- Email: [email protected]
Siberian continental drift
Tectonophysics
Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
SIBERIAN
CONTINENTAL
DRIFT
l
G.P. TAMRAZYAN * Institute of Geology, Academy
of Sciences of the Azerbaydzhan
S.S.R., Baku (U.S.S.R.)
(Received April 22, 1970) (Resubmitted March 17, 1971) ABSTRACT Tamrazyan, G.P., 1971. Siberian continental drift. Tectonophysics,
11: 433-460.
It is suggested that an ancient separation of the East European and Siberian platforms regions results in the formation of a major tectonic depression, the West Siberian trough and its continuation to the southwest, between them. This is supported by a great body of actual data ranging from present day tectonic movements to the distribution of geothermal and metallogenic provinces.
INTRODUCTION AND GENERAL SETTING
Ideas of continental migration existed even before theoretical geology came into being, some originating as early as the 17th century. During the last decade the concept of continental migration has gained wide recognition and new ideas of mobilisation are dominant. The main features in the development of continents and oceans, as well as folded and geosynclinal regions can now be explained more convincingly than previous ideas based on constancy. In 1962 Tamrazyan put forward the idea that continental migration might be found in the eastern hemisphere (summarised in Tamrazyan, 1964). This continental migration was called the Siberian continental drift and implied the separation of an East EuropeanSiberian platform assemblage into two individual platforms and that these are still moving apart, mainly latitudinally (Fig. 1). The separation of the original assembly took place along very deep fractural sutures extending deep into the asthenosphere. The sutures were sinuous but generally had a submeridional orientation and the now separated edges show striking correspondence. The major projections of the western edge (Pai-Khei-Novaya Zemlya, southern Urals, the High and Low Caucasus) correspond to concavities on the eastern edge (Yenisei-Khatange, Kulunda, Chui and North Kyzylkum troughs). Similarly the western concavities (Near Caspian and Kura troughs) correspond to eastern projections (Central Kazakhstan Massif and Karatau uplift) and straight sections also match each other on both
l With the full agreement of the author, this paper has been rewritten and shortened to about 25% of its original length by Dr. D.H. Tarling, Dept. of Geophysics and Planetary Physics, University of Newcastle, Newcastle upon Tyne, Great Britain. Every care has been taken to avoid misrepresentation of Prof. Tammzyan’s ideas, but naturally such a reduction must involve some loss of information. ** Chairman, Commission of Extraplanetary Phenomena of the International Association of Planetology
Tectonophysics,
11 (1971) 433-460
434
G.P.TAMRAZYAN
.^,...._/
,..
435
SIBERIAN CONTINENTAL DRIFT
sides. It is important to note that these structures have been mapped quite objectively and the correspondence was dete~ined subsequen~y, The West Siberian and Turan plates and the Turgai trough between them, together with the Near Caucasian trough, the pre-Caucasus and extreme western tip of the Big Donbas areas all lie in the region formed as a result of the separation of the two main continental blocks. The movement of these main structural units was by some 1,000 km in the north and by l,SOO--1,700 km in the south and took place mainly in pre-Mesozoic times and subsequently slowed down so that this ancient motion has, to some extent, been obscured by later deveiopments and any restoration must be based on matching the ages and characteristics of tectonic features which formed prior to the separation. TECTONIC RELATIONSHIPS
The most characteristic features of the different tectonic blocks are the pattern of consolidation of ancient major structures. There were three particularly distinct blocks prior to Siberian drifting. The first was the East European and Siberian platforms which were then conti~ous. The second was several sharply defined positive structures (the ~rai~ian shield, Voronezh and Volga-Urals~anteclisesand the Central Kazakhstan Massif) which are all genetically closely related to the first unit. The third block is the youngest and comprised the Polar Urals, Pai-Khoi, Novaya Zemlya and Taimyr areas which are all genetically related to the first unit. These blocks were separated by the Siberian fractural suture into separate units, but each unit continued to evolve in much the same way as before because of their inherited tectonic nature. Naturally, the evolution became faster in some areas and slowed in others so that the individual development of each major block and each of their component parts gradually obscured the sim~~ities between them and the geological picture became more diversified during the passage of time. In particular, the sedimentary picture continued to develop despite the migration of the blocks and each block retained the various characteristics of ablation and deposition, etc., so that it is not considered Fig. 1. Diagram of geological-geotectonic zoning and the Siberian continental drift. Precambrian folded structures: a = ancient shields (1 = the Baltic Shield, 2 = the Ukrainian shield, 3 = the Anabai shield, 4 = the Aldan shield); b = ancient platforms (5 = East-European, 6 = Siberian). Palaeozoic folded structures: c = regions of Csledonlan (Early- and Middle-Palaeozoic) foldings (7 = Central Kazakhstan folding, 8 = Karatauz folding, 9 = Salair-Sayan folding, 10 = Transbaikal folding); d = regions of Hercynian (Middle and Late Palaeozoic) foldings (II = the Urals folding, 1.2= the PaiKhoi folding, 13 = the Novaya Zemlya folding, 14 = the Taimyr folding, 1.5 = the Altai folding, 16 = the Near-%alkhash folding, I7 = the East-Transbaikal’fokling). Mesozoic-Cenozoic folded structures: e = the Alpine folded regions in the south of the U.S.S.R. (18 = the Crimean-High-Caucasian folded region, 19 = the Low-Caucasian folded region, 20 = the Kopetdag folded region, 21 = the Pamir folded region); f= troughs on the Precambrian folded base (22 = the Donbas trough, 23 = the Near-Caspian trough, 24 = the Yenise$-Khatauga trough; on the Palaeozoic folded base: 2.5 = the North-Caucasian trough, 26 = the North Kyzylkum trough, 27 = the Chui trough, 28 = the Kulunda trough); on the Palaeozoic-Precambrian folded base (29 = the West-Siberian plate, 30 = the Turan plate). Revived troughs having no granite layers in their major portions (31 = the Black Sea trough, 32 = the Sou~~asp~n trough). Edges of the Siberian fractural suture: g = western edge; h = eastern edge. Tectono#ysics,
11 (1971) 433-460
436
~.P.~rA~RAZYAN
S~3ER~AN CONT~~NTAL
DRIFT
437
possible to match sedimentary environments for these early times. However, certain similar features in their development can be seen, for example, the same stages of overall deformation can be recognised during the Precambrian in the previously adjacent Central Kazakhstan Massif and the Verenezh and Volga-Urals anteclises (particularly evident in maps of neotectanics of the U.S.S.R, compiled by NJ. Nikolayev and S.S. Shults, 1959). Similarly the Polar Urals, Novaya Zemlya and Taimyr regions belong to th& same rn~~nt~n-budding region and have similar grades of tectonic movement (Fig. 2). The newest subsidence regions are all confined to the area between the separated edges of the Siberian fracturaf suture and all of these basins show inherited gradients and crustal morphology. THE CRUST AND UPPER MANTLE
The influence of Siberian drift on the structure of the earth’s crust and upper mantle is best considered separately for individual areas and the main features are then summarised, The west Siberian lowland This region is situated between the stable blocks of the East European and Siberian platforms. The age of the basement rocks is in dispute with ages suggested as Hercynian, Caiedo~~, ~~~~-~~a~r and ~re~~b~an; the last age being supported by pre-Falaeozoic rocks found beneath the Mesozoic cover in deep drill holes in the central part of this region. The Mohorovi~~ discontinuity is at a depth of 3’+36 kni over most of the region, in marked contrast to depths of 40-50 km in the neighbouring East European and Siberian platforms (Fig. 3) and Central Kazakhstan Massif and Urals. The height of the Mohorovi~i~ discontinuity is matched by a corresponding reduction in the basement crust which is overlain by a substantial sedimentary cover which is up to 40 km thick in the centre of the lowland so that the crystalline crust is generally only some 23-25 km thick in contrast to the surrounding regions where it is in excess of 30-40 km thick. The overlying sediments were laid down during the Mesozoic-Cenozoic period and their floor was simultaneously being warped, probably in response to an elevation of the mantle during the Mesozoic or possibly earlier. Several major fault systems cross the region ol’ which the Gyda&k-Omsk fault is the largest and has been investigated seismically, ma~etica~y, by gravity studies and also deep
Fig. 2. Diagram of metalloge& zoning of the U.S.S.R. territory (according to V.M. Smirnov, 1965). Occurrence regions of deposits of different metallogenic epochs of geosynclinal cycles: a = Alpine; b = Cimmerian; c = Hercynian; d = Caledonian; e = Proterozoic; f= Archean. Occurrence regions of deposits of different rne~~e~c epochs for platforms: g = Gimmerian; k = Hercynian; i = trap occurrence region Ore provinces. Alpine provinces: I = the Far Northeast, 2 = the Caucasus, 3 = the Carpathtans, 4 = the Kopetdag, 5 = the Pa&s. Kimmerian provinces: 6 = the Transbaikal-Primorye territory; Hercynian provinces: 7s the Urals, 8= Kazakhstan, 9= Middle Asia, 10 = the Donbas, II = Taimyr, 12 = the Tom’-K&van zone; Caiedonian provinces: 13 = the A~~-Say~~ zone; Proterozoic provinces: $4 = the southern part of the Sz%&anplatform, IS = the Baltic shield, 16 = the Ukrainian shieid.
SIBERIAN CONTINENTAL DRIFT
439
drill~g, This fault extends from Gydansk bay in the north to the Omsk region in the south as a series of graben-like depressions in the basement rocks which have been filled by a complex of sedimentary and effusive deposits up to 2 km thick (Rorisov, 196% The fault is therefore some 2,000 km long but only 30-50 km wide. In the south the fault belt is deflected southwest and it is thought that the basement depressions become narrower until they are simple fractures. This southern extension, the ~rengoi-~oltogo~ ridge, can be traced for almost 1,000 km into Central Kazakhstan. Similar southerly extension as deep en-echelon faults can be traced along the Tokraus belt which has now been established from Chan Lake in the north to Issykkul Lake in the south. The total length of the Gydansk-Omsk-Tokraus fault belt is therefore at least 3,000 km and appears to correspond to the most stretched part of the crystalline basement within the west Siberian lowland. This, however, is only one of several major fault belts in this region. On the east of the lowland, 100-200 km west of the Yenisei River, there is a pronounced belt of gravity and magnetic positive anomalies corresponding to intrusions of
predominantly basic rocks which extend from the lower course of the Yenisei River as far as the Kuznetsk Alatau (Borisov, 1967). This belt corresponds, for most of its length, with the western edge of the buried Baikal and Salair structures of the Siberian platform and the eastern edge of the post-Prec~brian structures of the west Siberian lowland basement (Surkov, 1963). This belt, including its southern extension to the Altai and western Sayans exceeds 2,000 km. Within the lowland itself occur wide areas of transitional crustal densities, mostly associated with deeply warped zones and usually connected to the surface via cracks in the folded basement. These transitional densities usually consist of somewhat broken and sij~tly metamorphosed fo~ations interbedded between the basement and the overlying Mesozoic and Cenozoic cover (Surkov et al., 1969). They are usuahy of molasse-type but include effusive and carbonaceous formations, The volume of this intermediate material varies considerably in quantity and age. The older the folded basement, the wider the
age range SOthat it is of Riphean to Triassic age in areas of Archaean and Baikal folding but only of upper Palaeozoic age in regions of Hercynian folding; in some areas it is only of Triassic and Lower Jurassic age but are more commonly of Late Palaeozoic to Early Mesozoic age. The Turan lowland Most of the Turan lowland is underlaid by a Mohorovi~i~ ~sconti~uity at a depth of 30-40 km in contrast to depths of 40-50 km to the east beneath the Central Kazakhstan Massif and to the west beneath the Caucasus. As for the West Siberian lowland, the crust is therefore thinner than in surrounding regions. At depths of 2-5 km, the basement folding is usually represented by a high grade metamorphism, up to granitic gneiss, of the
Fig. 3. The MohoroviW(M) surface occurrence diagram and the Siberian fractural suture. a = occurrence depth of M surface: zones with a depth of M surface less than 35 km are shown by dots; b = bands of fragmentation, melting, positive gravity anomalies, and magnetic maxima; (points a and b are according to Borisov, 1967) c = edges of the Siberian fractural suture. ~ecr~~o~~ysjcs, 11 (1971) 433-460
440
G.P.TAMRAZYAN
Q,
-T
IlBil
.... . LIB -0
.-
v
L
:r:.:.::::: ::::.
01 \\ 0:f illn ,.:::s :::::. ....
a
0
m
w-
SIBERIAN CONTINENTAL DRIFT
441
Palaeozoic formations. Transitional densities occur between the crystalline basement and the Mesozoic cover, mainly in tectonic depressions and usually represented by compacted and dislocated terrigenous formations. These transitional densities are absent in elevated areas where Pre-Permian deposits are overlain directly by Mesozoic sediments. It appears that the geosynclinal deposition during the Palaeozoic was almost continuous and accompanied by intensive metamorphism, recrystallisation and granitization of the basement. The Near Caspian lowland The MohoroviEiC discontinuity is at some 38-42 km beneath this region which is somewhat less than beneath the Ukranian shield and adjacent areas where it is usually 45-50 km deep. The basement surface is deep, down to lo-15 km, in contrast with depths of 5-6 km in the surrounding areas. The eastern edge is marked by a chain of magnetic maxima along a fault line near the pre-Urals warping and appears to have been activated or initiated during the Permian-Mesozoic period. The pre-Caucasus and Crimean steppe (Skif block) The MohoroviEiC discontinuity is shallower here, 35-40 km, than in neighbouring regions, the Ukranian shield, Verenezh Massif and Caucasus where the discontinuity is at 50-60 km. The thickness of crystalline basement is also considerably reduced in this region. The south Caspian and Black Sea troughs The south Caspian trough comprises the southern and central Caspian Sea, the Apsheron Peninsula, the Lower Kura trough and the west Turkmenian depression. It is a morphological and tectonic depression characterised by an intensive negative gravity anomaly and tectonic non-uniformity. The MohoroviEiC discontinuity is shallow, 35-45 km deep; and the surface of the Palaeozoic crystalline basement is deep, 15-25 km. In the centre of the trough the granitic crust is absent and the sediments directly overlie a basaltic substratum. In other areas, the granitic crust is reduced, 15-20 km thick, and the trough as a whole was initiated in the Mesozoic and is now filed with Mesozoic-Cenozoic sediments which are up to 25 km thick, mostly of Neogene (particularly Pliocene) and Anthropogene age. The Black Sea trough is a complex structure although consisting superficially of a simple
Fig. 4. Consolidated earth crust (Borisov, 1967) and the Siberian continental drift. a = thickness of crust limited by the surfaces of MohoroviEiC and Precambrian foundation; b = thickness of crust limited by the, surface of MohoroviEiC and that of the Palaeozoic (and in some places Mesozoic) foundation. Thickness of consolidated crust: c = less than 30 km; d= 30-35 km; e = 35-60 km; f= projections of basalt layer (the granite layer is absent or thinned out considerably); g = zones of inland seas with no granite layers; h= crushing, foundering and downwarping bands in the foundation relief, bands of positive gravity anomalies and magnetic maxima; i = bands of intensive basaltification of granite layers in continental crust regions (the Urals); j = edges of the Siberian fractural suture. 7’ectonophysics, 11 (197 1) 433-460
442
G.P.TAMRAZYAN
SIBERIAN CONTINENTAL DRIFT
443
trough with deep-sea parts at its centre which have an associated gravity maximum. The MohoroviEiC discontinuity is very shallow beneath the central section, being only 20-25 km deep, but is deeper nearer the margins, being usually around 35-40 km deep. The crystalline basement is extremely thin throughout the trough, usually not more than 5-8 km thick; the granitic part being almost entirely absent in some areas so that the central trough has an oceanic crustal structure. Summary The regions situated on the edges of the Siberian fractural suture are characterised by the following features (Fig. 3-S). (1) Shallow MohoroviEiC discontinuity, as shallow as 20 km in parts of the Black Sea and generally 30-40 km deep in contrast to surrounding areas where the discontinuity is generally at SO-60 km depth. (2) The shallow MohoroviEiC discontinuity is matched by a correspondingly deep surface to the crystalline basement, i.e., the granitic basement is considerably thinned in all the regions being generally 25-30 km thick and almost absent in some areas. This is also in marked contrast to the surrounding regions where the crystalline basement is greater than 35 km thick and generally some 60 km thick. (3) The decrease in the thickness of crystalline basement is generally related to a reduction of the upper granitic-metamorphic layer although the underlying basaltic layer is often thinned also. (4) The depressions in the basement rocks are filled by very thick accumulation of Mesozoic and Cenozoic deposits which are in places as much as 25 km thick. This contrasts with comparatively thin deposits overlying the basement outside this region. These characteristics are related to an expansion in the area of crust in the course of continental drift in this region. The separation of the suture was accompanied by a thinning of the crust, particularly the granitic layer, which occasionally breaks into pieces which become isolated as further movement takes place. The thinning of the crust forms a basin in which the sediments accumulate and, beneath it, the mantle becomes elevated. These drift processes have resulted in extensive tensional fracturing of the basement, some fractures forming channels for the upward migration of igneous rocks from the mantle. Geothermal fields Within the European part of the U.S.S.R. the temperatures
at 1 km depth (Fig. 6) are
Fig. 5. Thickness of the crystalline portion of the earth crust of the Black Sea-Caucasian-Caspian region. The lower part shows a thickness distribution diagram for the crystallIne earth crust: II = 5-25 km (checked areas denote zones having thicknesses of up to 20 km); b = 25-45 km; c = 45-70 km; d= isopachytes of crystalline earth crust; e = zone of the Black Sea-Caspian depth fault; f= zone of southward petering out of granite-metamorphic layer. The upper part shows a diagrammatic section of the earth crust (with allowance made for the earth curvature) across the Black Sea, the High Caucasus and the Caspian Sea: a = sedimentary mass; b = granite-metamorphic layer; c = subcrustal matter (upper strata of the mantle); d = littoral zone. Tecrono~hysicr,
11 (1971) 433-460
444
G.P. TAMIUZYAN
SIflERIAN ORIENTAL
DRIFT
445
Fig. 7. Temperature distribution diagram of the earth interior of the European part and adjacent regions of the Asian part of the U.S.S.R. at a depth of 2 km below ocean level. Temperatures (with a possible correction of rS°C): a = 20°-50°C; b= SO’-70°C; c = 70*-100°C; d= 100°-130°C; e = isotherms; f = the Urals mountain structure.
mostly in the region of 1O”-3O”C, with lowest values in the north and northwest and increasing to the south. This is fringed by higher temperature regions, but particularly in the extreme south where temperatures 50”--100°C are present in the pre-Caucasus and Crimean steppe. The west Siberian temperature distribu~on at this depth is in marked contrast to both the East European and surface distribution. Most of the West Siberian lowland is characterised by temperatures 30’~65°C at 1 km depth and between latitudes 55” and 65” the temperatures at this depth are between 40” and 60°C; temperatures only reached on the European side south of the 50’ parallel and mostly even further south. At depths of 2 km, the same picture emerges (Fig. 7) with East European temperatures of mostly 40”-50°C in contrast to West Siberian lowland temperatures of 60*-80°C. These high temperatures at depth are also found in the Turan and Skif regions with temperatures generally in excess of 50°C at 1 km depth and well over 60°C at 2*km depth. A similar picture emerges from variations in the geothermal field gradient (Fig. 8). Within the fractural suture zone, the gradient is between 2.54.0 and 5-6.5”C/lOO m in contrast to 0.5-2”C/lOO m in regions outside it. The main cause for the temperature increase within the edges of the fractural suture is Tectonophysics,
11 (1971) 433-460
u
Jz
BE ~I --:.. v
TT
li
iy:: oc . :
Ll
v-
0
‘,
I.
:.
:..:
::..
::::..: . ...,. ... ._.. .
.
0
.._
.II... cl
*
<
c
a,
SIBERIAN CONTINENTAL DRIFT
447
that the earth’s crust is thinner
and the hot mantle is closer to the surface than in the other areas (Figs. 3,4). Furthermore, the tensional fracturing of the crust allows the conducted heat to be supplemented by convected and thermally diffused heat carried by water and other igneous emanations from depths along fracture zones. The isotherms therefore tend to reflect the relief of the MohoroviEiC discontinuity. Within the lowlands, the heat flow has also tended to be held and preserved within the thick blanket of sediments, which often have a high clay content and therefore high thermal resistance, particularly along the edges of the fractural suture. However, it is the heat flow at depth which is critical to this picture, rather than the thickness of sediments as other areas with thick sediments, e.g. the Apsheron Peninsula, do not show such sharp temperature increases. It is, of course, significant that geotectonic depressions formed on the continents and blanketed with sediments should preserve and maintain their high heat flow while depressions formed by continental drift which are filled with water, e.g., the Atlantic and Indian oceans, are cooled and there is correspondingly less likelihood of revealing differences in high geothermal fields due to continental drift. SIBERIAN CONTINENTAL DRIFT AND MINERAL DISTRIBUTION
The distribution of a number of useful minerals (Fig. 9) within the U.S.S.R. is very closely related to the Siberian fractural suture and the distribution of gold, copper and polymetallic deposits will be taken as examples of such geotectonically controlled deposits. Gold Nearly all the major gold deposits are confined to the marginal zone of the fractural suture (Fig. IO). The most important type of endogenous gold deposit is hydrothermal in origin, usually associated with granitoids and to a lesser extent with basic and alkaline rocks. Such intrusions and associated gold-bearing magmatic solutions are related to Caledonian, Hercynian and Alpine structures; each tectonic stage being accompanied by further intrusion along the migrating edge of the Siberian suture. Placer gold deposits are not as diagnostic as those of magmatic origin, although substantial placer deposits can only accumulate in association with the initial hydrothermal deposits. Copper AlI major copper deposits are confined to the edge of the Siberian fractural suture (Fig. 11). Furthermore, if the edges of the suture are closed, the types of copper deposit in now
Fig. 8. Geothermal field gradient in the upper part of the earth crust and the Siberian continental drift. Prevailing gradients (in oC/lOO m): a = 0.5-1.5; b = 1.5-2.5; c = 2.5-3.5; d = 3.5-4.5; e = 4.5-6.5; f= regions of salt-dome tectonics with sharp variations in the geothermal gradient; g = thickness isolines of multiyear frozen rocks (a-g are drawn up or presented according to data obtained by Makarenko et al., 1968);h = edges of the Siberian fractural suture (depression troughs with the highest values of geothermal fields are between the continental regions moved apart). Tecionophysics,
11 (1971) 433-460
/
/-
SIBERIAN CONTINENTAL DRIFT
449
separated areas match, e.g., disseminated and strew-dissem~ated deposits of Kazakhstan, Uzbekistan and Armenia and the copper-pyrite deposits of the Urals, north Caucasus and Altai regions. During the early development of folded zones, copper deposits are mainly of the pyrite type and usually originate from effusives and sub-volcanic intrusions. During the middle stage of the folding, disseminated and streaky-disseminated ores occur in relationship to moderate-acid granitoids and these form the major hydrotherm~ copper deposits. As the copper ores along the Siberian suture show a general change from predominantly pyrite type in the north to disseminated in the southwest, it seems probable that the phases of folding increase from north to southwest and that the age of the deposits also decreases from Palaeozoic to Mesozoic in that direction. PolymetaIIi~ deposits
Nearly all major lead and zinc deposits are confined to the southern part of the Siberian suture (Fig. 12) with a particular concentration in the Caucasian-Middle-Asian-Altai province. These types of deposit are usually related to moderate-acid granitoids intruded during the middle and late stages of folding and are often accompanied by tungsten (Fig. 12). These occurrences become highly concentrated if the edges of the Siberian suture are closed together. Other economic minerals
Many other minerals have distributions closely related to the margin of the Siberian suture. Iron ores, particularly the rich met~o~hosed type and se~enta~-residue types, are both related to either the suture itself or the zone it bounds. Hydrothermal deposits of magnetite and siderite occur to the east of the fractural suture. Many common features can be observed if these deposits are examined after closing the suture. Residual deposits of nickel ores are mostly confined to the edges of the suture as are graphite deposits. The formation
of Siberian metallogenic provinces.
The distribution of Palaeozoic metallogenic provinces (Smirnov, 1965) can be used as an example of the general distribution of these provinces. These have only been found on the edges of the Siberian suture and can only be understood as part of the evolution of the fractural suture itself, both directly in the formation of the magmatic ores, but also in the subsequent renewal of movement on previous hnes of weakness and the control of subsequent superficial deposits,
F&. 9. Useful minerals: I = iron; 2 = manganese; 3 = chromium; 4 = copper; 5 = polymet&; 6 = tin; 7= nickel; 8 = aluminium;9 = molybdenum; 10 = tungsten; II = mercury; 12 = antimony; 13 = gold; 14 = Platinum; 15 = bismuth; 16 = arsenic; I7= sulphur; 18 = pyrite; 19 = graphite. Tec~ono~~ysics, ll(1971)
433-460
450
G.P.TAMKAZYAN
SIBERIAN ~O~I~~NTAL
PALAEOZOK
DRIFT
451
COALS AND SIBERIAN DRIFTING
coal formation was taking place in the West Siberian and East European regions during the Upper Palaeozoic. Nearly all of these coal basins are confined to the edges of the Siberian fractural suture.(Fig. 13). The major basins consist of the Done% Kuznetsk, Pechora and Kraganda regions, together with the smaller Tungus and Taimyr reserves. The immense Tungus and Taimyr coal basins border the Siberian suture to the east and only two, comparatively minor basins, the Kama and near Moscow basins, are at any distance from the suture zone. The reconstruction of the suture therefore brings all of these Palaeozoic deposits into a narrow, but very long zone along the suture. The coal deposits are not, of course, p~rna~y controlled by deep faulting and intrusion but the tectonic conditions have here favoured the preservation of these phytogenic materials, Coal formation appears to have started as early as Mississippian times in the Donetz, Karaganda and Ekibastuz basins and also in the Kama and near Moscow basins. During Pennsylvanian times, coal accumulation in these areas appears to have been reduced, except in the Done& Basin, but commenced in the central part of the suture in the Kuznetsk and Minus basins and the Tungus Basin further east, In Permian times, coal formation ceased completely in the southwest, but continued rapidly in the central area and commenced in the northeast. On the reconstructed pattern, this migration of coal formation from the southwest to the northeast makes a simple pattern, but is difficult to explain by other means. In later hjesozoic times and in the Cenozoic, coal formation tended to be further east, although commencing on the eastern edge of the suture and spreading to the Lena and Irkutsk basins later, GE~MO~~~OL~GICAL
RELATIONSHIPS
The present day geomorphological situation (Fig. 14) shows the influence of Siberian continental drift. The main stable subsidence areas are represented by accumulation plans between the edges of the suture which extend for 2,200 km intc, olher stable subsidence areas of the Near Caspian and Turan Iowlands. There are, however, evidences of new trends in the development of Europe and Asia (Fig. 14) as there are traces of further fragmentation of the East European plain, for example from the Gulf of Finland, via Lake Ladoga and Lake Unega through to Czech Bay and even as far as the Kara Sea Gate straits. Another feature is that of recent upheavals in a number of areas of the Turan and Skif plates, probably associated with movements in neighbouring areas. In general, however, it is to be expected that matching of geomorphological features is more difficult in this area than, for example, across the South Atlantic Ocean. In any case, the only coastlines which can be matched are those of the Caspian Sea and Black Sea and such matches are clearly meaningless. In earlier times, however, sea level may have been 60-120 m higher (Tamrazyan
Fig. 10. Gold deposits and the Siberian fractural suture: II = shields (I = the Baltic shield, 2 = the UkGnian shield, 3 = the Anabar shield, 4 = the Aldan shield); B = pfatforrns (I = East-European, II = Siberian); c = edges of the Siberian fracturat suture; d = gold deposits, e = zone of maximum concentration of gold deposits. K?ctonophvsics, ll(1971)
433-460
452
G.P. TAMRAZYAN
s d
Q
SIBERIAN CONTINENTAL
0
Fig. 12. Legend see p.456.
DRIFT
4.54
G.P. TAMRAZYAN
Q
Es! ..j ,::;:. sl :. liz! -0
:‘::: :,:.:: : .:,, .:. :.:::, : :;;.:_ :. : :_: 2: ::.
v
n
•a 0
El
Fig. 13. Legend see p.4.56.
SIBERIAN CONTINENTAL
i -
Fig. 14. Legend see p.456.
DRIFT
455
456
C.P. TAMRAZYAN
1. Copper deposits and the Siberian fractnrat suture: a = shields {I = the Battic shield, I? = the Ukrainian shield, 3 = the Anabar shield, 4 = the AIdan shield); b = platforms (I= East-European, II= Siberian); c = edges of the Siberian Fractural suture; d = copper deposits; c = concentration zone of main copper deposits.
Fig, f
Fig. 12. Lead, zinc and tungsten deposits, and the Siberian fractural suture: a = shields (1 = the Baltic shield, ,7 = the Ukrainian shield, 3 = the A:abar shield, 4 = the Aidan shield); h = platforms fl = t&tEuropean, fl= Siberian); c = edges of the Siberian fractural suture; d = jead and zinc dep&ts; P Ltungsten deposits;f= concentration zones of main potymetallic deposits. Fig. 13. Upper-Palaeozoic coat basins and the Siberian fractural suture: u = shields (f = the Baltic shield, 2 = the Ukrainian shield, 3 = the Anabar shield, 4 = the Aldan shield); h = platforms (I = EastEuropean, II = Siberian); c = edges of the Siberian fractural suture; d = Mississippian coal accumulation; c = Pennsylvanian coal accumu~tjon; f= Permian coal accumulation; d, f, and fare expressed in per cent. Coal basins: 1= the Donetz Basin; a7 = the Kama B∈ 3 = the Near-Moscow Basin; 4 = the Pechora Basin; S = the Karaganda Basin, 6 = the Ekibastuz basin; 7 = the Corlovka hasin;S = the Kuznetsk basin; 9 = the Minus basin; If? = the Taimyr basin; IJ = the Tungns basin. Fig. 14. Geomorphological diagram and the Siberian drift: a = accumulation plains (stable-subsidence regions); b = structural denudation plains and plateaus (regions of predominantly slight newest up heavais); sloping piedmont alluvial- proluvial plains are also included here; c = mountains and plateaus (regions of stabIe intensive newest u~heav~s); 4 b, and c are taken from the ~eomo~ho~o~ca1 map of the U.S.S.R., 1966; d= edges of the Siberian fractural suture.
Fig_ 15. Physical map for the time when the ocean level was 140- 160 m above its pnZsent-daY level. a = land; b = sea; c = edges of the Siberian fractural suture.
SIBERIAN CONTINENTAL
DRIFT
451
as glacjal episodes only form l-5% of post-Cambrian times. Furthermore, the modern tectonic stage is exceptionally active as most of the earth’s present relief has come into being during the Pliocene-Quaternary so that the earth’s surface was generally more flatlying, Therefore it is necessary for earlier times to consider geomorphological features which would arise and can be matched for more normal conditions, i.e., with sea-level some 100-l 50 m higher than today. Under these conditions, the west Siberian, Turan and Near Caspian lowlands would be submerged beneath a shallow sea (Fig. 15) and matching of these shore lines then becomes possible. Clearly the contours for this ancient sea-level match each other and the reconstruction using matching shore-lines results in a single East-European-Siberian continental massif. THE SOUTHERN EXTENSION OF THE URALS
The relationship of the Urals, Tien Shan, Mangyshlak and Donbas regions has attracted considerable argument for a long time and no firm conclusions have previously been possible. Arkhangelskiy (cited in Yanshin, 1951) considered that the Urals plunged southwards and were subsequently cut by the folded Tien Shan structures. However, in 1937 he considered that there was in fact a direct connection of the Urals with the Donbas structure. Similar evolution and changes of ideas were shown by Yanshin who, in 1945, believed that the Urals extended to join the Tian Shan structures but later (Yanshin 1951) he thought the Urals must die out completely before reaching any of the more southerly structures. Yanshin, although demonstrating that the Urals could not extend further to either the southwest or southeast was not, however, able to explain why or how the Ural structures should die out so abruptly. He comments that the Hercynian section of the trans-Caspian zone is radically different from that of the Urals. It is so different that the two areas could only exist far apart and have only subsequently become adjacent. If, however, the areas are reconstructed by matching the Siberian suture, the Urals then pass via the Kulunda Basin to the Altai while to the southwest of the Urals lies the Central Kazakhstan Massif and the Sayans lie to the southeast. The ore deposits of the Urals are therefore genetically related to those of the Altai, in particular, the Hercynian ores matching in both areas. Small tectonic fragments further south (the Crimean High and Low Caucasus and the Pamir block) which belong to this general pattern belong to the southwest part of the Siberian suture but have been reworked during the Cimmerian and Alpine erogenic cycles which has obscured their Middle Asian affinities. COMMENTS
As the evidence of continental drift in the Siberian region is so strong, it is not proposed to draw obvious conclusions, but to consider two particular aspects which may be. of worldwide pertinance to continental drift movements. As the earth’s rotation is decreasing, this causes compression in some areas of crust and tension in others and there is a particular line of latitude, theoretically 35’;separating zones of compression in more equatorial latitudes from tension at higher latitudes (Fig. 16). The tension is greatest at 61”-62” but generally extends from 35” to 70” which is the limit Tecronophysics, 11 (1971) 433-460
458
G.P. TAMRAZYAN
70.-
I
I
60, 50 '1 J
40.. 30..
I
20. 10. 600
A
400
200
0
200
400 *In
I 20
0
40
60
80
8
Fig. 16. Variation of earth parallel length (A) with the rotation period changing from 6 h to its presentday duration. On the right-hand side the variation of the continentality coefficient is shown for the Northern Hemisphere IfI).
Yol
6Mm
5000
4000
3mO
2Oor
IOOC
C
Fig. 17. Diagram showing the variations in the gradual melting covering the earth core and the mantle foot layers (solid line), and the change in the conventional rate of movement of the frontal surface of the molten earth core (dotted line). (I = in case the melting started 3.5 milliard years ago; b = in case the melting started 4.5 milliard years ago, On the left along the Y-axis the distance from the earth centre is shown (just to the right the distance from the earth surface is plotted). The rates of move ment (km/million years) are plotted on the right hand side. The time as from now is plotted along the X-axis.
x
SIBERIAN CO~INENTAL
DRIFT
459
of the Siberian fractural suture. The second feature is that the core of the earth is gradually increasing at the expense of the lower strata of the mantle (Tamrazyan, 1967; Fig. 17). This means that IO9 years ago, the earth’s core was at a depth of either 4,612 or 4,270 km, depen~g if melting commenced 3.5 or 4.5 . IO9 years ago. As the liquid core grows, the links between different areas of the crust becomes weakened so that, for example, Pangaea was then able to break into separate blocks which were then free to drift apart. Calculations show that this state would be reached for Pangaea 206-267 million years ago although Laurasia and Gondwanaland may have already begun to drift apart by this time. The main break-up of Pangaea was slightly Iater than this, probably 200-210 million years ago with the Siberian drifting preceding that of the ~erican drift, so that the Siberian movement was the first sign of the commencement of a radically new change in earth structure. Such movements created the conditions for bringing magma from the depth with the development of major magmatic and metasomatic ore. Siberian continental drift is well established and marks the onset of the present mobilistic tectonic stage of our planet.
REFERENCES Aksenovich, G.I., Aronov, L.Ye., Gegelgants, A.A., Galperin, M.A., Kostninskaya, I.P..and Krashkina, R.M.,1962. Deep Seismic Sounding in the Central Part of the CaspianSea. Acad. Sci. U.S.S.R., Moscow, 152 pp. Balavadze, B.K. and Shengelaya, G. Sh., 1961. The main structural features of the earth crust in the High Caucasus according to gravimetric data. Dokl. Akad NaukS.S.S.R., 136(6): 1328-1331. Borisov, A.A., 1967. Depth Structure of the U.S.S.R. Territory Based on GeophysicalData Nedra, Moscow, 304 pp. Demenitskaya, R.M., 1967. Earth Crust and Mantle. Nedra, Moscow, 280 pp. Kropotkin, P.N., 1961. Palaeomagnetism, palaeoclimates and the problem of big horizontal movements of the earth crust. Sov. Geol., 5: 16-38. Magakyan, LG., 1959. Fund~ent~s of Continental Met~~eny. Acad. Sci. Armenian S.S.R., Yerevun, 280 pp. Makareriko, F.A. and Mavritskiy, B.F., 1963. General &valuation of underground waters of the U.S.S.R. as sources of heat. in: Thermal Waters of the U.S.S.R. and Questions Concerning the Use of their Thermal Energy. Acad. Sci U.S.S.R., MOSCOW, pp. S-14. Makarenko, F.A., Polak, B.G. and Smirnov, J.B., 1968. Geothermal field on the U.S.S.R. territory. In: GeologicalResults of Applied Geophysics. Nauka, Moscow, pp. 43-48. Neprochnov, Yu.P., 1960. The depth structure of the earth crust under the Black Sea according to &ismic data. Byul. Mask. ObshchestvaIspytateiei Prirody, Otd. Geol., 4: 30-36. Neprochnov, Y.P., 1962. The results of deep seismic sounding in the Black Sea. In: Deep Seismic Sounding of the Earth Crust in the U&!X.Gostoptekhisdat, Leningrad, pp. 211-282. Nikolayev, N;I., 1962. Neotectonics and its Expression in the Structure and Relief of the U.S.S.R. Territory. Gosgeoliidat, Moscow, 392 pp. Semenov, A.I., Sheglov, A.D., Bilibin T.V. et al., 1968. Geolo~~a~St~c~re of the U.S.S.R. IV. Nedra, Moscow, SO4 pp. Smimov, V.I., 1965. The GeoIoD of Usefil Minerals. Nedra, Moscow, 590 pp. Stovas, M.V., 1963. Some questions concerning the tectogenesis. In: Problems of Phmetary Geolom. Gosgeolizdat, Moscow, pp. 222-214. Surkov, VS., 1963. New ideas concerning the structure and age of the folded base of the West-Siberian lowland. Geol. Razvedka, 2~19-27. Surkov, V.S., Zhero, O.G. and Umantsev, L.F., 1969. The structure of the intermediate stage of the West-Siberia plate. Sov. Geol., 5: 104-108. Tectonophysics, 11 (1971) 433-460
460
G.P. TAMRAZYAN
Sydorenko, A.B. (Editor), 1968. The 50th Anniversary ofSoviet Geology. Nedra, Moscow, 420 pp. Tamrazyan, G.P., 1957. Geotectonic hypothesis. Izv. Arad. Sci. Azerb. S.S.R., 12: 85. 115. Tamrazyan, G.P., 1959. On the problem of the earth’s structure. Izv. Acad. Sci. Twkm. S.S.R., 1: 22-35. Tamrazyan, G.P., 1960. On the most important structural feature of the South-C’aspian trough, Dokl. Akad. NaukS.S.S.R., 131(4): 917-920. Tamrazyan, G.P., 1964. The European part of the U.S.S.R. compared to the contiguous Asiatic regions with reference to essential thermal regime differences in the earth’s interior. Dokl. A kad. Nauk S.S.S.R., 157(2): 337-340. Tamrazyan, G.P., 1967. Some of the main planetary tectonic regularities and their causal relations. Geol. Razvedka, 11: 3-- 17. Tamrazyan, G.P., 1967. Some sketches on the structure of the Earth, Moon and Mars. Intern. Lunar Sot., 3(4): 72-84. Tamrazyan, G.P., 1969. Seismic anomalies and the dynamic evolution of the earth’s crust and upper mantle.Zcams, 10(l): 164.-168. Taylor, F.B., 1910. Bearing of the tertiary mountain belt on the origin of the earth’s plan. Bull. C>eol. Sot. Am., 21:179 -226. Vasilijev, Yu.M., Dyakonov, D.I. and Charigin, M.M., 1968. Geothermy of deep subsurface of the North Caspian Depression from drilling data of deep Aralsor bore hole. In: Geological Results of Applied Geophysics. Nauka, pp. 55- 6 1. Volvovsky, I.S., Garetzky, R.G., Shlezinger, AX., and Shreibman, V.I., 1966. Tectonic of’ Turan Plate. Nauka, Moscow, 288 pp. Voronov, P.S., 1968. Essays on Regularities in the Morphometry of the Global Relief of the Earth. Nauka, Moscow, 124 pp. Wegener, A., 1924. The Origin of Continents and Oceans. English transl. J.G.A.Skerl, London, 212 pp. Yanshin, A.L., 1951. A.D. Arkhangelskiy’s views of the tectonic nature of the southeastern frame of the Russian platform and the modern ideas on this point. In: Commemoration of A.D. Arkhangelskiv. Acad. Sci. U.S.S.R., Moscow, pp. 253.-327. Yanshin, A.L. (Editor), 1966. The Tectonics of Eurasia. Nauka, Moscow, 488 pp.
Maps Atlas of the U.S.S.R. Nedra, Moscow, 1962. Geological Map of the U.S.S.R. Ministry of Geol. U.S.S.R., Moscow, lY66. Geomorphological Map of the U.S.S.R. G.S. Ganeshin (Editor), Ministry of Geol. U.S.S.R.,
MOSCOW,
1967. Geotectonic Map of the U.S.S.R. T.N. Spigarskiy (Editor), Ministry of Geol. U.S.S.R., Moscow, 1967. Metallogenic Map of the U.S.S.R. K.B. Iliyin (Editor), Ministry of Geol. U.S.S.R., Moscow, 1968. Neotectonical Map of the U.S.S.R. N.I. Nikolayev and S.S. Shults (Editors), Gosgeolizdat, Moscow, 1959.
Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
SIBERIAN
CONTINENTAL
DRIFT
l
G.P. TAMRAZYAN * Institute of Geology, Academy
of Sciences of the Azerbaydzhan
S.S.R., Baku (U.S.S.R.)
(Received April 22, 1970) (Resubmitted March 17, 1971) ABSTRACT Tamrazyan, G.P., 1971. Siberian continental drift. Tectonophysics,
11: 433-460.
It is suggested that an ancient separation of the East European and Siberian platforms regions results in the formation of a major tectonic depression, the West Siberian trough and its continuation to the southwest, between them. This is supported by a great body of actual data ranging from present day tectonic movements to the distribution of geothermal and metallogenic provinces.
INTRODUCTION AND GENERAL SETTING
Ideas of continental migration existed even before theoretical geology came into being, some originating as early as the 17th century. During the last decade the concept of continental migration has gained wide recognition and new ideas of mobilisation are dominant. The main features in the development of continents and oceans, as well as folded and geosynclinal regions can now be explained more convincingly than previous ideas based on constancy. In 1962 Tamrazyan put forward the idea that continental migration might be found in the eastern hemisphere (summarised in Tamrazyan, 1964). This continental migration was called the Siberian continental drift and implied the separation of an East EuropeanSiberian platform assemblage into two individual platforms and that these are still moving apart, mainly latitudinally (Fig. 1). The separation of the original assembly took place along very deep fractural sutures extending deep into the asthenosphere. The sutures were sinuous but generally had a submeridional orientation and the now separated edges show striking correspondence. The major projections of the western edge (Pai-Khei-Novaya Zemlya, southern Urals, the High and Low Caucasus) correspond to concavities on the eastern edge (Yenisei-Khatange, Kulunda, Chui and North Kyzylkum troughs). Similarly the western concavities (Near Caspian and Kura troughs) correspond to eastern projections (Central Kazakhstan Massif and Karatau uplift) and straight sections also match each other on both
l With the full agreement of the author, this paper has been rewritten and shortened to about 25% of its original length by Dr. D.H. Tarling, Dept. of Geophysics and Planetary Physics, University of Newcastle, Newcastle upon Tyne, Great Britain. Every care has been taken to avoid misrepresentation of Prof. Tammzyan’s ideas, but naturally such a reduction must involve some loss of information. ** Chairman, Commission of Extraplanetary Phenomena of the International Association of Planetology
Tectonophysics,
11 (1971) 433-460
434
G.P.TAMRAZYAN
.^,...._/
,..
435
SIBERIAN CONTINENTAL DRIFT
sides. It is important to note that these structures have been mapped quite objectively and the correspondence was dete~ined subsequen~y, The West Siberian and Turan plates and the Turgai trough between them, together with the Near Caucasian trough, the pre-Caucasus and extreme western tip of the Big Donbas areas all lie in the region formed as a result of the separation of the two main continental blocks. The movement of these main structural units was by some 1,000 km in the north and by l,SOO--1,700 km in the south and took place mainly in pre-Mesozoic times and subsequently slowed down so that this ancient motion has, to some extent, been obscured by later deveiopments and any restoration must be based on matching the ages and characteristics of tectonic features which formed prior to the separation. TECTONIC RELATIONSHIPS
The most characteristic features of the different tectonic blocks are the pattern of consolidation of ancient major structures. There were three particularly distinct blocks prior to Siberian drifting. The first was the East European and Siberian platforms which were then conti~ous. The second was several sharply defined positive structures (the ~rai~ian shield, Voronezh and Volga-Urals~anteclisesand the Central Kazakhstan Massif) which are all genetically closely related to the first unit. The third block is the youngest and comprised the Polar Urals, Pai-Khoi, Novaya Zemlya and Taimyr areas which are all genetically related to the first unit. These blocks were separated by the Siberian fractural suture into separate units, but each unit continued to evolve in much the same way as before because of their inherited tectonic nature. Naturally, the evolution became faster in some areas and slowed in others so that the individual development of each major block and each of their component parts gradually obscured the sim~~ities between them and the geological picture became more diversified during the passage of time. In particular, the sedimentary picture continued to develop despite the migration of the blocks and each block retained the various characteristics of ablation and deposition, etc., so that it is not considered Fig. 1. Diagram of geological-geotectonic zoning and the Siberian continental drift. Precambrian folded structures: a = ancient shields (1 = the Baltic Shield, 2 = the Ukrainian shield, 3 = the Anabai shield, 4 = the Aldan shield); b = ancient platforms (5 = East-European, 6 = Siberian). Palaeozoic folded structures: c = regions of Csledonlan (Early- and Middle-Palaeozoic) foldings (7 = Central Kazakhstan folding, 8 = Karatauz folding, 9 = Salair-Sayan folding, 10 = Transbaikal folding); d = regions of Hercynian (Middle and Late Palaeozoic) foldings (II = the Urals folding, 1.2= the PaiKhoi folding, 13 = the Novaya Zemlya folding, 14 = the Taimyr folding, 1.5 = the Altai folding, 16 = the Near-%alkhash folding, I7 = the East-Transbaikal’fokling). Mesozoic-Cenozoic folded structures: e = the Alpine folded regions in the south of the U.S.S.R. (18 = the Crimean-High-Caucasian folded region, 19 = the Low-Caucasian folded region, 20 = the Kopetdag folded region, 21 = the Pamir folded region); f= troughs on the Precambrian folded base (22 = the Donbas trough, 23 = the Near-Caspian trough, 24 = the Yenise$-Khatauga trough; on the Palaeozoic folded base: 2.5 = the North-Caucasian trough, 26 = the North Kyzylkum trough, 27 = the Chui trough, 28 = the Kulunda trough); on the Palaeozoic-Precambrian folded base (29 = the West-Siberian plate, 30 = the Turan plate). Revived troughs having no granite layers in their major portions (31 = the Black Sea trough, 32 = the Sou~~asp~n trough). Edges of the Siberian fractural suture: g = western edge; h = eastern edge. Tectono#ysics,
11 (1971) 433-460
436
~.P.~rA~RAZYAN
S~3ER~AN CONT~~NTAL
DRIFT
437
possible to match sedimentary environments for these early times. However, certain similar features in their development can be seen, for example, the same stages of overall deformation can be recognised during the Precambrian in the previously adjacent Central Kazakhstan Massif and the Verenezh and Volga-Urals anteclises (particularly evident in maps of neotectanics of the U.S.S.R, compiled by NJ. Nikolayev and S.S. Shults, 1959). Similarly the Polar Urals, Novaya Zemlya and Taimyr regions belong to th& same rn~~nt~n-budding region and have similar grades of tectonic movement (Fig. 2). The newest subsidence regions are all confined to the area between the separated edges of the Siberian fracturaf suture and all of these basins show inherited gradients and crustal morphology. THE CRUST AND UPPER MANTLE
The influence of Siberian drift on the structure of the earth’s crust and upper mantle is best considered separately for individual areas and the main features are then summarised, The west Siberian lowland This region is situated between the stable blocks of the East European and Siberian platforms. The age of the basement rocks is in dispute with ages suggested as Hercynian, Caiedo~~, ~~~~-~~a~r and ~re~~b~an; the last age being supported by pre-Falaeozoic rocks found beneath the Mesozoic cover in deep drill holes in the central part of this region. The Mohorovi~~ discontinuity is at a depth of 3’+36 kni over most of the region, in marked contrast to depths of 40-50 km in the neighbouring East European and Siberian platforms (Fig. 3) and Central Kazakhstan Massif and Urals. The height of the Mohorovi~i~ discontinuity is matched by a corresponding reduction in the basement crust which is overlain by a substantial sedimentary cover which is up to 40 km thick in the centre of the lowland so that the crystalline crust is generally only some 23-25 km thick in contrast to the surrounding regions where it is in excess of 30-40 km thick. The overlying sediments were laid down during the Mesozoic-Cenozoic period and their floor was simultaneously being warped, probably in response to an elevation of the mantle during the Mesozoic or possibly earlier. Several major fault systems cross the region ol’ which the Gyda&k-Omsk fault is the largest and has been investigated seismically, ma~etica~y, by gravity studies and also deep
Fig. 2. Diagram of metalloge& zoning of the U.S.S.R. territory (according to V.M. Smirnov, 1965). Occurrence regions of deposits of different metallogenic epochs of geosynclinal cycles: a = Alpine; b = Cimmerian; c = Hercynian; d = Caledonian; e = Proterozoic; f= Archean. Occurrence regions of deposits of different rne~~e~c epochs for platforms: g = Gimmerian; k = Hercynian; i = trap occurrence region Ore provinces. Alpine provinces: I = the Far Northeast, 2 = the Caucasus, 3 = the Carpathtans, 4 = the Kopetdag, 5 = the Pa&s. Kimmerian provinces: 6 = the Transbaikal-Primorye territory; Hercynian provinces: 7s the Urals, 8= Kazakhstan, 9= Middle Asia, 10 = the Donbas, II = Taimyr, 12 = the Tom’-K&van zone; Caiedonian provinces: 13 = the A~~-Say~~ zone; Proterozoic provinces: $4 = the southern part of the Sz%&anplatform, IS = the Baltic shield, 16 = the Ukrainian shieid.
SIBERIAN CONTINENTAL DRIFT
439
drill~g, This fault extends from Gydansk bay in the north to the Omsk region in the south as a series of graben-like depressions in the basement rocks which have been filled by a complex of sedimentary and effusive deposits up to 2 km thick (Rorisov, 196% The fault is therefore some 2,000 km long but only 30-50 km wide. In the south the fault belt is deflected southwest and it is thought that the basement depressions become narrower until they are simple fractures. This southern extension, the ~rengoi-~oltogo~ ridge, can be traced for almost 1,000 km into Central Kazakhstan. Similar southerly extension as deep en-echelon faults can be traced along the Tokraus belt which has now been established from Chan Lake in the north to Issykkul Lake in the south. The total length of the Gydansk-Omsk-Tokraus fault belt is therefore at least 3,000 km and appears to correspond to the most stretched part of the crystalline basement within the west Siberian lowland. This, however, is only one of several major fault belts in this region. On the east of the lowland, 100-200 km west of the Yenisei River, there is a pronounced belt of gravity and magnetic positive anomalies corresponding to intrusions of
predominantly basic rocks which extend from the lower course of the Yenisei River as far as the Kuznetsk Alatau (Borisov, 1967). This belt corresponds, for most of its length, with the western edge of the buried Baikal and Salair structures of the Siberian platform and the eastern edge of the post-Prec~brian structures of the west Siberian lowland basement (Surkov, 1963). This belt, including its southern extension to the Altai and western Sayans exceeds 2,000 km. Within the lowland itself occur wide areas of transitional crustal densities, mostly associated with deeply warped zones and usually connected to the surface via cracks in the folded basement. These transitional densities usually consist of somewhat broken and sij~tly metamorphosed fo~ations interbedded between the basement and the overlying Mesozoic and Cenozoic cover (Surkov et al., 1969). They are usuahy of molasse-type but include effusive and carbonaceous formations, The volume of this intermediate material varies considerably in quantity and age. The older the folded basement, the wider the
age range SOthat it is of Riphean to Triassic age in areas of Archaean and Baikal folding but only of upper Palaeozoic age in regions of Hercynian folding; in some areas it is only of Triassic and Lower Jurassic age but are more commonly of Late Palaeozoic to Early Mesozoic age. The Turan lowland Most of the Turan lowland is underlaid by a Mohorovi~i~ ~sconti~uity at a depth of 30-40 km in contrast to depths of 40-50 km to the east beneath the Central Kazakhstan Massif and to the west beneath the Caucasus. As for the West Siberian lowland, the crust is therefore thinner than in surrounding regions. At depths of 2-5 km, the basement folding is usually represented by a high grade metamorphism, up to granitic gneiss, of the
Fig. 3. The MohoroviW(M) surface occurrence diagram and the Siberian fractural suture. a = occurrence depth of M surface: zones with a depth of M surface less than 35 km are shown by dots; b = bands of fragmentation, melting, positive gravity anomalies, and magnetic maxima; (points a and b are according to Borisov, 1967) c = edges of the Siberian fractural suture. ~ecr~~o~~ysjcs, 11 (1971) 433-460
440
G.P.TAMRAZYAN
Q,
-T
IlBil
.... . LIB -0
.-
v
L
:r:.:.::::: ::::.
01 \\ 0:f illn ,.:::s :::::. ....
a
0
m
w-
SIBERIAN CONTINENTAL DRIFT
441
Palaeozoic formations. Transitional densities occur between the crystalline basement and the Mesozoic cover, mainly in tectonic depressions and usually represented by compacted and dislocated terrigenous formations. These transitional densities are absent in elevated areas where Pre-Permian deposits are overlain directly by Mesozoic sediments. It appears that the geosynclinal deposition during the Palaeozoic was almost continuous and accompanied by intensive metamorphism, recrystallisation and granitization of the basement. The Near Caspian lowland The MohoroviEiC discontinuity is at some 38-42 km beneath this region which is somewhat less than beneath the Ukranian shield and adjacent areas where it is usually 45-50 km deep. The basement surface is deep, down to lo-15 km, in contrast with depths of 5-6 km in the surrounding areas. The eastern edge is marked by a chain of magnetic maxima along a fault line near the pre-Urals warping and appears to have been activated or initiated during the Permian-Mesozoic period. The pre-Caucasus and Crimean steppe (Skif block) The MohoroviEiC discontinuity is shallower here, 35-40 km, than in neighbouring regions, the Ukranian shield, Verenezh Massif and Caucasus where the discontinuity is at 50-60 km. The thickness of crystalline basement is also considerably reduced in this region. The south Caspian and Black Sea troughs The south Caspian trough comprises the southern and central Caspian Sea, the Apsheron Peninsula, the Lower Kura trough and the west Turkmenian depression. It is a morphological and tectonic depression characterised by an intensive negative gravity anomaly and tectonic non-uniformity. The MohoroviEiC discontinuity is shallow, 35-45 km deep; and the surface of the Palaeozoic crystalline basement is deep, 15-25 km. In the centre of the trough the granitic crust is absent and the sediments directly overlie a basaltic substratum. In other areas, the granitic crust is reduced, 15-20 km thick, and the trough as a whole was initiated in the Mesozoic and is now filed with Mesozoic-Cenozoic sediments which are up to 25 km thick, mostly of Neogene (particularly Pliocene) and Anthropogene age. The Black Sea trough is a complex structure although consisting superficially of a simple
Fig. 4. Consolidated earth crust (Borisov, 1967) and the Siberian continental drift. a = thickness of crust limited by the surfaces of MohoroviEiC and Precambrian foundation; b = thickness of crust limited by the, surface of MohoroviEiC and that of the Palaeozoic (and in some places Mesozoic) foundation. Thickness of consolidated crust: c = less than 30 km; d= 30-35 km; e = 35-60 km; f= projections of basalt layer (the granite layer is absent or thinned out considerably); g = zones of inland seas with no granite layers; h= crushing, foundering and downwarping bands in the foundation relief, bands of positive gravity anomalies and magnetic maxima; i = bands of intensive basaltification of granite layers in continental crust regions (the Urals); j = edges of the Siberian fractural suture. 7’ectonophysics, 11 (197 1) 433-460
442
G.P.TAMRAZYAN
SIBERIAN CONTINENTAL DRIFT
443
trough with deep-sea parts at its centre which have an associated gravity maximum. The MohoroviEiC discontinuity is very shallow beneath the central section, being only 20-25 km deep, but is deeper nearer the margins, being usually around 35-40 km deep. The crystalline basement is extremely thin throughout the trough, usually not more than 5-8 km thick; the granitic part being almost entirely absent in some areas so that the central trough has an oceanic crustal structure. Summary The regions situated on the edges of the Siberian fractural suture are characterised by the following features (Fig. 3-S). (1) Shallow MohoroviEiC discontinuity, as shallow as 20 km in parts of the Black Sea and generally 30-40 km deep in contrast to surrounding areas where the discontinuity is generally at SO-60 km depth. (2) The shallow MohoroviEiC discontinuity is matched by a correspondingly deep surface to the crystalline basement, i.e., the granitic basement is considerably thinned in all the regions being generally 25-30 km thick and almost absent in some areas. This is also in marked contrast to the surrounding regions where the crystalline basement is greater than 35 km thick and generally some 60 km thick. (3) The decrease in the thickness of crystalline basement is generally related to a reduction of the upper granitic-metamorphic layer although the underlying basaltic layer is often thinned also. (4) The depressions in the basement rocks are filled by very thick accumulation of Mesozoic and Cenozoic deposits which are in places as much as 25 km thick. This contrasts with comparatively thin deposits overlying the basement outside this region. These characteristics are related to an expansion in the area of crust in the course of continental drift in this region. The separation of the suture was accompanied by a thinning of the crust, particularly the granitic layer, which occasionally breaks into pieces which become isolated as further movement takes place. The thinning of the crust forms a basin in which the sediments accumulate and, beneath it, the mantle becomes elevated. These drift processes have resulted in extensive tensional fracturing of the basement, some fractures forming channels for the upward migration of igneous rocks from the mantle. Geothermal fields Within the European part of the U.S.S.R. the temperatures
at 1 km depth (Fig. 6) are
Fig. 5. Thickness of the crystalline portion of the earth crust of the Black Sea-Caucasian-Caspian region. The lower part shows a thickness distribution diagram for the crystallIne earth crust: II = 5-25 km (checked areas denote zones having thicknesses of up to 20 km); b = 25-45 km; c = 45-70 km; d= isopachytes of crystalline earth crust; e = zone of the Black Sea-Caspian depth fault; f= zone of southward petering out of granite-metamorphic layer. The upper part shows a diagrammatic section of the earth crust (with allowance made for the earth curvature) across the Black Sea, the High Caucasus and the Caspian Sea: a = sedimentary mass; b = granite-metamorphic layer; c = subcrustal matter (upper strata of the mantle); d = littoral zone. Tecrono~hysicr,
11 (1971) 433-460
444
G.P. TAMIUZYAN
SIflERIAN ORIENTAL
DRIFT
445
Fig. 7. Temperature distribution diagram of the earth interior of the European part and adjacent regions of the Asian part of the U.S.S.R. at a depth of 2 km below ocean level. Temperatures (with a possible correction of rS°C): a = 20°-50°C; b= SO’-70°C; c = 70*-100°C; d= 100°-130°C; e = isotherms; f = the Urals mountain structure.
mostly in the region of 1O”-3O”C, with lowest values in the north and northwest and increasing to the south. This is fringed by higher temperature regions, but particularly in the extreme south where temperatures 50”--100°C are present in the pre-Caucasus and Crimean steppe. The west Siberian temperature distribu~on at this depth is in marked contrast to both the East European and surface distribution. Most of the West Siberian lowland is characterised by temperatures 30’~65°C at 1 km depth and between latitudes 55” and 65” the temperatures at this depth are between 40” and 60°C; temperatures only reached on the European side south of the 50’ parallel and mostly even further south. At depths of 2 km, the same picture emerges (Fig. 7) with East European temperatures of mostly 40”-50°C in contrast to West Siberian lowland temperatures of 60*-80°C. These high temperatures at depth are also found in the Turan and Skif regions with temperatures generally in excess of 50°C at 1 km depth and well over 60°C at 2*km depth. A similar picture emerges from variations in the geothermal field gradient (Fig. 8). Within the fractural suture zone, the gradient is between 2.54.0 and 5-6.5”C/lOO m in contrast to 0.5-2”C/lOO m in regions outside it. The main cause for the temperature increase within the edges of the fractural suture is Tectonophysics,
11 (1971) 433-460
u
Jz
BE ~I --:.. v
TT
li
iy:: oc . :
Ll
v-
0
‘,
I.
:.
:..:
::..
::::..: . ...,. ... ._.. .
.
0
.._
.II... cl
*
<
c
a,
SIBERIAN CONTINENTAL DRIFT
447
that the earth’s crust is thinner
and the hot mantle is closer to the surface than in the other areas (Figs. 3,4). Furthermore, the tensional fracturing of the crust allows the conducted heat to be supplemented by convected and thermally diffused heat carried by water and other igneous emanations from depths along fracture zones. The isotherms therefore tend to reflect the relief of the MohoroviEiC discontinuity. Within the lowlands, the heat flow has also tended to be held and preserved within the thick blanket of sediments, which often have a high clay content and therefore high thermal resistance, particularly along the edges of the fractural suture. However, it is the heat flow at depth which is critical to this picture, rather than the thickness of sediments as other areas with thick sediments, e.g. the Apsheron Peninsula, do not show such sharp temperature increases. It is, of course, significant that geotectonic depressions formed on the continents and blanketed with sediments should preserve and maintain their high heat flow while depressions formed by continental drift which are filled with water, e.g., the Atlantic and Indian oceans, are cooled and there is correspondingly less likelihood of revealing differences in high geothermal fields due to continental drift. SIBERIAN CONTINENTAL DRIFT AND MINERAL DISTRIBUTION
The distribution of a number of useful minerals (Fig. 9) within the U.S.S.R. is very closely related to the Siberian fractural suture and the distribution of gold, copper and polymetallic deposits will be taken as examples of such geotectonically controlled deposits. Gold Nearly all the major gold deposits are confined to the marginal zone of the fractural suture (Fig. IO). The most important type of endogenous gold deposit is hydrothermal in origin, usually associated with granitoids and to a lesser extent with basic and alkaline rocks. Such intrusions and associated gold-bearing magmatic solutions are related to Caledonian, Hercynian and Alpine structures; each tectonic stage being accompanied by further intrusion along the migrating edge of the Siberian suture. Placer gold deposits are not as diagnostic as those of magmatic origin, although substantial placer deposits can only accumulate in association with the initial hydrothermal deposits. Copper AlI major copper deposits are confined to the edge of the Siberian fractural suture (Fig. 11). Furthermore, if the edges of the suture are closed, the types of copper deposit in now
Fig. 8. Geothermal field gradient in the upper part of the earth crust and the Siberian continental drift. Prevailing gradients (in oC/lOO m): a = 0.5-1.5; b = 1.5-2.5; c = 2.5-3.5; d = 3.5-4.5; e = 4.5-6.5; f= regions of salt-dome tectonics with sharp variations in the geothermal gradient; g = thickness isolines of multiyear frozen rocks (a-g are drawn up or presented according to data obtained by Makarenko et al., 1968);h = edges of the Siberian fractural suture (depression troughs with the highest values of geothermal fields are between the continental regions moved apart). Tecionophysics,
11 (1971) 433-460
/
/-
SIBERIAN CONTINENTAL DRIFT
449
separated areas match, e.g., disseminated and strew-dissem~ated deposits of Kazakhstan, Uzbekistan and Armenia and the copper-pyrite deposits of the Urals, north Caucasus and Altai regions. During the early development of folded zones, copper deposits are mainly of the pyrite type and usually originate from effusives and sub-volcanic intrusions. During the middle stage of the folding, disseminated and streaky-disseminated ores occur in relationship to moderate-acid granitoids and these form the major hydrotherm~ copper deposits. As the copper ores along the Siberian suture show a general change from predominantly pyrite type in the north to disseminated in the southwest, it seems probable that the phases of folding increase from north to southwest and that the age of the deposits also decreases from Palaeozoic to Mesozoic in that direction. PolymetaIIi~ deposits
Nearly all major lead and zinc deposits are confined to the southern part of the Siberian suture (Fig. 12) with a particular concentration in the Caucasian-Middle-Asian-Altai province. These types of deposit are usually related to moderate-acid granitoids intruded during the middle and late stages of folding and are often accompanied by tungsten (Fig. 12). These occurrences become highly concentrated if the edges of the Siberian suture are closed together. Other economic minerals
Many other minerals have distributions closely related to the margin of the Siberian suture. Iron ores, particularly the rich met~o~hosed type and se~enta~-residue types, are both related to either the suture itself or the zone it bounds. Hydrothermal deposits of magnetite and siderite occur to the east of the fractural suture. Many common features can be observed if these deposits are examined after closing the suture. Residual deposits of nickel ores are mostly confined to the edges of the suture as are graphite deposits. The formation
of Siberian metallogenic provinces.
The distribution of Palaeozoic metallogenic provinces (Smirnov, 1965) can be used as an example of the general distribution of these provinces. These have only been found on the edges of the Siberian suture and can only be understood as part of the evolution of the fractural suture itself, both directly in the formation of the magmatic ores, but also in the subsequent renewal of movement on previous hnes of weakness and the control of subsequent superficial deposits,
F&. 9. Useful minerals: I = iron; 2 = manganese; 3 = chromium; 4 = copper; 5 = polymet&; 6 = tin; 7= nickel; 8 = aluminium;9 = molybdenum; 10 = tungsten; II = mercury; 12 = antimony; 13 = gold; 14 = Platinum; 15 = bismuth; 16 = arsenic; I7= sulphur; 18 = pyrite; 19 = graphite. Tec~ono~~ysics, ll(1971)
433-460
450
G.P.TAMKAZYAN
SIBERIAN ~O~I~~NTAL
PALAEOZOK
DRIFT
451
COALS AND SIBERIAN DRIFTING
coal formation was taking place in the West Siberian and East European regions during the Upper Palaeozoic. Nearly all of these coal basins are confined to the edges of the Siberian fractural suture.(Fig. 13). The major basins consist of the Done% Kuznetsk, Pechora and Kraganda regions, together with the smaller Tungus and Taimyr reserves. The immense Tungus and Taimyr coal basins border the Siberian suture to the east and only two, comparatively minor basins, the Kama and near Moscow basins, are at any distance from the suture zone. The reconstruction of the suture therefore brings all of these Palaeozoic deposits into a narrow, but very long zone along the suture. The coal deposits are not, of course, p~rna~y controlled by deep faulting and intrusion but the tectonic conditions have here favoured the preservation of these phytogenic materials, Coal formation appears to have started as early as Mississippian times in the Donetz, Karaganda and Ekibastuz basins and also in the Kama and near Moscow basins. During Pennsylvanian times, coal accumulation in these areas appears to have been reduced, except in the Done& Basin, but commenced in the central part of the suture in the Kuznetsk and Minus basins and the Tungus Basin further east, In Permian times, coal formation ceased completely in the southwest, but continued rapidly in the central area and commenced in the northeast. On the reconstructed pattern, this migration of coal formation from the southwest to the northeast makes a simple pattern, but is difficult to explain by other means. In later hjesozoic times and in the Cenozoic, coal formation tended to be further east, although commencing on the eastern edge of the suture and spreading to the Lena and Irkutsk basins later, GE~MO~~~OL~GICAL
RELATIONSHIPS
The present day geomorphological situation (Fig. 14) shows the influence of Siberian continental drift. The main stable subsidence areas are represented by accumulation plans between the edges of the suture which extend for 2,200 km intc, olher stable subsidence areas of the Near Caspian and Turan Iowlands. There are, however, evidences of new trends in the development of Europe and Asia (Fig. 14) as there are traces of further fragmentation of the East European plain, for example from the Gulf of Finland, via Lake Ladoga and Lake Unega through to Czech Bay and even as far as the Kara Sea Gate straits. Another feature is that of recent upheavals in a number of areas of the Turan and Skif plates, probably associated with movements in neighbouring areas. In general, however, it is to be expected that matching of geomorphological features is more difficult in this area than, for example, across the South Atlantic Ocean. In any case, the only coastlines which can be matched are those of the Caspian Sea and Black Sea and such matches are clearly meaningless. In earlier times, however, sea level may have been 60-120 m higher (Tamrazyan
Fig. 10. Gold deposits and the Siberian fractural suture: II = shields (I = the Baltic shield, 2 = the UkGnian shield, 3 = the Anabar shield, 4 = the Aldan shield); B = pfatforrns (I = East-European, II = Siberian); c = edges of the Siberian fracturat suture; d = gold deposits, e = zone of maximum concentration of gold deposits. K?ctonophvsics, ll(1971)
433-460
452
G.P. TAMRAZYAN
s d
Q
SIBERIAN CONTINENTAL
0
Fig. 12. Legend see p.456.
DRIFT
4.54
G.P. TAMRAZYAN
Q
Es! ..j ,::;:. sl :. liz! -0
:‘::: :,:.:: : .:,, .:. :.:::, : :;;.:_ :. : :_: 2: ::.
v
n
•a 0
El
Fig. 13. Legend see p.4.56.
SIBERIAN CONTINENTAL
i -
Fig. 14. Legend see p.456.
DRIFT
455
456
C.P. TAMRAZYAN
1. Copper deposits and the Siberian fractnrat suture: a = shields {I = the Battic shield, I? = the Ukrainian shield, 3 = the Anabar shield, 4 = the AIdan shield); b = platforms (I= East-European, II= Siberian); c = edges of the Siberian Fractural suture; d = copper deposits; c = concentration zone of main copper deposits.
Fig, f
Fig. 12. Lead, zinc and tungsten deposits, and the Siberian fractural suture: a = shields (1 = the Baltic shield, ,7 = the Ukrainian shield, 3 = the A:abar shield, 4 = the Aidan shield); h = platforms fl = t&tEuropean, fl= Siberian); c = edges of the Siberian fractural suture; d = jead and zinc dep&ts; P Ltungsten deposits;f= concentration zones of main potymetallic deposits. Fig. 13. Upper-Palaeozoic coat basins and the Siberian fractural suture: u = shields (f = the Baltic shield, 2 = the Ukrainian shield, 3 = the Anabar shield, 4 = the Aldan shield); h = platforms (I = EastEuropean, II = Siberian); c = edges of the Siberian fractural suture; d = Mississippian coal accumulation; c = Pennsylvanian coal accumu~tjon; f= Permian coal accumulation; d, f, and fare expressed in per cent. Coal basins: 1= the Donetz Basin; a7 = the Kama B∈ 3 = the Near-Moscow Basin; 4 = the Pechora Basin; S = the Karaganda Basin, 6 = the Ekibastuz basin; 7 = the Corlovka hasin;S = the Kuznetsk basin; 9 = the Minus basin; If? = the Taimyr basin; IJ = the Tungns basin. Fig. 14. Geomorphological diagram and the Siberian drift: a = accumulation plains (stable-subsidence regions); b = structural denudation plains and plateaus (regions of predominantly slight newest up heavais); sloping piedmont alluvial- proluvial plains are also included here; c = mountains and plateaus (regions of stabIe intensive newest u~heav~s); 4 b, and c are taken from the ~eomo~ho~o~ca1 map of the U.S.S.R., 1966; d= edges of the Siberian fractural suture.
Fig_ 15. Physical map for the time when the ocean level was 140- 160 m above its pnZsent-daY level. a = land; b = sea; c = edges of the Siberian fractural suture.
SIBERIAN CONTINENTAL
DRIFT
451
as glacjal episodes only form l-5% of post-Cambrian times. Furthermore, the modern tectonic stage is exceptionally active as most of the earth’s present relief has come into being during the Pliocene-Quaternary so that the earth’s surface was generally more flatlying, Therefore it is necessary for earlier times to consider geomorphological features which would arise and can be matched for more normal conditions, i.e., with sea-level some 100-l 50 m higher than today. Under these conditions, the west Siberian, Turan and Near Caspian lowlands would be submerged beneath a shallow sea (Fig. 15) and matching of these shore lines then becomes possible. Clearly the contours for this ancient sea-level match each other and the reconstruction using matching shore-lines results in a single East-European-Siberian continental massif. THE SOUTHERN EXTENSION OF THE URALS
The relationship of the Urals, Tien Shan, Mangyshlak and Donbas regions has attracted considerable argument for a long time and no firm conclusions have previously been possible. Arkhangelskiy (cited in Yanshin, 1951) considered that the Urals plunged southwards and were subsequently cut by the folded Tien Shan structures. However, in 1937 he considered that there was in fact a direct connection of the Urals with the Donbas structure. Similar evolution and changes of ideas were shown by Yanshin who, in 1945, believed that the Urals extended to join the Tian Shan structures but later (Yanshin 1951) he thought the Urals must die out completely before reaching any of the more southerly structures. Yanshin, although demonstrating that the Urals could not extend further to either the southwest or southeast was not, however, able to explain why or how the Ural structures should die out so abruptly. He comments that the Hercynian section of the trans-Caspian zone is radically different from that of the Urals. It is so different that the two areas could only exist far apart and have only subsequently become adjacent. If, however, the areas are reconstructed by matching the Siberian suture, the Urals then pass via the Kulunda Basin to the Altai while to the southwest of the Urals lies the Central Kazakhstan Massif and the Sayans lie to the southeast. The ore deposits of the Urals are therefore genetically related to those of the Altai, in particular, the Hercynian ores matching in both areas. Small tectonic fragments further south (the Crimean High and Low Caucasus and the Pamir block) which belong to this general pattern belong to the southwest part of the Siberian suture but have been reworked during the Cimmerian and Alpine erogenic cycles which has obscured their Middle Asian affinities. COMMENTS
As the evidence of continental drift in the Siberian region is so strong, it is not proposed to draw obvious conclusions, but to consider two particular aspects which may be. of worldwide pertinance to continental drift movements. As the earth’s rotation is decreasing, this causes compression in some areas of crust and tension in others and there is a particular line of latitude, theoretically 35’;separating zones of compression in more equatorial latitudes from tension at higher latitudes (Fig. 16). The tension is greatest at 61”-62” but generally extends from 35” to 70” which is the limit Tecronophysics, 11 (1971) 433-460
458
G.P. TAMRAZYAN
70.-
I
I
60, 50 '1 J
40.. 30..
I
20. 10. 600
A
400
200
0
200
400 *In
I 20
0
40
60
80
8
Fig. 16. Variation of earth parallel length (A) with the rotation period changing from 6 h to its presentday duration. On the right-hand side the variation of the continentality coefficient is shown for the Northern Hemisphere IfI).
Yol
6Mm
5000
4000
3mO
2Oor
IOOC
C
Fig. 17. Diagram showing the variations in the gradual melting covering the earth core and the mantle foot layers (solid line), and the change in the conventional rate of movement of the frontal surface of the molten earth core (dotted line). (I = in case the melting started 3.5 milliard years ago; b = in case the melting started 4.5 milliard years ago, On the left along the Y-axis the distance from the earth centre is shown (just to the right the distance from the earth surface is plotted). The rates of move ment (km/million years) are plotted on the right hand side. The time as from now is plotted along the X-axis.
x
SIBERIAN CO~INENTAL
DRIFT
459
of the Siberian fractural suture. The second feature is that the core of the earth is gradually increasing at the expense of the lower strata of the mantle (Tamrazyan, 1967; Fig. 17). This means that IO9 years ago, the earth’s core was at a depth of either 4,612 or 4,270 km, depen~g if melting commenced 3.5 or 4.5 . IO9 years ago. As the liquid core grows, the links between different areas of the crust becomes weakened so that, for example, Pangaea was then able to break into separate blocks which were then free to drift apart. Calculations show that this state would be reached for Pangaea 206-267 million years ago although Laurasia and Gondwanaland may have already begun to drift apart by this time. The main break-up of Pangaea was slightly Iater than this, probably 200-210 million years ago with the Siberian drifting preceding that of the ~erican drift, so that the Siberian movement was the first sign of the commencement of a radically new change in earth structure. Such movements created the conditions for bringing magma from the depth with the development of major magmatic and metasomatic ore. Siberian continental drift is well established and marks the onset of the present mobilistic tectonic stage of our planet.
REFERENCES Aksenovich, G.I., Aronov, L.Ye., Gegelgants, A.A., Galperin, M.A., Kostninskaya, I.P..and Krashkina, R.M.,1962. Deep Seismic Sounding in the Central Part of the CaspianSea. Acad. Sci. U.S.S.R., Moscow, 152 pp. Balavadze, B.K. and Shengelaya, G. Sh., 1961. The main structural features of the earth crust in the High Caucasus according to gravimetric data. Dokl. Akad NaukS.S.S.R., 136(6): 1328-1331. Borisov, A.A., 1967. Depth Structure of the U.S.S.R. Territory Based on GeophysicalData Nedra, Moscow, 304 pp. Demenitskaya, R.M., 1967. Earth Crust and Mantle. Nedra, Moscow, 280 pp. Kropotkin, P.N., 1961. Palaeomagnetism, palaeoclimates and the problem of big horizontal movements of the earth crust. Sov. Geol., 5: 16-38. Magakyan, LG., 1959. Fund~ent~s of Continental Met~~eny. Acad. Sci. Armenian S.S.R., Yerevun, 280 pp. Makareriko, F.A. and Mavritskiy, B.F., 1963. General &valuation of underground waters of the U.S.S.R. as sources of heat. in: Thermal Waters of the U.S.S.R. and Questions Concerning the Use of their Thermal Energy. Acad. Sci U.S.S.R., MOSCOW, pp. S-14. Makarenko, F.A., Polak, B.G. and Smirnov, J.B., 1968. Geothermal field on the U.S.S.R. territory. In: GeologicalResults of Applied Geophysics. Nauka, Moscow, pp. 43-48. Neprochnov, Yu.P., 1960. The depth structure of the earth crust under the Black Sea according to &ismic data. Byul. Mask. ObshchestvaIspytateiei Prirody, Otd. Geol., 4: 30-36. Neprochnov, Y.P., 1962. The results of deep seismic sounding in the Black Sea. In: Deep Seismic Sounding of the Earth Crust in the U&!X.Gostoptekhisdat, Leningrad, pp. 211-282. Nikolayev, N;I., 1962. Neotectonics and its Expression in the Structure and Relief of the U.S.S.R. Territory. Gosgeoliidat, Moscow, 392 pp. Semenov, A.I., Sheglov, A.D., Bilibin T.V. et al., 1968. Geolo~~a~St~c~re of the U.S.S.R. IV. Nedra, Moscow, SO4 pp. Smimov, V.I., 1965. The GeoIoD of Usefil Minerals. Nedra, Moscow, 590 pp. Stovas, M.V., 1963. Some questions concerning the tectogenesis. In: Problems of Phmetary Geolom. Gosgeolizdat, Moscow, pp. 222-214. Surkov, VS., 1963. New ideas concerning the structure and age of the folded base of the West-Siberian lowland. Geol. Razvedka, 2~19-27. Surkov, V.S., Zhero, O.G. and Umantsev, L.F., 1969. The structure of the intermediate stage of the West-Siberia plate. Sov. Geol., 5: 104-108. Tectonophysics, 11 (1971) 433-460
460
G.P. TAMRAZYAN
Sydorenko, A.B. (Editor), 1968. The 50th Anniversary ofSoviet Geology. Nedra, Moscow, 420 pp. Tamrazyan, G.P., 1957. Geotectonic hypothesis. Izv. Arad. Sci. Azerb. S.S.R., 12: 85. 115. Tamrazyan, G.P., 1959. On the problem of the earth’s structure. Izv. Acad. Sci. Twkm. S.S.R., 1: 22-35. Tamrazyan, G.P., 1960. On the most important structural feature of the South-C’aspian trough, Dokl. Akad. NaukS.S.S.R., 131(4): 917-920. Tamrazyan, G.P., 1964. The European part of the U.S.S.R. compared to the contiguous Asiatic regions with reference to essential thermal regime differences in the earth’s interior. Dokl. A kad. Nauk S.S.S.R., 157(2): 337-340. Tamrazyan, G.P., 1967. Some of the main planetary tectonic regularities and their causal relations. Geol. Razvedka, 11: 3-- 17. Tamrazyan, G.P., 1967. Some sketches on the structure of the Earth, Moon and Mars. Intern. Lunar Sot., 3(4): 72-84. Tamrazyan, G.P., 1969. Seismic anomalies and the dynamic evolution of the earth’s crust and upper mantle.Zcams, 10(l): 164.-168. Taylor, F.B., 1910. Bearing of the tertiary mountain belt on the origin of the earth’s plan. Bull. C>eol. Sot. Am., 21:179 -226. Vasilijev, Yu.M., Dyakonov, D.I. and Charigin, M.M., 1968. Geothermy of deep subsurface of the North Caspian Depression from drilling data of deep Aralsor bore hole. In: Geological Results of Applied Geophysics. Nauka, pp. 55- 6 1. Volvovsky, I.S., Garetzky, R.G., Shlezinger, AX., and Shreibman, V.I., 1966. Tectonic of’ Turan Plate. Nauka, Moscow, 288 pp. Voronov, P.S., 1968. Essays on Regularities in the Morphometry of the Global Relief of the Earth. Nauka, Moscow, 124 pp. Wegener, A., 1924. The Origin of Continents and Oceans. English transl. J.G.A.Skerl, London, 212 pp. Yanshin, A.L., 1951. A.D. Arkhangelskiy’s views of the tectonic nature of the southeastern frame of the Russian platform and the modern ideas on this point. In: Commemoration of A.D. Arkhangelskiv. Acad. Sci. U.S.S.R., Moscow, pp. 253.-327. Yanshin, A.L. (Editor), 1966. The Tectonics of Eurasia. Nauka, Moscow, 488 pp.
Maps Atlas of the U.S.S.R. Nedra, Moscow, 1962. Geological Map of the U.S.S.R. Ministry of Geol. U.S.S.R., Moscow, lY66. Geomorphological Map of the U.S.S.R. G.S. Ganeshin (Editor), Ministry of Geol. U.S.S.R.,
MOSCOW,
1967. Geotectonic Map of the U.S.S.R. T.N. Spigarskiy (Editor), Ministry of Geol. U.S.S.R., Moscow, 1967. Metallogenic Map of the U.S.S.R. K.B. Iliyin (Editor), Ministry of Geol. U.S.S.R., Moscow, 1968. Neotectonical Map of the U.S.S.R. N.I. Nikolayev and S.S. Shults (Editors), Gosgeolizdat, Moscow, 1959.