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Nigeria's free digital learning hub. Videos, lecture notes, practice questions and leaderboards aligned with CCMAS, NBTE, NCCE, WAEC, NECO, IJMB and JAMB curricula.
Geology · 400 Level
This is the complete lecture note for GEY 412 Global tectonics and structures, prepared for Geology students at 400 Level. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS GEY 412: Global Tectonics and Structures (2 Units C: LH 30) Course Code: GEY 412 Course Title: Global Tectonics and Structures Course Unit: 2 Units C Series 1: Major Structures Of The Earth Series 2: Plate Tectonics And Sea Floor Spreading Series 3: Heat Flow, Crustal Movements, And Mineral Resources Series 4: Origin, Growth, And Classification Of Basins Series 5: Orogeny, Orogenesis, And Crustal Evolution Series 1 Major Structures Of The Earth Part 1.1 Overview of the Earth’s major structures 1.1.1 Lithosphere and asthenosphere 1.1.2 Continental and oceanic crust 1.1.3 Structural features of the mantle and core Part 1.2 Continental separation and sea floor spreading 1.2.1 Continental drift theory 1.2.2 Mechanism of sea floor spreading 1.2.3 Evidence supporting continental separation Part 1.3 Mid-oceanic ridges and related features 1.3.1 Structure of mid-oceanic ridges 1.3.2 Role in plate movements 1.3.3 Associated geological processes Introduction The Earth is a dynamic planet with structures that constantly evolve and reshape its surface. From continents drifting apart to oceans expanding through sea floor spreading, these processes are fundamental to understanding global tectonics. This Series introduces you to the major
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS structures of the Earth, providing a foundation for the study of plate tectonics, basin formation, and orogeny in later Series. The aim of this Series is to familiarise you with the structural framework of the Earth, explain the processes of continental separation and sea floor spreading, and highlight the importance of mid-oceanic ridges in global tectonic activity. We shall commence this Series by examining the lithosphere, asthenosphere, and the composition of continental and oceanic crust. Next, we will move on to continental separation and sea floor spreading, considering both the mechanisms and the evidence that support these processes. Finally, we will conclude with mid-oceanic ridges, exploring their structure, role in plate movements, and associated geological phenomena. Series Learning Outcomes Upon completing this Series, you should be able to: SLO 1.1 describe the lithosphere, asthenosphere, and the composition of continental and oceanic crust, SLO 1.2 explain the processes of continental separation and sea floor spreading, SLO 1.3 analyse evidence supporting continental drift and sea floor spreading, and SLO 1.4 evaluate the structure and role of mid-oceanic ridges in global tectonics. 1.1 Overview Of The Earth’s Major Structures 1.1.1 Lithosphere and asthenosphere The lithosphere is the rigid outer shell of the Earth, consisting of the crust and the uppermost mantle. It is broken into tectonic plates that move and interact at their boundaries. Beneath the lithosphere lies the asthenosphere, a semi-molten layer of the mantle that allows the plates to move due to its plasticity. The interaction between these two layers is fundamental to tectonic processes such as continental drift and plate tectonics. Short description: Diagram showing the lithosphere and asthenosphere layers of the Earth.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Caption: Figure 1.1 Structure of the lithosphere and asthenosphere Fill in the blank: The rigid outer shell of the Earth is called the ______. 1.1.2 Continental and oceanic crust The Earth’s crust is divided into two types: continental crust and oceanic crust. Continental crust is thicker, less dense, and composed mainly of granitic rocks. Oceanic crust is thinner, denser, and composed largely of basaltic rocks. These differences explain why continents stand higher than ocean basins. Table 1.2 Comparison of continental and oceanic crust Property Continental Crust Oceanic Crust Average Thickness $35\text{ – }40\text{ km}$ (Up to $70\text{ km}$ under mountains). $6\text{ – }10\text{ km}$ (Relatively uniform). Average Density $\approx 2.7\text{ g/cm}^3$ (Lighter/Buoyant). $\approx 2.9\text{ – }3.0\text{ g/cm}^3$ (Heavier/Sinks).
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Property Continental Crust Oceanic Crust Primary Composition Felsic (Granitic); rich in Silica and Aluminum ($Sial$). Mafic (Basaltic); rich in Magnesium and Iron ($Sima$). Age of Rocks Very Old (Up to $4\text{ billion}$ years). Young (Less than $200\text{ million}$ years). Formation Complex accretion at subduction zones. Continuous creation at mid-ocean ridges. Recycling Rarely subducted; persists for eons. Constantly recycled via subduction. Fill in the blank: The crust beneath the oceans is mainly composed of ______ rocks. 1.1.3 Structural features of the mantle and core The mantle lies beneath the crust and extends to a depth of about 2,900 km. It is composed mainly of silicate minerals rich in iron and magnesium. Convection currents in the mantle drive plate movements. The core is divided into the outer core, which is liquid and generates the Earth’s magnetic field, and the inner core, which is solid and composed mainly of iron and nickel. Short description: Cross-section diagram showing crust, mantle, outer core, and inner core.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Caption: Figure 1.3 Internal structure of the Earth Fill in the blank: The Earth’s magnetic field is generated by movements in the ______ core. Pilot questions 1.1 What is the lithosphere composed of? Name the semi-molten layer beneath the lithosphere. State one difference between continental and oceanic crust. Which type of crust is denser? What generates the Earth’s magnetic field? 1.2 Continental Separation And Sea Floor Spreading 1.2.1 Continental drift theory The continental drift theory was first proposed by Alfred Wegener, who suggested that continents were once joined together in a single landmass called Pangaea. Over millions of years, this supercontinent broke apart, and the continents drifted to their present positions. Evidence for this theory includes the matching coastlines of South America and Africa, similarities in rock formations, and fossil records found on widely separated continents. Short description: Diagram showing the breakup of Pangaea and the drift of continents.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Caption: Figure 1.4 Continental drift from Pangaea to present day Fill in the blank: The supercontinent proposed by Alfred Wegener was called ______. 1.2.2 Mechanism of sea floor spreading Sea floor spreading is the process by which new oceanic crust is formed at mid-oceanic ridges and gradually moves away from them. Magma rises from the mantle, solidifies to form new crust, and pushes older crust outward. This mechanism explains the widening of ocean basins and supports the theory of plate tectonics. Short description: Diagram showing sea floor spreading at a mid-oceanic ridge.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Caption: Figure 1.5 Sea floor spreading process Fill in the blank: New oceanic crust is formed at ______ ridges. 1.2.3 Evidence supporting continental separation Several lines of evidence support continental separation and sea floor spreading. These include: Palaeomagnetism, which shows symmetrical magnetic patterns on either side of mid-oceanic ridges. Distribution of fossils, such as Mesosaurus found in both South America and Africa. Geological similarities, including matching mountain ranges across continents. Age of oceanic crust, which is youngest near ridges and older further away. Table 1.6 Evidence supporting continental separation and sea floor spreading Type of Evidence Key Contribution Description & Implication Continental Jigsaw Fit Suggests a previous supercontinent. Coastline Matching: When the continents (especially South America and Africa) are reassembled, their geometric boundaries fit together with remarkable precision, suggesting they were once a single landmass.
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