chapter_3_-_Plate_Tectonics
Chapter 3: Plate Tectonics and Associated Structural Landforms
Introduction
Focuses on the study of plate tectonics and landform structures.
Page 1: Overview
Institution: University of UAE, College of Humanities and Social Sciences, Department of Geography and Urban Planning.
Course: GEO 413 - 51 Geomorphology, Fall 2022.
Page 2: Outline of Topics
Overview of plate tectonics and their movements over geological time.
Definition and characteristics of tectonic plates.
Types of plate boundaries and their significance.
Sea-floor exploration techniques.
Processes of mountain building, faults, and folds.
The creation and alteration of landforms.
Page 3: Theoretical Foundations
Early 20th-century scientific theories fail to explain Earth's structures and processes.
Continental Drift Theory: Proposed by Alfred Wegener (1910-1928).
Suggests continents are on tectonic plates and have drifted apart from a super-continent.
In the 1960s, continental drift theory merged with sea-floor spreading to form the Plate Tectonics Theory.
Page 4: Evidence Supporting Continental Drift
Fossil Evidence: Identical plant and animal fossils found in disparate locations (e.g. Mesosaurus in Africa and South America).
Glacial deposits in warm climates and similar rock formations on separate continents.
Alfred Wegener noted the snug fit of South America and Africa.
Page 5: Historical Formation of Super-Continents
Rodinia existed around 1,100 million years ago, broke apart leading to pre-Pangea about 400 million years ago.
Formation of Pangea around 250 million years ago, enabling animal migration across poles.
Page 6: Pangea and Its Subsequent Split
Pangea divided into Laurasia (North) and Gondwanaland (South) around 200 million years ago.
Laurasia formed North America, Eurasia, and Greenland; Gondwanaland formed the rest (Africa, etc.).
Page 7: Future Continental Changes
Predictions in 50 million years: potential collision of Africa and Europe could close the Mediterranean.
250 million years from now, another Pangea may form.
Page 8: Topic Continuation
Continents are dynamically changing due to tectonic activities.
Page 9: Understanding Tectonic Plates
Earth consists of:
Core: Inner and outer sections, primarily solid iron and very dense.
Mantle: Layer surrounding the core, partially molten upper layer known as the asthenosphere.
Crust: Rigid outer layer, thick continental crust underlies continents, and thinner oceanic crust underlies oceans.
Page 10: Earth Layers Breakdown
Core:
Thickness: 1,216 km (inner) and 2,270 km (outer).
Composition: Solid iron, very dense.
Mantle:
Thickness: 2,900 km; behaves like melted plastic in uppermost section.
Crust:
Thickness: 35-90 km (continental), 7-8 km (oceanic).
Page 11: Sublayers of Earth
Lithosphere: Combination of the crust and upper mantle.
Asthenosphere: Partly molten upper mantle allowing tectonic plates' movement.
Page 12: Movement of Tectonic Plates
The crust consists of about a dozen large slabs called tectonic plates; they can move several centimeters per year.
Plates can be created and destroyed, influencing geological activities.
Tectonics refers to the building and deformation of the lithosphere resulting in mountain formation.
Page 13: Driving Forces of Plate Motion
Plate motion is driven by heat from the mantle creating convection currents.
Mantle movement is analogous to a convection process enabling plate displacement.
Page 14: Plate Interactions and Boundaries
Convergent Boundary: Plates collide, leading to geological features.
Divergent Boundary: Plates separate; new material is created.
Transform Boundary: Plates slide past one another, causing earthquakes.
Page 15: Convergent Boundary - Ocean-Continent Collision
Denser oceanic crust subducts below continental crust, forming subduction zones and deep-sea trenches.
Example: Mariana Trench (11 km deep).
Page 16: Continental-Continental Collision
Collision leads to mountain building; significant earthquake activity, few volcanoes due to low density of crust.
Example: Himalayas forming due to Ind-Australian and Eurasian Plate collision.
Page 17: Ocean-Ocean Collision
Older oceanic plate subducts, leading to volcanic island formation (volcanic arcs).
Example: Mariana Islands.
Page 18: Volcanism at Convergent Boundaries
New magma forms as an old slab is subducted, resulting in surface volcanoes (e.g. Andes Mountains).
Page 19: Divergent Boundary - Sea-floor Spreading
Oceanic plates pull apart, and new magma rises through existing crust, forming mid-ocean ridges (e.g. Mid-Atlantic Ridge).
Page 20: Mid-Atlantic Ridge
The world’s longest underwater mountain chain, spreading at different rates (1-2 cm/year).
East Pacific Rise is a fast-spreading ridge (6-8 cm/year).
Page 21: Sea-floor Exploration
Deep Sea Drilling Project (DSDP) initiated in 1968; provided vital information about oceanic and continental crust.
Determined that continental crust is thicker, younger crust forms at mid-ocean ridges.
Page 22: Age of Oceanic Crust
Oldest oceanic crust is ~180 million years.
Ocean crust formation and recycling occur approximately every 180 million years.
Page 23: Transform Boundary Characteristics
Plates slide past each other, creating transform faults (e.g. San Andreas Fault).
Characterized by earthquake activity due to built-up strain energy.
Page 24: Contributions of J. Tuzo Wilson
Introduced concepts such as stationary hotspots for volcanic islands and the transform boundary.
Proposed the Wilson Cycle describing supercontinent evolution.
Page 26: Geological Features from Tectonics
Plate tectonics lead to features like volcanoes, earthquakes, and faults.
Example: Right-lateral strike-slip fault demonstrates horizontal movement of tectonic plates.
Page 27: Fault Types - Normal Faults
Normal Faults occur from tension; hanging wall moves downwards.
Form fault-block mountains, characterized by dropping land areas.
Page 28: Fault Types - Reverse Faults
Reverse Faults occur from compression; hanging wall moves upward over footwall.
Associated with mountain ranges and is commonly accompanied by folding.
Page 29: Folding Processes
Rocks may deform into folds under heat and pressure.
Extensive folding observed in mountain ranges such as Appalachians.
Page 30: Mountain-building Forces
Collision of continental plates at convergent boundaries produces mountain ranges.
Example: Himalayas, formed from compression, differ in age and erosion states.
Page 31: Geomorphic Concepts
Elevation: Height above sea level.
Slope: Spatial gradients in elevation.
Relief: Terrain diversity; different elevations across features like mountains, valleys, and plains.
Page 32: Effects of Slope and Relief
Slope impacts hillside stability and sediment transport.
Relief affects erosion rates and sediment yield; generally, high elevation correlates with high relief.
Page 33: Uplift and Subsidence
Uplift/Subsidence: Vertical crust motions; ultimate elevation change formula incorporates both.
Page 34: Accumulation and Denudation
Processes affecting land surface position; denudation leads to landscape elevation reduction.
Important: net rate of elevation change includes uplift and denudation balance.
Page 35: Erosion Feedback in Geomorphology
High elevation increases erosion rate; direct relationship between elevation and erosion.
W.M. Davis’ landscape evolution theory emphasizes this negative feedback postulates.
Page 37: Climate Influences
Topography can affect the climate and vice versa; climate fluctuations can enhance or reduce rates of weathering and erosion.
Page 38: Uplift and Erosion Relationship
Positive Feedback: Isostasy dictates that erosion may lead to uplift due to changing crustal loads.
Page 39: Volcano Formation
Most volcanoes form near subduction zones due to melting and magma rise.
Volcanoes create new land forms but can also cause destructive eruptions.
Page 40: Volcanic Eruptions
Volcanic explosiveness linked to magma viscosity; thicker magma results in more explosive eruptions.
New magma formation occurs at subduction zones, causing eruptions or quiet flows.
Page 41: Eruption Dynamics
Fluid magma leads to less explosive eruptions; pyroclastic flows pose significant destructive risks.
Page 42: Case Study: Mount St. Helens
Erupted May 18, 1980, from Juan de Fuca plate subduction under North American plate.
Resulted in significant destruction, altering the landscape and making it a notable geological event.