The expansion of the Atlantic bed in the Late Jurassic and especially in the Early Cretaceous was accompanied not only by the breakups of continental megablocks, but also by their mutual movements. Thus, after the birth of the Central Atlantic Basin, the Gondwana block began to rapidly move eastward relative to Laurasia. Such movements had far-reaching consequences for the Tethys Ocean, the southern margins of which "floated" east relative to the northern ones. Then, after the opening of the South Atlantic and the breakup of Gondwana into several continental blocks, the Afro-Arabian block began to press against the northern margins of the Tethys Ocean. It started slamming.
During the opening of the Atlantic African continent moved more than 1500 km. The speed of its movement in the interval of 180–100 Ma was 2–3 cm/yr. During this time, he turned around in relation to Eurasia by 40 °. In the same direction as the African continent, the Iberian continental block began to migrate, turning slightly to the south. As a result, the Pyrenean trough was formed, a deep-water trough in which Early Cretaceous turbidites accumulated. At the same time, the Bay of Biscay opened up on its western extension, and "black" clays were deposited in its vicinity - sediments enriched in organic matter.
The continental margin of Gondwana, facing the Tethys Ocean, experienced a steady subsidence for almost 140 Ma, which led to the formation of a thick lens of Mesozoic and Cenozoic rocks. At the beginning of the Campanian, the northeastern ledge of the Afro-Arabian block began to move closer to the opposite screen Eurasia. This was accompanied by powerful compressions, splits of the continental crust and subsidence of its marginal blocks. The Tethys bed, which was between the continents, was broken open, its individual fragments were literally squeezed out onto the edge of the Nubian shield in the Oman region. At present, rocks that are completely uncharacteristic of the continents rise in the depths of the coast of Oman in the form of low mountains. These allochthonous massifs are composed of an ophiolite association, which includes rocks of obviously oceanic origin.
The closure of the eastern branch of the Tethys was accompanied by the collapse of the young ocean floor, which caused a drop in the sea level in the Maastrichtian. Surface currents revived, including cold boundary currents, due to which in many parts of the margins of Africa - from Cameroon, Senegal and Morocco in the Central Atlantic to Algeria, Tunisia and Syria in the Tethys Ocean - there was an intensive rise of deep waters. The formation of phosphorites, siliceous rocks, and palygorskite-sepiolite clays was associated with it.
The blockage that arose as a result of the convergence of the Afro-Arabian and Eurasian continental blocks in the Oman band continued from the Campanian to the Middle Eocene, i.e., 72-48 million years ago. On the northern margins in the Tethys Ocean, the collision led to the drainage of many areas previously covered by the sea. In the North Caucasus, in the region of the Dagestan wedge, in Maastricht, numerous landslides occurred, which continued in Denmark and the Eocene. In the entire strip of the Tethys Ocean, traces of shallowing and drying of part of the continental shelves are found.
In the Eocene, the collapse of the Laurasian continental megablock was completed. Having separated from North America, Eurasia began to move eastward at a speed exceeding the speed of the Afro-Arabian block. This was expressed in shear dislocations and breaks in the continental crust, which are characteristic mainly of Western Europe. However, Tethys was still directly connected with the oceanic basins of the Atlantic. They were united by a circulation system, and on the vast expanses of the continental margins of this region deposits of very similar composition accumulated. They were characteristic of vast shallow seas confined to the shelves of Africa and Eurasia. Over many areas of the outskirts, the rise of deep waters, which began as early as in Maastricht (and in some places still in the Turonian), continued, with which the distribution of palygorskites, sepiolites, cherts and limestones with phosphorites was associated in the Ypresian and Lutetian times. It is in the Paleocene and Eocene strata of passive margins that largest deposits phosphorites, which are currently being mined in Mauritania, Western Sahara, Morocco and other regions.
Approximately 48 million years ago, the African continent collided with the Iberian block in the strip of the northern outskirts of Morocco. This led to a slow roll of Africa to the north, as a result of which the western arm of the Tethys Ocean soon closed. A global restructuring of the oceanic circulation system has begun. Along the margins of the North and South American continents, near-bottom contour currents rushed to the equator, and warm waters of the Gulf Stream flowed from low latitudes to the pole. On the outskirts of Morocco and southern Spain, the rocks of the ocean bed were squeezed out, forming here the Rif mountain range and the Cordillera of Beta. This was followed by tectonic activation, which captured almost the entire African continent and the Iberian Peninsula. The Pyrenees trough finally slammed shut, and the Pyrenees rose in its place.
From that time begins the complex and largely undiscovered history of Mesogeia. The ancient Tethys ocean gradually closed, and the Alpine-Himalayan fold belt grew in its place. Its Himalayan branch arose in the late Miocene, after the Hindustan continental block, which broke away from Gondwana in the Middle Cretaceous, collided with the southern margins of Eurasia. Around the same time, the Arabian Peninsula also drew close to the margin of this continent, this time in a wide strip from Turkey to the Strait of Hormuz. As both megablocks approached, the Tethys oceanic crust gradually assimilated under its northern margin, disappearing in the Benioff zones. One of them was located in the area of the Zagros mountain range (southwestern regions of Iran). The latter is part of an ancient accretionary ridge that once bordered the active continental margin of Eurasia.
It must be said that in the Mesozoic and Cenozoic Tethys, apparently, was not very wide, so any restructuring in the system of movement of lithospheric plates led to a collision of the northern and southern continental blocks. At the same time, smaller massifs often broke away from them, subsequently moving independently. Each collision was accompanied by a crushing of sediments accumulated on convergent continental margins. Precipitation often formed powerful folds that rose from the bottom of the sea in the form of mountainous countries, from which the sea left. Similar events in geology are defined as folding phases. Each of them is given a name according to the region where it manifested itself most clearly. Thus, the Pyrenean and Alpine phases of folding are known. The first refers to the middle and late Oligocene, the second to the Miocene, when the fold systems of the Alps, Carpathians and the Caucasus, which are part of a single Alpine fold belt, began to form.
It is believed that the Alps, Dinarides and other mountain ranges of Southern Europe arose as a result of the intrusion of the Adriatic ledge of Africa into the Eurasian block. Now this ledge is the bed of the Adriatic and partly the Ionian Seas. On the other hand, the rocks that once formed the bottom of the Tethys and Mesogean oceans are now crumpled into folds or collected in a series of covers. They make up the Apennine Peninsula, certain areas of the islands of Corsica and Sardinia. In the zone of collision of the African and Eurasian plates, south of the island of Crete and the Peloponnese peninsula, the East Mediterranean shaft grows - a system of underwater ridges separated by small depressions. Over time, the peaks of these ranges will rise above sea level and eventually turn into a large mountain-fold belt, similar in structure to the Alpine. Since the uplift of a mountainous country is accompanied by a sagging of the crust in the adjacent parts of the platforms and middle massifs, this process has already led to the subsidence of individual blocks of Africa. The Levantine depression that emerged here is a foredeep, where a rather thick cover of continental, including salt-bearing, and marine sediments has already formed. Similar troughs in the Late Cenozoic existed at the edge of the European Platform, at the junction with the growing mountain systems of the Caucasus, the Carpathians, and the Alps.
Even Leonardo da Vinci found fossilized shells of marine organisms on the tops of the Alps and came to the conclusion that there used to be a sea on the site of the highest ridges of the Alps. Later, marine fossils were found not only in the Alps, but also in the Carpathians, the Caucasus, the Pamirs, and the Himalayas. Indeed, the main mountain system of our time - the Alpine-Himalayan belt - was born from the ancient sea. At the end of the last century, the contour of the area covered by this sea became clear: it stretched between the Eurasian continent in the north and Africa and Hindustan in the south. E. Suess, one of the greatest geologists of the end of the last century, called this space the Tethys Sea (in honor of Thetis, or Tethys, the sea goddess).
A new turn in the idea of Tethys came at the beginning of this century, when A. Wegener, the founder of the modern theory of continental drift, made the first reconstruction of the Late Paleozoic supercontinent Pangea. As you know, he pushed Eurasia and Africa to North and South America, combining their coasts and completely closing the Atlantic Ocean. At the same time, it was found that, closing the Atlantic Ocean, Eurasia and Africa (together with Hindustan) diverge to the sides and between them, as it were, a void appears, a gaping several thousand kilometers wide. Of course, A. Wegener immediately noticed that the gap corresponds to the Tethys Sea, but its dimensions corresponded to those of the ocean, and one should have spoken of the Tethys Ocean. The conclusion was obvious: as the continents drifted, as Eurasia and Africa moved away from America, a new ocean opened up - the Atlantic and at the same time the old ocean - Tethys closed (Fig. 1). Therefore, the Tethys Sea is a vanished ocean.
This schematic picture, which emerged 70 years ago, has been confirmed and detailed in the last 20 years on the basis of a new geological concept that is now widely used in studying the structure and history of the Earth - lithospheric plate tectonics. Let us recall its main provisions.
The upper solid shell of the Earth, or the lithosphere, is divided by seismic belts (95% of earthquakes are concentrated in them) into large blocks or plates. They cover the continents and oceanic spaces (today there are 11 large plates in total). The lithosphere has a thickness of 50-100 km (under the ocean) to 200-300 km (under the continents) and rests on a heated and softened layer - the asthenosphere, along which plates can move in a horizontal direction. In some active zones - in the mid-ocean ridges - lithospheric plates diverge to the sides at a speed of 2 to 18 cm / year, making room for the uplift of basalts - volcanic rocks melted from the mantle. Basalts, solidifying, build up the divergent edges of the plates. The process of spreading the plates is called spreading. In other active zones - in deep-sea trenches - lithospheric plates approach each other, one of them "dives" under the other, going down to depths of 600-650 km. This process of submerging plates and absorbing them into the Earth's mantle is called subduction. Above the subduction zones, extended belts of active volcanoes of a specific composition (with a lower content of silica than in basalts) arise. The famous ring of fire of the Pacific Ocean is located strictly above the subduction zones. Catastrophic earthquakes recorded here are caused by the stresses necessary to pull the lithospheric plate down. Where plates approaching each other carry continents that are not capable of sinking into the mantle due to their lightness (or buoyancy), a collision of continents occurs and mountain ranges arise. The Himalayas, for example, were formed during the collision of the continental block of Hindustan with the Eurasian continent. The rate of convergence of these two continental plates is now 4 cm/year.
Since lithospheric plates are rigid in the first approximation and do not undergo significant internal deformations during their movement, a mathematical apparatus can be applied to describe their movements on the earth's sphere. It is not complicated and is based on L. Euler's theorem, according to which any movement along the sphere can be described as rotation around an axis passing through the center of the sphere and intersecting its surface at two points or poles. Therefore, in order to determine the movement of one lithospheric plate relative to another, it is sufficient to know the coordinates of the poles of their rotation relative to each other and the angular velocity. These parameters are calculated from the values of directions (azimuths) and linear velocities of plate movements at specific points. As a result, for the first time, a quantitative factor was introduced into geology, and it began to move from a speculative and descriptive science into the category of exact sciences.
The above remarks are necessary in order for the reader to further understand the essence of the work done jointly by Soviet and French scientists on the Tethys project, which was carried out within the framework of an agreement on Soviet-French cooperation in the study of the oceans. The main goal of the project was to restore the history of the disappeared Tethys Ocean. On the Soviet side, the Institute of Oceanology named after A.I. P. P. Shirshov Academy of Sciences of the USSR. Corresponding members of the USSR Academy of Sciences A. S. Monin and A. P. Lisitsyn, V. G. Kazmin, I. M. Sborshchikov, L. A. Savostii, O. G. Sorokhtin and the author of this article took part in the research. Employees of other academic institutions were involved: D. M. Pechersky (O. Yu. Schmidt Institute of Physics of the Earth), A. L. Knipper and M. L. Bazhenov (Geological Institute). Great assistance in the work was provided by employees of the Geological Institute of the Academy of Sciences of the GSSR (Academician of the Academy of Sciences of the GSSR G. A. Tvalchrelidze, Sh. and M. I. Satian), Faculty of Geology, Moscow State University (Academician of the Academy of Sciences of the USSR V.: E. Khain, N. V. Koronovsky, N. A. Bozhko and O. A. | Mazarovich).
From the French side, the project was headed by one of the founders of the theory of plate tectonics, K. Le Pichon (University named after Pierre and Marie Curie in Paris). Experts in the geological structure and tectonics of the Tethys belt took part in the research: J. Derkur, L.-E. Ricou, J. Le Priviere and J. Jeyssan (University named after Pierre and Marie Curie), J.-C. Cibuet (Center for Oceanographic Research in Brest), M. Westphal and J.P. Lauer (University of Strasbourg), J. Boulin (University of Marseille), B. Bijou-Duval (State Oil Company).
The research included joint expeditions to the Alps and the Pyrenees, and then to the Crimea and the Caucasus, laboratory processing and synthesis of materials at the University. Pierre and Marie Curie and at the Institute of Oceanology of the USSR Academy of Sciences. The work was started in 1982 and completed in 1985. Preliminary results were reported at the XXVII session of the International Geological Congress, held in Moscow in 1984. The results of the joint work were summed up in a special issue of the international journal "Tectonophysics" in 1986. An abbreviated version of the report on French published in 1985 in the Bulletin societe de France, the History of the Tethys Ocean was published in Russian.
The Soviet-French project "Tethys" was not the first attempt to restore the history of this ocean. It differed from the previous ones in the use of new, better-quality data, in the significantly greater extent of the region under study - from Gibraltar to the Pamirs (and not from Gibraltar to the Caucasus, as it was before), and most importantly, in the involvement and comparison of materials from various independent sources. Three main groups of data were analyzed and taken into account during the reconstruction of the Tethys Ocean: kinematic, paleomagnetic and geological.
Kinematic data relate to the mutual movements of the main lithospheric plates of the Earth. They are entirely related to plate tectonics. Penetrating into the depths of geological time and successively moving Eurasia and Africa closer to North America, we obtain the relative positions of Eurasia and Africa and reveal the contour of the Tethys Ocean for each specific moment in time. Here a situation arises that seems paradoxical to a geologist who does not recognize plate mobilism and tectonics: in order to represent events, for example, in the Caucasus or in the Alps, it is necessary to know what happened thousands of kilometers from these areas in the Atlantic Ocean.
In the ocean, we can reliably determine the age of the basalt base. If we combine coeval bottom bands located symmetrically on opposite sides of the axis of the mid-ocean ridges, we will obtain the parameters of plate movement, that is, the coordinates of the pole of rotation and the angle of rotation. The procedure for searching for parameters for the best combination of coeval bottom bands is now well developed and is carried out on a computer (a series of programs is available at the Institute of Oceanology). The accuracy of determining the parameters is very high (usually fractions of a degree of a great circle arc, that is, the error is less than 100 km), and the accuracy of reconstructions of the former position of Africa relative to Eurasia is just as high. This reconstruction serves for each moment of geological time as a rigid frame, which should be taken as a basis for reconstructing the history of the Tethys Ocean.
The history of plate movement in the North Atlantic and the opening of the ocean in this place can be divided into two periods. In the first period, 190-80 million years ago, Africa separated from the united North America and Eurasia, the so-called Laurasia. Prior to this split, the Tethys Ocean had a wedge-shaped outline, expanding with a bell to the east. Its width in the region of the Caucasus was 2500 km, and on the traverse of the Pamirs it was at least 4500 km. During this period, Africa shifted to the east relative to Laurasia, covering a total of about 2200 km. The second period, which began about 80 million years ago and continues to the present day, was associated with the division of Laurasia into Eurasia and North America. As a result, the northern edge of Africa along its entire length began to converge with Eurasia, which ultimately led to the closure of the Tethys Ocean.
The directions and speeds of Africa's movement relative to Eurasia did not remain unchanged throughout the Mesozoic and Cenozoic eras (Fig. 2). In the first period, in the western segment (west of the Black Sea), Africa moved (albeit at a low speed of 0.8-0.3 cm/year) to the southeast, allowing the young ocean basin between Africa and Eurasia to open up.
80 million years ago, in the western segment, Africa began to move northward, and in recent times it has been moving northwest with respect to Eurasia at a rate of about 1 cm/year. In full accordance with this are folded deformations and the growth of mountains in the Alps, Carpathians, Apennines. In the eastern segment (in the region of the Caucasus), Africa began to approach Eurasia 140 million years ago, and the rate of approach fluctuated noticeably. Accelerated approach (2.5-3 cm/year) refers to the intervals 110-80 and 54-35 million years ago. It was during these intervals that intense volcanism was noted in the volcanic arcs of the Eurasian margin. The slowdown of movement (up to 1.2-11.0 cm/year) falls on the intervals of 140-110 and 80-54 million years ago, when stretching occurred in the rear of the volcanic arcs of the Eurasian margin and deep-water basins of the Black Sea were formed. The minimum approach rate (1 cm/year) refers to 35-10 million years ago. Over the past 10 million years in the Caucasus region, the rate of convergence of plates has increased to 2.5 cm / year due to the fact that the Red Sea began to open, the Arabian Peninsula broke away from Africa and began to move north, pressing its protrusion into the edge of Eurasia. It is no coincidence that the mountain ranges of the Caucasus grew on the top of the Arabian ledge. The paleomagnetic data used in the reconstruction of the Tethys Ocean are derived from remanent magnetization measurements. rocks. The fact is that many rocks, both igneous and sedimentary, at the time of their formation were magnetized in accordance with the orientation of the magnetic field that existed at that time. There are methods that allow you to remove layers of later magnetization and establish what the primary magnetic vector was. It should be directed to the paleomagnetic pole. If the continents do not drift, then all vectors will be oriented in the same way.
Back in the 50s of our century, it was firmly established that within each individual continent, paleomagnetic vectors are indeed oriented in parallel and, although they are not elongated along modern meridians, are still directed to one point - the paleomagnetic pole. But it turned out that different continents, even nearby ones, are characterized by completely different orientation of the vectors, that is, the continents have different paleomagnetic poles. This alone has given rise to the assumption of large-scale continental drift.
In the Tethys belt, the paleomagnetic poles of Eurasia, Africa, and North America also do not coincide. For example, for the Jurassic period, the paleomagnetic poles have the following coordinates: near Eurasia - 71 ° N. w „ 150 ° in. d. (region of Chukotka), near Africa - 60 ° N. latitude, 108° W (region of Central Canada), near North America - 70 ° N. latitude, 132° E (the area of the mouth of the Lena). If we take the parameters of plate rotation relative to each other and, say, move the paleomagnetic poles of Africa and North America together with these continents to Eurasia, then a striking coincidence of these poles will be revealed. Accordingly, the paleomagnetic vectors of all three continents will be oriented subparallel and directed to one point - a common paleomagnetic pole. This kind of comparison of kinematic and paleomagnetic data was made for all time intervals from 190 million years ago to the present. There was always a good match; by the way, it is a reliable evidence of the reliability and accuracy of paleogeographic reconstructions.
The main continental plates - Eurasia and Africa - bordered the Tethys Ocean. However, there were undoubtedly smaller continental or other blocks inside the ocean, as now, for example, inside the Indian Ocean there is a microcontinent of Madagascar or a small continental block of the Seychelles. Thus, inside the Tethys there were, for example, the Transcaucasian massif (the territory of the Rion and Kura depressions and the mountain bridge between them), the Daralagez (South Armenian) block, the Rhodope massif in the Balkans, the Apulia massif (covering most of the Apennine Peninsula and the Adriatic Sea). Paleomagnetic measurements within these blocks are the only quantitative data that allow us to judge their position in the Tethys Ocean. Thus, the Transcaucasian massif was located near the Eurasian margin. The small Daralagez block appears to be of southern origin and was previously annexed to Gondwana. The Apulian massif did not shift much in latitude relative to Africa and Eurasia, but in the Cenozoic it was rotated counterclockwise by almost 30°.
The geological group of data is the most abundant, since geologists have been studying the mountain belt from the Alps to the Caucasus for a good hundred and fifty years. This group of data is also the most controversial, since it can be least of all applied to a quantitative approach. At the same time, geological data in many cases are decisive: it is geological objects - rocks and tectonic structures - that were formed as a result of the movement and interaction of lithospheric plates. In the Tethys belt, geological materials have made it possible to establish a number of essential features of the Tethys paleoocean.
Let's start with the fact that it was only by the distribution of marine Mesozoic (and Cenozoic) deposits in the Alpine-Himalayan belt that the existence of the Tethys sea or ocean in the past became obvious. Tracing different geological complexes over the area, it is possible to determine the position of the seam of the Tethys ocean, that is, the zone along which the continents that framed Tethys converged at their edges. Of key importance are the outcrops of rocks of the so-called ophiolite complex (from the Greek ocpir - a snake, some of these rocks are called serpentines). Ophiolites consist of heavy rocks of mantle origin, depleted in silica and rich in magnesium and iron: peridotites, gabbro and basalts. Such rocks form the bedrock of modern oceans. Given this, 20 years ago, geologists came to the conclusion that ophiolites are the remains of the crust of ancient oceans.
Ophiolites of the Alpine-Himalayan belt mark the bed of the Tethys Ocean. Their outcrops form a winding strip along the strike of the entire belt. They are known in the south of Spain, on the island of Corsica, stretching in a narrow strip along the central zone of the Alps, continuing into the Carpathians. Large tectonic scales of ophiolites were found in the Dealer Alps in Yugoslavia and Albania, in the mountain ranges of Greece, including the famous Mount Olympus. The outcrops of ophiolites form an arc facing south between the Balkan Peninsula and Asia Minor, and then are traced in Southern Turkey. Ophiolites are beautifully exposed in our country in the Lesser Caucasus, on the northern shore of Lake Sevan. From here they extend to the Zagros range and into the mountains of Oman, where ophiolite plates are pushed over the shallow sediments of the margin. Arabian Peninsula. But even here the ophiolite zone does not end, it turns to the east and, following parallel to the coast of the Indian Ocean, goes further northeast to the Hindu Kush, the Pamirs and the Himalayas. Ophiolites have different age- from Jurassic to Cretaceous, but everywhere they are relics of the earth's crust of the Mesozoic ocean Tethys. The width of the ophiolite zones is measured by several tens of kilometers, while the original width of the Tethys Ocean was several thousand kilometers. Consequently, during the approach of the continents, almost the entire oceanic crust of Tethys went into the mantle in the zone (or zones) of subduction along the edge of the ocean.
Despite the small width, the ophiolite, or main, suture of the Tethys separates two provinces that are sharply different in geological structure.
For example, among the Upper Paleozoic deposits accumulated 300-240 million years ago, north of the suture, continental sediments predominate, some of which was deposited in desert conditions; while to the south of the suture, thick strata of limestones, often reefs, are widespread, marking a vast shelf sea in the equator region. The change of Jurassic rocks is just as striking: detrital, often coal-bearing, deposits north of the seam again oppose limestone south of the seam. The seam separates, as geologists say, different facies (conditions for the formation of sediments): the Eurasian temperate climate from the Gondwanan equatorial climate. Crossing the ophiolite seam, we get, as it were, from one geological province to another. To the north of it we find large granite massifs surrounded by crystalline schists and a series of folds that arose at the end of the Carboniferous period (about 300 million years ago), to the south - layers of sedimentary rocks of the same age occur consistently and without any signs of deformation and metamorphism . It is clear that the two margins of the Tethys Ocean - the Eurasian and the Gondwana - differed sharply from each other both in their position on the earth's sphere and in their geological history.
Finally, we note one of the most significant differences between the areas north and south of the ophiolite suture. To the north of it are belts of volcanic rocks of the Mesozoic and Early Cenozoic age, formed over 150 million years: from 190 to 35-40 million years ago. The volcanic complexes in the Lesser Caucasus are especially well traced: they stretch in a continuous strip along the entire ridge, going west to Turkey and further to the Balkans, and east to the Zagros and Elburs ranges. The composition of the lavas has been studied in great detail by Georgian petrologists. They found that the lavas are almost indistinguishable from the lavas of modern island arc volcanoes and active margins that make up the ring of fire of the Pacific Ocean. Recall that the volcanism of the rim of the Pacific Ocean is associated with the subduction of the oceanic crust under the continent and is confined to the boundaries of the convergence of lithospheric plates. This means that in the Tethys belt, volcanism similar in composition marks the former boundary of convergence of plates, on which subduction of the oceanic crust took place. At the same time, south of the ophiolite suture, there are no coeval volcanic manifestations; throughout the Mesozoic era and during most of the Cenozoic era, shallow-water shelf sediments, mainly limestone, were deposited here. Consequently, the geological data provide solid evidence that the margins of the Tethys Ocean were fundamentally different in tectonic nature. The northern, Eurasian margin, with volcanic belts constantly forming at the boundary of the convergence of lithospheric plates, was, as geologists say, active. The southern, Gondwana margin, devoid of volcanism and occupied by a vast shelf, calmly passed into the deep basins of the Tethys Ocean and was passive. Geological data, and primarily materials on volcanism, make it possible, as we see, to restore the position of the former boundaries of the lithospheric plates and outline ancient subduction zones.
The above does not exhaust all the factual material that must be analyzed for the reconstruction of the disappeared Tethys Ocean, but I hope this is enough for the reader, especially far from geology, to understand the basis of the constructions made by Soviet and French scientists. As a result, color paleogeographic maps were compiled for nine moments of geological time from 190 to 10 million years ago. On these maps, according to kinematic data, the position of the main continental plates - the Eurasian and African (as parts of Gondwana) was restored, the position of the microcontinents inside the Tethys Ocean was determined, the boundary of the continental and oceanic crust was outlined, the distribution of land and sea was shown, and paleolatitudes were calculated (from paleomagnetic data)4 . Particular attention is paid to the reconstruction of the boundaries of lithospheric plates - spreading zones and subduction zones. The displacement vectors of the main plates are also calculated for each moment of time. On fig. 4 shows diagrams compiled from color maps. To make clear the prehistory of Tethys, they also added a diagram of the location of continental plates at the end of the Paleozoic (Late Permian era, 250 million years ago).
In the Late Paleozoic (see Fig. 4, a), the Paleo-Tethys ocean extended between Eurasia and Gondwana. Already at that time, the main trend of tectonic history was determined - the existence of an active margin in the north of the Paleo-Tethys and a passive one in the south. From the passive margin at the beginning of the Permian, relatively large continental masses were split off - Iranian, Afghan, Pamir, which began to move, crossing the Paleo-Tethys, to the north, to the active Eurasian margin. The Paleo-Tethys oceanic bed in the front of drifting microcontinents was gradually absorbed in the subduction zone near the Eurasian margin, and in the rear of the microcontinents, between them and the Gondwana passive margin, a new ocean opened - the Mesozoic Tethys proper, or Neo-Tethys.
In the Early Jurassic (see Fig. 4b), the Iranian microcotinent joined the Eurasian margin. When they collided, a folded zone arose (the so-called Cimmerian folding). In the Late Jurassic, 155 million years ago, the opposition of the Eurasian active and Gondwana passive margins was clearly marked. At that time, the width of the Tethys Ocean was 2500-3000 km, that is, it was the same as the width of the modern Atlantic Ocean. The distribution of Mesozoic ophiolites made it possible to mark the spreading axis in the central part of the Tethys Ocean.
In the Early Cretaceous (see Fig. 4, c), the African plate - the successor to the Gondwana that had disintegrated by that time - moved towards Eurasia in such a way that in the west of the Tethys the continents parted somewhat and a new ocean basin arose there, while in the eastern part of the continents they converged and the bed of the Tethys ocean was absorbed under the Lesser Caucasian volcanic arc.
At the end of the Early Cretaceous (see Fig. 4, d), the oceanic basin in the west of the Tethys (it is sometimes called the Mesogea, and its remains are the modern deep-water basins of the Eastern Mediterranean) ceased to open up, and in the east of the Tethys, judging by the dating of the ophiolites of Cyprus and Oman , the active stage of spreading was completed. In general, the width of the eastern part of the Tethys Ocean decreased to 1500 km by the middle of the Cretaceous at the traverse of the Caucasus.
By the Late Cretaceous, 80 million years ago, there was a rapid reduction in the size of the Tethys Ocean: the width of the strip with oceanic crust at that time was no more than 1000 km. In places, as in the Lesser Caucasus, collisions of microcontinents with an active margin began, and the rocks underwent deformation, accompanied by significant displacements of tectonic sheets.
At the turn of the Cretaceous and Paleogene (see Fig. 4, e) there were at least three important events. First, ophiolite plates, torn off the oceanic crust of Tethys, were pushed over the passive margin of Africa by a wide front.
Good, friends! From time to time I write small notes related to diving, adventures or interesting facts. This time I want to introduce you to two news.
Of course, you know where the name of our portal - Tethys - came from. Just in case, let me remind you that in ancient times there was a huge Tethys ocean, part of which was located on the territory modern Russia, in the North Caucasus.
The mountains are just over 200 km away from me, and like any restless person, I am interested in no less than diving. From time to time, in the mountains, on “untrodden” tourist routes, in riverbeds or in rock outcrops, my friends and I found traces of the existence of the Tethys Ocean - fossils. In the form of huge spiral shells, the imprint of half of an outlandish fish or a fossilized fragment of a coral reef.
The existence of the Tethys stone sea on the Lago-Naki highlands (it is correct to say the highlands, not the plateau, read the definition in the reference literature) has long been written on various tourist sites, as well as on the sites of hotels and recreation centers in the Republic of Adygea and the Apsheron region of the Krasnodar Territory.
The place is well-known, the road is quite easy, you can get to the cordon on the "puzoterka". But somehow it didn't work to get there. There were many interesting hikes before, in principle I did not want to pay 300 rubles for entrance to the reserve for no reason, and my colleagues did not aspire to go there.
At the end of May this year, desires and opportunities came together. We decided to "close the gap" in our mountain hikes. At the same time to prepare for the expedition, about which a little later. They didn't regret it. It was worth the game of candles.
Having paid the money and leaving the car after 1 km from the cordon, there is no further passage, we move on foot. Along the way, friends help us carry a transport bag with mountain equipment, we still have a difficult descent into the cave. Beauty is all around - nature is waking up, a lot of Red Book flowers, wonderful panoramas, delicious air. Nevertheless, the road is difficult, you have to look under your feet, rocky slopes are replaced by snowfields, where it is easy to fall through to the waist and break a leg. We're trying to move along a well-travelled path.
Our goal is the pass, from where a beautiful view of Oshten, the Tethys stone sea (as it is called in Adygea) and a memorial obelisk to the soldiers of the border detachment who defended it from the Nazis during the war opens. The road there is constantly on the rise, we make small stops, because each of us has different training and opportunities. Approximately after 6 km we reach the pass, amazingly beautiful views, worthy of our efforts, open up to us. Everyone takes lots and lots of photos. Followed by a small snack. And Olga and I are going to the cave together. The cave is a kind of birthday present from my friends. Well, preparing for the expedition.
The descent is 80 meters vertically, three crossings, the glacier is about 35 meters high. But then - fearless beauty, huge icicles, stalagmites, a dark and gloomy well with water, going into the abyss. After that, I had to “jump” up the glacier for a long time and patiently. But everything worked out and I was happy. I won’t tell you the location, the cave is not for everyone. Maybe a commemorative plaque at the entrance about a climber who died in the 70s will make you think about life and death and the magnitude of the risk. We returned at dusk, happy but tired. The main group was waiting near the car. We returned home at midnight.
Now for the main point. The whole trip - 13.5 km along the snowfield and rocky slope, descent into the cave and ascent, high mountains - for me was a kind of training and preparation for the August high-altitude underwater search expedition to Karachay-Cherkessia. We do not want to reveal all the secrets and our ideas yet, but the expedition will be unique. We must be first. Our research will be closely related to the events of the Great Patriotic War. We have a lot of hard work to do. We do not ask for help, but we need it. I am ready to answer all questions through my Facebook profile. Partial support for our project was provided, unfortunately, not by the Krasnodar branch of the Russian Geographical Society, but by the Black Shark diving club, Moscow, for which we are very grateful to them.
P.S.: If you have learned a little new about the Tethys Ocean and the Caucasus, then I did not write in vain.
Always yours,
Ernst Antonov
Photo: E. Antonov, S. Evdokimov, O. Dzhemelinskaya
This short word contains the history of the origin of the seas and mountains, the secrets of lost civilizations and the charm of ancient mythology.
TETIS- an ancient ocean that stretched across the entire globe, starting on the eastern side of the Atlantic Ocean and ending on the western. TETHYS separated the ancient foremothers Laurasia and Gondwana, which gave rise to modern continents. The name TETIS was proposed at the end of the 19th century by the Austrian geologist E. Suess after the ancient Greek goddess of the sea, Thetis (Thetis).
According to the assumptions of scientists, the very first continent of the Earth - the ancestor of Pangea split into two supercontinents: the northern one - Laurasia and the southern one - Gondwana about 200 million years ago. Between the separated supercontinents, the TETIS ocean was formed.
Gondwana is a supercontinent of the southern hemisphere, which consisted of the main parts of modern South America, Africa, Arabia, Antarctica, Australia, the Hindustan Peninsula and about. Madagascar. Laurasia is a northern hemisphere supercontinent that consisted of present-day North America and Eastern Europe.
The young Earth was in a powerful movement - separate continents broke away from the giant foremother, mountains were buried in the depths of the sea and, conversely, continents grew from the bottom of the ocean. In the depths of TETIS, a giant volcanic belt of the planet passed, volcanoes erupted here, the earth's crust shifted, torn and swelled. It is here, on the site of the ancient seas, that the highest mountain ranges will subsequently rise, and entire continents will drown in the abyss. Slowly but inexorably, Europe, North America, India, Africa, Australia, and Antarctica dispersed. At the same time, the Atlantic, Indian, and Arctic oceans began to form. The area of the TETIS ocean began to decrease, while giant mountain ranges encircling the planet - the Atlas, the Alps, the Caucasus, the Pamirs, the Himalayas - grew out of its bowels. The ocean turned into a sea, in the end, only the Mediterranean, Black, Caspian Seas, the Persian Gulf and the seas of the Malay Archipelago remained from it.
Maybe some of you want to know what will happen next?
According to the forecasts of scientists, the shift of the plates of Europe and Africa, which left only the Mediterranean basin from TETIS, will continue in the future, and in 50 million years the remnants of TETIS in the form of the Mediterranean Sea will disappear altogether, and Europe will be closely connected with North Africa.
This mysterious ocean left a memory of itself in the form of mighty mountain ranges stretching almost across the entire planet, which arose from its depths along the volcanic belt of the planet. It reminds of itself with global catastrophes, earthquakes and volcanic explosions, incredible paleontological finds, it is with the TETIS ocean that the greatest maritime mysteries, myths about sunken civilizations, including the Flood and the mystery of the disappeared Atlantis, are associated.
It is no coincidence that the ancient ocean was named after the ancient Greek goddess. For the first time the name of the goddess TETIS is mentioned in the myths about the creation of the world and the gods. TETHYS sister, and later the wife of the Ocean, who gave rise to the seas and rivers. In addition, in later myths, TETIS (Thetis) is a kind goddess of the sea. TETIS, the first of the immortals who married a man, belongs to the category of good gods - patrons who help, protect and save those who get into trouble at sea. Thetis immediately and disinterestedly came to the aid of people and gods, it was not for nothing that seafarers of all times decorated the bow of ships with her image. TETIS, the eldest of the fifty Nereids - the daughters of the sea elder Nereus, who had the gift of divination and reincarnation, is one of the most attractive tragic and humane heroines of the myths of antiquity. Beautiful, kind and sympathetic, she was too good and smart to be happy.
All the difficulties of her fate began when two of the greatest gods at once - Poseidon and Zeus himself simultaneously turned their attention to her. Maybe she would have become the wife of the Thunderer and the ruler of Olympus, if not for the prophecy of the titan Prometheus, who predicted to Zeus that she would give birth to a son who would surpass his father. After that, Zeus forcibly married her to a mortal - the Thessalian king Peleus.
The wedding took place in the cave of the ketaur Chiron, all the gods of Olympus walked on it, the only one who was not invited was the goddess of discord Eris, who managed to take revenge by throwing a golden apple from the garden of the Hesperides with the inscription “Most Beautiful”. It was because of this “apple of discord” that Athena, Aphrodite and Hera quarreled and, ultimately, the Trojan War began.
From Peleus, TETIS gave birth to Achilles, whose prediction promised either great fame and early death, or a long, but unremarkable life. Of course, the life of Achilles was dearer than fame to a loving mother, wanting to save her son from death, she protected him by all possible means.
To make him immortal, she dipped the baby into the waters of the magical Styx, but only one place remained unwashed with water - the heel by which she held him (the same Achilles heel). TETIS asked Hephaestus to forge wonderful armor in which his son was invulnerable. In this armor, Achilles was impossible to defeat. Only the revenge of the god Apollo himself, who directed the arrow precisely at the vulnerable heel, interrupted the life of the greatest hero of the Trojan War.
According to legend, Thetis took the soul of Achilles to the island of Levka, where one can sometimes hear the powerful voice of the hero.
But, surprisingly, we find evidence from ancient authors that Hercules not only “raised the Pillars” on the shores of Spain and Africa, but also separated the continents, creating the Strait of Gibraltar. “... Then follows the very high mountain of Abila, directly opposite which another mountain rises on the Spanish coast - Calpe. Both mountains are called the Pillars of Hercules, according to Pomponius Mela. - According to legend, these mountains were once connected by a continuous ridge, but Hercules separated them and the ocean, which until then was held back by the dam of this ridge, flooded the territory that now forms the Mediterranean basin. East of the Pillars of Hercules, the sea becomes wider and pushes the land with great force.
Pliny the Elder, starting the sixth book of his Natural History, believes that not the legendary Hercules, but the very real ocean could “break through the washed-out mountains and, tearing Calpe from Africa, absorb much more land than it left.” According to Eratosthenes, a mathematician and geographer, with amazing accuracy in the 3rd century BC. e. which determined the diameter of our planet, “at the time of the Trojan War there was still no rupture of the mainland at the Pillars of Hercules, and therefore the outer sea at the isthmus between the Egyptian Sea and the Arabian Gulf was on the same level as the inner one and, being higher than the isthmus, covered the latter, and after that, as a breakthrough at the Pillars of Hercules (Gadir) took place, the inland sea dropped and exposed the land that is near Kasia and Pelusium to the Red Sea.
An echo of these ideas are the stories of Arab geographers, heirs of ancient traditions, according to which there was a land bridge between Africa and Europe, and if some authors considered it a creation of nature, others attributed the creation of this bridge to people. “Between Andalusia and Tangier there once existed in a place called Hadra, which is near Fars el-Maghrib (Fez), a bridge that was made up of large stones and along which herds passed from the western coast of Andalusia to the northern coast of Africa,” reports an Arab geographer. X century" Masudi. - The sea penetrated freely through the gorges of this huge bridge, making up several channels. From here began the Mediterranean Sea, flowing from the ocean, or the Great Sea. However, for centuries, the sea, constantly; leaning on the shore, took possession of the lands so that every generation of people noticed the constant decline of the shores, ”and finally broke the dam. “The memory of this dam: preserved among the inhabitants of Andalusia and Fetz. Navigators even indicated the place where it existed. She was 12 miles long. Its width and elevation were quite significant,” concludes Masudi. According to another Arab geographer, Ibn Yakut, the mythical king Darokut, who ruled Egypt, "in defense of the Greeks, spilled the Atlantic Ocean into the Mediterranean Sea in order to protect Egypt from Greece."
Of course, the exploits of Hercules, and the deeds of Darokut, and the bridge between Europe and Africa, along which cattle were driven, belong to the field of mythology. But, surprisingly, research recent years showed that the Strait of Gibraltar really once did not exist and the Mediterranean Sea did not connect with the Atlantic Ocean. Moreover, at one time the sea itself did not exist: having lost its connection with the waters of the Atlantic, it dried up and turned into salt lakes, lagoons, swamps ... However, we will tell more about the history of the Mediterranean Sea in the light of the latest data from Earth sciences in the next chapter.
Part five:
Tethys seas
“Tetia (Tythia, Tethys, Tethys) is a titanide, daughter of Uranus and Gaia, sister and wife of the Ocean, mother of streams and oceanids. Tethys was considered the goddess who gives life to everything that exists - the universal mother ... In geology, the name Tethys is assigned to the ancient ocean, the remnants of which are the Mediterranean, Black and Caspian Seas.
"Mythological Dictionary"
What is the Tethys Sea?
The Mediterranean basin became the cradle of European civilization. The history of the Mediterranean Sea, according to many scientists, can also become the "key" to the history of our planet, to the history of the origin of the continents and oceans. A lot of hypotheses trying to explain the geological evolution of the Earth have been put forward over the past centuries. In principle, they can be divided into two groups. The first combines hypotheses that explain the history of the Earth by vertical movements of the crust - the uplifting of mountains, the failures of oceanic depressions, the formation of continents in place of deep seas, or, conversely, the "oceanization" of the continental crust. The second group, in addition to these vertical movements of the crust, also suggests horizontal ones, caused by the drift of the continents, the expansion of the Earth, etc.
The most venerable age is the hypothesis according to which our planet was originally dressed in continental pores. The oceans arose at the site of the sinking of the ancient continents - the Atlantic where Atlantis used to be, the Pacific - on the site of the "Pacific Atlantis", or Pacifida, the Indian - on the site of Lemuria. The Mediterranean Sea, according to supporters of this hypothesis, is also generated by the failure of the earth's crust: the Aegean and Tyrrenida became the bottom of the sea, the Balearic Islands, Malta, and Cyprus are the fragments of the former land. In a word, the area of the Mediterranean Sea is the area of the underdeveloped ocean, which divided Europe and Africa, which previously constituted a single ancient continent.
Over a hundred years ago, the largest American geologist J. Dana put forward a diametrically opposite hypothesis: not the continents, but the oceans are the primary, initial formation. The entire planet was covered by an oceanic-type crust, which was formed even before the formation of the atmosphere. "An ocean is always an ocean," was Dan's thesis. Its modern formulation is: "The great oceanic basins are a permanent feature of the earth's surface, and they have existed where they are now, from minor changes outlines since the waters first arose." The evolution of the earth's crust is a steady increase in the area of the continents and a reduction in the area of the oceans. The Mediterranean Sea is the remnant of the ancient Tethys Ocean, which separated Europe and North Asia from Africa, Hindustan and Indochina tens of millions of years ago.
The sea - or ocean - Tethys is given a large place in the constructions of mobilists - supporters of the hypothesis of continental drift. At the end of the Paleozoic, about 200 million years ago, as the creator of this hypothesis suggested, the remarkable German scientist Alfred Wegener, a single land mass, Pangea, surrounded by the Pacific Ocean, split into two supercontinents: northern - Laurasia and southern - Gondwana. The “gap” between these supercontinents, steadily expanding, gave rise to the Tethys Sea, a kind of bay of a single pra-ocean or all-ocean (Pantalassa) that embraced the entire planet. Then the split of Laurasia and Gondwana into separate continents began, the movement of continental plates became more complicated. As Europe, North America, India, Africa, Australia, Antarctica "dispersed", the Atlantic, Indian, Arctic oceans were formed - and at the same time the area of the Tethys Sea was reduced. The majestic Alps of the Caucasus, the Pamirs, the Himalayan mountains, which were once the bottom of the Tethys, rose. And from the Tethys Sea itself, only the Mediterranean and the Black Sea associated with it remained.
Proponents of the continental drift hypothesis in its modern version It is believed that the Mediterranean Sea arose as a result of the "spreading" of the seabed (the so-called spreading) in a dynamic band between the continental plates of Europe and Africa. Scientists who believe that the main cause of continental drift is the expansion of the Earth, which began hundreds of millions of years ago - they also belong to the mobilists - believe that the Mediterranean Sea is also generated by this expansion.
What happened before the collapse of Pangea, surrounded by Panthalasse, began? This question has been asked by both supporters and opponents of the continental drift hypothesis. Does the history of the face of the Earth cover only some 200 million years, when, according to the mobilists, the Tethys Sea split the single land into Laurasia and Gondwana? The Soviet geologists L. P. Zonenshain and A. M. Gorodnitsky tried to draw, from the standpoint of mobilism, a picture of the changes that have taken place on our planet over the past half a billion years. In the Cambrian period, beginning the "ancient era of life" - the Paleozoic, a single supercontinent Gondwana, the European, Siberian, Chinese and North American paleocontinents were separated by paleooceans - the Paleoatlantic and Paleoasian. In the next period, the Ordovician, which began about 480 million years ago, the Siberian and Chinese paleocontinents moved, the southern part of the Paleo-Atlantic Ocean closed, but a new ocean formed - Paleotethys, which separated the northern continents from the eastern ones and from the Gondwana supercontinent, parts of which are present-day Africa, South America , Australia, India, Madagascar, Antarctica.