t a k e place only as a result of m a n t l e outflow possibly in t h e low velocity layer. This , flow >, of course is a v e r y slow creep of t h e rock mass in t h e low velocity layer. This flow will be t e r m e d in s h o r t as plastic flow or creep. T h e velocity profile of this plastic flow is c h a r a c t e r i z e d s c h e m a t i c a l l y in F i g u r e 5. T h e schem a t i c r e p r e s e n t a t i o n of t h e velocity of t h e plastic flow or creep versus d e p t h shows t h a t this flow occurs n o t only in t h e low velocity layer b u t , according to the plastic beh a v i o u r of t h e rocks, on t h e t o p of t h e low velocity layer including t h e crust. T h e more elastic c r u s t resists t h e t r a n s p o r t i n g effect of t h e low v e l o c i t y layer a n d t h e v e l o c i t y in t h e c r u s t is d i m i n i s h e d . T h e oceanic c r u s t will be dragged t o w a r d s t h e rising c o n t i n e n t a l portion. In this way p a r t s of the oceanic c r u s t a n d even c o n t i n e n t a l c r u s t blocks can t r a v e l g r e a t distan-
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Fro. 4. - - Contours of the M o h o in Hungary (in km).
65
VELOCITY, C/"n/,~6',~/" CRUST
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Velocity o/ the plastic /low vs. depth.
ces, w h e n t h e process described a b o v e is a s t e a d y one. B u t w h e r e t h e m o v e m e n t is a r a n d o m one, i t will b e err a t i c a n d s o m e t i m e s t h e c r u s t b l o c k r e t u r n s n e a r to t h e original p o s i t i o n a f t e r h a v i n g t r a v e l l e d a g r e a t distance. T h e geological a n d geophysical s t r u c t u r e of t h e e a r t h c r u s t inside t h e c o n t i n e n t s a n d a t t h e m a r g i n a l p a r t s does n o t c o n v i n c e m e t h a t geologic a n d g e o p h y s i c a l processes gove r n i n g t h e s c u l p t u r e of t h e global surface are simple a n d regular processes. O n t h e c o n t r a r y , as e v e r y w h e r e in physics a n d engineering, where h e a t a n d mass t r a n s f e r are c o n c e r n e d , t h e s e processes are n o t r e g u l a r a n d c o n s i d e r i n g p h a s e c h a n g e s in t h e m a n t l e it is impossible to give a simple m e c h a n i s m of t h e c r u s t a l h i s t o r y of t h e e a r t h . T h e r e is m o r e t h a n one possibility of a r r i v i n g from one stage to t h e n e x t one. As far as t h e C a r p a t h i a n b a s i n is c o n c e r n e d it c a n b e said t h a t as t h i s t e r r i t o r y is a n i n t e g r a l p a r t of t h e worldwide T e r t i a r y c r u s t b u i l d i n g s y s t e m , t h e t h i c k e n i n g of t h e c r u s t in t h i s region possibly s t a r t e d in t h e Mesozoic, slowed d o w n d u r i n g t h e Paleocene a n d ceased in t h e Miocene. F r o m t h e Miocene t h e m a n t l e u n d e r t h e C a r p a t h i a n b a s i n s u p p o r t e d , b y slow plastic flow or m a s s creep, t h e b u i l d i n g u p of t h e C a r p a t h i a n arc a n d Dinarids, a n d t h e b a s i n subsided. T h e c i r c u l a r s t r u c t u r e of c h a i n m o u n t a i n s a r o u n d t h e b a s i n n e e d e d m o r e m a n t l e m a t e r i a l to s u p p o r t t h e i r rising t h a n could possibly b e o b t a i n e d f r o m t h e Mediterranean and Atlantic and dragged the mantle from t h e inside area w h i c h t h u s b e c a m e a s i n k i n g b a s i n . W h i l e t h e c r u s t t h i c k n e s s in t h e C a r p a t h i a n s is b e t w e e n 4o a n d 60 km, u n d e r t h e basin it is o n l y 26-28 k m . T h e i n t e n s e radial outfflow of m a t e r i a l from t h e b a s i n c a u s e d t h e lower p a r t of t h e u p p e r m a n t l e to rise. I n this way, owing to v e r t i c a l mass t r a n s p o r t , t h e h i g h h e a t flow c a n be, a t least p a r t l y , explained.
Exaggerated ideas in modern earth sciences Geophysics has b e e n d o m i n a t e d d u r i n g t h e last few years b y t h e so-called , new global t e c t o n i c s , , b a s e d o n t h e old idea of c o n t i n e n t a l d r i f t i n t r o d u c e d b y WEG~NER, t h e s y m m e t r i c a l m a g n e t i c p a t t e r n s i n t e r p r e t e d b y VINE a n d MATTHEWS as , sea floor s p r e a d i n g ~ a n d finally t h e
~66
, p l a t e tectonics ~) p r o p o s e d b y m a n y , a m o n g w h o m ISAACKS, OLIVER, S~KES, LE PICHON, MORGAN etc. T h e v e l o c i t y of t h e m o t i o n of t h e c r u s t a n d underlying m a n t l e p o r t i o n s is n o t m o r e t h a n a few c e n t i m e t r e s per year. i.e. a b o u t io --7 c m / s . This slow m o v e m e n t is w i t h i n t h e r a n g e of t h e e x t r e m e l y slow plastic flow of t h e o t h e r w i s e h i g h l y elastic silicates. T h e d r i v i n g force b e h i n d this peculiar flow of c o m p r e s s e d solid silicates of not more t h a n a few t h o u s a n d degrees of t e m p e r a t u r e is u n k n o w n . I t is guessed t h a t o n l y t h e t h e r m a l energy is big e n o u g h to i n i t i a t e a n d m a i n t a i n this slow m o t i o n for some t h o u s a n d million years. M a n y a u t h o r s use t h e movem e n t due to t h e r m a l c o n v e c t i o n a n d it is even supposed t h a t c o n v e c t i o n cells exist in t h e m a n t l e . F o r m e it is difficult to imagine, t h a t in such a rigid m a t e r i a l as are t h e m a n t l e silicates, such a low t e m p e r a t u r e g r a d i e n t w h i c h in t h e m a n t l e really exists can cause c o n v e c t i o n . The sions of existence to more
size of t h e , plates ~ h a s increased to t h e dimenc o n t i n e n t s a n d oceans, so t h e y are - - if t h e i r is a c c e p t a b l e --- shells, a n d t h e y c a n be referred correctly as , shell tectonics ,.
I t seems to m e t h a t t h e usual vertical e x a g g e r a t i o n of l : i o to i : i o o , which in t h e past, s o m e t i m e s forgotten or overlooked b y t h e geologist, h a d led to erroneous de d u c t i o n s (e.g. n a p p e theories of A l p i n e s t r u c t u r e s , d r i f t i n g c o n t i n e n t s , m a g m a t i c intrusions, etc.), is n o w a d a y s influencing geophysics. W i t h o u t v e r t i c a l e x a g g e r a t i o n t h e surficial f e a t u r e s of t h e e a r t h are not v e r y significant a n d I believe t h a t w i t h o u t g e o m e t r i c a l a n d p h y s i c a l exaggera t i o n s m a n y theories would loose t h e i r seemingly a t t r a c t i v e power. It can h a r d l y b e i m a g i n e d t h a t in t h e v e r y d i s t a n t p a s t g r e a t c o n t i n e n t a l masses were c r e a t e d j u s t b y h a v i n g been b r o k e n into smaller blocks a n d f l o a t i n g a w a y from each other, colliding w i t h o t h e r b r o k e n p a r t s to c r e a t e new c o n t i n e n t a l masses. U n i f y i n g t h e old W e g e n e r t h e o r y with sea-floor spreading, t h e c o n t i n e n t s are a s s u m e d n o t only to h a v e floated a w a y - - which i~ easier to i m a g i n e b u t t h e y are p u s h e d a p a r t b y m e a n s of t h i n oceanic c r u s t , p l a t e s ,, e x t e n d i n g from t h e M i d - A t l a n t i c ridge to t h e c o n t i n e n t a l mass of E u r a s i a - A f r i c a on t h e one side a n d t(~ A m e r i c a on t h e other. T h e essence of t h e t h e o r y of t h e r m a l c o n v e c t i o n in t h e m a n t l e is b a s e d on a g r e a t p h y s i c a l e x a g g e r a t i o n . In reality t h e r e is no c o n v e c t i v e h e a t a n d mass t r a n s p o r t owing to t h e real s m a l l t e m p e r a t u r e g r a d i e n t in t h e m a n t l e , because u n d e r a t h r e s h o l d v a l u e of t h e G r a s h o f n u m b e r no m o v e m e n t a t all will t a k e place. A n o t h e r f r e q u e n t l y used expression is t h e , i n t r u s i o n , of m a g m a into t h e c o u n t r y rock a n d t h e m e l t i n g or fusion of t h e l a t t e r to m a k e w a y for t h e v o l u m e of i n t r u s i o n . In reality i n t r u s i o n a n d fusion are n o t e n o u g h to e x p l a i n correctly t h e widely o b s e r v e d p h e n o m e n o n . I t is possible t h a t t h e i n t r u s i o n really occurs b y c h a n g i n g places, i.e. t h e i n t r u d e d m a g m a goes up into t h e v o l u m e left , e m p t y ~; b y t h e c o u n t r y rock a n d t h e c o u n t r y rock goes d o w n into t h e e m p t y space left b y t h e m a g m a . T h i s c h a n g e of place or diapiric uprise occurs b y m e a n s of slow pLastic flow a n d i t is n o t necessary to believe t h a t t h e whole v o l u m e of m a g m a is m o l t e n . P a r t i a l m e l t i n g t a k e s place a t t h e per i p h e r y , where t e n s i o n a l f r a c t u r e of t h e rock causes a decrease in pressure.
C o m p l e t e tuslon of c o u n t r y rock to m a k e r o o m for m a g m a t i c i n t r u s i o n is also n o t a correct e x p l a n a t i o n ; t h e v o l u m e of t h e m o l t e n c o u n t r y rock exists a n d should b e deposited somewhere. F r o m t h e p o i n t of view of h e a t conduction, m e l t i n g a n d fusion are o n l y possible in t h e t h i n c o n t a c t b o u n d a r y region, where t h e t e m p e r a t u r e is h i g h e n o u g h to m e l t t h e c o u n t r y rock. T h e mass of t h e p l a n e t e a r t h seems to h a v e been p r a c t i c a l l y c o n s t a n t , a t least d u r i n g t h e last 10oo-2ooo million years. If this is so, t h e v o l u m e of t h e e a r t h c a n c h a n g e o n l y b y t h e r m a l a n d pressure effects. These are t h e r m a l d i l a t a t i o n - s h r i n k i n g a n d p h a s e changes b y v a r i a t i o n ot pressure. T h e i r cause is t h e r m a l energy change, e i t h e r b y c o n v e r s i o n of nuclear energy into h e a t or h e a t loss b y c o n d u c t i o n into space. T h e e a r t h v o l u m e is too g r e a t for an easy e x p l a n a t i o n of t h e slight surficial irregularities of t h e c r u s t s i m p l y b y clear t h e r m a l a n d pressure effects, chiefly w i t h i n t h e u p p e r m a n t l e . T h e e x p l a n a t i o n of these small changes b y supposing regular a n d worldwide c o n v e c t i o n d o w n to t h e lower m a n t l e or to t h e core, i.e. regular m o v e m e n t s of i m m e n s e masses in r e l a t i o n to t h e r e l a t i v e l y small volumetric v a r i a t i o n s in t h e c r u s t d u r i n g geological times, is i n a p p r o p r i a t e , a n d t h e small effect b y no m e a n s corresponds to t h e g r e a t e v e n t s causing it. Geology has b a s e d its o b s e r v a t i o n s chiefly on t h e cont i n e n t s a n d is therefore c o n t i n e n t a l l y - m i n d e d w h e n f o r m i n g global tectonics. T h e , new global tectonics )~ of m o d e r n geophysics is b a s e d on new o b s e r v a t i o n s on t h e ocean floor, t h e island arcs a n d c o n t i n e n t a l m a r g i n s a n d its bias is t y p i c a l l y oceanic. T h e r e is no tie-up b e t w e e n o b s e r v a t i o n s a n d theories of geology a n d geophysics a n d new t e x t b o o k s of geology are needed, in which old, obsolete c o n c e p t s are d r o p p e d a n d are replaced b y a new knowledge of geophysics, especially t h e r m a l a n d t h e r m o d y n a m i c a l aspects of m o d e r n petrology. Looking a t t h e e a r t h from t h e moon, one is i m p r e s s e d b y t h e blue oceans a n d t h e ever c h a n g i n g w h i t e clouds. I t is u n q u e s t i o n a b l e , t h a t t h e presence of t h e h y d r o s p h e r e a n d a t m o s p h e r e m a y be t h e c a u s e of m a n y i m p o r t a n t changes in t h e c o n t i n e n t a l crust. T h e i r role p e r h a p s , is more i m p o r t a n t t h a n has b e e n suspected d u r i n g t h e u p p e r m a n t l e p r o j e c t investigations. T h e differentiation of t h e m a g m a a n d t h e p r o d u c t i o n of lighter acid fraction, t h e isostatic rise of this p r o d u c t were recognised v e r y early a n d are now a c c e p t e d b y m o s t a u t h o r s . This p h e n o m e n o n explains the presence of t h e e l e v a t e d light c o n t i n e n t a l c r u s t
cores, l h e growing of t h e c o n t i n e n t a l cores is m a i n t a i n e d b y t h e hydrological cycle, b y orosion a n d deposition. T h e rising c o n t i n e n t s c a u s e subsidence on t h e i r m a r g i n s a n d if this t a k e s place on t h e ocean side, t h e l i g h t sedim e n t coverings spread o v e r t h e ocean m a r g i n s a n d d i s t u r b t h e isostatic q u a s i - e q u i l i b r i u m . O w i n g to this d i s t u r b a n c e t h e effects of t h e rising c o n t i n e n t a l block s p r e a d t o w a r d t h e oceanic crust. One of t h e volcanoes of t h e Tharsis area o n Mars rises o v e r 26 k m a b o v e t h e o t h e r s : differences in h e i g h t are considerable on t h e m o o n too. This shows t h a t g r e a t surficial irregularities exist owing to i n t e r n a l rock mass m o v e m e n t s as is t h e case on earth. I n e q u a l i t i e s of d e n s i t y d i s t r i b u t i o n (mascons) exist on t h e m o o n a n d possibly on o t h e r e a r t h l i k e i n n e r p l a n e t s . T h e s e d e n s i t y irregularities a n d t h e r a d i o a c t i v e h e a t sources c a n cause slow plastic flow of rock masses, as on t h e earth, w i t h o u t t h e presence of t h e h y d r o s p h e r e . B u t t h e presence of t h e h y d r o s p h e r e , c a u s i n g erosion, deposition t h u s o b s c u r i n g a n d influencing t h e p r i m a r y cause of s u b c r u s t a l mass creep, g r e a t l y c o m p l i c a t e s t h e process of c r u s t a l d e v e l o p m e n t a n d m a k e s t h e o b s e r v a t i o n a n d e x p l a n a t i o n of t h e geological a n d geophysical p h e n o m ena more difficult.
REFERENCES ADAM A. 1970 - - Gutleitende Schicht. Acta Geod. Geophys. Mont. Acad. Sci Hung., 5, I06. BOLDIZSAR T. 1956 - - Measurement of Terrestrial Heat Flow in the Coal Mining District Koml6. Acta Technica Acad. Sci. Hung., XV, 219-228. BOLDIZSAR T. 1958a - - Geothermic Investigations in the Hungarian Plain. Acta Geologica, V, 245-254 BOLDIZSAR T. 1958b - - New Terrestrial Heat Flow Values from Hungary. Geo/isica Pura e Applicata, 39, 102-125. BOLI)IZSAR T. 1959 - - Terrestrial Heat Flow in the Nagylengyel Oilfield. Publ. Min. Fac. Sopron, XX, 27-34. BOLDIZSAR T. 1964a - - Heat Flow in the Hungarian Basin. Nature, 202, 1278-1280. BOI~DlZSART. 1 9 6 4 b - Terrestrial Heat Flow in the Carpathians. J. Geophys. Res., 69, 5269-5275. BOLDIZSAR T. 1 9 6 7 - Terrestrial Heat and Geothermal Resources in Hungary. Bulletin Volconologique, XXX, 221-227. CE~MAK C. 1967 - - Results of Geothermic Investigation. Studia Geoph. et Geod., 11, 342-?44. LUBIMOVA E. A. 1966 - - Ocenka Raspedatenia Glubimogo Teplovogo Potoka. Isdateltstvo Nauka, Moskva, 50-51. MITUCH E., Pos6AY K. 1972 - - Geophys. Transactions Spec. Ed. M/iszaki K6nyvkiad6, 118-129 SCI.ATER I. G. 1972 - - Heat Flow and Elevation of the Marginal Basins of the Western Pacific. J. Geophys. Res., 77, 5705-5719.
67
(i973) - VOL. 2, N o . 2
Positive Heat Flow Anomaly in the Carpathian Basin T. I~OLDIZSAR *
ABSTRACT Intensive geothermal investigations in the central Hungarian Tertiary sedimentary basin show uniform high temperature gradients between 45 and 70"C/kin. New temperature measurements between 3000-5800 m depth confirm previous values between 400-2000 meters. Sixteen heat flow measurements showed values between 2.0 and 3.3 Itcal/cm~s (84 and 138 mW/m 2 respectively). Sporadic measurements outside the Carpathian basin have shown invariably average or low heat flow and low temperature gradients. The investigation of the crustal structure in Hungary along 5 profiles indicates the depth of the Moho as being between 24.5 and 30.4 kin. Comparing the isobaths of the Moho with the temperature gradient map there is an evident relation between high temperature gradients, the consequent high heat flow and the elevated position of the Moho. Areas with high heat flow are found where the Moho is 24.5-26 km deep. The Carpathian basin can be compared with the Black Sea depression where the Moho is 20 km deep. An interesting geothermal similarity exists between the Carpathian basin and the marginal basins of the western Pacific. The Okhotsk, Iapan, Shikoku, Parace-Vela basins have a high mean heat flow above 2 !tcal/cm 'e s. In the southwestern Pacific, the Fiji plateau and the Lan basin are also characterized by high heat flow. The Japan and Okhotsk seas may represent a subsidence similar to the Carpathian basin, caused by the uplift of the surrounding mountain ranges e.g., Kurili island arc.
Introduction G e o t h e r m a l i n v e s t i g a t i o n s in H u n g a r y s t a r t e d in 1952. S y s t e m a t i c c o l l e c t i o n of t e m p e r a t u r e m e a s u r e m e n t s m a d e in d e e p m i n e s a n d e x p l o r a t i o n b o r e h o l e s , f u r t h e r m e a s u r e m e n t a n d c o r r e c t i o n of t h e t e m p e r a t u r e o f o u t f l o w i n g h o t w a t e r wells m a d e it p o s s i b l e to e s t a b l i s h t h e d i s t r i b u t i o n o f t h e t e m p e r a t u r e g r a d i e n t s in t h e H u n g a r i a n b a s i n . S y s tematical arrangement of the great amount of temperature data, by dropping those values which were obviously incorrect, showed that temperature gradients everywhere w e r e b e t w e e n 45 a n d 7 o ° C / k m a v e r a g i n g a b o u t 5 6 ° C / k i n for t h e tvhole c o u n t r y . (BOLDIZSAR 1958 a, 1958 b). I n o r d e r to i n v e s t i g a t e t h i s n e w a n d i n t e r e s t i n g geothermal phenomenon the author established a geothermal l a b o r a t o r y in t h e T e c h n i c a l U n i v e r s i t y o f S o p r o n w h e r e c o n d u c t i v i t y m e a s u r e m e n t s w e r e m a d e . T h e first m e a s u r e d h e a t flow v a l u e , w h i c h w a s t h e first m e a s u r e m e n t o n t h e European continent, showed a value more than twice as h i g h as t h e w o r l d a v e r a g e r e g a r d e d in t h e m i d d l e fifties to b e as h i g h as 1.2 ! t e a l / e r a 2 s. (]~OLDIZSAR1965, BOLDIZSAR t959). F o l l o w i n g m e a s u r e m e n t s c o n f i r m e d t h a t in t h e w h o l e t e r r i t o r y o f H u n g a r y , w i t h o u t e x c e p t i o n , t h e h e a t flow is a b o u t 2.o-3. 4 I t c a l / c m 2 s (84-138 m W / m 2 ) . I n t h e N E p a r t of t h e b a s i n , o u t s i d e of H u n g a r y , S o v i e t m e a s u r e m e n t s s h o w e d t h e s a m e e l e v a t e d h e a t flow as in t h e c e n t r a l p a r t
* Technical University, H-3515 Miskolc-Egyetemvfiros, Hungary.
of t h e b a s i n (LUBIMOVA 1966) a n d m e a s u r e m e n t s in t h e n o r t h e r n p a r t o f t h e L i t t l e H u n g a r i a n P l a i n (CERMAK 1967) also c o n f i r m e d m y p r e v i o u s o p i n i o n t h a t t h e p o s i t i v e geothermal anomaly occupies the whole territory within the C a r p a t h i a n a r c (BOLDIZSAR I964b). M e a s u r e m e n t s p u b l i s h e d u p to n o w a r e s h o w n in T a b l e t. TABLE 1. - - Heat ~low values in the Carpathian basin. Place Zob~k Nagylengyel Hosszuhet~ny Banska Stiavnica Hajduszoboszl6 Bakonya Szentendre Edeldny Zalush Malacky L~ib Kol~rovo Ptruksa Stretava-5 Stretava-7
Longitude east
Latitude north
Heat flow !tcal/cm 2 s
Author
46°11 ' 46°46 ' 46010 , 48°27 ' 47026 , 46°05 ' 47041 , 48018 , 22042 ' 17°00 ' 16057' 18001, 22004 , 22°03 ' 22004 '
18014' 16'45" 18022, I8'>5Y
3.31 1.9-2.0
BOLDIZSAR ~,
2.49
~>
2.66
~>
21°23"
2.2-2.6
~>
18o05' 19°05 ' 20"46' 48°24' 48027 , 48023 , 47o56 ' 48029 , 48°37 ' 48036 ,
2.46 2.01 3.1 2.60 1.57
>> >> >> LUBIMOVA CERMAK
2.22 2.32
, ,>
2.45 2.70 2.70
~> >> ,
S i n c e h e a t flow v a l u e s a n d t e m p e r a t u r e g r a d i e n t s w e r e obtained from rocks relatively near the surface, generally b e t w e e n 3OO-lOOO m f o r h e a t flow a n d IOO-200o in f o r temperature gradients, it has always been an open question as to t h e r e l a t i o n b e t w e e n n e a r s u r f a c e h e a t flow a n d t h e i n t e r n a l h e a t of t h e e a r t h .
Geothermal exploration I n t h e m e a n t i m e e x p l o i t a t i o n of t h e g e o t h e r m a l potentialities of the Hungarian positive geothermal anomaly r e s u l t e d in t h e d r i l l i n g of 80 wells of a b o u t 2ooo-25oo m d e p t h b e t w e e n 1965 a n d 1972 a n d a c c u r a t e r o c k t e m p e r atures were obtained by measuring the temperature of the h o t w a t e r a t t h e d e p t h of t h e a q u i f e r . D e e p e x p l o r a t i o n o f oil a n d g a s wells b e t w e e n 30o0 a n d 6ooo m g a v e r o c k temperatures by measuring the temperature of the fluid d u r i n g f l o w - r a t e m e a s u r e m e n t s b y m e a n s of a J o h n s o n tester. Fluid temperature measurements are far superior to t h o s e of b o t t o m t e m p e r a t u r e r e c o r d s , as f a r as r o c k t e m p e r a t u r e s a r e c o n c e r n e d , b e c a u s e in d e e p b o r e h o l e s t h e d i s t u r b a n c e o f t h e t e m p e r a t u r e field b y m u d c i r c u l a t i o n is a p p r e c i a b l e a n d in m o s t c a s e s t h e r m a l e q u i l i b r i u m is n e v e r a t t a i n e d . T h a t is w h y b o t t o m t e m p e r a t u r e r e c o r d s o n t h e s a m e p e t r o l e u m or g e o t h e r m a l field g i v e s c a t t e r e d 61
g r a d i e n t values, while fluid t e m p e r a t u r e d a t a are c o n s i s t e n t a n d even small local t e m p e r a t u r e variations can be evaluated by the latter method. T e m p e r a t u r e g r a d i e n t m a p s h a v e been published since ~96o a n d revised yearly using new reliable d a t a f u r n i s h e d b y m o r e r e c e n t m e a s u r e m e n t s , which also enabled d r o p p i n g old values of d o u b t f u l accuracy. More t h a n ~ooo d a t a h a v e been i n v e s t i g a t e d a n d the r e c e n t g e o t h e r m a l m a p (Figure 2) c o n t a i n s only 567 grad i e n t values. All values b e t w e e n ~oo a n d 400 m d e p t h from the surface were d r o p p e d , whereas in I96o several values b e t w e e n 6o-too m existed on t h e m a p . T h e d e p t h of the average t e m p e r a t u r e m e a s u r e m e n t s has increased from 420 m to zo5o m during ~2 years of i n v e s t i g a t i o n . The t e m p e r a t u r e g r a d i e n t s have b e c o m e more a c c u r a t e a n d v e r y few d o u b t f u l d a t a exist where reliable t e m p e r a t u r e m e a s u r e m e n t s are not available. In Figure ~ a n d Table ~ gradients are d i s t r i b u t e d over t h r e e territories. I
Table ~ shows t h a t w i t h i n each region t h e average t e m p e r a t u r e g r a d i e n t decreases as t h e d e p t h increases. Only two g r a d i e n t s f r o m 18 values c o n t r a d i c t this t e n d e n c y . The cause of this decreasing t e n d e n c y is regarded to be '~s follows :
- - deeper strata are more compact and have higher conductivity values; - - lower gradient values are obtained in those areas where the basin is deeper; consequently the heat flow is diminished owing to rl~e pattern of the bottom of the basin (BoLmzsag 1964a). TABLE 2, - - Distribution o/ temperature gradients according to region and depth, in Hungary. Transdanubia I Depth interval m
400-1000 1000-1500 1500-2000 200%2500 2500-3000 more than 3000 Total or average
Transdanubia, west of ~he Danube, including the Mid-Hungarian Mountains. II -Inter-Danube-Tisa lowland, including the eastern part of the Mid-Hungarian Mountains. I I I - Transtisian lowland east of the Tisza river. -
A l t h o u g h this d i s t r i b u t i o n is p u r e l y g e o g r a p h i c a l , Table 2 shows a n i n t e r e s t i n g e a s t w a r d increase of t h e t e m p e r a t u r e g r a d i e n t f r o m I to I I I .
Inter Danube-Tiscia I.I
Number Average Numbei' of temp. of values gradient values "C/kin
Transtisian III
Average Number Average temp. of temp. gradient values gradient c'C/km "C/kin
34 31 37 30 14 13
51.57 48,64 48,10 48.74 44,51 46,43
83 34 50 18 3 1
55.79 53.11 49,93 48.20 50.60 45,20
95 44 46 25 3 6
56.60 56.60 55.1) 50.35 49.40 47,71
159
48,00
189
50.47
219
52.56
567
50,34
For Hungary
/
, I I
~
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-
i
47 °
o 1
77°
18 ~
t9 °
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20 °
Fro. 1, - - Pattern o[ the base o[ the Paleo-Mesozoic lormations in Hungary. Contours in position o[ boreholes deeper than 3000 meters,
62
21 ° metres"
below
sea level,
Black circles,
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l@--_\ \ " ~ I ~ " ~ _ ) S.~0Contour lines of the ~L_~~ ,-, t~q temperature --]\t 5~3 ~ ) ---~s~ ~67~,2~ f ~ . k . ; ~c gradientin'C/km ~./t~[ \~ f~," ~A ,-~ "'*~'5"~.x..i-.. " ~~5-0 \) ~o,1 ~ Miocene and older ' "Ill ~ \ ~ ~ ~ J Z,/" !0/~ .,r 60 :b - ' I outcrops, volcanics
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. 19 °
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FIG. 2. - - G e o t h e r m a l gradient m a p o/ Hungary. G r a d i e n t values represent an average b e t w e e n the sur/ace and the b o t t o m ot the basin (1000-3000 m).
V'
F r o m this it follows t h a t t h e high t e m p e r a t u r e gradients o b s e r v e d in the C a r p a t h i a n basin are n o t related to a near surface p h e n o m e n o n , b u t t h a t t h e elevated rock t e m p e r a t u r e s really exist down to t h e b o t t o m of the basin. In the last few years oil and gas p r o s p e c t i n g wells reached 3ooo - 58oo m. Very a c c u r a t e rock t e m p e r a t u r e m e a s u r e m e n t s (Table 3) i n d i c a t e d elevated values and only slightly lower average t e m p e r a t u r e gradients. Since these boreholes are s i t u a t e d in the d e e p e s t p a r t of the basin (Figure I) these gradients can b e regarded as m i n i m a l values, w h e r e the h e a t flow is also a t m i n i m u m . I n these <, g r a b e n s , of t h e basin, Pliocene and Pleistocene sedim e n t s are 4000 - 50o0 m thick, which m e a n s an average speed of deposition a m o u n t i n g to 0.5-0.6 r a m / y e a r over 8 million years. Since t h e subsidence of t h e b o t t o m of the basin centres is still continuing, it is clear t h a t this sinking process has d i m i n i s h e d t h e t e m p e r a t u r e increase a n d the h e a t flow. Accordingly t h e deep regional h e a t flow m u s t be slightly higher t h a n values related to b o t h grabens. There are regions where t h e m o v e m e n t of w a t e r und e r g r o u n d d i s t u r b s t h e t e m p e r a t u r e field. In t h e Middle H u n g a r i a n Mountains t h e m o v e m e n t of deep k a r s t w a t e r transfers h e a t in a lateral direction a n d diminishes h e a t flow considerably, I n some places this effect can b e felt down to 600 m. On t h e o t h e r h a n d in the Tisza valley of the Great H u n g a r i a n Plain t h e vertical p e r m e a b i l i t y of Pleistocene sands a n d gravels is high enough to allow vertical m o v e m e n t of t h e w a t e r T h e r e exists a circulation
T.xr;J.r. 3. - - Rock temperatures and gradients measured in boreholes over 300) 7": deep
Borehole
Depth m
T e m p e r - Temp. " Average ature gradient °C/km "C °C/km
I - Transdanubian Bajcsa-I B6s~rk~iny-1 Budafa-I Budafa-VI
3590.0 4474.0 4071.0 4067.0 4060.0 3208.0 3220.6 3220.0 3120.0 3076.0 3125.0 3392.0 3440.0
Budafa-500 Budafa-501 Budafa-III Budafa-502 Szentgy6r~yv~l~v-5 Fels6szentm~4rton-1 III-
180.0 126.0 183.0 214.0 219.0 165.0 154.4 163.0 159.0 160.0 149.5 154.4 158.0
47.2 48.1 42.2 50.0 51.3 48.1 44.5 47.2 47.4 48.4 44.2 42.3 42.7
47.3
42.5
Inter-Danube-Tiscia
Algy6-21
3209.6 156.0 I I I - Transtisian
45.2
Filbi~insebestydn-3 Kondoros-1
2980.0 (1t 3177.0 3118.0 3775.0 3175.0 3020.0 5750.0
46.6 48.5 49.5 50.3 47.8 47.4
Szarvas-DNy-1 Hddmez6vflrhely-I
50.65
150.0 165.5 165.5 170.5 162.8 154.0 217.0 (21
49.03
(1) Depth of the borehole 3600 m. (2) No thermal equilibrium. Probable value 272°C.
63
p a t t e r n , w h e r e w a t e r slowly goes u p in t h e m i d d l e of t h e area a n d cold w a t e r i n t a k e is p r e s e n t o n t h e p e r i p h e r y . I n t h e region of Tiszak6cske, near t h e surface, in 50 m deep boreholes g r a d i e n t s u p to i 5 o ~ C / k m were m e a s u r e d , whereas on t h e p e r i p h e r y o n l y i 6 - 2 o ° C / k m were o b s e r v e d in a n area where t h e n o r m a l g r a d i e n t is a b o u t 5 o ° C / k m (BoLmZSAR 1967). A deep b o r e h o l e of 16oo m showed t h a t u n d e r 4oo m t h e a n o m a l y d i s a p p e a r e d . B o t h t y p e s of anom a l y areas h a v e b e e n left o u t in t h e c o n s t r u c t i o n of t h e geothermal map. T h e rock t e m p e r a t u r e in deep boreholes shows a s l i g h t decrease in t h e a v e r a g e g r a d i e n t , as a f u n c t i o n of d e p t h . This is t h e c o n s e q u e n c e of t h e increasing c o n d u c t i v i t y of t h e more c o m p a c t e d s e d i m e n t s in d e e p e r regions. Conseq u e n t l y t h e a v e r a g e g r a d i e n t s a n d t h e h e a t flow m e a s u r e d a n d c o m p u t e d below 4oo m c a n be used w i t h confidence for e s t a b l i s h i n g h e a t flow c o m i n g from g r e a t e r d e p t h , from u n d e r t h e b o t t o m of t h e b a s i n . T h e region from w h i c h t h e h e a t flow rises is a t least 6-8 k m deep. T a b l e i lists t h e m e a s u r e d h e a t flow values in t h e C a r p a t h i a n b a s i n . T h e e a s t w a r d increase of t e m p e r a t u r e g r a d i e n t s shows t h a t deep h e a t flow s h o u l d also increase t o w a r d s t h e east. T h e r e are h i g h g r a d i e n t a n d h e a t flow v a l u e s in t h o s e places w h e r e t h e b o t t o m rock is e i t h e r on t h e surface (Zob&k-Hosszuhet~ny) or near t h e surface ( s o u t h e a s t T r a n s d a n u b i a w h e r e t h e M e s o z o i c - b o t t o m is uplifted). T h e s e values are considered to d i m i n i s h d o w n w a r d s , b e i n g caused b y t h e t o p o g r a p h i c effect of t h e Meso-Pateozoic b o t t o m w h i c h h a s a good t h e r m a l c o n d u c t i v i t y . Figure 3 i l l u s t r a t e s t h e h e a t flow m e a s u r e d a t t h e surface a n d
t h e regional h e a t flow" a t 6-8 k m d e p t h ( n u m b e r s in brackets). C o m p a r i n g F i g u r e 3 w i t h t h e i s o b a t h m a p of t h e Moho, d r a w n up along 6 profiles (Figure 4), it seems t h a t t h e high t e m p e r a t u r e g r a d i e n t a n d high h e a t flow region across t h e m i d d l e p a r t of H u n g a r y coincides with a n ele v a t e d Moho area with d e p t h values of 24.5 2fi km, whereas in o t h e r p a r t s of t h e c o u n t r y t h e Moho goes down to 28-30 k m (MITuCH, POSGAV 1972 ). I t seems t h a t the t o p o g r a p h y of t h e Moho acts in t h e same m a n n e r on t h e h e a t flow as t h e t o p o g r a p h y of t h e Meso-Paleozoic basem e n t . T h a t m e a n s a b e t t e r crustal a n d s u b c r u s t a l conduct i v i t y u n d e r t h e Paleozoic a n d m e t a m o r p h i c rocks of t h e bottom. T h e C a r p a t h i a n b a s i n s u b s i d e d in t h e Miocene whereas t h e a d j a c e n t Dinarids, t h e C a r p a t h i a n arc a n d t h e eastern Alps were uplifted. T h e subsidence c o n t i n u e d in t h e Pliocene a n d Pleistocene. T h e slow- plastic flow of rocks from u n d e r t h e C a r p a t h i a n b a s i n t o w a r d s t h e u p l i f t e d zone was needed to s u p p o r t t h e b u i l d i n g u p a n d t h i c k e n i n g of t h e crust under the mountain system. M a g n e t o t e l l u r i c m e a s u r e m e n t s a l o n g specific profiles in t h e H u n g a r i a n b a s i n i m p l y t h a t t h e d e p t h of t h e good c o n d u c t i n g layer is b e t w e e n 55-ioo kin, a v e r a g i n g 7o k m whereas in t h e Baltic a n d U k r a i n i a n shield region of t h e S o v i e t U n i o n it is more t h a n 20o k m deep (ADAM I97O ). T h e h i g h position of t h i s layer is t h e c o n s e q u e n c e of t h e high e n v i r o n m e n t t e m p e r a t u r e a t 5o-Ioo k m w h i c h causes t h e rock to flow. T h i s ,, flow ,, is a very slow plastic: flow of high t e m p e r a t u r e rock m a t e r i a l . I t can be b e t t e r t e r m e d
,1
--
?~ ~ 1 t [2.3] (X"
7/
/
I
t'
a Yl
o 20 ~-. ~--..,.j--" 17 °
18 °
k 79 °
I, 20 °
Fro. 3. - - Heat /low map o/ Hungary. 64
2t °
40 k ~
as a high t e m p e r a t u r e c o n t i n u o u s mass creep of high t e m p e r a t u r e a n d high pressure rocks. F r o m t h e e l e v a t e d position of t h e Moho a n d t h e good c o n d u c t i n g layer i t c a n b e safely c o n c l u d e d t h a t t h e regional high t e m p e r a t u r e gradient, a n d c o n s e q u e n t h i g h h e a t flow, e x t e n d from near surface (6-8 k m deep) d o w n to a t least 8 o - m o km, t h r o u g h t h e Moho-level d o w n to t h e good c o n d u c t i n g layer. Similar basins w i t h high heat flow a n d i n t e r m e d i a t e c r u s t t h i c k n e s s are s i t u a t e d in t h e s o u t h e r n p a r t of t h e Black Sea, in t h e J a p a n a n d O k h o t s k seas. T h e Moho in t h e Black Sea basin is 2o-3o k m deep, in t h e J a p a n Sea a b o u t 25 km, in the O k h o t s k Sea 2o-3o k m . These basins can be considered as depressions in t h e process of b e i n g filled up, while in t h e C a r p a t h i a n b a s i n this process is n e a r l y complete. H i g h h e a t flow in t h e Fiji p l a t e a u a n d Lau basin, in t h e S h i k o k u a n d P a r e c a Vela basins (ScLaTER ~972), c a n n o t be correlated to these basins m e n t i o n e d before, since t h e y are b o r d e r e d b y oceanic t r e n c h e s a n d are a p a r t of t h e Circumpacific s y s t e m . T h e c h a r a c t e r i s t i c s a n d origin of t h e h e a t source w h i c h is o b v i o u s l y s i t u a t e d u n d e r t h e high c o n d u c t i v i t y layer, below a b o u t IOO km, are n o t k n o w n a n d it is difficult to give an e x p l a n a t i o n of such. Theories of worldwide conv e c t i o n c u r r e n t s are no longer in fashion a n d I do n o t consider it necessary to r e p e a t m y negation of t h e i n c o r r e c t usage of this h y d r a u l i c engineering t e r m in geophysics for t h e high t e m p e r a t u r e c o n t i n u o u s mass creep of m a n t l e rock t a k i n g place a t d e p t h . I consider this peculiar m a n t l e m o v e m e n t in t h e low v e l o c i t y region responsible for causing uplift a n d subsidence a t t h e same t i m e in various places of t h e globe. U p l i f t a n d subsidence are interconnected b y t h e same process emerging from t h e same cause.
T h e t h i c k n e s s a n d mass of t h e conti,Jental c r u s t are regulated b y t h e isostatic b a l a n c e in such a way t h a t t h e b o t t o m a n d t h e c r u s t of t h e oceans are sinking w h e n new c o n t i n e n t a l c r u s t is b e i n g created (BOLDrZSaR ~959). On t h e c o n t r a r y , if t h e c o n t i n e n t a l c r u s t is b e i n g a n n i h i l a t e d , immersed or a s s i m i l a t e d into t h e mantle, which I do not believe to be t h e general situation, t h e b o t t o m of a c e r t a i n oceanic region reacts w i t h a n a p p r o p r i a t e uplift, Geological o b s e r v a t i o n s s t r o n g l y s u p p o r t t h e view t h a t t h e r e is a growing of t h e c o n t i n e n t a l c r u s t or a t least t h e quasi c o n s t a n c y of it. In t h e l a t t e r case t h e e v o l u t i o n oI t h e c o n t i n e n t a l c r u s t does not m e a n an increase in size a n d mass, b u t only its cyclic r e w o r k i n g c o n n e c t e d w i t h u p h e a v a l a n d subsidence of various p o r t i o n s a t different times. F o r m o u n t a i n b u i l d i n g t h e underflow of m a n t l e material is needed and, on t h e c o n t r a r y , subsidence of c o n t L nental c r u s t should t a k e place only as a result of m a n t l e outflow possibly in t h e low velocity layer. This , flow >, of course is a v e r y slow creep of t h e rock mass in t h e low velocity layer. This flow will be t e r m e d in s h o r t as plastic flow or creep. T h e velocity profile of this plastic flow is c h a r a c t e r i z e d s c h e m a t i c a l l y in F i g u r e 5. T h e schem a t i c r e p r e s e n t a t i o n of t h e velocity of t h e plastic flow or creep versus d e p t h shows t h a t this flow occurs n o t only in t h e low velocity layer b u t , according to the plastic beh a v i o u r of t h e rocks, on t h e t o p of t h e low velocity layer including t h e crust. T h e more elastic c r u s t resists t h e t r a n s p o r t i n g effect of t h e low v e l o c i t y layer a n d t h e v e l o c i t y in t h e c r u s t is d i m i n i s h e d . T h e oceanic c r u s t will be dragged t o w a r d s t h e rising c o n t i n e n t a l portion. In this way p a r t s of the oceanic c r u s t a n d even c o n t i n e n t a l c r u s t blocks can t r a v e l g r e a t distan-
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ces, w h e n t h e process described a b o v e is a s t e a d y one. B u t w h e r e t h e m o v e m e n t is a r a n d o m one, i t will b e err a t i c a n d s o m e t i m e s t h e c r u s t b l o c k r e t u r n s n e a r to t h e original p o s i t i o n a f t e r h a v i n g t r a v e l l e d a g r e a t distance. T h e geological a n d geophysical s t r u c t u r e of t h e e a r t h c r u s t inside t h e c o n t i n e n t s a n d a t t h e m a r g i n a l p a r t s does n o t c o n v i n c e m e t h a t geologic a n d g e o p h y s i c a l processes gove r n i n g t h e s c u l p t u r e of t h e global surface are simple a n d regular processes. O n t h e c o n t r a r y , as e v e r y w h e r e in physics a n d engineering, where h e a t a n d mass t r a n s f e r are c o n c e r n e d , t h e s e processes are n o t r e g u l a r a n d c o n s i d e r i n g p h a s e c h a n g e s in t h e m a n t l e it is impossible to give a simple m e c h a n i s m of t h e c r u s t a l h i s t o r y of t h e e a r t h . T h e r e is m o r e t h a n one possibility of a r r i v i n g from one stage to t h e n e x t one. As far as t h e C a r p a t h i a n b a s i n is c o n c e r n e d it c a n b e said t h a t as t h i s t e r r i t o r y is a n i n t e g r a l p a r t of t h e worldwide T e r t i a r y c r u s t b u i l d i n g s y s t e m , t h e t h i c k e n i n g of t h e c r u s t in t h i s region possibly s t a r t e d in t h e Mesozoic, slowed d o w n d u r i n g t h e Paleocene a n d ceased in t h e Miocene. F r o m t h e Miocene t h e m a n t l e u n d e r t h e C a r p a t h i a n b a s i n s u p p o r t e d , b y slow plastic flow or m a s s creep, t h e b u i l d i n g u p of t h e C a r p a t h i a n arc a n d Dinarids, a n d t h e b a s i n subsided. T h e c i r c u l a r s t r u c t u r e of c h a i n m o u n t a i n s a r o u n d t h e b a s i n n e e d e d m o r e m a n t l e m a t e r i a l to s u p p o r t t h e i r rising t h a n could possibly b e o b t a i n e d f r o m t h e Mediterranean and Atlantic and dragged the mantle from t h e inside area w h i c h t h u s b e c a m e a s i n k i n g b a s i n . W h i l e t h e c r u s t t h i c k n e s s in t h e C a r p a t h i a n s is b e t w e e n 4o a n d 60 km, u n d e r t h e basin it is o n l y 26-28 k m . T h e i n t e n s e radial outfflow of m a t e r i a l from t h e b a s i n c a u s e d t h e lower p a r t of t h e u p p e r m a n t l e to rise. I n this way, owing to v e r t i c a l mass t r a n s p o r t , t h e h i g h h e a t flow c a n be, a t least p a r t l y , explained.
Exaggerated ideas in modern earth sciences Geophysics has b e e n d o m i n a t e d d u r i n g t h e last few years b y t h e so-called , new global t e c t o n i c s , , b a s e d o n t h e old idea of c o n t i n e n t a l d r i f t i n t r o d u c e d b y WEG~NER, t h e s y m m e t r i c a l m a g n e t i c p a t t e r n s i n t e r p r e t e d b y VINE a n d MATTHEWS as , sea floor s p r e a d i n g ~ a n d finally t h e
~66
, p l a t e tectonics ~) p r o p o s e d b y m a n y , a m o n g w h o m ISAACKS, OLIVER, S~KES, LE PICHON, MORGAN etc. T h e v e l o c i t y of t h e m o t i o n of t h e c r u s t a n d underlying m a n t l e p o r t i o n s is n o t m o r e t h a n a few c e n t i m e t r e s per year. i.e. a b o u t io --7 c m / s . This slow m o v e m e n t is w i t h i n t h e r a n g e of t h e e x t r e m e l y slow plastic flow of t h e o t h e r w i s e h i g h l y elastic silicates. T h e d r i v i n g force b e h i n d this peculiar flow of c o m p r e s s e d solid silicates of not more t h a n a few t h o u s a n d degrees of t e m p e r a t u r e is u n k n o w n . I t is guessed t h a t o n l y t h e t h e r m a l energy is big e n o u g h to i n i t i a t e a n d m a i n t a i n this slow m o t i o n for some t h o u s a n d million years. M a n y a u t h o r s use t h e movem e n t due to t h e r m a l c o n v e c t i o n a n d it is even supposed t h a t c o n v e c t i o n cells exist in t h e m a n t l e . F o r m e it is difficult to imagine, t h a t in such a rigid m a t e r i a l as are t h e m a n t l e silicates, such a low t e m p e r a t u r e g r a d i e n t w h i c h in t h e m a n t l e really exists can cause c o n v e c t i o n . The sions of existence to more
size of t h e , plates ~ h a s increased to t h e dimenc o n t i n e n t s a n d oceans, so t h e y are - - if t h e i r is a c c e p t a b l e --- shells, a n d t h e y c a n be referred correctly as , shell tectonics ,.
I t seems to m e t h a t t h e usual vertical e x a g g e r a t i o n of l : i o to i : i o o , which in t h e past, s o m e t i m e s forgotten or overlooked b y t h e geologist, h a d led to erroneous de d u c t i o n s (e.g. n a p p e theories of A l p i n e s t r u c t u r e s , d r i f t i n g c o n t i n e n t s , m a g m a t i c intrusions, etc.), is n o w a d a y s influencing geophysics. W i t h o u t v e r t i c a l e x a g g e r a t i o n t h e surficial f e a t u r e s of t h e e a r t h are not v e r y significant a n d I believe t h a t w i t h o u t g e o m e t r i c a l a n d p h y s i c a l exaggera t i o n s m a n y theories would loose t h e i r seemingly a t t r a c t i v e power. It can h a r d l y b e i m a g i n e d t h a t in t h e v e r y d i s t a n t p a s t g r e a t c o n t i n e n t a l masses were c r e a t e d j u s t b y h a v i n g been b r o k e n into smaller blocks a n d f l o a t i n g a w a y from each other, colliding w i t h o t h e r b r o k e n p a r t s to c r e a t e new c o n t i n e n t a l masses. U n i f y i n g t h e old W e g e n e r t h e o r y with sea-floor spreading, t h e c o n t i n e n t s are a s s u m e d n o t only to h a v e floated a w a y - - which i~ easier to i m a g i n e b u t t h e y are p u s h e d a p a r t b y m e a n s of t h i n oceanic c r u s t , p l a t e s ,, e x t e n d i n g from t h e M i d - A t l a n t i c ridge to t h e c o n t i n e n t a l mass of E u r a s i a - A f r i c a on t h e one side a n d t(~ A m e r i c a on t h e other. T h e essence of t h e t h e o r y of t h e r m a l c o n v e c t i o n in t h e m a n t l e is b a s e d on a g r e a t p h y s i c a l e x a g g e r a t i o n . In reality t h e r e is no c o n v e c t i v e h e a t a n d mass t r a n s p o r t owing to t h e real s m a l l t e m p e r a t u r e g r a d i e n t in t h e m a n t l e , because u n d e r a t h r e s h o l d v a l u e of t h e G r a s h o f n u m b e r no m o v e m e n t a t all will t a k e place. A n o t h e r f r e q u e n t l y used expression is t h e , i n t r u s i o n , of m a g m a into t h e c o u n t r y rock a n d t h e m e l t i n g or fusion of t h e l a t t e r to m a k e w a y for t h e v o l u m e of i n t r u s i o n . In reality i n t r u s i o n a n d fusion are n o t e n o u g h to e x p l a i n correctly t h e widely o b s e r v e d p h e n o m e n o n . I t is possible t h a t t h e i n t r u s i o n really occurs b y c h a n g i n g places, i.e. t h e i n t r u d e d m a g m a goes up into t h e v o l u m e left , e m p t y ~; b y t h e c o u n t r y rock a n d t h e c o u n t r y rock goes d o w n into t h e e m p t y space left b y t h e m a g m a . T h i s c h a n g e of place or diapiric uprise occurs b y m e a n s of slow pLastic flow a n d i t is n o t necessary to believe t h a t t h e whole v o l u m e of m a g m a is m o l t e n . P a r t i a l m e l t i n g t a k e s place a t t h e per i p h e r y , where t e n s i o n a l f r a c t u r e of t h e rock causes a decrease in pressure.
C o m p l e t e tuslon of c o u n t r y rock to m a k e r o o m for m a g m a t i c i n t r u s i o n is also n o t a correct e x p l a n a t i o n ; t h e v o l u m e of t h e m o l t e n c o u n t r y rock exists a n d should b e deposited somewhere. F r o m t h e p o i n t of view of h e a t conduction, m e l t i n g a n d fusion are o n l y possible in t h e t h i n c o n t a c t b o u n d a r y region, where t h e t e m p e r a t u r e is h i g h e n o u g h to m e l t t h e c o u n t r y rock. T h e mass of t h e p l a n e t e a r t h seems to h a v e been p r a c t i c a l l y c o n s t a n t , a t least d u r i n g t h e last 10oo-2ooo million years. If this is so, t h e v o l u m e of t h e e a r t h c a n c h a n g e o n l y b y t h e r m a l a n d pressure effects. These are t h e r m a l d i l a t a t i o n - s h r i n k i n g a n d p h a s e changes b y v a r i a t i o n ot pressure. T h e i r cause is t h e r m a l energy change, e i t h e r b y c o n v e r s i o n of nuclear energy into h e a t or h e a t loss b y c o n d u c t i o n into space. T h e e a r t h v o l u m e is too g r e a t for an easy e x p l a n a t i o n of t h e slight surficial irregularities of t h e c r u s t s i m p l y b y clear t h e r m a l a n d pressure effects, chiefly w i t h i n t h e u p p e r m a n t l e . T h e e x p l a n a t i o n of these small changes b y supposing regular a n d worldwide c o n v e c t i o n d o w n to t h e lower m a n t l e or to t h e core, i.e. regular m o v e m e n t s of i m m e n s e masses in r e l a t i o n to t h e r e l a t i v e l y small volumetric v a r i a t i o n s in t h e c r u s t d u r i n g geological times, is i n a p p r o p r i a t e , a n d t h e small effect b y no m e a n s corresponds to t h e g r e a t e v e n t s causing it. Geology has b a s e d its o b s e r v a t i o n s chiefly on t h e cont i n e n t s a n d is therefore c o n t i n e n t a l l y - m i n d e d w h e n f o r m i n g global tectonics. T h e , new global tectonics )~ of m o d e r n geophysics is b a s e d on new o b s e r v a t i o n s on t h e ocean floor, t h e island arcs a n d c o n t i n e n t a l m a r g i n s a n d its bias is t y p i c a l l y oceanic. T h e r e is no tie-up b e t w e e n o b s e r v a t i o n s a n d theories of geology a n d geophysics a n d new t e x t b o o k s of geology are needed, in which old, obsolete c o n c e p t s are d r o p p e d a n d are replaced b y a new knowledge of geophysics, especially t h e r m a l a n d t h e r m o d y n a m i c a l aspects of m o d e r n petrology. Looking a t t h e e a r t h from t h e moon, one is i m p r e s s e d b y t h e blue oceans a n d t h e ever c h a n g i n g w h i t e clouds. I t is u n q u e s t i o n a b l e , t h a t t h e presence of t h e h y d r o s p h e r e a n d a t m o s p h e r e m a y be t h e c a u s e of m a n y i m p o r t a n t changes in t h e c o n t i n e n t a l crust. T h e i r role p e r h a p s , is more i m p o r t a n t t h a n has b e e n suspected d u r i n g t h e u p p e r m a n t l e p r o j e c t investigations. T h e differentiation of t h e m a g m a a n d t h e p r o d u c t i o n of lighter acid fraction, t h e isostatic rise of this p r o d u c t were recognised v e r y early a n d are now a c c e p t e d b y m o s t a u t h o r s . This p h e n o m e n o n explains the presence of t h e e l e v a t e d light c o n t i n e n t a l c r u s t
cores, l h e growing of t h e c o n t i n e n t a l cores is m a i n t a i n e d b y t h e hydrological cycle, b y orosion a n d deposition. T h e rising c o n t i n e n t s c a u s e subsidence on t h e i r m a r g i n s a n d if this t a k e s place on t h e ocean side, t h e l i g h t sedim e n t coverings spread o v e r t h e ocean m a r g i n s a n d d i s t u r b t h e isostatic q u a s i - e q u i l i b r i u m . O w i n g to this d i s t u r b a n c e t h e effects of t h e rising c o n t i n e n t a l block s p r e a d t o w a r d t h e oceanic crust. One of t h e volcanoes of t h e Tharsis area o n Mars rises o v e r 26 k m a b o v e t h e o t h e r s : differences in h e i g h t are considerable on t h e m o o n too. This shows t h a t g r e a t surficial irregularities exist owing to i n t e r n a l rock mass m o v e m e n t s as is t h e case on earth. I n e q u a l i t i e s of d e n s i t y d i s t r i b u t i o n (mascons) exist on t h e m o o n a n d possibly on o t h e r e a r t h l i k e i n n e r p l a n e t s . T h e s e d e n s i t y irregularities a n d t h e r a d i o a c t i v e h e a t sources c a n cause slow plastic flow of rock masses, as on t h e earth, w i t h o u t t h e presence of t h e h y d r o s p h e r e . B u t t h e presence of t h e h y d r o s p h e r e , c a u s i n g erosion, deposition t h u s o b s c u r i n g a n d influencing t h e p r i m a r y cause of s u b c r u s t a l mass creep, g r e a t l y c o m p l i c a t e s t h e process of c r u s t a l d e v e l o p m e n t a n d m a k e s t h e o b s e r v a t i o n a n d e x p l a n a t i o n of t h e geological a n d geophysical p h e n o m ena more difficult.
REFERENCES ADAM A. 1970 - - Gutleitende Schicht. Acta Geod. Geophys. Mont. Acad. Sci Hung., 5, I06. BOLDIZSAR T. 1956 - - Measurement of Terrestrial Heat Flow in the Coal Mining District Koml6. Acta Technica Acad. Sci. Hung., XV, 219-228. BOLDIZSAR T. 1958a - - Geothermic Investigations in the Hungarian Plain. Acta Geologica, V, 245-254 BOLDIZSAR T. 1958b - - New Terrestrial Heat Flow Values from Hungary. Geo/isica Pura e Applicata, 39, 102-125. BOLI)IZSAR T. 1959 - - Terrestrial Heat Flow in the Nagylengyel Oilfield. Publ. Min. Fac. Sopron, XX, 27-34. BOLDIZSAR T. 1964a - - Heat Flow in the Hungarian Basin. Nature, 202, 1278-1280. BOI~DlZSART. 1 9 6 4 b - Terrestrial Heat Flow in the Carpathians. J. Geophys. Res., 69, 5269-5275. BOLDIZSAR T. 1 9 6 7 - Terrestrial Heat and Geothermal Resources in Hungary. Bulletin Volconologique, XXX, 221-227. CE~MAK C. 1967 - - Results of Geothermic Investigation. Studia Geoph. et Geod., 11, 342-?44. LUBIMOVA E. A. 1966 - - Ocenka Raspedatenia Glubimogo Teplovogo Potoka. Isdateltstvo Nauka, Moskva, 50-51. MITUCH E., Pos6AY K. 1972 - - Geophys. Transactions Spec. Ed. M/iszaki K6nyvkiad6, 118-129 SCI.ATER I. G. 1972 - - Heat Flow and Elevation of the Marginal Basins of the Western Pacific. J. Geophys. Res., 77, 5705-5719.
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