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Questions and Answers
What describes a divergent boundary?
What describes a divergent boundary?
Which type of rock is formed from the rapid cooling of magma?
Which type of rock is formed from the rapid cooling of magma?
What is characteristic of composite volcanoes?
What is characteristic of composite volcanoes?
What is required to melt the mantle through decompression melting?
What is required to melt the mantle through decompression melting?
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Which mineral is associated with high crystallization temperatures?
Which mineral is associated with high crystallization temperatures?
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What accurately describes a batholith?
What accurately describes a batholith?
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Which of the following is NOT a method to melt the mantle?
Which of the following is NOT a method to melt the mantle?
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Which statement about intrusive igneous rocks is true?
Which statement about intrusive igneous rocks is true?
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What distinguishes andesite lavas from basaltic lavas?
What distinguishes andesite lavas from basaltic lavas?
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Which type of pyroclastic material is described as lumps of frothy magma?
Which type of pyroclastic material is described as lumps of frothy magma?
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Which of the following statements about mudflows is true?
Which of the following statements about mudflows is true?
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What is a defining characteristic of clastic sedimentary rocks?
What is a defining characteristic of clastic sedimentary rocks?
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What characterizes mature sediment?
What characterizes mature sediment?
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Which of the following is a poorly resistant mineral to weathering?
Which of the following is a poorly resistant mineral to weathering?
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Which clastic rock is described as having rounded particles?
Which clastic rock is described as having rounded particles?
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What does sediment maturity refer to in sedimentary geology?
What does sediment maturity refer to in sedimentary geology?
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What type of sedimentary rock forms from the chemical precipitation of minerals from water?
What type of sedimentary rock forms from the chemical precipitation of minerals from water?
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What process describes the transition from sediment to sedimentary rock?
What process describes the transition from sediment to sedimentary rock?
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Which type of inorganic sedimentary rock is formed from evaporation of shallow lakes?
Which type of inorganic sedimentary rock is formed from evaporation of shallow lakes?
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Which mineral is most commonly found in clastic sedimentary rocks?
Which mineral is most commonly found in clastic sedimentary rocks?
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What is a characteristic feature of beds and strata in sedimentary rock?
What is a characteristic feature of beds and strata in sedimentary rock?
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Which type of sedimentary rock is predominantly formed from the accumulation of fossils?
Which type of sedimentary rock is predominantly formed from the accumulation of fossils?
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What defines the evaporite mineral sequence in order of increasing solubility?
What defines the evaporite mineral sequence in order of increasing solubility?
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Which mineral is primarily found in geodes?
Which mineral is primarily found in geodes?
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What characterizes high-grade metamorphic rocks compared to low-grade rocks?
What characterizes high-grade metamorphic rocks compared to low-grade rocks?
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Which of the following sequences correctly lists the metamorphic rock types from low to high grade?
Which of the following sequences correctly lists the metamorphic rock types from low to high grade?
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What is the primary condition for the formation of high-P, low-T metamorphic environments?
What is the primary condition for the formation of high-P, low-T metamorphic environments?
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Which of the following minerals is characteristic of the rock named 'Schist'?
Which of the following minerals is characteristic of the rock named 'Schist'?
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What is the defining process of metasomatism in metamorphic rocks?
What is the defining process of metasomatism in metamorphic rocks?
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Which rock is produced from the metamorphism of limestone?
Which rock is produced from the metamorphism of limestone?
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During regional metamorphism, how does the metamorphic grade change with depth in the crust?
During regional metamorphism, how does the metamorphic grade change with depth in the crust?
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What is a characteristic feature of porphyroblasts in metamorphic rocks?
What is a characteristic feature of porphyroblasts in metamorphic rocks?
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Study Notes
Earth's Plates
- The Earth's surface is made of thirteen lithospheric plates that are constantly in motion.
- These plates are composed of the lithospheric mantle (solid) and crust (solid).
- The plates are underlain by the upper mantle (asthenosphere) which is hot, plastic, and convects.
- Three major types of plate boundaries exist: divergent, convergent, and transform.
Minerals & Rocks
- A mineral is a naturally occurring, inorganic solid with a specific chemical composition and a well-defined, repetitive crystal structure.
- Rocks are composed of minerals.
- There are approximately 4,000 known minerals, and knowing 25 of them is important for studying geology.
- Bone is not a mineral as it is organic.
Igneous Rocks
- Igneous rocks form from the cooling and solidification of magma or lava.
- Intrusive igneous rocks cool slowly at depth, resulting in large, uniform grain sizes.
- Extrusive igneous rocks cool rapidly on the surface, leading to small grain sizes.
- A rock's mineral composition, texture, and chemical composition help determine its name.
Mantle Melting
- The mantle can melt in several ways:
- Decompression melting: Occurs when pressure decreases, allowing the mantle to melt.
- Dehydration melting: Occurs when volatile compounds like water and carbon dioxide are added to the mantle.
- Hot mantle plumes: Decompression melting can occur at hot mantle plumes.
- Plate melting: Melting of oceanic plates is possible, but less common.
Crystallization Temperatures
- Minerals crystallize at different temperatures:
- High temperature: Olivine, pyroxene, calcium-feldspar
- Intermediate temperature: Amphibole, sodium-feldspar, biotite
- Low temperature: Biotite, sodium-potassium feldspar, quartz
- The vast majority of magma crystallizes at depth.
Plutonic Structures
- Plutonic igneous rocks are exposed by erosion.
- The general term for a large, massive intrusion is a "pluton".
- Other types of intrusive bodies include sills and dykes:
- Sills: Thin, tabular intrusions that are horizontal.
- Dykes: Thin, tabular intrusions that are predominantly vertical.
- Batholith: An assemblage of plutons, often composed of granodiorite or granite.
- Neck: A solidified dyke within a volcano.
Volcanic Structures
- Batholiths are often the eroded roots of subduction-related volcanic complexes.
- There are five types of volcanic structures:
- Shield volcano: Formed by fluid lavas, have low slopes.
- Composite volcano: Formed by alternating layers of lava flows and pyroclastic materials. These volcanoes have steep slopes, are tall, often snowcapped, and can erupt explosively.
- Cinder cone: Composed of basaltic pyroclasts (scoria). Have steep slopes, small size, and a crater in the center.
- Lava flows: Include types like pahoehoe, A'a', and pillow lavas.
- Domes: Formed by the extrusion of viscous lava.
Pyroclastic Materials
- Pyroclastic materials are fragments of volcanic rock ejected during eruptions.
- Pumice or Scoria: Lumps of frothy magma.
- Ash, dust: Fine particles that can affect climate.
- Bombs: Ejected lava blobs, often aerodynamically shaped.
- Blocks: Ejected solid pre-existing rock.
- Pyroclastic flows are highly dangerous and can reach temperatures over 800°C.
Mudflows (Lahar)
- Mudflows can occur when eruptions melt snow, which mixes with ash.
- Hot mudflows are considered lahar.
Sedimentary Rocks
- Sedimentary rocks form from the weathering, erosion, deposition, and lithification of pre-existing rocks.
- They are classified into two types: clastic and chemical.
Clastic Sedimentary Rocks
- Clastic rocks are formed from the breakdown of rocks, transportation of particles, deposition, and then lithification.
- The most common minerals in clastic rocks are quartz, feldspar, and clay minerals.
- Clastic rocks are named based on their particle size:
- Gravel: Angular= breccia, rounded= conglomerate.
- Sand: Sandstone.
- Mud: Shale or mudstone.
Clastic Rock Properties
- Properties used to describe clastic rocks include:
- Grain size
- Roundness
- Sorting
- Mineral composition
- The farther a sediment travels from its source, the smaller, rounder, better-sorted, and more quartz-rich the grains become.
Chemical Sedimentary Rocks
- Chemical rocks form from the precipitation of minerals from water.
- They are classified into two types: inorganic and organic.
Inorganic Chemical Rocks
-
SiO2 (Silica):
- Chert, Opal: Microcrystalline silica, deposited in cavities in rocks.
-
CaCO3 (Calcium carbonate), SiO2:
- Travertine (CaCO3), Sinter (SiO2): Precipitate inorganically at hot springs.
- Stalactites, Stalagmites (CaCO3): Found in caves.
-
CaCO3:
- Limestone: Formed by the inorganic precipitation of calcium carbonate in warm, supersaturated, agitated marine environments.
- Ooids: Layers of calcium carbonate deposited around sand grains.
Evaporite Minerals
- Evaporation of shallow lakes and inland seas causes the precipitation of minerals in order of increasing solubility:
- Gypsum (CaSO4.H2O), Anhydrite (CaSO4): Least soluble.
- Halite (NaCl)
- Sylvite (KCl): Most soluble.
Organic Chemical Rocks
- Organisms extract calcium carbonate from seawater to form shells. When they die, their shells sink to the bottom of the ocean, forming biochemical sediment.
-
CaCO3:
- Limestone: Most common chemical sediment, often formed from fossils (coquina, coral reefs).
-
SiO2:
- Chalk: Formed from the accumulation of microscopic organisms (plankton).
Metamorphism
- Metamorphism is the process of transforming pre-existing rocks into new rocks by changes in temperature, pressure, and fluid interaction.
- It involves the growth of new minerals and textural changes.
Metamorphism Types
- Three main types of metamorphism:
- Contact metamorphism: Occurs when rocks are heated by an intruding pluton.
- Regional metamorphism: Occurs due to the increase in temperature and pressure associated with burial.
- Metasomatism: Involves chemical reactions between fluids and pre-existing rocks, leading to the formation of new minerals.
Metamorphic Grade
- Metamorphic grade refers to the intensity of metamorphism. It is indicated by:
- Mineral assemblages
- Texture
- Increasing metamorphic grade corresponds to:
- Increased grain size
- Development of foliation (a layered or banded texture)
Foliated Metamorphic Rocks
- Rocks that have developed a layered or banded texture are called foliated.
- The name of a foliated metamorphic rock reflects its metamorphic grade:
- Slate: Lowest grade.
- Phyllite: Intermediate grade.
- Schist: Higher grade.
- Gneiss: Highest grade.
- Migmatite: Partially melted gneiss.
Non-foliated Metamorphic Rocks
- Rocks that do not exhibit foliation are called non-foliated.
- Quartzite: Metamorphosed sandstone.
- Marble: Metamorphosed limestone.
- Amphibolite: Metamorphosed basalt (medium grade).
- Eclogite: Metamorphosed basalt (high grade).
Migmatite
- Migmatite is a partially melted gneiss.
- It exhibits ribbons of quartz and potassium feldspar (representing the melt) within a matrix of biotite and hornblende.
Index Minerals
- Index minerals are minerals that are diagnostic of specific metamorphic grades. They can be used to determine the conditions of metamorphism.
Subduction Zones
- Subduction zones are areas where one lithospheric plate is forced beneath another.
- These zones are characterized by:
- High pressure
- Low temperature
- These conditions produce distinctive metamorphic rocks, such as eclogite.
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