Geotectonics Lecture_Tectonics_Fualts.pptx

Lecture of Geotectonics

1. Definition "Geotectonics" refers to the scientific study of the Earth's structure in relation to tectonic processes. The word geotectonics is derived from two Greek words ge = earth , and tectonicon =to build. It consequently means literally the science of the Earth's structure, but such a defnition is too wide since it embraces, in essence, almost, the whole of geology. We need to give more precision to just what is the true content of geotectonics. Tectonics involves the deformation of the Earth's lithosphere (the rigid outer layer of the Earth) and the interactions between its major components, including the crust and upper mantle. Being a geological discipline, geotectonics is concerned with the structure, not of the whole Earth, but mainly of its crust. In truth, however, it is necessary, in order to understand the causes determining the observed structure of the crust and the patterns of the evolution of its structure, to investigate the globe's deeper lying envelopes as well, but we are then already outside the scope of geotectonics proper and are relying on the data of geophysics and geochemistry.

2. Geotectonics Dr. Dawod Salman Bannay Dr. Meelad Ali Hussein

3. Definition Geotectonics is a branch of geology dealing with the study of largescale structural or deformational features of the Earth’s crust and their relations , origin and historical evolution. Comparison Geotectonics and Structural Geology Tectonics and structural geology both deal with motion and deformation in the Earth’s crust and upper mantle. They differ in that tectonics is predominantly the study of the history of motion and deformation on a regional to global scale , whereas structural geology is predominantly the study of deformation in rocks at a scale ranging from sub-microscopic to regional . Geotectonics Structural Geology

4. Key concepts and features of geotectonics include: Overview: Understanding geotectonics is crucial for explaining the dynamic nature of the Earth's surface and the geological processes that have shaped and continue to shape the planet. Researchers and geologists use a variety of tools and techniques, including seismology, GPS measurements, and geological mapping, to study and monitor tectonic activity.

5. Geotectonics and its linkage with other Geological Branches Geotectonics is closely linked with several other branches of Earth science and geology, as it involves the study of the Earth's structure and the processes that shape its lithosphere. Some of the major disciplines that are interconnected with geotectonics include : 1- Geophysics : Geophysics involves the application of physics principles to study the Earth's physical properties . Techniques such as gravity and magnetic surveys, as well as seismic imaging , contribute to our understanding of the Earth's interior structure and tectonic processes . 2- Geochemistry: Geochemists study the chemical composition of rocks and minerals . The distribution of elements and isotopes can provide information about the origin and evolution of the Earth's crust , which is intimately tied to geotectonic processes .

6. Geotectonics and its linkage with other Geological Branches 3- Volcanology: Volcanology deals with the study of volcanoes, volcanic activity, and associated phenomena. Geotectonics is closely tied to the understanding of how and why volcanoes form at plate boundaries, and the movement of magma beneath the Earth's surface . 4 - Seismology: Seismology is the study of earthquakes and seismic waves . Since earthquakes are often associated with tectonic activity, seismologists play a crucial role in understanding the Earth's internal structure and the dynamics of plate interactions .

7. Geotectonics and its linkage with other Geological Branches 5 - Paleontology and Stratigraphy: The study of fossils and ancient life forms is often linked with geotectonics to understand how Earth's changing environments , driven by tectonic processes, have influenced the evolution and distribution of life over geological time . Stratigraphy the stratigraphic sequences is arrangement of layers that indicate whether or not they have been subjected to overturning or a change in direction. 6 . Hydrogeology : The study of groundwater and its interaction with geological formations is influenced by geotectonics. Tectonic activity can affect the distribution of aquifers, the movement of water, and the formation of geological structures that impact groundwater flow. 7. Geomorphology: Geomorphologists study the landforms and surface features of the Earth. Geotectonics influences the creation of various landforms, including mountains, valleys, and rifts, providing the foundation for many geomorphic processes.

8. Key concepts and features of geotectonics include: 1- Plate Tectonics: The Earth's lithosphere is divided into several large and rigid plates that float on the semi-fluid asthenosphere beneath them. These plates interact at their boundaries, leading to various geological phenomena such as earthquakes, volcanic activity, and the creation of mountain ranges. 2- Tectonic Boundaries: The interactions between tectonic plates occur at boundaries, which are classified into three main types: Divergent Boundaries: Plates move away from each other, often resulting in the formation of new oceanic crust. Convergent Boundaries: Plates move toward each other, leading to subduction (one plate moving beneath another) or collision and the formation of mountain ranges. Transform Boundaries: Plates slide past each other horizontally, causing earthquakes along fault lines. 3- Earthquakes and Volcanism: Geotectonics is closely associated with the occurrence of earthquakes and volcanic activity. These phenomena are often concentrated along plate boundaries.

9. Key concepts and features of geotectonics include: 4- Mountain Building: The collision and convergence of tectonic plates can lead to the formation of mountain ranges . The Himalayas , for example, were formed by the collision of the Indian and Eurasian plates. 5- Plate Motions: The movement of tectonic plates is driven by forces such as mantle convection , gravitational pull , and the sinking of dense oceanic crust into the mantle at subduction zones. 6- Geological Features: Geotectonics explains the distribution of various geological features on Earth's surface, including ocean basins , mountain belts, rift valleys, and mid-ocean ridges.

10. Theories in Earth Structure Recall that a “ hypothesis ” is simply a reasonable idea that has the potential to explain observations. A “ theory ” is an idea that has been rigorously tested and has not yet failed to explain relevant observations. Nevertheless, a theory could someday be proven wrong .

11. Theories in Earth Structure There are many theories that attempted to explain the structures found in the Earth's crust or lithosphere. The most prominent of these theories are : نظرية الانكماش (Contraction theory) نظرية الجيوسنكلاين الحوض الترسيبي القديم (Geosynclines theory) نظرية زحزحة القارات (Continental drift theory) نظرية تيارات الحمل الحراري ( Thermal convection currents) نظرية انتشار قاع المحيط (Sea floor spreading) نظرية الأطباق أو الصفائح التكتونية (Plate tectonics theory)

12. History 1830-1850 1860-1870 1915 1930-1944 1960 1965-1967

13. Theories in Earth Structure The first and second theories are no longer useful today, and they are considered part of the history of geological scientific knowledge. As for the third, fourth, and fifth theories, they were brought together and a lot of new knowledge and evidence was added to them, represented by paleomagnetism evidence, to create the sixth theory, which is considered the most accepted theory today in scientific circles.

14. Theories in Earth Structure Prior to the proposal of plate tectonics theory, most geologists had a “fixist” view of the Earth, in which continents were fixed in position through geologic time. In this context geologists viewed mountain building to be a consequence predominantly of vertical motions. Pre–plate tectonics ideas to explain mountain building included: (1) The contracting Earth hypothesis, which stated that mountains formed when the Earth cooled, shrank, and wrinkled, much like a baked apple removed from the oven ; (2) The geosyncline hypothesis, which stated that mountain belts formed out of the deep, elongate sedimentary basins (known as “geosynclines”) that formed along the margins of continents . According to this hypothesis, mountain building happened when the floor of a geosyncline sank deep enough for sediment to melt; the resulting magma rose and in the process deformed and metamorphosed surrounding rock. Both ideas have been thoroughly discredited .

15. Continental Drift Theory This theory, which was developed by the German scientist Alfred Wegener in 1914 , states that the Earth at its beginning was composed of a single large land mass or continent called Pangea , surrounded by a single ocean . With the passage of geological time, this mother continent was divided into smaller continents that began to move and move away from each other. Each other, and these continents have not taken a fixed position since the Earth was formed, as they have been moving continuously, but very slowly, from time immemorial until now. Wagner explained that this continent was divided into two continents: the large continent of Eurasia , which includes Europe , Asia , and North America to the north, and the large southern continent , Gondwanaland , which includes South America , Africa , the Arabian Peninsula , India , and Australia , and is separated by the ancient Mediterranean Sea (Tethys Sea). Alfred Wegener Overthinking

16. Strengths of the theory Evidences: 1- the fit between the Continents. (Matching rock types and Mountain Ranges) 2- Similarity of the Fossils Remains and Animals Classes. 3- Rock types that indicate ancient climate conditions distribution . 4- Evidence of ancient glacier movement

17. the fit between the Continents. (Matching rock types and Mountain Ranges) Similarity of the Fossils Remains and Animals Classes

18. Sandstones may be ancient sand dunes. Rock types that indicate ancient climate conditions distribution.

19. Map of ancient glacial movement, above, and glacial striations, indicating direction of glacial movement, right Evidence of ancient glacier movement

20. Why was Wegener’s theory mostly rejected ? Objection Lack of a mechanism The main limitation was the lack of a convincing mechanism to explain how continents could move through the solid oceanic crust. The theory failed to explain how the continents drifted apart. The two forces doesn’t enough to move continents ( tidal forces due to lunar-solar , forces of the earth’s rotation ).

21. Preface Before talking about the scientific ideas and opinions that led to the concept of plate tectonics, we must review the physical and chemical properties that make up the Earth, which contributed to developing a deeper and uniform context for understanding the dynamic of the Earth’s surface ( how is the earth not constant/ for to how much the earth move? (Up or Down, Left or Right). As a result we make for answering the question (Why do the plates move?) Earth Structure

22. Earth Structure 1- Chemical Properties Crust is the hard outer part of the Earth that consists of different elements that form rocks that do not differ greatly from each other in physical or mechanical properties. The crust is (2%) of the Earth’s volume and (2%) of the Earth’s mass. The Earth’s crust consists of two parts. They are: The continental crust has a thickness of ( 70 km ), and it consists of granitic rocks with a density of about ( 2.7 g/cm 3 ). It is subject to significant deformation and contains rocks whose age reaches ( 3800 billion years ). While the oceanic crust reaches a thickness of ( 8 km ), and it consists of volcanic rocks called basalt , its density is ( 3 g/cm 3 ), and it is generally not subject to distortion by the folding process , and it is younger, reaching the age of The oldest of them is ( 200 million years ). These differences between the continental and oceanic crusts are very essential to understanding the Earth.

23. Earth Structure 1- Chemical Properties 2- The mantle, which is the second mantle of the Earth, has a thickness of about ( 2900 km ) and is the largest part of the Earth, as it constitutes ( 82% ) of the Earth’s volume and (68%) of the Earth’s mass. Mantle consists of silicate rocks . It consists of silicon and oxygen ( SiO 4 ) and also contains iron and magnesium. Parts of Mantle appear on the surface of the Earth by volcanic eruptions. Due to the pressure of the upper rock layers, the density increases with depth from ( 3.4 g/cm 3 ) at the top of the Mantle to ( 5.5 g/cm 3 ) near its edge with the core . 3- Core: It is the central part of the Earth that extends from a depth of ( 2900-6371 km ), that is, to the center of the Earth. Its density increases with depth, but its average is about ( 10.8 g/cm 3 ). The core constitutes only (16%) of the Earth's volume, but it constitutes ( 32% ) of the Earth's mass due to its high density. Indirect evidence indicates that the core consists mainly of iron metal, so it differs from the core composed of silicate materials .

24. Earth Structure 2- Physical Properties The term  lithosphere  is used to describe the rigid outer part of the Earth, consisting of the crust and upper mantle. Compared with other layers of the Earth, the lithosphere is a relatively cool, rigid shell and averages about 60 miles (100 km) in thickness, but may be about 155 miles (250 km) or more thick beneath the older portions of the continents. The lithosphere is broken up into moving plates, and the movements of these plates are responsible for all the large-scale features observable on the surface—including ocean basins, continents, and mountain ranges . The term  asthenosphere  refers to a semi-fluid layer beneath the lithosphere (within the  upper mantle ), between about 60 to 400 miles (100-650 km) below the outer rigid lithosphere (oceanic and continental crust) forming part of the mantle. The asthenosphere, although solid, is very hot and is thought to be able to flow vertically and horizontally, enabling sections of lithosphere to undergo movements associated with plate tectonics. Geologist use the term  plastic  to describe how hot solid materials, including rocks, can deform and flow slowly.

25. Earth Structure 2- Physical Properties Mesosphere (or Lower Mantle) This region is a rigid layer between the depths of about ( 650 km and 2900 km), but the rocks at these depths are very hot and capable of gradual flow. Heat from the core drives mantle gravitational convection. Outer core:  the outer core is a liquid layer composed mostly of an iron-nickel alloy (a mixture with similar composition to metallic meteorites). Convective flow within the outer core generates Earth’s magnetic field . Inner core:  Geophysical studies show that the inner core behaves like a solid , but is very dense, around 16 gm/cm 3 (similar to the physical properties of an iron-nickel meteorite).

26. Chemical and Physical Properties of the Earth (table) Density i ncreasing with depth

27. Chemical and Physical Properties of the Earth (figure)

28. Convention Current Theory By Arthur Holmes Geologists consider convection currents to be responsible for the movement of molten rocks in the interior of the Earth, especially since they are in a semi-liquid state, and thus they move in a movement similar to the movement of fluids, as the molten rocks rise from the mantle layer, or what is called the mantle, to the top as their temperature rises and decrease its density , and as the rocks in the earth’s crust lose their heat , their temperature decreases and their density increases, causing them to fall downwards. Geologists believe that this movement is responsible for heating the earth’s crust , and a number of geologists consider this continuous movement to be one of the main causes that contribute to the occurrence of earthquakes . Volcanoes may also cause continental drift

29. Why Do the Plates Move? Convection Currents

30. Sea Floor Spreading Theory The Beginning of the Theory After World War II , thanks to scientific development or progress, this was accompanied by the frequent use of exploratory submarines and their carrying of Water Bathymetric Surveys devices and technologies, such as sonar devices and probes . They are the results of exploratory voyages via submarines such as the Alvin voyage and the Challenger , as well as efforts and endeavors to link mail and telegraph communications in the Atlantic Ocean between the coasts of Northern Ireland and Canada. Alvin Submersible A device that determines the distance of an object under water by recording echoes of sound waves

31. The features of the seafloor gives us clues as to how plates move. Mid-ocean ridges are areas of high heat flow & volcanic activity Sea Floor Spreading Theory

32. Sea Floor Spreading by Harry Hess (1903-1969) It is the mechanism proposed by Harry Hess for the first time in 1960, which is mainly based on the idea of convection currents arising in the mantle and its upper part. It assumes the origin of oceanic crust at the crests of the oceanic Mid-Oceanic Ridge , where plates diverge at a rate of several centimeters each year, over many geological eras . Hess found that the ocean floor contains two important phenomena: Mid-Oceanic Ridges and Oceanic Trenches , and that these mid-oceanic mountain ranges contain many cracks whose study can be inferred to have resulted from the movement of the sides of these elongated ridges in opposite directions similar to Limit the idea of conveyor belts . If the continents were moving above the ocean floor, as Wegener believed, this means that they would slide across the ocean floor, leaving behind smooth surfaces. This means that there is an objection to the theory of continental shift, and this objection must be overcome with a new theory

33. Evidences Support Sea Floor Spreading Evidence from molten material near the center of the Oceanic Ridges is younger than that far from centers Evidence from Magnetic stripes Basalt , the bedrock of the ocean floor, contains magnetite, a magnetic mineral. When basalt forms, it aligns with the direction of the Earth's magnetic field. The Earth's magnetic field changes regularly, so the rocks' alternating magnetic polarity indicates that they formed at different times in Earth's history . Evidence from heat sensors . Heat sensors showed that the area around the Mid-Atlantic Ridge was hotter than the rest of the ocean.

34. Plate Tectonics By Wilson Plate boundaries can be classified by motion into three types: 1- Divergent plate Boundaries 2- Convergent plate Boundaries 3- Transform plate Boundaries.

35. How do plates move ? 1- Divergent (constructive) plate boundaries حافات متباعدة انتشارية (بناءة) Mid-ocean ridges Continental rifting 2- Convergent (destructive) plate boundaries حافات متقاربة تصادمية (هدامة) Subduction zones Oceanic /Continent Convergent Continent/continent convergent 3- Transform plate boundaries 4- Mantle Plumes

36. Plate Boundaries Type of Boundary نوع الحافة Types of Plates Geomorphological Feature الشكل الجيومورفولوجي Geologic Events الأحداث الجيولوجية Modern Examples الأمثلة في العالم Divergent تباعد Ocean-ocean P. طبق محيطي-محيطي Mid-oceanic ridge Sea-floor spreading, Shallow Earthquakes, Rising Magma, Volcanoes. Mid-Atlantic ridge Continent-continent P. طبق قاري-قاري Rift valley Continents torn apart, Earthquakes, Rising Magma, Volcanoes East African rift Convergent تصادم Ocean-ocean P. طبق محيطي-محيطي Island arcs and ocean trenches Subduction, deep Earthquakes, rising Magma, Volcanoes, deformation of rocks Western Aleutians Ocean-continent P. طبق محيطيي-قاري Mountains and ocean trenches Same Events Above Andes جبال الأنديز Continent-continent P. طبق قاري-قاري Mountains Deep earthquakes, deformation of rocks Himalayas جبال الهملايا Transform انتقالي Ocean-ocean P. طبق محيطي-محيطي Major offset of mid- oceanic ridge axis Earthquakes Offset of East Pacific rise in South Pacific Continent-continent P. طبق قاري-قاري Small deformed mountain ranges, deformations along fault Earthquakes, deformation of rocks San Andreas fault فالق سان أندرياس

37. Examples San Andreas Fault Mid Oceanic Ridge East Pacific rise East African Rift Western Aleutians