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231 Cards in this Set
- Front
- Back
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steps of scientific method
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hypothesis => theory => scientific model
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topography
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the general configuration of varying heights that give shape to earth's surface. Measure in respect to sea level.
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geology record
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the information preserved in rocks formed at various times throughout Earth's long history.
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principle of uniformitarianism
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(James Hutton) "the present is the key to the past". Geo processes we see in action today have worked in much the same way throughout geologic time.
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seismic waves
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ground vibrations produced by earthquakes or explosions
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mantle
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the region that forms the main bulk of the solid Earth, between the crust and the core, randing from depths of about 40 km to 2900 km. It is composed of rocks of intermediate density, mostly compounds of oxygen with magnesium, iron, and silicon.
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core
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the cental part of the earth below a depth of 2900 km, comprising a liquid outer core and a solid inner core. The core is composed of iron and nickel, with minor amounts of some lighter element, such as oxygen or sulfur.
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compressional waves
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expand and compress as they travel through solid, liquid, or gas. Push-pull motion of a material.
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shear waves
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involve side-to-side motion (shearing). These waves cannot propagate through any fluid- air, water, or the liquid iron in Earth's outer core.
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crust
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the thin outer layer of the earth, averaging about 8 km thick under the oceans to about 40 km thick under the continents, consisting of relatively light materials that melt at low temperatures. Continental crust consists largely of granite and granodiorite. Oceanice crust is mostly basalt.
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mohorovicic discontinuity
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(Moho) the boundary between the crust and the mantle, at a depth of 5 to 45 km, marked by an abrupt increase in the P-wave (first seismic wave to arrive from the focus of an earthquake; a type of compressional wave) velocity to more than 8 km/s
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inner core
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the central part of the earth from a depth of 5150 to 6370 km, composed of iron and nickel. a solid metallic sphere with a radius of 1220 km- about 2/3s the size of the Moon- suspended within the liquid outer core.
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outer core
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a liquid zone- composed of iron, nickel, and minor amounts of some lighter element, such as O or sulfur- below the mantle, from a depth of 2890 to 5190 km, that surrounds a solid iron-nickel inner core.
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transition zone
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seperates the upper and lower mantles. rock density increases in a series of steps.
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open system
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the earth is an open system because it exchanges mass and energy with the rest of the cosmos.
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geosystems
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a specialized subsystem of the earth system that encompasses specific types of terrestrial behavior. Geosystems include the plate tectonic system, the climate system, the geodynamo system, and other smaller subsystems. The earth system can be thought of as the collection of all these open, interacting (and often overlapping) geosystems.
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climate system
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a geosystem that includes all parts of the earth system and all the interactions among these components needed to describe how climate behaves in space and time.
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greenhouse effect
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the sun warms the earth's surface, some of the heat is trapped by water vapor, CO2, and other gases in the atmosphere, much as heat is trapped by frosted glassin a greenhouse. This explains why the earth has a pleasant climate that makes life possible.
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plate tectonics
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the theory proposing that the lithosphere is broken into about a dozen large plates that move over earth's surface. each plate acts as a distinct rigid unit that rides on the asthenosphere, which also is in motion. The theory attempts to explain seismicity, volcanism, mountain building, and evidence of paleomagnetism in terms of these plate motions.
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volcanic eruptions and earthquakes are caused by...
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he earth's internal heat, which escapes through the circulation of material in the earth's solid mantle.
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lithosphere
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the strong, rigid outer shell of the earth that encases the ashtenosphere and contains the crust and the uppermost part of the mantle down to an average depth of about 100 km and forms the rigid plates
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asthenosphere
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the weak layer of soft but solid rock comprising the lower part of the upper mantle (below the lithosphere) and over which the plates slide. Movement in the asthenosphere occurs by plastic deformation. (from the greek word asthenes, meaning "weak").
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Why do the plates move across Earth's surface instead of locking up into a completely rigid shell?
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the forces that push and pull the plates around the surface come form the heat engine in the Earth's solid mantle. Driven by heat, hot mantle material rises where plates seperate.
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convection
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a mechanism of heat transfer in which a heated fluid expands and rises because it has become less dense than the surrounding material. Colder material flows in to take the place of the hot rising fluid, is itself heated, and then rises to continue the cylcle. (think boiling soup example from class).
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plate tectonic system
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a geosystem that includes all parts of the earth system, and all the interactions among these components needed to describe how plate tectonics works in space and time.
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magnetic field
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the region of influence of a magnetized body or an electric current
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geodynamo
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the geosystem that sustains Earth's magnetic field, driven by convection in the outer core.
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magentic reversals
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found very useful to geologists b/c they can use their imprint on the geological record to help them figure out the motions of the tectonic plates
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What are the Earth's major layors?
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earth's interior is divided into concentric layers of different compositions, separated by sharp, nearly spherical boundaries. The outer layer is the crust, which varies from about 40 km thick beneath continents to about 8 km beneath oceans. Below the crust is the mantle, the thick shell of denser rock that extends to the core-mantle boundary at a depth of 2900 km The central core, which is composed primarily of iron and nickel, is divided into 2 layers: a liquid outer core and a solid inner core, seperated by a boundary at a depth of 5150 km.
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continental drift
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the large-scale motion of continents across Earth's surface driven by plate tectonics.
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Pangea
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a supercontinent that coalesced in the latest Paleozoic era and comprised all present continents. The breakup of Pangea began in Mesozoic time, as infered from paleomagnetic and other data.
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seafloor spreading
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the mechanism by which new seafloor is created along the rift at the crest of a mid-ocean ridge as adjacent plates move apart. The crust seperates along the rift, and new seafloor forms as hot new crust upwells into these cracks. the new seaflorr spreads laterally away from the rift and is replaced by even newer crust in a continuing process of plate creation.
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name the 3 basic types of plate boundaries
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divergent: plates move apart and new lithosphere is created (plate area increases)
convergent: plates come together and one is recycled back into the mantle (plate area decreases) transform-fault: plates slide horizontally past each other (plate area remains constant). |
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Continental crust v. oceanic crust
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cont. => lighter, not as easily recycled, weaker (plate boundaries are more spread out and more complicated than oceanic crust)
Oceanic => stronger, heavier, easily recycled, less spread out and less complicated |
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spreading centers
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the region at the crest of a mid-ocean ridge, where new crust is being formed by seafloor spreading.
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oceanic plate separation
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rifting and spreading along a narrow zone have created the mid-atlantic ridge, a mid-ocean mountain chain where volcanoes and earthquakes are concentrated. mid-ocean ridges exhibit active volcanism, earthquakes, and rifting caused by tensional (stretching) forced that are pulling the two plates apart.
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continental plate separation
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characterized by rift valleys, volanic activity, and earthquakes distributed over a wider zone than is found at oceanic spreading centers. Red Sea. Gulf of California are examples of rifts that are further along the spreading process. The East African Rift, the Rhine Valley are examples that haven't allowed water to fill in.
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ocean-ocean convergence
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when 2 oceanic plates converge, they form a deep-sea trench and a volcanic island arc. Subduction of a plate.
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ocean-continent convergence
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when an oceanic plate meets a continetal plate, the ocean plate subducts and a volcanic belt of mountains is formed at the continental plate margin. Ex: Andes Mountains
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continent-continent convergence
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when 2 continental plates collide, the crust crumples and thickens, creating high mountains and a wide plateau. Ex: Himalayas next to Tibetan Plateau.
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mid-ocean ridge transform fault
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spreading centers are offset by mid-ocean ridge transform faults, where the 2 oceanic plates slide horizontally past each other. Ex: Eurasian plate
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continental transform fault
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the San Andreas fault (california) where the Pacific Plate slides past the North American plate, is an example of a transform fault that offsets continental crust.
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subduction
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the sinking of an oceanic plate beneath an overriding oceanic or continental plate at a convergent plate boundary.
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island arc
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a linear or arc-shaped chain of volcanic islands formed on the seafloor at a convergent plate boundary. The islands are formed in the overriding plate from rising melt derived from fluid-induced melting of the mantle wedge above the downgoing lithospheric slab.
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transform faults
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a plate margin at which the plates slide past each other and lithosphere is neither created nor destroyed. Relative displacement occurs along the fault as horizontal slip between the adjacent plates.
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magnetic anomalies
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a pattern of long, narrow bands of high and low magnetic fields on teh seafloor that are parallel to and almost perfectly symmetrical with respect to the crest of a mid-ocean ridge. The detection of such patterns was one of the great discoveries tht confirmed seafloor spreading and lef to plate tectonics theory.
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thermoremanent magnetization
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A permament magnetization acquired by minerals in igneous rocks when groups of atoms of the mineral align themselves in the direction of teh magnetic field that existed when teh material was hot. When the material has cooled, these atoms are locked in place and therefore are always magnetized in teh same direction
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magnetic time scale
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teh detailed history of earth's magnetic field reversals going back into geologic time, as determined by measuring the thermoremanent magnetization of rock samples
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magnetic chrons
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major periods when the magnetic field is normal or reversed. seem to last about .5 million years
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magnetic subchrons
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short-lived reversals of the field, which may last anywhere from several thousand to 200,000 years.
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positive magnetic anomaly
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rocks magnetized in the normal direction, stronger field
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negative magnetic anomaly
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rocks magnetized in the reversed direction, weaker field
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relative plate velocity
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the velocity at which one plate moves relative to the other
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geodesy
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the ancient science of measuring teh shape of the earth and locating points on its surface
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GPS
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Global Positioning System. signals from GPS satellites can be used to monitor plate motions.
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name the 2 principles that explain the direction of movement of one plate in relation to another...
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1. Trasnform-fault boundaries indicate the directions of relative plate movemnt.
2. Seafloor isochrons reveal the positions of divergent boundaries in earlier times |
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Rodina
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a supercontinent that formed about 1.1 Ga and began to break up about 750 Ma.
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How can the age of teh seafloor be determined?
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we can measure teh age of teh ocean's floor by comparing magnetic anomaly bands mapped on the seaflor with the sequence of magnetic reversals worked out on land. The procedure has been verified and extended by deep-sea drilling. Geologists can now draw isochrons for most of the world's oceans, enabling them to reconstruct the history of seafloor spreading over the past 200 years. Using this method and other geologic data, geologists have developed a detailed model of how Pangea broke apart and the continents drifted into their present configuration.
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What is the engine that drives plate tectonics?
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The plate tectonic system is driven by mantle convection, and teh energy comes from Earth's internal heat. The plates temselves play an active role in this system. For ex, the most important forces in plate tectonics come from teh cooling lithosphere as it slides away from spreading centers and sinks back into the mantle in subduction zones. Lithospheric slabs extend as deep as the core-mantle boundary, indicating that the whole mantle is involved in the convection system that recycles teh plates. Rising convection currents may include mantle plumes, intense upwellings from the deep mantle that cuase localized volcanism at hot sports such as Hawaii.
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things that constitute a mineral
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1. must be naturally occuring/found in nature.
2. they must be solid crystalline substances - they are niether gases nor liquids. Crystalline means that tiny particles of matter, or atoms, that compose it are arranged in an orderly, repeating, 3D array. 3. Generally inorganic. 4. Specific Chemcial Composition. |
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atomic number
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# of protons
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atomic mass
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protons + neutrons
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isotopes
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atoms with different numbers of neutrons
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chemical reactions
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interactions of teh atoms of 2 or more chemical elements in certain fixed proportions that produce chemical compounds.
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chemical compounds are formed through...
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e- sharing or e- transfering
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electron sharing
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the mechanism by which a covlant bond is formed btwn the elements in a chemical reaction
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electron transfering
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the mechanism by which an ionic bond is formed between the elements in a chemical reaction
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cation
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positively charged ion, meaning less e-s
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anion
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negatively charged ion, meaning more e-s
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chemical bonds
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electrical attractions btwn shared e-s or btwn gained or lost e-s. May be weak or strong. Two major types are ionic and covalent.
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ionic bond
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a bond btwn atoms formed by electrical attractions between ions of the opposite charge.
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covalent bond
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a bond btwn atoms in which the outer e's are shared.
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metallic bond
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a covalent bond in which freely mobile e's are shared and dispersed among ions of metallic elements, which have the tendency to lose e's and pack toegher as cations
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crystallization
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the growth of a solid from a gas or liquid whose constituent atoms come together in the proper chemical proportions and ordered 3D arrangement.
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cation substitution
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cations of sim sizes and charges tend to substitute for one another and to form compounds having the same crystal structure but differing chemical composition.
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crystal
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an ordered 3D array of atoms in which the basic arrangement is repaeted in all directions
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precipitate
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the crystals that drop out of a saturated solution
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polymorphs
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one of 2 or more alternative possible crystal structures for a single chemical compound; for ex, teh minerals quartz and cristobalite are polymorphs of silica.
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most common rock forming minerals
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silicates, carbonates, oxides, sulfides, sulfates
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silicates
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most abundent in earth's crust, composed of O and Si (silicon) - the 2 most abundent elements in the crust.
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carbonates
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minerals made of C and O in the form of the carbonate anion in combination with Ca and Mg.
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oxide
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compounds of the O anion (O^2-) and metallic cations; an exmaple is hematite
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sulfides
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compounds of the sulfide anion (S^2-) and metallic cations, a group that includes the mineral pyrite.
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sulfates
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compounds of the sulfate anion (SO4^2-) and metallic cations, a group that includes mineral anhydrite.
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hardness scale
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talc -1
gypsum, fingernail - 2 calcite, copper coin- 3 fluorite - 4 apatite, knife blade - 5 orthoclase, window glass - 6 quartz, steel file - 7 topaz- 8 corundum - 9 diamond - 10 |
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cleavage
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the tendency of a crystal to break along flat planar surfaces
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cleavage is classified by..
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number of planes and quality of surfaces and ease of cleaving
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fracture
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tendency of a crystal to break along irregular surfaces other than cleavage planes.
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types of luster
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metallic: strong reflections produced by opaque substances
Vitreous: bright, as in glass resinous: ex: amber greasy Pearly silky adamantine: brilliant luster of diamond and similar materials |
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specific gravity
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a standard measure of density. It is the weight of a mineral divided by the weight of an equal volume of pure water at 4 degrees C.
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crystal habit
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a mineral's crystal habit is the shape in which its individual crystals or aggregates of crystals grow. Named after geometric shapes (blades, plates, needles).
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igneous rocks
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a rock formed by the solidification of a magma, before or after it reaches the surface
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sedimentary rocks
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formed as the burial product of layers of sediments (such as sand, mud, and calcium carbonate shells), whether they were laid down on teh land or under the sea
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metamorphic rocks
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rock formed by the transformation of preexisting solid rocks under the influence of high pressure and temperature
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intrusive igneous rocks
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an igneous rock midway in composition between mafic and felsic, niether as rich in silica as the felsic rocks nor as poor in it as the mafic rocks. AKA plutonic. Phanetic - coarse enough to see crystals all through the rock. The kind of rock has forced its way into surrounding rock
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extrusive igneous rocks
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a fine-grained or glassy igneous rock formed from a rapidly cooled magma that erupts at the surface though a volcano. AKA volcanic. Aphanitic - ground mass too fine grained to see. This kind of rock forms when lava or other materials erupt from volcanoes.
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weathering
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the general process that breaks up rocks into fragments of various sizes by a combination of physical fracturing and chemical disposition.
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erosion
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the set of processes that loosen soil and rock and move them downhill or downstream, where they are deposited as layers of sediment
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siliciclastic sediments
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clastic sedmient produced by teh weathering of rocks composed largely of silicate minerals.
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chemical and biochemical sediments
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new chemical substances that form y precipitation when some of a rock's components dissolve durign weathering andare carried in river waters to teh sea.
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lithification (list all)
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process that converts sediments into solid rock, and it occurs in one of two ways:
compaction: grains squeezed together by the weight of overlying sediment into a mass denser than the original and cementation: minerals precipitate around deposited particles and bind them together. |
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bedding
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the formation of parallel layers of sediment as particles settle to teh bottom of the sea, a river, or a land surface.
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examples of siliciclastic minerals
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quartz, feldspar, clay minerals
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ex s of chemically or biochemically precipitated sediments
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carbonates (calcite, the main constituent of limestone), dolomite (also found in limestone), gypsum, and halite (which both form by precipitation as sea water evaporates)
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regional metamorphism
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metamorphism caused by high pressures and temperatures that extend over large regions, as happens where plates collide
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contact metamorphism
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changes in teh mineralogy and texture of rock resulting from the heat and pressure in a small area, such as the rocks near and in contact with an igenous intrusion.
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foliation
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a set of flat or wavy parallel planes produced by deformation
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rock cycle
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teh set of geologic processes that convert each type of rock into teh other two types
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ore
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a mineral deposit from which valuable metals can be recovered profitably
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list out the rock cycle
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1. rifting and development of a divergent margin within a continent. sediments erode from teh continental interior and are deposited in rift basins, where they are buried to form sedimentary rocks.
2.) rifting and spreading continue, and a new ocean basin develops. magma rises from the asthenosphere at mid-ocean ridges and chills to form igneous rock (ex: basalt) 3.) subsidence of the continental margin- sinking of earth's lithosphere- leads to accumulation of sediment and formation of sedimentary rock during burial. 4.) oceanic crust subducts beneath a continent, building a volcanic mountian chain. The subducting plate melts as it descends. Magma rises from teh melting plate and mantle and cools to make granitic igneous rocks. 5.) Further closing of the ocean basin leads to continental collision, forming high mountain ranges. Where continets collide, rocks are buried deeper or modified by heat and pressure, forming metamorphic rocks. Uplifted mountains froce moisture-laden air to rise, cool, condense, and precipitate. Weathering creates loose material- soils and sediment - that erosion strips away. 6.) streams transport sediment away from collision zones to oceans, where it is deposited as layers of sand and silt. Layers of sediment are buried and lithify to form sedimentary rock. |
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hydrothermal solutions
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a hot solution formed around bodies of molten rock when circulating groundwater comes into contact with a hot intrusion, reacts with it, and carries off significant quantities of elements and ions released by teh reaction. These elements and their ions then interact with one another to deposit ore minerals, usually as the fluid cools.
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vein deposits/veins
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a sheetlike deposit of minerals precipitated in fractures or joints that are foreign to the host rock.
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what's a mineral?
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minerals, the building blocks of rocks, are naturally occuring, inorganic solids with specific crystal structures and cehmical compositions that either are fixed or vary within a defined range. A mineral is constructed of atoms, the small units of matter that combine in chemical rxns. An atom is composed of a nucleus of protons and nuetrons, surrounded by e-s. The atomic # of an element is the # of protons in its nucleus, and its atomic mass is the sum of the masse of its ps and ns.
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country rock
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the rock surrounding an intrsive igneous rock
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pyroclasts
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a volanic rock fragment ejected into the air during an eruption
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volcanic ash
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extremely small fragments, usually of glass, that form when escaping gases force a fine spray of magma from a volcano.
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tuff
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any volcanic rock lithified from pyroclasts
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pumice
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a frothy mass of volcanic glass with a great number of holes (vesicles) that remain after trapped gas has escaped from the solidifying melt.
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obsidian
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a dense, dark, glassy volcanic rock, usually of felsic composition.
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poryphyry
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a lava of mixed texture in which large crystals (phenocrysts) "float" in a predominantly fine crystalline matrix.
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examples of extrusive pyroclasts
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volcanic ash, bomb, pumice
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examples of extrusive igneous rocks
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basalt (mafic), rhyolite (felsic)
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examples of intrusive igneous rocks
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gabbro (mafic), granite (felsic)
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Felsic rocks
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poor in iron and Mg and rich in minerals igenous rocks that are high in silica. These rocks/minerals tend to be light in color. They crystallize in lower temps than mafic rocks
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examples of felsic rocks
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quartz, potassium feldspar, plagioclase feldspar, muscovite (mica)
granite contains a lot of felsic rocks/silica. Rhyolite (the extrusive equivolent of granite) has a lot of felsic minreals in it, too. |
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granite
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a felsic, coarse-grained, intrsuive ign rock composed of quartz, orthoclase feldspar, sodium-rich pagioclase feldspar, and micas. The intrusive equivalent of rhyolite.
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rhyolite
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a light-brown to gray, fine grained extrusive ign rock with a felsic composition. The extrusive equivalent of granite.
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intermediate igenous rocks
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are neither felsic nor mafic, in the middle.
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diorite
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a coarse-grained intrusive ign. rock with composition intermediate btwn granite and gabbro. The intrusive equivalent of andesite.
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andesite
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a volcanic rock type intermediate in composition between rhyolite and basalt. The extrusive equivalent of diorite.
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mafic rocks
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characteristics of igneous rocks, crystallize at higher temps than felsic. Poor in silica but rich in Mg and Fe. Dark colors.
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examples of mafic rocks
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gabbro, basalt
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gabbro
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a dark grey, coarse-grained intrusive ign rock with an abundance of mafic minerals, particularly pyroxene. The intrusive equivalent of basalt.
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basalt
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a fine-grained, dark, mafic igneous rock composted largely of plagioclase feldspar and pyroxene. Ther extrusive equivalent of gabbro.
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ultramafic rocks
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an igneous rock that consist primarily of mafic minerals and contain less than 10% feldspar. Example is peridotite.
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viscosity
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the measure of a liquid's resistance to flow. Increases as silica content increases.
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partial melting
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the incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures.
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decompression melting
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melting that occurs when mantle material rises to an area of lower pressure at a mid-ocean ridge. As the mantle material rises adn the pressure decreases below a critical point, solid rocks melt spontaneously, without the introduction of any additional heat
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magma chambers
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a magma filled cavity in the lithosphere that forms as ascending drops of melted rock push aside surrounding solid rock.
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magmatic differentiation
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a process by which rocks of varying composition can arise from a unofrm parent magma. Various mineras crystallize at diff temps, and the composition of the magma changes as it is depleted of the chemical elements withdrawn to amke the crystallized minerals.
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fractional crystallization
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the process by which the crystalls formed in a cooling magma are segregated from teh remaining liquid at pogressively lower temps.
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magma rising through the crust makes space for itself in 3 ways (which may be referred to collectively as magmatic stoping)
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1.) weding open the overlying rock. As the magma lifts that great weight, it fractures the rock, penetrates the cracks, wedges them open, and so flows into the rock. Overlying rocks may bow up during this process.
2.) Breaking off large blocks of rock. Magma can push its way upward by breaking off blocks of the invaded crust. 3.) Melting surrounding rock. Magma also makes its way by melting walls of country rock. |
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plutons
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a large ign intrusion ranging in size from a cubic kilometer to hundreds of cubic kilometers, formed at depth in the crust
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sills
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a sheetlike concordant intrusion formed by the injection of magma btwn parallel layers of preexisting bedded rock.
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concordant intrusions
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an intrusive ign rock whose boundaries lie parallel to layers of preexisting bedded rock.
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sills differ from layers of lava flows and pyroclastic materal (even though they resemble them) in 4 ways:
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1.) They lack teh ropy, blocky, and vesicle-filled strctures that characterize many volcanic rocks.
2.) they are more coarsely grained than volcanics because the sills have cooled more slowly. 3.) rocks above and below sills show the effects of heating: their color may have been changed or they may have been mineralogically altered by contact metamorphism. 4.) Many lava flows overlie weathered older flows or soils formed btwn successive flows; sills do not. |
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dikes
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a tabular ign intrusion that cuts across layers of bedding in country rock.
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magma forms at 2 types of plate boundaries:
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mid-ocean ridges, and subduction zones
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how are ign rocks classified?
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1.) coarsely crystalline rocks, which are intrusive and therefor cooled slowly
2.) finely crystalline rocks, extrusive, cooled rapidly |
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how and where do magams form?
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magams form at places in teh lower crust and mantle where temps and pressures are high enough for at least partial metling of water-containing rock. Basalt can partially mely in the upper mantle, where convection currents bring hot rock upward at mid-ocean ridges. Mixtures of basalt and other ign rocks with sed rocks, which contain significant quantities of water, have lower melting points than dry ign rocks. Thus, different source rocks may melt at different temps and thereby affect magma compositions.
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how are ign rocks related to plate tectonics?
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the 2 major magmatic geosystems are the mid-ocean ridges, where basalt wells up from the upper mantle and melts during decompression to form oceanic crust, and subduction zones, where subducting oceanic lithosphere partially melts by addition of fluid to generate differntiated magams that rise through the crust and form island or continental volcanic arcs.
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rock cycle in forming sedimentary rocks
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1.) weathering breaks down rocks
-physically -chemically 2.) erosion carries away particles produced by weathering 3.) transportation via water, glaciers, and wind moves particles downhill 4.) deposition (or sedimentation) occurs when particles settle out or dissolved minerals precipitate 5.) burial occurs as layers of sediment accumulate and compact previous layers 6.) diagenesis, which involves pressure, heat, and chemical reactions, lithifies the sediment to make sedimentary rocks. |
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physical weathering v. chemical weathering
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chem. weathering: occurs when the minerals in a rock are chemically altered or dissolved
physical: solid rock is fragmented by mechanical processes that do not change its chemical composition. |
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clastic particles
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a physically transported rock fragment produced by the weathering of preexisting rocks.
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clastic sediments
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an accumulation of clastic particles laid down by running water, wind, or ice and forming layers of sand, silt, or gravel.
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biological sediments v. chemical sediments v. bioclastic sediments
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bio:forms near its place of deposition as a result of mineral precipitation within organisms as they grow
chem: dissolved product of weathering precipitated from water (usually seawater) by chemical reactions and formed at or near its place of deposition. |
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sorting
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the tendency for variations in current velocity to segregate sediments according to size
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salinity
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the total ammount of dissolved substances in a given volume of water
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sedimentary environment (important charactaristics)
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def of sed. env: a geographic location characterized by a particular combination of climate conditions and physical, chemical, and biological processes
- the type and amount of water (ocean, lake, river, arid land) - the type and strength of transport agent (water, air, ice) - the topography (lowland, mountain, coastal plain, shallow ocean, deap ocean) - biological activity (precipitation of shells, growth of coral refs, churning of sediments by worms and other burrowing organisms) - the tectonic setting of sediment source areas (volcanic arc, collision zone) and sedimentary basins (rift, thermal subsidence, flexural). -the climate (cold climates may form glaciers; arid climates form deserts and precipitate evaporite minerals) |
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rift valley
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a deep, narrow, elongate basin with thick successiions of sed rocks and also extrsive and intrsuive ign rocks. Current examples include the rift valleys of East Africa, Rio Grande, and the Jordan Valley in the Middle East.
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thermal subsidence basins
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a basin produced in the later stages of rifting, when newly formed continental plates ar drifing away from each other. The lithosphere that was thinned and heated during the earlier rfiting stage cools, leading to an incerase in density, which in turn leads to subsidence below sea level, where sediments can accumulate.
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continental shelf
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a broad, flat, sand and mud covered platform that is slightly submerged part of a continent and extends to the edge of the continetnal slope.
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flexural basin
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a basin that develops within zones of tectonic convergence, where 1 lithospheric plate pushes up over the other and the weight of the overriding plate causes teh overriden plate to bend or flex downward.
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sedimentary environments are built around...
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lakes, rivers (alluvial), deserts, and glaciers
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stratification
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aka bedding. Sediments and sed rocks are characterized by this, which occurs when layers of different grain sizes or compositions are deposited on top of one another.
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cross-bedding
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a sed structure cnstitign of bedded material deposited by currents of wind or water and inclines at angles as large as 35 degrees from teh horizontal.
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graded bedding
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a bed that formed horizontal or nearly horizontal layers at the time of deposition, in which the coarsest particles are conentrated at the bottom and grade gradually upward into fine silt.
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bioturbation
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the process by which organisms rework existing sediments by burrowing through muds and sands.
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bedding sequences
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a pattern of interbedded and vertically stacked layers of sandstone, shale ,and other sed rock types.
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porosity
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the % of a rock's volume constiting of open pores btwn grains.
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diagenesis
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the physical and chemical changes - including pressure, heat, and chemical reactions- by which buried sediments are lithified into sed rocks.
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cementation
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a major cheical diagenetic change in whcih minerals are precipitated in the pores of sediments, forming cements that bind clastic sediments and rocks.
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compaction
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a decrease in the volume and porosity of a sediment that occurs when the grains are squeezed closer together by the weight of overlying sediment.
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process that converts sediments to sedimentary rocks
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1.) sediments are buried, compacted, and lithified at shallow depths of earth's crust
2.) ...or they may be subjectd to higher pressure and heat 3.) diagenesis includes the processes- physical and chemical- that change sediments to sedimentary rocks 4.) compaction by burial squeezes out water 5.) precipitation or addition of new minerals cements sediment particles |
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lithification
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the hardening of soft sediment into rock
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gravel
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the coarsest clastic sediment, constitng of particles larger than 2 mm in diameter and including pebbles, cobbles, and boulders.
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conglomerates
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a sed rock composed of pebbles, cobbles, and boulders. The lithified equivalent of gravel.
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examples of fine and really fine clastic seds and sed rocks
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fine: mud, silt, which make siltstone
really fine: clay, which makes mudstone, shale, and claystone |
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sand and sandstone
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sand: a clastic sediment consisting of medium-sized particles, ranging from .062 to 2 mm in diameter
sandstone: clastic rock composed of grains of quartz, feldspar, and rock fragments, bound together by a cement of quartz, carbonate, or other minerals, or by a matrix of clay minerals. The lithified equivalent of sand. |
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examples of coarse grained sed rocks and clastic sediments
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coarse (largest classification)
gravel, boulder, cobble, pebble make => conglomerate |
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examples of medium particle sized sed rocks
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sand, sandstone
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major types of sandstone
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quartz arenties: made up of almost entirely quartz grains, usually well sorted and well rounded.
arkoses: more than 25% feldspar. Poorly rounded. Less well sorted than pure quartz sandstones. lithic sandstones: many fragments derived from fine-grained rocks, mostly shales, volcanic rocks, and fine-grained metamorphic rocks. graywacke: heterogeneous mixture of rock fragments and angular grains of quartz and feldspar, the sand grains being surrounded by a fine-grained clay matrix. |
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silt and siltstone
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silt: a siliciclastic sed in which most of the grains are between .0039 and .062 in diameter. Siltstone looks similar to mudstone or very fine grained sandstone.
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mud
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siliciclastic sediment, mixed with water, in which most particles are less than .062 in diameter. Muds are deposited in rivers and tides.
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mudstones
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blocky and show poor or no bedding.
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shales
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composed of silt plus a signif component of clay, which causes them to break readily along bedding planes.
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clay, claystone
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most abundent component of fine-grained sediments and sedimentary rocks and consists largely of clay minerals.
Clay can make claystones, rocks made up exclusively of clay-sized particles. |
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carbonate environments
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a marine setting where calcium carbonate, principally of biochemical origin, is the main sediment
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carbonate sediments, carbonate rocks
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seds: formed from the accumulation of carbonate minerals precipitated organically or inorganically
rocks: formed from teh accumulation of carbonate minerals precipitated organically or inorganically |
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examples of rocks with carbonate (aka can FIZZ)
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calcite, aragonite, dolomite, limestone
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limestone
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a biochemical sed rock lithified from carbonate seds and composed mainly of calcium carbonate in the form of mthe mineral calcite
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dolostone
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an abundent carbonate rock composed primarily of dolomite and formed by the diagenesis of carbonate seds and limestones
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foraminifer (forams)
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one of a group of tiny single-celled organisms tht live in surface waters and whose secretions and calcite shells account for most of the ocean's carbonate sediments
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reefs
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a moundlike or ridgelike organic structure constructed of the carbonate skeletons of millions of organisms
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carbonate platforms
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an extensive flat, shallow area where both biological and nonbiological carbonates are depositied.
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evaporite sediments, evaporite rocks
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seds: an accumulation of materials precipitated inorganically from evaporating seawater and from water in arid-region lakes that have no river outlets
rocks: a sed rock formed from evaporite seds |
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the way in which large quantaties of seawater evaporate is very clear in bays or arms of the sea that meet the following conditions:
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- the freshwater supply from rivers is small
- connections to the open sea are constricted - the climate is arid |
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chert
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a sed rock made up of chemically or biochemically precipitated silica
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peat
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a rich organic material that contains more than 50% Carbon
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organic sedimentary rock
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a sed rock that consists entirely or partly of organic carbon-rich deposits formed by the decay of once-living material that has been buried.
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What are the 2 major classifications of sediments and sed rocks?
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siliciclastic or chemical and biological
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Why do geologists study metamorphic rock?
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to understand how earth's crust has evolved over geologic time
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metamorphic changes occur when..
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a rock is subjected to new temps and pressures. given enough time, the rock changes mineralogically and texturally until it is in equilibrium w/the new temps and pressures.
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2 kinds of pressure (AKA STRESS) that a solid rock is subjected to:
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1. Confining pressure: general force applied equally in all directions, like the pressure a swimmer feels. Greater depths in the earth.
2. directed pressure (aka differential stress): force extended in a particular direction, such as when a ball of clay is squeezed betwen thumb and forefinger. |
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pressure is recorded in...
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kilobars
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metasomatism
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change in a rock's bulk composition by fluid transport of chemical substances into or out of the rock.
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regional metamorphism
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where both high temp and high pressure are imposed over large parts of the crust. Characteristic of convergent plate tectonic settings. Occurs in volcanic island arcs and in the cores of mountain chains produced by the collision of continents.
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contact metamorphism
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the heat from ign intrusions metamorphoses the immediately srrounding rock. localized trasnformation. Normally affects only a thin region of country rock along the contact. Mineral and chemical transformations are largely related to teh high temp of the magma.
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seafloor metamophism (aka metasomatism)
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metamorphism assocaiated with mid-ocean ridges, in which changes in a rock's bulk chemical composition are produced by fluid transprt of chemical components into or out of the rock.
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low-grade/burial metamorphism
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metamorphism in which buried sed rocks are altered by the progressive increase in pressure exerted by overlying sediments and sed rocks and by the increase in heat associated with increased depth of burial in the earth
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ultra-high-pressure metamorphism
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metamorphism occuring at high pressure (8 to 12 kbar) and utra high pressure (greater than 28 kbar)
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shock metamorphism
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occurs when meteorite collides with Earth.
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foliation
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most prominent textural feature of regionally metamorphosed rocks. A set of flat or wavy parallel planes produced by deformation.
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foliated rocks are classified according to 4 man criteria:
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1. the size of their crystals
2. the nature of their foliation 3. the degree to which their minerals are segregated into lgihter and darker bands 4. their metamorphic grade |
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slate
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(met)
lowest grade of met. rocks so fine-grained that their individ minerals cannot be seen easily w/out microscope dark grey to black split into thin, perfect sheets |
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phyllite
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(met)
slightly higher grade than slate but similar in character and origin tend to have a more or less glossy sheen tend to split into thin sheets, but less perfectly than slates |
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schist
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(met)
low grade, crystals too small to be seen, layers very thin, parallel arrangement of sheet minerals produces teh pervasive coarse, wavy foliation known as schistosity |
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gneiss
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(met)
high grade, light colored rocks iwth coarse bands of segregated light and dark minerals throughout the rock. segregation of lighter-colored quartz and feldspar and darker amphiboles and other mafic materials. little tendency to split, poor foliation |
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granoblastic rocks
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composed mainly of crystals that grow in equant (equidimensional) shapes, such as cubes and spheres, rather than in platy or elongate shapes. These rocks result of metamorphism in which deformation is absent, such as contact metamorphism.
Examples are quartzites, marbles, greenstones, amphibole |
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quartzites
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(met)
hard, nonfoliated white rocks derived from quartz-rich sandstones. Some are massive, unbroken by preserved bedding or foliation. |
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marble
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(met)
met products of heat and pressure acting on limestones and dolomites |
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greenstones
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(met)
met mafic volcanic rocks. an abundance of chlorite gives these rocks their greenish cast. |
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amphibole
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product of medium to high grade metamorphism of mafic volcanics. Foliated ampiboles are produced when deformation occurs.
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metamorphic facies
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groupings of rocks of various mineral compositions formed under diff grades of metamorphism from diff parent rocks.
two essetial points: 1. diff kinds of metamorphic rocks from from parent rocks of diff composition at the same grade of metamorphism. 2. diff kinds of met rocks form at diff grades of metamorphism from parent rocks of the same comp |
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nebular hypothesis:
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(explains the evolution of the solar system)
1. a diffuse, roughyl spherical, slowly rotating nebula begins to contract 2. as a result of contraction and rotation, a flat, rapidly rotating disk froms with the matter concentrated at teh center that will become the proto-Sun 3. the enveloping disk of gas and dust forms grains that collide and clump together into small chunks or planetesimals 5. the terrestrial planets build up by multiple collisions and accretion of planetesimals by gravitational attraction. Giant outer planets grow by gas accretion. |
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solar nebula
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a disk of gas and dust that srrounded the sun during the fomation of teh early solar system. Once formed, the disk began to cool, and many of the gases condensed. Gravitational attraction caused the dust and condensing material to clump together into planetesimals, then moon-sized bodies, finally planets.
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planetesimals
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any of numerous kilometer-sized solid celestial bodies that aggregated through teh clumping by gravitational attraction of dust and smalller chunks of material at an early stage of the development of teh solar system
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asteroids
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one of teh small celestial bodies orbiting the sun, most of them between mars and jupiter.
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meteorites
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a solid particle from interplanetary space that survives the flight thru Earth's atmosphere and falls to the ground in one or more pieces. Most meteorites that strke Eath are tiny peices of asteroids ejected during collisions with one antoher.
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magama ocean
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an outer molten layer hundreds of kilmoeters thick that surrounded earth after it collided with a mars-sized body about 4.5 Ga
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differentiation
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the transformation of random chunks of primordial matter into a body whose interior is divided into concentric layers that differ from one another both physically and cehmically. Differentiation occured in Earth's history, when the planet got hot enough to melt.
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