3.3 Mountain building and continental formation
3 min read•august 7, 2024
Mountain building shapes Earth's surface through tectonic collisions, creating folded and faulted rocks. This process involves , , and , forming iconic ranges like the and .
Continents grow through , adding new material at plate boundaries. Stable form continental cores, while terranes and mountain belts like cordilleras contribute to landmass expansion. These processes sculpt Earth's ever-changing landscape.
Orogenic Processes
Formation and Deformation of Mountain Ranges
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- , the process of mountain building through tectonic plate collisions and convergence
- Involves uplift, , , and metamorphism of rocks
- Examples include the formation of the Himalayas and the Andes
- Folding occurs when rock layers are compressed and bent into wave-like shapes
- Anticlines are upward-arching folds (Grand Staircase-Escalante National Monument)
- Synclines are downward-curving folds (Sideling Hill road cut in Pennsylvania)
- Faulting involves the fracturing and displacement of rock layers along a fault plane
- form when the hanging wall moves down relative to the footwall (Basin and Range Province in the western United States)
- occur when the hanging wall moves up relative to the footwall (Rocky Mountains)
- have horizontal movement of rock layers (San Andreas Fault in California)
Metamorphism and Isostatic Adjustment
- Metamorphism is the transformation of rock under high temperature and pressure conditions without melting
- Regional metamorphism occurs over large areas during mountain building events ( in the Scottish Highlands)
- happens when magma intrudes and heats surrounding rock (Skiddaw Granite in the Lake District, England)
- Isostasy is the gravitational equilibrium between Earth's crust and mantle
- When mountains form, the crust thickens and becomes more buoyant, causing uplift ()
- As mountains erode, the crust becomes thinner and denser, leading to subsidence ()
Continental Growth
Accretion and Terrane Addition
- Accretion is the process of adding new material to continents through the collision and amalgamation of tectonic plates and terranes
- Occurs at , such as and continental collisions
- Examples include the accretion of and to North America's western margin
- Terranes are fault-bounded crustal blocks with distinct geologic histories that have been accreted to continents
- Can include island arcs, seamounts, continental fragments, and accretionary wedges
- The in western North America is a well-studied example
Cratons and Continental Stability
- Cratons are stable, ancient cores of continents that have remained relatively undeformed for billions of years
- Composed of Precambrian crystalline basement rock, often covered by younger sedimentary layers
- Examples include the , the , and the in South Africa
- Cratons form the nucleus around which younger terranes and sedimentary basins accumulate
- Provide a stable foundation for continental growth and the development of extensive sedimentary cover
- Act as rigid blocks during later tectonic events, influencing the deformation of surrounding regions
Mountain Belts
Cordilleran Orogens
- refers to a linear chain of mountains formed along a convergent plate boundary, typically associated with subduction zones
- Characterized by a series of parallel mountain ranges, volcanic arcs, and associated basins
- The North American Cordillera extends from Alaska to Mexico and includes the Rocky Mountains, the Sierra Nevada, and the Cascade Range
- develop through the accretion of terranes, the formation of , and the deformation of sedimentary basins
- Subduction of oceanic crust beneath a continental margin leads to the growth of a and the formation of an (Andes Mountains)
- Collision of an or microcontinent with the margin can result in the obduction of and high-pressure metamorphism (Coast Mountains of British Columbia)
Key Terms to Review (33)
Accretion: Accretion is the geological process by which material, such as sediment or other geological formations, gradually accumulates and adds to landforms over time. This process is essential in mountain building and continental formation, as it contributes to the growth and development of land masses through the accumulation of material from various sources, including tectonic activity, erosion, and sediment deposition.
Accretionary Wedge: An accretionary wedge is a geological formation that occurs at convergent plate boundaries, where oceanic crust is subducted beneath continental or oceanic plates, leading to the accumulation of sediments and material scraped off the subducting plate. This process contributes to mountain building and continental formation as the wedge grows over time, becoming an important feature in understanding tectonic activity and the geological processes involved in shaping the Earth's surface.
Andes: The Andes is the longest continental mountain range in the world, stretching over 7,000 kilometers along the western edge of South America. This magnificent range was formed primarily through tectonic plate interactions, particularly the subduction of the Nazca Plate beneath the South American Plate, leading to significant geological features such as volcanic activity and diverse ecosystems.
Appalachian Mountains: The Appalachian Mountains are a major mountain range in eastern North America, stretching from Newfoundland in Canada to central Alabama in the United States. Formed over 480 million years ago, they play a crucial role in understanding mountain building processes and the evolution of the North American continent.
Barrovian Metamorphism: Barrovian metamorphism refers to a specific type of regional metamorphism characterized by the progressive changes in mineral assemblages due to increasing temperature and pressure, commonly associated with mountain-building processes. This metamorphic process leads to the formation of distinct rock types, particularly schist, gneiss, and other foliated rocks, which are indicative of the geological conditions found during the formation of mountain ranges. Understanding Barrovian metamorphism provides insight into the history of continental collision and the tectonic forces that shape the Earth's crust.
Canadian Shield: The Canadian Shield is a vast geological region characterized by exposed Precambrian rocks, covering parts of Canada and extending into the northern United States. This ancient landform is one of the largest and oldest continental shields in the world, shaped by glacial activity and erosion over millions of years, playing a crucial role in the formation and stability of North America's crust.
Contact Metamorphism: Contact metamorphism is the process of mineralogical and textural changes in rocks due to the heat from nearby molten rock or magma intrusions. This localized transformation occurs when existing rocks, called protoliths, are subjected to intense heat but not significant pressure, leading to changes primarily in the mineral composition and structure of the surrounding rock. The result is typically the formation of new minerals, often characterized by a distinctive texture known as 'hornfels.'
Convergent plate boundaries: Convergent plate boundaries are regions where two tectonic plates move toward each other, leading to interactions that can result in significant geological features and phenomena. These boundaries are crucial for understanding mountain building, as they often lead to the formation of mountain ranges through processes such as subduction or continental collision. The interaction between the colliding plates can also lead to earthquakes and volcanic activity, making these boundaries vital in the study of Earth's dynamic processes.
Cordillera: A cordillera is a system or group of parallel mountain ranges that are often found in a continuous chain. These mountain ranges can span vast distances and are formed primarily through tectonic processes such as plate tectonics, which lead to the uplift and folding of the Earth's crust. Cordilleras can have significant impacts on climate, ecosystems, and human activities in the regions they traverse.
Cordilleran orogens: Cordilleran orogens refer to mountain ranges that have formed due to tectonic processes, particularly the collision and interaction of tectonic plates. These orogens are characterized by their extensive linear chains of mountains and are primarily found along the western margins of continents, playing a significant role in the formation and evolution of continental crust.
Cratons: Cratons are large, stable portions of the Earth's continental crust that have survived the cycles of tectonic activity and have remained relatively unchanged for billions of years. They form the ancient core of continents and are usually found in the interior regions, often characterized by thick sequences of metamorphic and igneous rocks. Their stability makes them key players in understanding mountain building processes and continental formation.
Faulting: Faulting is the process by which rocks break and slide past each other along fractures in the Earth's crust, resulting in the creation of faults. This geological phenomenon plays a critical role in mountain building and continental formation, as it can lead to the uplift of land and the formation of various geological features such as mountains and valleys. The movement along faults can occur suddenly, leading to earthquakes, or gradually over time, influencing the landscape and geological stability.
Folding: Folding refers to the geological process in which layers of rock are bent or curved due to tectonic forces, typically occurring at convergent plate boundaries. This process can lead to the formation of complex structures like mountains, ridges, and valleys, showcasing the immense pressure and heat that reshape the Earth's crust over time. Folding is a crucial mechanism in understanding how mountain ranges are created and how continental formations evolve.
Himalayas: The Himalayas are a vast mountain range in Asia, home to some of the highest peaks in the world, including Mount Everest. Formed primarily through the collision of the Indian and Eurasian tectonic plates, this range is a prime example of mountain building and continental formation, showcasing the processes involved in creating large-scale geological features.
Island arcs: Island arcs are curved chains of volcanic islands that form at tectonic plate boundaries, primarily where an oceanic plate subducts beneath another oceanic plate. These geological features are a result of the melting of the subducted plate, which creates magma that rises to the surface, leading to volcanic activity. Island arcs are significant for understanding mountain building processes and the dynamics of continental formation due to their role in the tectonic interactions between plates.
Isostatic adjustment: Isostatic adjustment refers to the process of Earth's crust responding to changes in surface load, such as the addition or removal of ice sheets, sediment, or water. This phenomenon occurs as the lithosphere (the rigid outer layer of the Earth) floats on the more fluid asthenosphere beneath it, leading to vertical movements of the crust that can take thousands of years to achieve equilibrium. The concept is crucial for understanding how mountain building and continental formation can alter Earth's surface over geologic time.
Kaapvaal Craton: The Kaapvaal Craton is one of the world's oldest geological formations, located in southern Africa, primarily in South Africa and Botswana. It represents a stable continental crust that has survived the processes of mountain building and continental formation for billions of years, showcasing ancient rocks that provide critical insights into Earth's early history and tectonic activity.
Magmatic Arcs: Magmatic arcs are linear regions of volcanic activity that form above subduction zones where an oceanic plate is being forced under a continental plate or another oceanic plate. This geological phenomenon results from the melting of the descending slab and the generation of magma that rises to the surface, leading to the formation of a chain of volcanoes. These arcs play a crucial role in mountain building and continental formation, as they contribute to the uplift and growth of mountain ranges through volcanic activity and tectonic processes.
Metamorphism: Metamorphism is the process by which rocks undergo changes in mineral composition and texture due to exposure to heat, pressure, and chemically active fluids. This process transforms existing rocks, primarily igneous and sedimentary, into metamorphic rocks, contributing significantly to the rock cycle and the formation of mountain ranges. Metamorphism is crucial for understanding how different rock types evolve over geological time and how continental formations are shaped by tectonic forces.
Microcontinents: Microcontinents are small landmasses that can form as part of continental crust, often resulting from tectonic processes like rifting or plate interactions. These fragments of continental crust are typically smaller than major continents and can include island arcs, continental fragments, or tectonic blocks that have been isolated from larger landmasses. They play an essential role in understanding the dynamics of continental formation and the processes involved in mountain building.
Normal Faults: Normal faults are a type of geological fault where the hanging wall moves downward relative to the footwall, caused by extensional forces that pull the Earth's crust apart. These faults are key players in mountain building and continental formation, as they help create rift valleys and can lead to the uplift of mountain ranges during tectonic activity.
Oceanic plateau: An oceanic plateau is an extensive, flat region of the ocean floor that rises significantly above the surrounding seafloor, often formed by volcanic activity or the uplift of large submarine volcanic islands. These plateaus play a crucial role in understanding the geological processes associated with mountain building and continental formation, particularly in relation to tectonic plate movements and hotspot volcanism.
Ophiolites: Ophiolites are segments of the Earth's oceanic crust and the underlying upper mantle that have been uplifted and exposed above sea level. They provide valuable insights into the composition and structure of oceanic crust, as well as the processes involved in mountain building and continental formation, particularly in areas where tectonic plates converge and interact.
Orogeny: Orogeny refers to the process of mountain formation, particularly through tectonic forces like the collision and convergence of Earth's tectonic plates. This process not only creates mountain ranges but also plays a crucial role in shaping the continents and their geological features. Orogeny can involve complex interactions between various geological processes, including faulting, folding, and volcanic activity.
Reverse faults: Reverse faults are geological structures where the hanging wall moves upward relative to the footwall due to compressional forces. This type of faulting is commonly associated with mountain building processes, as it results from tectonic plate movements that create folds and uplift landforms, contributing significantly to the formation of mountains and continental crust.
Siberian Craton: The Siberian Craton is a large, stable portion of the Earth's crust located in Siberia, Russia, which forms the ancient geological core of the continent. This craton is significant because it represents some of the oldest rocks on Earth, providing valuable insights into the processes of mountain building and continental formation, as it has been a stable platform upon which younger geological formations have developed over billions of years.
Strike-slip faults: Strike-slip faults are fractures in the Earth's crust where two blocks of rock slide past each other horizontally, with minimal vertical movement. This horizontal motion typically occurs along plate boundaries, and the friction between the rocks can lead to earthquakes. These faults are crucial in understanding the processes that shape mountain building and the formation of continents over time.
Subduction Zones: Subduction zones are regions where one tectonic plate moves under another and sinks into the mantle as the plates converge. These areas are crucial for mountain building and continental formation, as the intense geological activity at subduction zones leads to volcanic eruptions and the creation of mountain ranges, reshaping the Earth's surface over millions of years.
Terrane: A terrane is a fragment of crustal material that has a geological history distinct from the surrounding regions. These land masses often have unique rock types, structures, and ages that differentiate them from their adjacent areas, playing a crucial role in mountain building and continental formation through processes such as tectonic plate movements and collisions.
Tibetan Plateau: The Tibetan Plateau, often referred to as the 'Roof of the World,' is a vast high-altitude region in Central Asia, encompassing much of the Tibet Autonomous Region and parts of China, India, Nepal, and Bhutan. It is the highest and largest plateau in the world, playing a crucial role in influencing global climate patterns and the hydrology of major river systems in Asia.
Uplift: Uplift refers to the geological process where regions of the Earth's crust are raised due to tectonic forces. This phenomenon is crucial for understanding how mountains are formed and continents evolve over time, as it leads to significant changes in topography and landscape. Uplift can occur through various mechanisms, including tectonic plate collisions and volcanic activity, shaping the Earth's surface and contributing to the formation of mountain ranges and highlands.
Volcanic arc: A volcanic arc is a chain of volcanoes formed above a subduction zone, where one tectonic plate is forced under another. These arcs typically develop parallel to the trench created by the subduction and are a direct result of the melting of the descending plate, leading to magma formation that rises to the surface. Volcanic arcs play a crucial role in shaping mountainous regions and can significantly influence the geology and ecology of the surrounding areas.
Wrangellia Terrane: The Wrangellia Terrane is a geological formation that comprises a sequence of volcanic and sedimentary rocks located in parts of Alaska and British Columbia. It is significant in understanding mountain building processes and continental formation, as it represents a fragment of the oceanic crust that was accreted to the North American continent during tectonic activity.