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Questions and Answers
Which discipline places emphasis on the purely descriptive part of rock science from textural, mineralogical, and chemical points of view?
Which discipline places emphasis on the purely descriptive part of rock science from textural, mineralogical, and chemical points of view?
What is the average thickness of the continental crust?
What is the average thickness of the continental crust?
What is the composition of the Earth's mantle?
What is the composition of the Earth's mantle?
Which layer of the Earth is characterized by a Fe-Ni metallic alloy?
Which layer of the Earth is characterized by a Fe-Ni metallic alloy?
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What type of boundary involves the collision of two plates resulting in the descent of oceanic lithosphere into the mantle or the collision of two continental blocks?
What type of boundary involves the collision of two plates resulting in the descent of oceanic lithosphere into the mantle or the collision of two continental blocks?
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Where do subduction zones, a type of convergent boundary, occur?
Where do subduction zones, a type of convergent boundary, occur?
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What are deep-ocean trenches characterized by?
What are deep-ocean trenches characterized by?
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What does oceanic-continental convergence lead to?
What does oceanic-continental convergence lead to?
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What does oceanic-oceanic convergence involve?
What does oceanic-oceanic convergence involve?
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What type of boundary involves two plates grinding past each other without the production or destruction of lithosphere?
What type of boundary involves two plates grinding past each other without the production or destruction of lithosphere?
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What are fracture zones on the seafloor encompassing?
What are fracture zones on the seafloor encompassing?
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What does igneous genesis encompass?
What does igneous genesis encompass?
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What does petrology deal with?
What does petrology deal with?
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How do igneous rocks form?
How do igneous rocks form?
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What does igneous petrology focus on?
What does igneous petrology focus on?
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Which process involves minerals crystallizing at different temperatures, changing the magma's composition?
Which process involves minerals crystallizing at different temperatures, changing the magma's composition?
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What explains the order in which minerals crystallize from a basaltic magma based on temperature?
What explains the order in which minerals crystallize from a basaltic magma based on temperature?
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Which process involves two magmas with different compositions coming into contact and creating a mixed magma with an intermediate composition?
Which process involves two magmas with different compositions coming into contact and creating a mixed magma with an intermediate composition?
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What occurs when magma reacts with the surrounding country rock, altering the magma's composition?
What occurs when magma reacts with the surrounding country rock, altering the magma's composition?
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What can result from distinct melting events from different sources or various degrees of partial melting from the same source?
What can result from distinct melting events from different sources or various degrees of partial melting from the same source?
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What form of fractional crystallization can change liquid compositions by removing crystals from the liquid as they form?
What form of fractional crystallization can change liquid compositions by removing crystals from the liquid as they form?
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What can result in distinct mineral assemblages and chemical evidence when two or more magmas are mixed?
What can result in distinct mineral assemblages and chemical evidence when two or more magmas are mixed?
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In which state do two liquids with different compositions coexist without mixing, forming an emulsion?
In which state do two liquids with different compositions coexist without mixing, forming an emulsion?
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Based on what can igneous rocks be classified, involving determining the percent by weight of silica?
Based on what can igneous rocks be classified, involving determining the percent by weight of silica?
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In which type of volcanic rocks are normative classification systems commonly used?
In which type of volcanic rocks are normative classification systems commonly used?
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What does classification based on composition involve, and does not necessarily align with the conventional acidic/basic chemistry definitions?
What does classification based on composition involve, and does not necessarily align with the conventional acidic/basic chemistry definitions?
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What are divergent boundaries primarily known for?
What are divergent boundaries primarily known for?
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What characterizes oceanic ridges?
What characterizes oceanic ridges?
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What is the primary reason for the elevated position of the oceanic ridge?
What is the primary reason for the elevated position of the oceanic ridge?
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What is the typical rate of seafloor spreading along the oceanic ridge system?
What is the typical rate of seafloor spreading along the oceanic ridge system?
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Where does continental rifting occur?
Where does continental rifting occur?
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What are rift valleys evidence of?
What are rift valleys evidence of?
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What is seafloor spreading?
What is seafloor spreading?
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What is the primary mechanism that operates along the oceanic ridge system to create new seafloor?
What is the primary mechanism that operates along the oceanic ridge system to create new seafloor?
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What is the average time for the temperature of newly created oceanic crust to stabilize and contraction to cease?
What is the average time for the temperature of newly created oceanic crust to stabilize and contraction to cease?
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Where were some of the earliest human remains discovered, which is considered the 'birthplace' of the human race?
Where were some of the earliest human remains discovered, which is considered the 'birthplace' of the human race?
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What are the three recognized types of magma based on chemical composition?
What are the three recognized types of magma based on chemical composition?
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What heat sources contribute to magma generation?
What heat sources contribute to magma generation?
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Where does decompression melting occur?
Where does decompression melting occur?
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What is the common mechanism of magma generation in subduction zones?
What is the common mechanism of magma generation in subduction zones?
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What dictates the initial composition of magma?
What dictates the initial composition of magma?
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What does magmatic differentiation refer to?
What does magmatic differentiation refer to?
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What mechanism can raise the geothermal gradient, causing partial melting?
What mechanism can raise the geothermal gradient, causing partial melting?
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What can repeated intrusions of magmas into cold crust lead to?
What can repeated intrusions of magmas into cold crust lead to?
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What process involves raising the geothermal gradient or lowering the melting temperature of rocks?
What process involves raising the geothermal gradient or lowering the melting temperature of rocks?
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What is the primary role of the geothermal gradient and partial melting in magma generation?
What is the primary role of the geothermal gradient and partial melting in magma generation?
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What are the heat transfer mechanisms contributing to magma generation?
What are the heat transfer mechanisms contributing to magma generation?
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What is the mechanism that can lower the melting temperature of rocks and cause partial melting?
What is the mechanism that can lower the melting temperature of rocks and cause partial melting?
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What is the average thickness of the continental crust?
What is the average thickness of the continental crust?
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What is the composition of the Earth's mantle?
What is the composition of the Earth's mantle?
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What characterizes oceanic ridges?
What characterizes oceanic ridges?
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What is the primary role of the geothermal gradient and partial melting in magma generation?
What is the primary role of the geothermal gradient and partial melting in magma generation?
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What process results in the generation of continental volcanic arcs?
What process results in the generation of continental volcanic arcs?
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What is the branch of geology dealing with the origin, occurrence, structure, and history of rocks?
What is the branch of geology dealing with the origin, occurrence, structure, and history of rocks?
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What type of boundary involves two plates grinding past each other without the production or destruction of lithosphere?
What type of boundary involves two plates grinding past each other without the production or destruction of lithosphere?
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What is the primary mechanism that operates along the oceanic ridge system to create new seafloor?
What is the primary mechanism that operates along the oceanic ridge system to create new seafloor?
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What is the mechanism that can lower the melting temperature of rocks and cause partial melting?
What is the mechanism that can lower the melting temperature of rocks and cause partial melting?
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What characterizes oceanic ridges?
What characterizes oceanic ridges?
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What does igneous petrology focus on?
What does igneous petrology focus on?
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What does oceanic-oceanic convergence involve?
What does oceanic-oceanic convergence involve?
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What can result from distinct melting events from different sources or various degrees of partial melting from the same source?
What can result from distinct melting events from different sources or various degrees of partial melting from the same source?
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What is the composition of the Earth's mantle?
What is the composition of the Earth's mantle?
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What are fracture zones on the seafloor encompassing?
What are fracture zones on the seafloor encompassing?
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What is the typical rate of seafloor spreading along the oceanic ridge system?
What is the typical rate of seafloor spreading along the oceanic ridge system?
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What is the primary reason for the elevated position of the oceanic ridge?
What is the primary reason for the elevated position of the oceanic ridge?
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What is the average rate of seafloor spreading along the oceanic ridge system?
What is the average rate of seafloor spreading along the oceanic ridge system?
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Where is the East African Rift located?
Where is the East African Rift located?
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What are rift valleys evidence of?
What are rift valleys evidence of?
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What is the mechanism that operates along the oceanic ridge system to create new seafloor?
What is the mechanism that operates along the oceanic ridge system to create new seafloor?
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What is the longest topographic feature on Earth's surface?
What is the longest topographic feature on Earth's surface?
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What is the primary composition of the Earth's lithosphere?
What is the primary composition of the Earth's lithosphere?
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What characterizes divergent boundaries?
What characterizes divergent boundaries?
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What are the major tectonic plates mentioned in the text?
What are the major tectonic plates mentioned in the text?
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What is the average length of the global ridge system?
What is the average length of the global ridge system?
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What is the primary type of boundaries where rift valleys are found?
What is the primary type of boundaries where rift valleys are found?
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What is the mechanism that leads to the creation of new ocean floor at divergent boundaries?
What is the mechanism that leads to the creation of new ocean floor at divergent boundaries?
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What mechanism can raise the geothermal gradient, causing partial melting?
What mechanism can raise the geothermal gradient, causing partial melting?
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What is the primary reason for the elevated position of the oceanic ridge?
What is the primary reason for the elevated position of the oceanic ridge?
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What are the heat transfer mechanisms contributing to magma generation?
What are the heat transfer mechanisms contributing to magma generation?
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What characterizes oceanic ridges?
What characterizes oceanic ridges?
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What is the branch of geology dealing with the origin, occurrence, structure, and history of rocks?
What is the branch of geology dealing with the origin, occurrence, structure, and history of rocks?
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What explains the order in which minerals crystallize from a basaltic magma based on temperature?
What explains the order in which minerals crystallize from a basaltic magma based on temperature?
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What is the common mechanism of magma generation in subduction zones?
What is the common mechanism of magma generation in subduction zones?
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What are rift valleys evidence of?
What are rift valleys evidence of?
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What does igneous petrology focus on?
What does igneous petrology focus on?
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What is the composition of the Earth's mantle?
What is the composition of the Earth's mantle?
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What is the typical rate of seafloor spreading along the oceanic ridge system?
What is the typical rate of seafloor spreading along the oceanic ridge system?
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What is the average thickness of the continental crust?
What is the average thickness of the continental crust?
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Which process involves the reaction between magma and the surrounding country rock, leading to changes in magma composition?
Which process involves the reaction between magma and the surrounding country rock, leading to changes in magma composition?
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What demonstrates the order in which minerals crystallize from a basaltic magma, impacting the evolution of magma composition with falling temperature?
What demonstrates the order in which minerals crystallize from a basaltic magma, impacting the evolution of magma composition with falling temperature?
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What involves the classification of igneous rocks based on composition, fabric, and field relations?
What involves the classification of igneous rocks based on composition, fabric, and field relations?
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What classification system is commonly used for volcanic rocks based on normative mineralogy?
What classification system is commonly used for volcanic rocks based on normative mineralogy?
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What is a key factor in the classification of igneous rocks based on composition?
What is a key factor in the classification of igneous rocks based on composition?
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What is the primary method for determining the composition-based classification of igneous rocks?
What is the primary method for determining the composition-based classification of igneous rocks?
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What is the process where minerals crystallize at different temperatures, leading to changes in magma composition as certain minerals are removed from the liquid?
What is the process where minerals crystallize at different temperatures, leading to changes in magma composition as certain minerals are removed from the liquid?
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What occurs when two magmas with different compositions come into contact, resulting in a mixed magma with an intermediate composition?
What occurs when two magmas with different compositions come into contact, resulting in a mixed magma with an intermediate composition?
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What is the primary consideration for the CIPW norm classification system in igneous petrology?
What is the primary consideration for the CIPW norm classification system in igneous petrology?
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What is the main factor impacting magma composition with falling temperature?
What is the main factor impacting magma composition with falling temperature?
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What is the primary role of magmatic assimilation in controlling magma composition and differentiation?
What is the primary role of magmatic assimilation in controlling magma composition and differentiation?
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What is the primary focus of igneous petrology?
What is the primary focus of igneous petrology?
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Study Notes
Magmatic Differentiation Processes
- Magmatic differentiation involves processes such as fractional crystallization, magmatic mixing, and assimilation.
- Fractional crystallization occurs as minerals crystallize at different temperatures, changing the magma's composition.
- Magma mixing involves two magmas with different compositions coming into contact and creating a mixed magma with an intermediate composition.
- Magmatic assimilation occurs when magma reacts with the surrounding country rock, altering the magma's composition.
- Bowen's Reaction Series explains the order in which minerals crystallize from a basaltic magma based on temperature.
- Magmatic differentiation can result from distinct melting events from different sources or various degrees of partial melting from the same source.
- Crystal fractionation, a form of fractional crystallization, can change liquid compositions by removing crystals from the liquid as they form.
- Mixing of two or more magmas can result in distinct mineral assemblages and chemical evidence.
- Liquid immiscibility is a state in which two liquids with different compositions coexist without mixing, forming an emulsion.
- Igneous rocks can be classified based on composition, fabric and texture, and field relations.
- Normative classification systems are commonly used in aphanitic or glassy volcanic rocks, where a rock's modal mineral composition cannot be determined visually.
- Classification based on composition can involve determining the percent by weight of silica and does not necessarily align with the conventional acidic/basic chemistry definitions.
Plate Tectonics and Divergent Boundaries
- The Earth's lithospheric plates are composed of both continental and oceanic lithosphere
- Major plates include North American, South American, Pacific, African, Eurasian, Australian-Indian, and Antarctic plates
- Divergent boundaries are where new crust is generated as the plates pull away from each other
- They are located along the crests of oceanic ridges and are also known as spreading centers
- Oceanic ridges are elevated areas of the seafloor characterized by high heat flow and volcanism
- The primary reason for the elevated position of the oceanic ridge is that newly created oceanic crust is hot and less dense
- It takes about 80 million years for the temperature of the crust to stabilize and contraction to cease
- Rift valleys are deep down-faulted structures that are evidence of tensional forces pulling the ocean crust apart at the ridge crest
- Seafloor spreading is the mechanism that operates along the oceanic ridge system to create new seafloor
- Typical rates of spreading average around 5 cm (2 inches) per year
- Continental rifting occurs where opposing tectonic forces act to pull the lithosphere apart
- The remains of some of the earliest humans were discovered in the East African Rift, considered the "birthplace" of the human race
Formation and Composition of Magma
- Magma can form extrusive (volcanic) or intrusive (plutonic) igneous rocks on the Earth's surface or beneath it.
- Types of magma are determined by chemical composition, with three recognized types: basaltic, andesitic, and rhyolitic magma.
- Magma is generated from the Earth’s mantle through partial melting, and it does not come from the molten outer core.
- Heat sources for magma generation include early Earth accretion, radioactive breakdown, and heat transfer mechanisms like radiation, conduction, and convection.
- The geothermal gradient and partial melting play a key role in magma generation, where rocks melt over a range of temperatures, leading to partial melts from which the liquid portion forms magma.
- Magma generation in the solid part of the Earth can occur through raising the geothermal gradient or lowering the melting temperature of rocks, for example, by decompression melting or flux melting.
- Decompression melting occurs at divergent plate boundaries, where stretching of lithospheric plates causes mantle material to rise, experiencing lower pressure and leading to partial melting.
- Convection is a mechanism that can raise the geothermal gradient, causing partial melting, and basaltic magmas are believed to originate in this way, particularly beneath oceanic ridges and hot spots.
- Repeated intrusions of magmas into cold crust can transfer heat and increase the local geothermal gradient, causing the surrounding rock to melt and generate new magmas.
- Addition of water or carbon dioxide lowers the melting temperature, leading to partial melting of rocks, and this flux melting is a common mechanism in subduction zones.
- The initial composition of magma is dictated by the composition of the source rock and the degree of partial melting, with melting of a mantle source resulting in mafic/basaltic magmas and crustal sources yielding more siliceous magmas.
- Magmatic differentiation refers to the process by which a homogeneous magma changes its composition or becomes heterogeneous, and mechanisms include fractional crystallization and magma mixing.
Plate Tectonics and Igneous Genesis
- Convergent boundaries are also known as destructive margins where two plates move together, resulting in oceanic lithosphere descending beneath an overriding plate or in the collision of two continental blocks to create a mountain system.
- Subduction zones are sites where lithosphere is descending into the mantle because of the density difference between the tectonic plate and the underlying asthenosphere.
- Deep-ocean trenches are large linear depressions produced as oceanic lithosphere descends into the mantle at convergent boundaries.
- Oceanic-continental convergence triggers melting within the wedge of hot asthenosphere when a descending oceanic slab reaches a depth of about 100 km, resulting in the generation of continental volcanic arcs.
- Oceanic-oceanic convergence involves the sideways and downward movement of the edge of a plate into the mantle beneath another plate, leading to the formation of volcanic island arcs and obduction.
- Continental-continental convergence is an example of convergent boundaries.
- Transform boundaries, also known as conservative margins, involve two plates grinding past each other without the production or destruction of lithosphere.
- Fracture zones are prominent linear breaks in the seafloor that include both active transform faults and their inactive extensions into the plate interior.
- Igneous genesis includes various processes such as mid-ocean ridges, intracontinental rifts, island arcs, active continental margins, back-arc basins, and ocean island basalts.
- Petrology is the branch of geology dealing with the origin, occurrence, structure, and history of rocks, including igneous, sedimentary, and metamorphic rocks.
- Igneous rocks directly solidify from molten or partially molten material, while sedimentary rocks result from the consolidation of loose particles or chemicals precipitating from solution, and metamorphic rocks derive from pre-existing rocks by mineralogical, chemical, or structural changes.
- Rocks are classified based on outcrop characteristics, general texture, mineral assemblages present, and abundance of different rock types on the continents and in ocean sediments.
Plate Tectonics and Divergent Boundaries
- The Earth's lithosphere is composed of massive, irregularly shaped slabs of solid rock, which make up the tectonic plates.
- Major tectonic plates include the North American, South American, Pacific, African, Eurasian, Australian-Indian, and Antarctic plates, while minor plates include the Caribbean, Nazca, Philippine, Arabian, Cocos, Scotia, and Juan de Fuca plates.
- Divergent boundaries are constructive margins where two plates move apart, leading to the creation of new ocean floor.
- These boundaries are located along the crests of oceanic ridges and are characterized by high heat flow and volcanism.
- The global ridge system, including the Mid-Atlantic Ridge, East Pacific Rise, and Mid-Indian Ridge, is the longest topographic feature on Earth's surface, exceeding 70,000 kilometers in length.
- The primary reason for the elevated position of the oceanic ridge is that newly created oceanic crust is hot and less dense than cooler rocks found away from the ridge axis.
- Rift valleys, such as the Thingvellir fracture zone in Iceland, are evidence of tensional forces actively pulling the ocean crust apart at the ridge crest.
- Seafloor spreading is the mechanism that operates along the oceanic ridge system to create new seafloor at an average rate of around 5 cm per year.
- Continental rifting occurs where opposing tectonic forces act to pull the lithosphere apart, leading to the sinking of crustal fragments.
- The East African Rift is considered the "birthplace" of the human race, as it is where remains of early humans, Homo habilis and Homo erectus, were discovered.
- The text provides various sources for further information on plate tectonics and divergent boundaries.
- The text also mentions the relative atomic abundances of the seven most common elements comprising 97% of the Earth's mass and references to additional resources for geological principles.
Magmatic Differentiation and Igneous Petrology Overview
- Magmatic differentiation processes, including crystal fractionation, magmatic mixing, and assimilation, play a crucial role in controlling magma composition and differentiation.
- Crystal fractionation occurs as minerals crystallize at different temperatures, leading to changes in magma composition as certain minerals are removed from the liquid.
- Magmatic mixing occurs when two magmas with different compositions come into contact, resulting in a mixed magma with an intermediate composition.
- Magmatic assimilation involves the reaction between magma and the surrounding country rock, leading to changes in magma composition due to the incorporation of material from the wall rock.
- Bowen’s Reaction Series demonstrates the order in which minerals crystallize from a basaltic magma, impacting the evolution of magma composition with falling temperature.
- Igneous petrology involves the classification of igneous rocks based on composition, fabric, and field relations.
- Classification based on composition can be determined by either modal mineralogy or normative mineralogy, with the CIPW norm classification being a commonly used normative classification system for volcanic rocks.
- The percentage by weight of silica is a key factor in the classification of igneous rocks based on composition, with basic and acidic classifications differing from their chemical pH-related meanings.
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Explore the processes of magmatic differentiation, plate tectonics at divergent boundaries, and igneous genesis through this quiz. Learn about fractional crystallization, magma mixing, divergent boundaries, subduction zones, and the formation and composition of magma.
