In the previous chapters, we discussed the reflection of geological structures in the relief and the influence of various types of tectonic movements on the relief, regardless of the time of manifestation of these movements. It has now been established that the main role in the formation of the main features of the modern relief of endogenous origin belongs to the so-called latest tectonic movements, by which researchers most often understand the movements that took place in the Neogene-Quaternary time. This is convincingly evidenced, for example, by a comparison of large relief features on a hypsometric map. former USSR and maps of recent tectonic movements in the same area (Fig. 12). Thus, areas with weakly pronounced vertical positive tectonic movements in the relief correspond to plains, low plateaus and plateaus with a thin cover of Quaternary deposits: the East European Plain, a significant part of the West Siberian Plain, the Ustyurt Plateau, the Central Siberian Plateau.
Areas of intense tectonic subsidence, as a rule, correspond to low-lying plains with a thick layer of sediments.
Rice. 12. Scheme of the latest (Neogene-Quaternary) tectonic movements on the territory of the former USSR (according to N.I. Nikolaev, greatly simplified):
1 - areas of very weakly expressed positive movements; 2 - areas of weakly expressed linear positive movements; 3 - areas of intense arched uplifts; 4 - areas of weakly expressed linear uplifts and subsidences; 5 - areas of intense linear uplifts with large (a) and significant (b) gradients of vertical movements; 6 - areas of emerging (a) and prevailing (b) subsidence; 7 - area border strong earthquakes(7 points or more); 8 - boundary of manifestation of Neogene-Quaternary volcanism; 9 - the border of the distribution of existing
volcanoes
Neogene-Quaternary age: the Caspian lowland, a significant part of the Turan lowland, the northern part of the West Siberian Plain, the Kolyma lowland, etc. Mountains correspond to areas of intense, predominantly positive tectonic movements: the Caucasus, Pamir, Tien Shan, the mountains of the Baikal and Transbaikalia, etc.
Consequently, the relief-forming role of the latest tectonic movements manifested itself, first of all, in the deformation of the topographic surface, in the creation of positive and negative forms reliefs of different order. Through the differentiation of the topographic surface, the latest tectonic movements “control” the location on the Earth's surface of areas of removal and accumulation and, as a consequence, areas with a predominance of denudation (worked out) and accumulative relief. The speed, amplitude and contrast of the latest movements significantly affect the intensity of manifestation of exogenous processes and are also reflected in the morphology and morphometry of the relief.
The expression of geological structures in the modern relief depends on the type and nature of neotectonic movements, the lithology of the rocks that compose them, and specific physical and geographical conditions. Some structures are directly reflected in the relief, in the place of others an inverted relief is formed (as mentioned above), in the place of the third - various types of transitional forms from direct to inverted relief. The variety of relationships between relief and geological structures is especially characteristic of small structures; large structures, as a rule, find direct expression in the relief.
Landforms of the earth's surface, in the formation of which the main role belongs to endogenous processes and in the morphology of which geological structures are clearly reflected, are called morphostructures. This concept was introduced in 1946 by I.P. Gerasimov. However, until now, there is no consensus among researchers in the interpretation of the concept of “morphostructure”, neither in relation to the scale of forms, nor in relation to the nature of the correspondence between the structure and its expression in relief. Some researchers understand by morphostructures both direct and inverted, and any other relief that has arisen at the site of a geological structure, while others understand only direct relief. Some researchers classify only active geological structures as morphostructures, while prepared, passive structures are called lithomorphostructures.
The data currently available to geology and geomorphology indicate that the earth's crust is undergoing deformations almost everywhere and of a different nature. So, at present, the territory of Fennoscandia and a significant part of the territory of North America, adjacent to the Hudson Bay, are experiencing uplift. The uplift rates of these territories are very significant. In Fennoscandia, immediately after the melting of the glacier, they were 10–13 cm/year, at present they are about 10 mm/year (sea level marks made in the 18th century on the shores of the Gulf of Bothnia are raised above the present level by 1.5–2, 0 m) (Fig. 13). The shores of the North Sea within Holland and its neighboring areas are sinking, forcing residents to build dams to protect the territory from the onset of the sea.
Intense tectonic movements are experienced by areas of Alpine folding and modern geosynclinal belts. According to available data, the Alps, the Himalayas and the Pamirs for the Neogene-Thursday 
Rice. 13. Glacioisostatic uplift of the Baltic Shield after the disappearance of the last ice sheet (according to N. I. Nikolaev):
1 - isohypses (m); 2 - border of the Caledonides; 3 - border of the Baltic shield
vertical time has risen several kilometers. Against the background of uplifts, some areas within the areas of Alpine folding experience intense subsidence. Thus, against the background of the uplift of the Greater and Lesser Caucasus, the Kura-Araks lowland enclosed between them experiences intense subsidence. Evidence of the multidirectional movements existing here is the position of the coastlines of the ancient seas, the predecessors of the modern Caspian Sea. Coastal sediments of one of these seas - late Baku, the level of which is located at an absolute height of 10-12 m, are currently traced within the southeastern periclinal of the Greater Caucasus and on the slopes of the Talysh Mountains at absolute elevations of +300 and +200 m, respectively, and in within the Kura-Araks lowland, they were opened by wells at absolute elevations of -250-300 m.
The manifestation of neotectonic movements can be judged by numerous and very diverse geomorphological features: 1) the presence of sea and river terraces, the formation of which is not associated with the impact of climate change or any other reasons; 2) deformations of sea and river terraces and ancient surfaces of denudation alignment; 3) deeply submerged or highly elevated coral reefs; 4) flooded marine coastal forms and some underwater karst sources, the position of which cannot be explained by eustatic fluctuations in the level of the World Ocean or other causes; 5) antecedent valleys, formed as a result of sawing by the river that occurs on it 
paths of tectonic elevation - an anticline fold or an uplifting block formed by faults (Fig. 14).
Rice. 14. Antecedent through gorges of the branches of the river. Gerdymanchay in the eastern end of the Karamaryan ridge (Azerbaijan, according to V.A. Grossheim)
The manifestation of neotectonic movements can also be judged by a number of indirect signs. Fluvial landforms are sensitive to them. Thus, areas experiencing tectonic uplifts are usually characterized by an increase in the density and depth of erosional dissection compared to areas that are tectonically stable or experiencing subsidence. In such areas, the morphological appearance of erosional forms also changes: valleys usually become narrower, slopes become steeper, there is a change in the longitudinal profile of rivers and sharp changes in the direction of their flow in plan, which cannot be explained by other reasons, etc. All these (and a number of other) signs make it possible to use the geomorphological method to identify positive tectonic structures, in particular, when searching for oil and gas fields.
Depending on the ratio of the velocities of tectonic movements (T) and denudation processes (D), the relief can develop according to an ascending or descending type. If T gt; D, the relief develops according to an ascending type. In this case, the absolute heights of the territory experiencing uplifts increase, which
stimulates intensification of deep erosion of permanent and temporary streams and leads to an increase in relative heights. River valleys such as gorges, gorges and canyons are formed, characterized by steep or even steep slopes, which, in turn, leads to intensive development landslide (under favorable hydrogeological conditions) and landslide-scree processes. Due to the sharp predominance of deep erosion over lateral erosion, floodplains and river terraces are poorly developed or completely absent in river valleys. The longitudinal profiles of the rivers are characterized by large slopes and underdevelopment: more or less gentle slopes at the outcrops of easily eroded rocks alternate with rapids and ledges at the outcrops of rocks resistant to erosion. Increasing the intensity of denudation processes contributes to the rapid removal of loose products of destruction of rocks, resulting in a good exposure of “fresh” rocks that have not yet been destroyed, preparation of more resistant rocks and, as a result, a clear reflection of geological structures in the relief (structurality of the relief), especially under conditions arid climate. An increase in absolute heights, length and steepness of slopes leads not only to the intensification of previously existing relief-forming processes, but also to the emergence of new ones: snow avalanches and mudflows, and when the territory rises above the climatic snow boundary, to processes associated with the activity of ice and snow. As a result, a new type of relief is formed in the upper part of the mountains - alpine, the characteristics of which were given above. Thus, a change in quantitative characteristics - an increase in absolute and relative heights, length and steepness of slopes - leads to qualitative changes in the entire complex of relief-forming processes. These changes are also reflected in the territories adjacent to the rising mountains: here the nature of correlated deposits changes. As mountains grow, the amount and size of detrital material carried by permanent and temporary watercourses increase.
If Tlt; D, the process of relief formation develops in the opposite direction: the absolute and relative heights decrease, the slopes flatten, the river valleys expand, alluvium begins to accumulate at their bottom, the longitudinal profiles of the rivers level out and become more gentle, the intensity of erosion and slope processes decreases. When the mountains decrease below the snow line, the relief-forming activity of snow and ice stops. Accumulation of clastic material at the bottom of erosional forms and slopes leads to shading of the structure.
roughness of the relief, a decrease in the area of outcrop of fresh rocks. The peaks and crests of the ridges take on rounded outlines. All this leads to a decrease in the amount of clastic material carried out and its fineness.
The noted relationship between the change in relief-forming processes in the territories experiencing uplift and the nature of correlated deposits accumulating in the area of subsidence makes it possible to use correlated deposits for paleogeographic reconstructions: determining the intensity of tectonic movements of past geological epochs, the location of demolition areas, determining the age of manifestation of tectonic movements and the formation of denudation relief. That is why geomorphologists study not only the relief itself, but also the rocks that make it up, in particular the correlated deposits.
Thus, there is a close relationship between the nature and intensity of recent tectonic movements, the morphology of the relief at different stages of its development, and correlated deposits. This connection allows the wide use of geomorphological methods in the study of neotectonic movements and the geological structure of the earth's crust.
In addition to the latest tectonic movements, there are so-called modern movements, which are understood as movements that have manifested themselves in historical time and are manifesting now. The existence of such movements is evidenced by many historical and archaeological data, as well as data from repeated leveling. The high speeds of these movements noted in a number of cases (up to 10 cm per year or more) dictate the need to take them into account in the construction of long-term structures - canals, oil and gas pipelines, railways and etc.
To describe the whole variety of reality, any language needs an expression duration, intensity and direction. For SAE and many others language systems characteristic description of these concepts metaphorically. The metaphors used in this case are metaphors of spatial extension, i.e. size, number (plurality), position, form and movement. We express duration, in words: long "long", short "short". great "big", much "a lot", quick "fast", slow "slow", etc., intensity- words: large "big", much "many", heavy "heavy", light "easy", high "high", 1ow "low", sharp "sharp", faint "weak", etc.; orientation- in words: can "more", increase "increase", grow "grow", turn "turn", get "become", approach "approach", go "go", come "come", rise "rise", fall " fall", stop "stop", smooth "smooth", even "smooth" , rapid "fast", slow "slow", etc. One could make an almost endless list of metaphors that we are hardly aware of as such, since they are practically the only linguistic means available. Non-metaphorical means of expressing these concepts, as well as eagle "early", late "late", soon "soon", lastilig "long", intense "tense", very "very", are so few that they can in no way be sufficient.
It is clear how this situation came about. It is part of our whole system - objectification - mental representation of qualities and potencies as spatial, although they are not actually spatial (as far as it is felt by our senses). The meaning of nouns (in SAE), starting from the names of physical bodies, leads to designations of a completely different nature. And since physical bodies and their form in visible space are denoted by terms related to shape and size, and are calculated by various kinds of numerals, then such methods of designation and calculation turn into symbols that are devoid of spatial significance and presuppose an imaginary space. physical phenomena: move "move", stop "stop", rise "rise", sink "fall", approach "approach", etc. - in the visible, in our opinion, they fully correspond to their designations in the mental space. It has gone so far that we constantly turn to metaphors, even when we are talking about the simplest non-spatial situations. I "grab" the "thread" of my interlocutor's reasoning, but if their "level" is too "high", my attention may "scatter" and "lose connection" with their "flow", so that when he "fits" to the final " point", we are already "widely" separated and our "views" are so "spaced" from each other that the "things" he speaks of "appear" to be "very" conventional or even a "heap" of nonsense.
The complete absence of this kind of metaphor in the Hopi is striking. The use of words expressing spatial relationships, when there really are no such relations, it is simply impossible in the Hopi, in this case, they are, as it were, imposed an absolute ban. This becomes clear when one considers that there are numerous grammatical and lexical means to describe duration, intensity and direction as such, and the grammatical laws in it are not adapted to draw analogies with a conceivable space. Numerous kinds of verbs express duration and focus one or the other action, while some forms pledges express the intensity, direction and duration of causes and factors that invoke these actions. Further, the special part of speech intensifier(thetensors) - the most numerous class of words - expresses only intensity, direction, duration and sequence. The main function of this part of speech is to express the degree of intensity, "strength", as well as the state in which they are and how they change: thus, general concept intensity, considered from the point of view of constant change, on the one hand, and continuity, on the other, also includes the concepts of direction and duration. These special temporal forms - intensifiers - indicate differences in degree, speed, continuity, repetition, increase and decrease in intensity, direct sequence, sequence interrupted by some time interval, etc., as well as quality tension, which we would express metaphorically through such words as smooth "smooth", even "smooth", hard "hard", rough "rough". What is striking is the complete absence in these forms of similarity with words expressing the real relations of space and movement, which for us mean the same thing. There are almost no traces of direct derivation from spatial terms in them.
Thus, although Hopi seems to be an extremely concrete language when considering the forms of its nouns, in the forms of intensifiers it reaches such an abstraction that it almost exceeds our understanding.
The main role in the formation of the main features of the modern relief of endogenous origin belongs to latest tectonic movements, which refers to the movements that took place in the Neogene-Quaternary time, and created the observed relief.
1) So areas with mild“+” tectonic movements in the relief correspond to plains, low plateaus and plateaus with a thin cover of Quaternary deposits: West Siberian Plain, Ustyurt Plateau, Central Siberian Plateau.
2) Regions intensive tectonic subsidence, as a rule, correspond to low-lying plains with a thick layer of sediments of the Neogene-Quaternary age: Caspian lowland.
3) Regions intensive, predominantly “+” tectonic movements correspond to the mountains: the Caucasus, the Pamirs, the Tien Shan.
Consequently, the relief-forming role of the latest tectonic movements manifested itself primarily in the deformation of the surface, in the creation of “ + " And " - ” landforms of different orders. Through the differentiation of the topographic surface, new tectonic movements control the location on the surface of the earth of areas of demolition and accumulation, and as a result of this, areas with a predominance of denudation (worked out) and accumulative relief. The speed, amplitude and contrast of the latest movements significantly affect the intensity of manifestation of exogenous processes and are also reflected in the relief morphometry.
The type of modern relief of geological structures depends on the type and nature of neotectonic movements, the lithology of the rock that composes them, and the physical and geographical conditions. Some structures are found direct reflection in the relief, in place of others are formed inverted relief, in place of the third - various types transitional forms from direct relief to converted. The variety of relationships between relief and geological structures is especially characteristic of small structures; large structures, as a rule, find direct expression in the relief.
In to modern times high mountains there was practically no, since there was no activation. The analysis of the latest movements is based on the relief. Geomorphological methods for studying the latest relief. The current method is to study the deformation of the geomorphological levels of the alignment surface. Example: there is a tectonic deformation and different parts have risen/sinked to different heights. By studying the skew of the terrace, it is possible to identify isostatic movement.
Depending on the ratio of the rates of tectonic movements (T) and denudation processes (D) terrain can develop by ascending type and descending type:
1) If T > D, the relief develops along ascending type. In this case, the absolute territories experiencing uplifts increase.
2) If T< Д, рельеф развивается по descending type. The absolute and relative heights decrease, the slope flattens out.
End of work -
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All topics in this section:
Subject of geomorphology
Geomorphology as an independent science
Geomorphology is the science of the structure, origin, history and modern dynamics of the relief of the earth's surface → the object of study of geomorphology is the relief. Those. totality
Relationships with other sciences
The relief is the interface and the interaction surface of various shells the globe(lithosphere, atmosphere, hydrosphere and biosphere). Therefore, the most fruitful study of the relief and
The place and significance of the doctrine of the morphology of the relief of the earth's surface in geomorphology. Morphodynamic concept
Geomorphology studies: 1) Appearance (description). 2) Genesis. 3) History of development. 4) Dynamics. Geomorphology, like other sciences,
Discreteness and continuity
The relief is a discrete formation - discontinuous. Those. consists and
morphological system. Systematics of elements of the earth's surface
The systematics of relief elements is a formalized model that universally reflects the relief of the earth's surface. It considers the relief as a whole, i.e. without relativity. And all his
By relative altitude
A) at the top. L1.0. b) on the slopes. L5.6. B) at the bottom. L2.0. The upper layers are initial - they are being demolished. They supply material - L1,0. Slope elements - transi
Selection and reflection of elements of the earth's surface on static geomorphological models
The value of breaklines and elementary surfaces. The value of points is not large, lines and elementary surfaces are important. The elementary surface is a certain relative
Analysis of the vertical position of elements and forms of the earth's surface
Planetary mega and macro forms differ not only in the size of the area, but also in p
Morphometric studies in geomorphology
Often considered as part of morphological analysis. At this stage of studying the relief, only the collection of facts takes place. Differences between morphometric and morphological
Meaning
Morphometric and Morphological characteristics relief are of great practical importance. Without knowledge of these characteristics, the construction of buildings, the laying of railways and highways is unthinkable.
relief genesis. Endogenous and exogenous processes
The main starting point of modern geomorphology is the idea that the relief is formed as a result of the interaction of endogenous and exogenous
The age of the relief and its definition
An important task of geomorphology is to determine the age of the relief. Determination of relief - determination of the age of the form as a whole, when it acquired these features to this day
The idea of morphostructures morphosculptures
Introduced into use in the middle of the last century by Academician Gerasimov. Now this term is used by geographers and soil scientists.
Tectonic movements and their relief-forming role
Endogenous processes cause various types of tectonic movements and related deformations of the earth's crust. They are the cause of earthquakes, intrusive and effusive ma
Folded (plicative) tectonic dislocations and their manifestation in the relief
The elementary types of folds, regardless of origin, are anticlines and synclines. In the simplest case, anticlines
Discontinuous (disjunctive) tectonic dislocations and their manifestation in the relief
Discontinuities (disjunctive dislocations) are various tectonic discontinuities in rocks, often accompanied by movement
Deep ruptures (up to the upper mantle)
The largest faults, extending to a great depth, up to the upper mantle and having a significant depth and width, are called deep faults. deep times
The main structural elements of the earth's crust and lithosphere and planetary landforms
The largest landforms - planetary - owe their origin to the internal forces of the earth, which underlie the formation of various types of earth
Plate tectonics
Different researchers distinguish different types of tectonic movements. Summing up modern ideas about tectogenesis, two types of tectonic
Continents. The main regularities of their geological structure and relief
Mainland (continent), a large massif of the earth's crust, most of which protrudes above the level of the World Ocean, and the periphery is below its level (see Underwater
Structure
Structure
Platforms are one of the main deep structures of the earth's crust, characterized by low intensity of tectonic movements, magmatic activity and flat relief. Platforms opposed
Mega-relief of mobile belts of continents (orogens)
There are two types of mobile belts of continents: 1) Epigeosynclinal - represented by mountainous landforms formed in alpine
Understanding geosynclines
Within the continents, relatively stable (more stable) areas are distinguished, called platforms, and areas (belts),
Megarelief of intracontinental geosynclinal belts
Geosyncline - (geosynclinal belt), long (tens and hundreds of kilometers) relatively narrow and deep trough of the earth's crust that occurs at the bottom of the m
Mega-relief of epiplatform mountain belts
Platforms are the main elements of the structure of the continents, which, unlike geosynclines, are characterized by a calmer tectonic regime, less intensity of magma manifestation.
Megarelief of transitional zones of active type (marginal continental geosynclinal belts)
By modern transitional or geosynclinal regions, we mean areas of modern mountain building occurring at the junction of continents and oceans.
Mega-relief of the underwater margins of the continents (transitional zones of the passive type)
The underwater margin of the mainland is the peripheral part of the mainland, covered by the waters of the ocean and representing, in terms of geological structure and relief, a continuation of the adjacent
Mega-relief of the ocean floor
The ocean floor is characterized by the oceanic type of the earth's crust, which is characterized by low thickness (5–10 km) and the absence of a granite layer. The bed of the ocean corresponds structurally to the ocean
Hilly abyssal plain
They are developed in all oceans. Hilly less leveled. The height of the hills is ≈ hundreds of meters. Most likely - these are former volcanoes. Hilly plains dominate pacific ocean, and flat ones - in the Atlantic
Relief of mid-ocean ridges
Mid-ocean ridges are morphologically
Ideas about the geomorphological stage in the geological history of the earth
This concept was introduced by Gerasimov. I) The latest stage - 30 million years - in established forms. II) Geomorphological
It consists of 3 macrocycles
1) Mesozoic, early Mesozoic. Laurasia and Gondwana united into a single mainland - Pangea. There was a global leveling surface - the Mesozoic peneplain (t
Representation of alignment surfaces. Genesis of alignment surfaces
Leveling surface - leveled surfaces (in the mountains and on the plains) of various genesis (denudation and accumulative) formed under conditions
William Davis proposed the implementation of the cycle in different conditions
a) Erosive (fluvial). b) Arid (high temperature, and low rainfall). c) Glacial (glacier) 1) Davis also suggested
Fluvial processes and landforms. Temporary watercourses and the landforms they create
Surface flowing water is one of critical factors transformation of the earth's relief. The totality of geomorphological processes carried out by flowing waters, floor
Fluvial processes and landforms. Permanent streams (rivers) and the landforms they create
Surface flowing water is one of the most important factors in the transformation of the Earth's relief. The set of geomorphological processes carried out by the current
Morphological types of river valleys. Valley asymmetry
The morphology of river valleys is determined by the geological and physiographic conditions of the area crossed by the river, the history of the development of the valley. Valleys according to the morphology of the transverse profile
Valley (river network). Determining the orders of valleys (rivers)
The collection of river valleys within a certain territory is called a river or valley network. Set of watercourses
Glacial processes and landforms. Forms of mountain-glacial relief
Glacial relief-forming processes are due to the activity of ice. A prerequisite for the development of such processes is glaciation, i.e. prolonged
Ice Formation Methods
Forms of mountain-glacial relief
The formation of a mountain glacier begins with the formation of a snow patch or firn spot. There is a process of nivation or destruction of the slope under the influence of snow and ice, accompanied by the removal
Glacial processes and landforms.
Glacial relief-forming processes are due to the activity of ice. A prerequisite for the development of such processes is glaciation, i.e. long existence m
Ice Formation Methods
1) Frozen water (land or ocean). 2) Metamorphization of snow (snow turns into firn, and then into glacier ice). Glacier - time-stable accumulation
Integumentary glaciation and landforms
Integumentary glaciers, unlike mountain glaciers, occupy entire islands and continents. Due to the large thickness of more than 3-4 km, their distribution and the nature of the surface of the subglacial relay
Relief of areas of cover Quaternary glaciation
There are 2 types of glacier: 1) Mountain. It occupies negative relief elements in the mountains. Ice movement is driven by
Integumentary glaciation and landforms
Integumentary glaciers, unlike mountain glaciers, occupy entire islands and continents.
Slopes and slope processes
Slope - (an area of the earth's surface with a slope > 2o), an area of the earth's surface with a slope, the magnitude of which is large enough to determine
Karst and karst landforms
Karst is a combination of special landforms and features of surface and underground hydrography, characteristic of some areas composed of dissolved rock formations.
Surface karst landforms
1) After rain, melt water, flowing down the surface of the limestone, corrodes the walls and cracks. As a result, a microrelief of carr and shratt is formed, -
underground karst
A karst cave is an established landform associated with underground activities.
Tectonic movements are one of the most important factors in the development of geological processes that change the face of the Earth. They lead to the transformation of the earth's crust, change the forms of the surface relief, the outlines of land and sea, thereby affecting the climate.
Tectonic movements affect volcanism, sedimentation processes and determine the distribution of minerals in the earth's crust.
Tectonic movements are expressed in the form of slow ups and downs, leading to transgressions and regressions of the sea in the form of a general collapse of the earth's crust with the formation of high
mountain ranges and deep depressions, the formation of folds, as well as in the form of destructive earthquakes, which are accompanied by the appearance of cracks with a significant displacement of crustal blocks vertically and horizontally.
Depending on the direction of stress, tectonic movements are divided into vertical (radial) and horizontal (tangential) movements. In the analysis of vertical movements, ascending (positive) and descending (negative) movements are distinguished. These movements often correspond to slow, smooth ups and downs, covering the territories of continents and oceanic depressions or their parts. These are epeirogenic movements (Greek "epeiros" - mainland).
Tangential movements (tangential to the surface of the earth's crust) are associated with certain zones and lead to significant deformations of the earth's crust. These are orogenic movements (Greek "oros" - mountain).
Tectonic movements and the resulting structures of the earth's crust are studied by geotectonics and structural geology.
To restore the tectonic movements of past eras, special methods are used to recreate the overall picture of tectonic movements for a particular era.
We judge the nature of modern tectonic movements by observing modern processes, which are clearly manifested in areas of active earthquakes and volcanism: 1) modern vertical tectonic movements are fixed by repeated leveling; 2) the latest movements, i.e. that occurred in the Neogene-Quaternary time, are studied using geomorphological methods, analyzing the topography of the Earth's surface, the morphology of river valleys, the location of sea terraces, and the thickness of Quaternary deposits.
I, "It is much more difficult to study the tectonic movements of past geological epochs. The methods for studying these movements are: 1) analysis of the stratigraphic section; 2) analysis of lithological-paleogeographic maps; 3) analysis of thicknesses; 4) analysis of breaks and unconformities; 5) structural analysis, 6) paleomagnetic analysis, 7) formational analysis.
- The analysis of the stratigraphic section makes it possible to trace the tectonic movements
large area of the earth's crust for a long time. Starting material for analysis
is a stratigraphic section (column) that needs to be investigated from the standpoint of change
of the conditions of accumulation of rocks in their stratigraphic sequence.By studying the material composition, structural and textural features of rocks, and the fossils contained in them, it is possible to identify the types of deposits that accumulate on various hypsometric
levels relative to the water line of the sea basin and, accordingly, characterize the situation of sedimentation. Negative tectonic movements under conditions of stable removal of clastic material into the basin lead to a deepening of its bottom and a change up the section of shallow-water deposits by deeper ones. On the contrary, positive tectonic movements lead to the shallowing of the basin and the replacement of deep-water sediments along the section by shallow-water, terrestrial ones and further erosion of previously accumulated sediments. Negative tectonic movements contribute to the development of marine transgressions, while positive ones cause regression.
2) Lithological-paleogeographical analysis. Analysis of lithological-paleogeographic maps makes it possible to judge the direction of movements and the distribution of troughs and uplifts in the area. Usually
areas of accumulation of sediments correspond to a negative structure, areas of denudation - put
body. Due to the differentiation of movements against the background of a large negative structure, areas of relative uplifts with marine shallow-water deposits can be distinguished among deeper ones. Such a site is an underwater uplift - shallow and may correspond to a growing anticline structure. Distribution area relatively deep-sea
sediments among shallow waters should correspond to a depression at the bottom of the basin.Usually, the nature of tectonic movements is more clearly revealed in the analysis of lithological-paleogeographic maps compiled for several successive periods of time.
3) Power analysis. In areas of accelerated subsidence, precipitation of greater
power, in areas of slow deflection - less power, in areas of uplift -
powers are zero.Data on the thicknesses of deposits of the same age are put on maps; points of equal power are connected by lines - isopachs (Fig. 23). Maps with isopachs can be used to judge the distribution of areas of relative troughs and uplifts. However, the power analysis must be combined with the analysis of facies
Rice. 23. Map of equal thicknesses of a coeval sandy-argillaceous stratum (thickness contours indicate the position of a trough formed during sedimentation): / - measurement point and thickness (in m); 2 - power isolines (isopakhites). (Borrowed from G.I. Nemkov et al., 1986)
noah environment of sediment accumulation, tk. it is applicable only for certain conditions of sedimentation, when the rate of subsidence of the bed is compensated by the rate of accumulation on it
precipitation. In the case of a decompensated incision for huge periods of time,
a thin layer of sediment accumulates.
4) Analysis of breaks and disagreements. Positive tectonic movements in the stratigraphic section are expressed by the change of relatively deep-water deposits by shallow ones,
shallow water - coastal and continental. In this case, if these movements led to
rise of accumulated precipitation above sea level, their erosion begins. On the next dive New episode precipitation falls on a eroded surface, which is called the break surface or the unconformity surface. These surfaces are fixed by falling out of the normal sequence of certain stratigraphic units that are present.
where there were no positive developments. If deposits are above and below the surface,
fixing a break in sedimentation, occur with the same angles of inclination (stratigraphic unconformity), we can talk about slow positive movements that engulfed
large areas. If sharply different slope angles (angular unconformity) are observed, then the previously accumulated sediments experienced folding by the time of the new subsidence and sedimentation and could be broken by ruptures (Fig. 24). The depth of erosion of the underlying stratum and
the duration of the break in sedimentation indicates the amplitudes
Rice. Fig. 24. Stratigraphic (a) and angular (b) unconformity Sequence of events: a - accumulation of sediments of the lower member, uplift, erosion of the top of the lower member, subsidence, accumulation of sediments of the upper member; b - accumulation of sediments of the lower members, uplift, folding and movement of blocks along the fault, erosion, accumulation of sediments of the upper member (borrowed from G.I. Nemkov et al., 1986)
tectonic movements that led to disagreement between rock strata. The rock strata separated from the underlying and overlying deposits by the surfaces of angular unconformities are called structural floors. Each structural stage corresponds to a natural historical-tectonic stage in the development of the territory, which began with transgression and sedimentation during negative movements and ended with the rise of the territory and folding. Each structural floor is characterized by specific forms of layer occurrence.
5) Structural analysis is important in the study of horizontal movements,
as it allows to qualitatively and quantitatively estimate the magnitude of horizontal movements during
Rice. Fig. 25. Layer folded under lateral compression d is the length of the wing of the fold, w is the width of the fold, a is the angle of the fold (borrowed from G.I. Nemkov et al., 1986)
layer deformation time. If you mentally straighten a layer that is folded into folds formed during lateral compression, the length of such a straightened layer will correspond to the initial width of the deflection before the layer was deformed. The difference between the sum of the lengths of the wings of the folds and the sum of the widths of the same folds will be the value of the horizontal compression of the layer (Fig. 25). Using a graphical method or geometric formulas, it is possible to estimate the amplitude of horizontal movements that led to the formation of folds. For example, according to fig. 25, it can be seen that if the average fold angles are 60°, the horizontal contraction of the surface was twofold.
6) Paleomagnetic analysis. The ability of rocks to become magnetized during their
formations in accordance with the direction of the geomagnetic field and maintain this magnetization
allows not only to create a paleomagnetic geochronological scale, but also to use data from paleomagnetic analysis to identify horizontal tectonic movements. Having determined the average direction of the magnetization of rocks of a certain age, taken from any
point on the surface of the Earth, it is possible to calculate the position of the magnetic pole of that time in
coordinates. By examining the rocks in their stratigraphic sequence, the trajectory of the relative movement of the pole is drawn from the coordinates for the time corresponding to the studied interval of the stratigraphic section. Having done the same study on samples taken from another point, the trajectory of the movement of the pole relative to the point for the same period of time is drawn.
Rice. 26. Trajectory of movement North Pole relative to Europe and North America over the past 400 million years (borrowed from G.I. Nemkov et al., 1986)
If both trajectories coincide in shape, then both points have retained a constant position relative to the poles. If the trajectories do not coincide, then both points have changed their position relative to the pole in different ways. For example, the trajectories of the movement of the North Pole, calculated for the territory of North America and for Europe over the past 400 million years, are significantly different (Fig. 26). This allows us to draw a conclusion about the horizontal displacements of the continents at the specified time.
7) Formational analysis is a method of studying the structure and history of development
the earth's crust based on the study of the spatial relationships of rock associations -
geological formations.
A geological formation is a material category that occupies a certain position in the hierarchy of the matter of the earth's crust: chemical element- mineral - rock -geological formation - formational complex - shell of the earth's crust, -k Under formations is understood a set of facies that were formed on a more or less significant area of the earth's surface under certain tectonic and climatic conditions and differ from others in features of composition and structure. Separate facies can be formed in different parts of the earth's surface. However, their stable and long-term combinations, which allow them to be grouped into formations, occur only under strictly defined tectonic and climatic conditions. According to another definition, a geological formation can be called natural associations of rocks associated with the unity of the material composition and structure, due to the commonality of their origin (or co-location).
The term "formation" was introduced by the famous German geologist A.G. Werner back in the 18th century. long time before the beginning of the 20th century. it was used as a stratigraphic category, as suggested by the author. Until now, in the United States, the term "formation" is used to designate stratigraphic units. In our country, formational analysis has found wide application in connection with tectonic zoning and the prediction of minerals. The credit for its development belongs to many Russian scientists, in particular N.S. Shatsky, N.P. Kheraskov, V.E. Khain, V.I. Popov, N.B. Vassoevich, L.B. Rukhin and other researchers.
There are three types of formations: sedimentary, igneous and metamorphic. When studying formations, the main (obligatory) and secondary (optional) members of the association are distinguished. The main members of the association characterize a certain formation, i.e. stable association, repeating in space and time. The name of the formation is given by the name of the main members of the association. The set of minor members is subject to significant changes. Depending on the material composition, the types of formations are divided into groups. For example, among the sedimentary formations, groups of clay-shale, limestone, sulfate-halogen, siliceous, fine-clastic-quartz, fine-clastic polymictic, etc. can be distinguished; among volcanogenic - groups of basalt-diabase (trap), liparite-dacitic, andesitic formations, etc.
The main factors determining the formation of stable associations of sedimentary rocks are the tectonic regime and climate, and igneous and metamorphic rocks - the tectonic regime and thermodynamic environment.
The main features of sedimentary formations are: 1) a set of their constituent associations of the main rocks, which together correspond to facies or genetic types; 2) the nature of the interbedding of these rocks in a vertical section; rhythmic structure; 3) the shape of the body of the formation and its thickness; 4) the presence in it of some characteristic authigenic minerals, peculiar rocks or ores; 5) the predominant color, to some extent carrying genetic information; 6) the degree of diagenetic or metamorphic changes.
The names of sedimentary and sedimentary-volcanic formations are usually given according to the predominant lithological components (sandy-argillaceous, limestone, dolomitic, evaporite) with the simultaneous indication of the physical and geographical setting of the formation (marine, continental, limnic), often many formations are named according to the presence of accessory minerals (glauconite) or minerals (coal-bearing, bauxite-bearing).
The main factors that determine the appearance of sedimentary formations are the following: 1) the nature of the tectonic regime in the areas of erosion and accumulation; 2) climatic conditions; 3) intensity of volcanism. From the multiple combination of these conditions and rapid variability in space and time, an alternation of genetic types of rocks that make up the formations is created. The general distribution of formations on the earth's surface also depends on these factors.
Depending on the tectonic regime, three classes of formations are distinguished: platform, geosynclinal, orogenic. Most sedimentary formations can serve reliably
mi indicators of the tectonic regime. For example, formations of marl-chalk, kaolin
clays, quartz sandstones, clay-flask testify to the platform mode of sedimentation
co-accumulations, and sedimentary flysch, siliceous-carbonate, siliceous-shale, jasper
formations are indicators of the geosynclinal regime. The wide development of sedimentary groups
clastic formations indicates an orogenic regime.
An even more definite conclusion about tectonic regimes can be made on the basis of an analysis of igneous formations, if we keep in mind that a number of rocks: basic - medium - acid ~alkaline ones correspond to the sequence of development of magmatic eruptions when the geosynclinal regime changes to orogenic and then to platform.
The areas of distribution of certain formations are controlled by tectonic structures, the development of which determines the spatial limitation of formations. Therefore, by studying the patterns of distribution of formations in space, we thereby establish the placement of tectonic structures during the formation of formations. The evolution of the tectonic regime leads to a successive change in the context of geological formations. Having data on the conditions for the formation of rock complexes that change vertically, we can conclude that the tectonic regime has changed.
So, for example, if a thick layer of flysch formations with characteristic thin, regularly rhythmically interbedded layers of sandstones, siltstones and mudstones, is overlain by a layer of coarse clastic marine and continental deposits - molasses, it is concluded that geosynclinal conditions have been replaced by orogenic ones. This conclusion is based on existing ideas about the tectonic conditions for the accumulation of flysch and molasse formations.
Formation analysis makes it possible to classify tectonic structures, highlighting their special types, for example, types of troughs. The repetition of typical formations in spatially separated structures makes it possible to outline the general stages in the history of the tectonic development of structures, to compare sets of formations of structures similar in type different ages etc.
A special direction in the study and classification of sedimentary formations was the direction based on taking into account the content of industrial concentrations of certain types of minerals in them. On this basis, coal-bearing, salt-bearing, phosphorite-bearing, bauxite-bearing, iron ore, laterite, oil-bearing and a number of other formations are distinguished.
The sequence in studying and identifying formations is as follows. First, in the section, rock strata are identified that differ in lithological composition, separated by clearly defined bedding surfaces, breaks or erosion boundaries (stratigraphic break and unconformities). Then, a group of rocks (associations) that are part of the selected natural complex is studied, i.e. paragenetic analysis. At the same time, the cyclicity of the formation structure or other structural and textural features are determined and studied. Next, the facies nature of each rock type included in the formation and their combination in the section are clarified, i.e. facies analysis is carried out. On this basis, the genetic type of deposits is determined, and the physical-geographical (landscape) environment of formation formation is established. In the final phase of formational analysis, the climatic and tectonic regimes of time and places of formation formation are determined. Thus, paleoclimatic and formation-tectonic analyzes are carried out.
The theoretical significance of the study of sedimentary and sedimentary-volcanogenic formations lies in the possibility of reconstructing ancient tectonic, climatic and landscape zonality based on them. The practical significance of formational analysis is determined by the confinement to certain formations of the corresponding types of minerals.
Platforms are called relatively stable areas of the earth's crust. They develop on the site of consolidated folded structures that arose during the closure of geosynclines. These are vast, mostly flat areas of the earth's crust, often of irregular polygonal shape. This shape is determined by large marginal faults separating the platforms from adjacent mobile geosynclinal regions. Examples in Russia are the Russian (East European) and Siberian platforms. The platforms are characterized by the following features.
In the structure of the platform, two main structural tiers are distinguished - lower and upper. The lower stage was formed in the geosynclinal (pre-platform) stage of development and consists of highly deformed metamorphosed rocks penetrated by intrusions and deep faults. It is called the foundation, folded base or platform plinth. The upper tier is a sedimentary platform cover composed of calmly occurring sedimentary rocks. In some places, the foundation protrudes to the surface. Such sections of platforms are called shields. Platform sections on which the foundation is submerged to a depth and covered everywhere with a sedimentary cover are called slabs.
Relatively weak and slow small amplitude, vertical oscillatory movements of the earth's crust. At the same time, movements of the same sign - slow bending or slow lifting - capture large sections of the platforms and can change in time. Periodic transgressions and regressions of sea basins are associated with the oscillatory nature of tectonic movements in the development of platforms. Some parts of the platforms are still flooded by epicontinental seas - the Baltic, the North, etc.
Relatively small thickness of sedimentary rocks of the platform cover - usually up to 2-4 km, i.e., several times less than in geosynclinal areas, which changes gradually.
The composition of sedimentary rocks is more or less uniform. In the epicontinental platform seas, either carbonate rocks - limestones, dolomites, or shallow sandy-argillaceous deposits accumulate. From the minerals here, sedimentary iron and manganese ores, phosphorites, bauxites, etc. were formed in places. During periods of regression, continental deposits accumulated on the site of the former seas - lacustrine, alluvial, marsh, and in arid climate - eolian and lagoonal. The formation of iron ores (in swamps and lakes), coals and salts is associated with these stages of continental development.
Horizontal or almost horizontal occurrence of layers of sedimentary rocks, complicated in places by isolated gentle masonry (discontinuous folding). The largest structural elements of the platforms - syneclises - are huge gentle isometric depressions - troughs that occupy vast areas, reaching hundreds and even thousands of kilometers in diameter. They are distinguished by a very gentle fall of the layers - the first meters per kilometer, which corresponds to a tilt angle of several minutes. An example is the Moscow syneclise with a central part near Moscow. Its cross section (from north to south) reaches 1300 km, and the fall of the layers is 2-2.5 m/km. Large flat uplifts of platforms are called anteclises. An example of them are the Belarusian and Voronezh anteclises. In addition to syneclises and anteclises, within the platforms there are jelly-like tectonic depressions, linearly oriented and limited by deep faults, stretching for many hundreds of kilometers with a width of tens to 100-200 km. These depressions were named by N. S. Shatsky as aulacogenes (Greek "Avlakon" - a furrow). They show an increased tectonic activity, large thicknesses of sedimentary rocks (an example is the Dnieper-Donetsk depression). Of the smaller folded forms, shafts, brachifolds, domes, and flexures are developed.
