Geology Quiz: Greenstone Belts & Theories

Course Information

• Course Title: Geography of Ethiopia and the Horn
• Course Code: GeES 1011
• Credit hours: 3
• Instructor's Name: Ashenafi Z. (PhD Candidate)
• Date: Nov, 2024

Chapter Two: The Geology of Ethiopia and the Horn

2.1 The Geology of Ethiopia and the Horn

• Geology is the Earth science that studies the evolution of the planet, its materials, and the processes that affect it.
• Much of geology focuses on events from the distant past, and features located deep within the Earth, which are not directly observable.
• Understanding relies heavily on indirect evidence and inferences based on what can be seen and measured on the surface.
• Clues include various rock and landform observations, and indirect methods like geophysics (studying earthquake waves), geochemistry (analyzing rock composition), and geochronology (determining rock ages).

2.2 Origin of the Universe: The Big Bang Theory

• The universe is all of space and everything within it.
• The Big Bang theory explains the universe's origin as the result of a massive explosion from a high-density, high-temperature point.
• All the matter in the known universe was once concentrated in a single point, known as a cosmic egg.
• After the explosion, the universe expanded, and cooled down to form an expanding cloud of gases, primarily hydrogen (73%) and helium (27%).
• Thermonuclear fusion occurred, giving rise to stars. The Sun's first rays arose from a tremendous temperature of 11 million °C about 4.5 billion years ago after the birth of the stars and formation of the first galaxies.
• The Earth formed from the collapsing nebular material and took about 700 million years to cool down and solidify.

2.3 The Theory of Continental Drift

• Alfred Wegener, a German meteorologist, proposed the theory of continental drift.
• Wegener's theory suggests that the Earth's continents were once joined together as a single large landmass called Pangaea.
• Pangaea was surrounded by a vast ocean known as Panthalassa.
• Pangaea broke apart into Gondwanaland and Laurasia during the Mesozoic era, roughly 200 million years ago.
• Gondwanaland further separated into South America, Africa, the Arabian Peninsula, India, Australia, and Antarctica.
• Laurasia separated into North America and Eurasia.
• Supporting evidence for the theory includes the fit of continents, similarities in mountain belts and rock types, distribution of fossils, and similar ancient climates.

2.4 The Geological Processes

• Geological processes are broadly categorized into internal (endogenic) and external (exogenic) processes.
•  Internal processes (endogenic): include earthquakes, volcanism, mountain building, and landmass sinking.
•  External processes (exogenic): include weathering, mass transfer, erosion, and deposition.
• The landforms of Ethiopia are formed by the combined effect of both types of processes.

2.5 The Geological Time Scale

• The Geological Time Scale is a record of Earth's history, organized into four major divisions: Eon, Eras, Periods, and Epochs.
• This scale is structured based on significant geological events, major shifts in life forms, and environmental changes.
• The categories do not have uniform lengths of time.

2.5.1 Age Dating Techniques

• Scientists use two main techniques of determining rock ages:
• Relative dating: uses geological evidence to show comparative ages of fossils, identifying which layer is older or younger.
• Absolute dating (Radiometric): determines the actual age of rocks, using radioactive decay to calculate the age.

2.5.1.A. Carbon-14 Technique

• Using the known and predictable rate of carbon-14 decay after an organism dies. The half-life is 5730 years.

2.5.1.B. Potassium-40 Technique

• Potassium-40 decays into Argon-40, which is measured to determine the rock's age.
• The method relies on the abundance of potassium-40 in minerals like micas, feldspars and hornblendes.
• Potential problem: Leakage of Argon from a rock due to high temperatures affecting the accuracy of the measurements.

2.6 Geological Processes and the Resulting Landforms of Ethiopia and the Horn

• Covers the geologic events from 4.5 Billion years ago to the present.

2.6.1 The Precambrian Era (4.5 - 600 Million Years Ago)

• Covers the oldest and longest period of Earth's history.
• Major geological events include: crystalline basement rock formation, orogenesis (mountain building), metamorphism (formation of metallic minerals), intensive volcanic activity, and the first forms of life emerged.
• Our understanding of this era is limited due to its remoteness in time and the absence of well-preserved fossils.

2.6.2 The Paleozoic Era (600-225 million years ago)

• The second-longest and second-oldest Era.
• Major geological processes: Denudation, peneplanation (reducing mountains to a flat surface), heavy erosion, and coal formation.
• Limited significant rock formations in Ethiopia during this period due to limited deposition.

2.6.3 The Mesozoic Era (225-70 million years ago)

• The third-largest and third-oldest Era.
• Major geological processes involved in the shaping of landmasses: movement of continents (continental drift), sinking and uplifting of land masses (epeirogenesis), formation of 3 layers of marine sediments, emergence and extinction of dinosaurs, and the emergence of mammals, birds, and flowering plants.
• Landmass has experienced alternating periods of sinking and uplift, and is the period when Pangaea split into Gondwanaland and Laurasia.

2.6.4 The Cenozoic Era (70 million years ago - Present)

• This is the most recent Era.
• Major geological processes: Uplift of the Arabo-Ethiopian landmass, outpouring of huge quantities of lava, formation of the Rift Valley, and quaternary volcanism and deposition.

2.7 Rock and Mineral Resources of Ethiopia

• Rocks are naturally formed aggregates of one or more minerals. These are considered natural, inorganic substances with definite chemical compositions and specific internal structures.
• Metallic mineral occurrence primarily associated with Precambrian rocks.
• Mineral potential in Ethiopia is high but not adequately or fully utilized because of a lack of technology, skill, and capital.

2.7.1 Brief Facts and Current State of Main Minerals in Ethiopia

• Ethiopia has an abundance of resources of metals and precious metals, coal, and industrial minerals like Gold, Platinum, Tantalum, Gemstones, Potash, Gypsum, etc.
• However, there is a gap between the mineral potential and current level of utilization, due to the absence of technology, capital, and skilled personnel.

2.7.2 Mineral Potential Sites of Ethiopia

• Based on Ethiopian geological surveys, the potential mineral occurrence areas include three major greenstone belts and other formations. These areas (Western and South-Western, Southern, and Northern) are known to contain various mineral types including, primary gold, platinum, base metals, etc.,

3. Quaternary Volcanic Eruptions and Depositions

• Recent volcanic activities after the formation of the Rift Valley during Pliocene-Pleistocene Epochs.
• Volcanic activity is generally limited to Rift Valley floor and the region south of Lake Tana, with more extensive activity in the Afar region.
• Well-preserved volcanic morphological features are readily seen in the Afar area owing to their recent occurrence. (volcanic cones, hills, mountains, lava fields, ridges).

Quaternary Deposition

• Earth experienced marked climatic change with alternating warmer and colder periods during the Quaternary. Pluvial periods (periods with heavy rainfall) also occurred in Africa.
• Excessively increased pluvial rainfall caused significant effects on land including increased surface flow, river erosion of the Ethiopian plateau, sediment and water transport by the rivers, and creation of numerous lakes.
• These effects have led to the formation of lacustrine, fluvial, and glacio-fluvial deposits which cover considerable areas in the form of lakebeds, river valleys, etc.