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

1. Convergent Boundary: Plates collide, leading to geological features.

2. Divergent Boundary: Plates separate; new material is created.

3. 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.