EPS 5O Midterm
What is the difference between a rhyolite and a granite?
(Both felsic) Granite is intrusive, crystallizes deep in the crust, forms large crystals and coarse-grains Rhyolite is extrusive, breaks through to the surface to crystallize, forms fine-grained
What is the difference between a gabbro and a basalt?
(Both mafic) Gabbro is intrusive which cool slowly and have coarse-grained crystals. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals. Form mostly on ocean floor.
In going from more mafic to more silicic rocks how do the abundances of Si, Mg, and Fe change? Explain this in terms of Bowen's reaction series.
-Si increases -Mg decrease -Fe increases Bowen's reaction series: A schematic description of the order in which minerals form during the cooling and solidification of magma and of the way the newly formed minerals react with the remaining magma to form yet another
Describe 4 important lines of evidence/observations supporting the theory of platetectonics.
1. Convincing evidence emerged from extensive explo- ration of the seafloor after World War II. The mapping of the undersea Mid-Atlantic Ridge and the discovery of the deep, cracklike valley, or rift, running down its center sparked much speculation. Geologists found that almost all earthquakes in the Atlantic Ocean occur near this rift val- ley. Because tectonic faulting generates most earthquakes, these results indicated that the rift was a tectonically active feature. Other mid-ocean ridges with similar rifts and earth- quake activity were found in the Pacific and Indian oceans. 2. Alfred Wegener, a German meteorologist who was recovering from wounds suffered in World War I, wrote a book on the breakup and drift of continents. In it, he laid out the remarkable similarity of rocks, geologic structures, and fossils on opposite sides of the Atlantic. In the years that followed, Wegener postulated a supercontinent, which he called Pangaea (Greek for "all lands"), that broke up into the continents as we know them today. 3. Identical 300-million-year-old fossils of the reptile Mesosaurus, for example, are found only in Africa and South America, suggesting that the two continents were joined at that time. The animals and plants on different continents showed similarities in evolution until the postulated breakup time. After that, they followed different evolutionary paths, presumably because of the isolation and changing environments of the separating continents. 4. In addition, rocks deposited by glaciers that existed 300 million years ago are now distributed across South America, Africa, India, and Australia. If the southern continents had once been part of Gondwanaland near the South Pole, a single continental glacier could account for these glacial deposits.
The crust
A chemically distinct layer at the surface of the earth. Crust mantle contains lighter elements like Si, O, Al, Ca, K, Na etc that form felsic rocks. Feldspars are common minerals in the crust. It is divided into 2 types: oceanic and continental Density differences in these cause subduction. The crust is made of the upper portion of the lithosphere.
intrusive igneous rock
A coarse-grained igneous rock that crystallized slowly when magma intruded into country rock deep in Earth's crust.
mafic rock
A dark-colored igneous rock containing minerals (such as pyroxenes and olivines) rich in iron and magnesium and relatively poor in silica.
Pumice
A frothy mass of volcanic glass with a great number of holes (vesicles) that remain after trapped gas has escaped from the solidifying melt.
Felsic rock
A light-colored igneous rock that is poor in iron and magnesium and rich in high-silica minerals such as quartz, orthoclase feldspar, and plagioclase feldspar.
What is a mineral? What are the main chemical differences among the major mineral groups (silicates, carbonates, oxides, etc)? Which minerals are abundant in the Earth's mantle?
A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition. FOCUS ON CHEMICAL AND ELEMENTAL COMPOSITION AND NOT ITS STRUCTURE. Silicates: Silicates, the most abundant minerals in Earth's crust, are composed of oxygen (O) and silicon (Si)—the two most abundant elements in the crust—mostly in combination with the cations of other elements. The basic building block of all silicate mineral structures is the silicate ion. It is a tetrahedron—a pyramidal structure with four sides—composed of a central silicon ion (Si4 + ) surrounded by four oxygen ions (O2- ), giving the formula Si0 4 ~ (Figure 3.9). Because the silicate ion has a negative 4 charge, it often bonds to cations to form electrically neutral minerals. Six classes of Silicates based on tetrahedra linkage: Isolated, Single chain, Double chain, Sheet, Framework. Carbonates: The non-silicate mineral calcite (calcium carbonate, CaC03) is one of the abundant minerals in Earth's crust and is the chief constituent of a group of rocks called limestones. Its basic building block, the carbonate ion (C03 2 ~), consists of a carbon ion surrounded by three oxygen ions in a triangle. The carbon atom shares electrons with the oxygen atoms. Groups of carbonate ions are arranged in sheets somewhat like the sheet silicates and are bonded by layers of cations. The sheets of carbonate ions in calcite are separated by layers of calcium ions. Oxides: Oxide minerals are compounds in which oxygen is bonded to atoms or cations of other elements, usually metallic ions such as iron (Fe2+ or Fe3+). Most oxide minerals are ionically bonded, their structures varying with the size of the metallic cations. This group is of great economic importance because it includes the ores of most of the metals, such as chromium and titanium, used in the industrial and technological manufacture of metallic materials and devices(Ore and gemstones). Sulfides: The chief ores of many valuable minerals—such as copper, zinc, and nickel—are members of the sulfide group. This group includes compounds of the sulfide ion (S2~) with metallic cations. In the sulfide ion, a sulfur atom has gained two electrons in its outer shell. Most sulfide minerals look like metals, and almost all are opaque and hydrothermal. Sulfates: The basic building block of all sulfates is the sulfate ion (S0 2 ~). It is a tetrahedron made up of a central sulfur atom. surrounded by four oxygen ions ( O 2 - ) . One of the most abundant minerals of this group is gypsum, the primary component of plaster. Gypsum forms when seawater evaporates. The Mantle is almost completely silicate, and is rich in magnesium. The minerals of olivine(upper mantle) and pyroxene are most common, and an aluminum-bearing mineral.
sedimentary rock
A rock formed as the burial product of lay- ers of sediments (such as sand, mud, and calcium carbonate shells), whether they were laid down on the land or under the sea.
What 4 elements make up 90% of the mass of the Earth? In contrast, what are the two most abundant elements in our solar system.
About 90% of the Earth consists of only four elements: iron, oxygen, silicon, and magnesium(iron and oxygen are the most abundant). When Wiechert turned to the solar system, and in particular, to meteorites, he knew that some meteorites are made of a mixture of two heavy metals, iron and nickel, and that these elements are relatively abundant throughout our solar system
ultramafic rocks
An igneous rock consisting primarily of mafic minerals and containing less than 10 percent feldspar.
Describe the positive feedback between physical and chemical weathering processes.
As erosion occurs, more surface area of the rock is exposed. That leads to further physical and chemical weathering.
What is the difference between relative dating and absolute dating?
Both are ways to tell time with rocks. Relative dating is the order or sequence known, but not the actual date of occurrence. Can be seen as a "Time line". Ex: Sorting from youngest to oldest. Absolute dating is the actual date determined by radioactive decay. "Clocks in rocks". Ex: 50 million years ago.
What is the difference between lithosphere asthenosphere?
Both the lithosphere and asthenosphere are part of Earth and are made of similar material. Lithosphere is made up of Earth's outermost layer, the crust, and the uppermost portion of the mantle. In comparison, the asthenosphere is the upper portion of Earth's mantle (which is also the middle layer of Earth). The lithosphere lies over the asthenosphere. In fact, if any material from the asthenosphere were to solidify, it would become part of the lithosphere. Being closer to the Earth's core, the asthenosphere is a higher temperature as compared to the lithosphere and hence its rocks are plastic and can flow. In comparison, the lithosphere's rocks are more rigid. The asthenosphere is more dense and viscous in comparison to the lithosphere. The lithosphere is comprised of a large number of fragments, each of which is known as the tectonic plate. These tectonic plates are in constant motion and are floating over the plastic material underneath. -difference in strength (elastic vs ductile solid on geological time scales) - Both the lithosphere and asthenosphere are part of Earth and are made of similar material. - Lithosphere is made up of Earth's outermost layer, the crust, and the uppermost portion of the mantle. -In comparison, the asthenosphere is the upper portion of Earth's mantle (which is also the middle layer of Earth).
What does Bowen's reaction series describe? What is meant by a discontinuous series? What is the continuous series?
Bowen's reaction series is a means of ranking common igneous silicate minerals by the temperature at which they crystallize. Minerals at the top have a relatively high crystallization temperature, which means that they will be the first minerals to crystallize from a magma that is cooling. IF they are chemically compatible with the magma as it continues to cool, they will grow larger by addition of external layers of additional material. The continuous branch (right) describes the evolution of the plagioclase feldspars as they evolve from being calcium-rich to more sodium-rich. The discontinuous branch (left) describes the formation of the mafic minerals olivine, pyroxene, amphibole, and biotite mica.
What minerals make up chert? and limestone? In what settings, and how, do the sediments that make up these rocks form.
Chert is made up of silica (Si02). The silica in most cherts is in the form of extremely fine crystalline quartz. Some geologically young cherts consist of opal, a less well crystallized form of silica. Like calcium carbonate, much silica sediment is precip- itated biologically, secreted by ocean-dwelling organisms. These organisms grow in surface waters where nutrients are abundant. When they die, they sink to the deep-ocean floor, where their shells accumulate as layers of silica sediment. After these silica sediments are buried by later sediments, they are diagenetically cemented into chert. The dominant biological sedimentary rock lifhified from carbonate sediments is limestone, which is composed mainly of calcium carbonate (CaC03 ) in the form of the mineral calcite. Limestone-Forming Environment: Marine. Most limestones form in shallow, calm, warm marine waters. That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can easily extract the needed ingredients from ocean water. -> How:It forms predominantly on the sea floor where material rich in calcium carbonate ('calcareous' material) accumulates. This calcareous material may be organic, chemical or detrital in origin.
Describe processes that lead to regional and contact metamorphism. What can be learned from the foliation of metamorphic rocks?
Contact metamorphism is a type of metamorphism where rock minerals and texture are changed, mainly by heat, due to contact with magma. Regional metamorphism is a type of metamorphism where rock minerals and texture are changed by heat and pressure over a wide area or region.
Explain the essence and differences between the theory of continental drift, sea floor spreading, and plate tectonics. What occurred in the 1960s that allowed the proposal of the theory of plate tectonics and furthered its development? What key observations led to the theory (and supported the theory) of plate tectonics?
Continental drift: Continental drift - large-scale movements of continents "Jigsaw puzzle" fit of continents - the basis of Wegener's theory Similarity of rock assemblages and ages across oceans Distribution of certain fossils Pangea "Wegener and other advocates of the drift hypothesis pointed not only to the geographic matching of geologic features but also to similarities in rock ages and trends in geologic structures on opposite sides of the Atlantic. They also offered arguments, accepted now as good evidence of drift, based on fossil and climate data." Sea Floor spreading: New crust formed here as the plates move apart Evidence emerged from extensive explorations of the seafloor after WWII "In the early 1960s, Harry Hess of Princeton University and Robert Dietz of the Scripps Institution of Oceanography proposed that Earth's crust separates along the rifts in mid-ocean ridges, and that new crust is formed by the upwelling of hot molten rock into these cracks. The new seafloor—actually the surface of newly created lithosphere—spreads laterally away from the rifts and is replaced by even newer crust in a continuing process of plate creation." Discovery of tectonically active rifts on mid-ocean ridges provided important evidence for seafloor spreading Plate tectonics: "According to the theory of plate tectonics, the lithosphere is not a continuous shell, but is broken into a mosaic of rigid plates that move over Earth's surface (Figure 2.7). Each plate travels as a distinct unit, riding on the asthenosphere, which is also in motion." The lithosphere is broken into mobile pieces, called plates... The theory of plate tectonics states that theses plate are (nearly) rigid and move with respect to each other over Earth surface... driven by mantle convection Theory of plate tectonics - another example of the scientific method Driven by observations Verified by accurate measurements (has survived many attempts to prove it wrong) Theoretically consistent with the physical laws and properties of Earth's interior The strength of the theory lies in its simplicity, its generality, and its consistency with many types of observations
What is a cosmogenic isotope? What can they be used for (at least one use)?
Cosmogenic isotopes are created when elements in the atmosphere or earth are bombarded by high energy particles (µ-mesons and protons, collectively known as cosmic rays) that penetrate into the atmosphere from outer space. Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment. By measuring cosmogenic isotopes, scientists are able to gain insight into a range of geological and astronomical processes. Cosmogenic nuclides can be used to directly determine the timing of events and rates of change in the Earth's surface by measuring their production due to cosmic ray-induced reactions in rocks and sediment.
Explain and compare the terms "crust", "lithosphere", "mantle", and "core," and the types of materials that formeach.
Crust: The Earth's crust is divided into two types of crust, oceanic crust and continental crust. The continental crust is the thin outer layer of Earth, that consists of relatively low-density silicates that melt at relatively low temperatures. The Earth's crust averages about 8 km thick under the oceans to about 40 km thick under the continents. Continental crust is thicker but less dense than oceanic crust. Continental crust consists of mostly granite and granodiorite. Oceanic crust is denser but less thicker than continental crust, and is mostly made of basalt. Lithosphere: The lithosphere is broken into mobile pieces, called plates. Part of Earth that comprises of the crust and the uppermost part of the mantle down to an average depth of about 100 km. The crust is made of low density silicates and the upper mantle is mainly made up of oxygen, magnesium, silicone, iron. Mantle: The region that forms the main bulk of Earth, between the crust and the core, containing rocks of intermediate density, mostly compounds of oxygen with magnesium, iron, and silicon. Core: The innermost layer and has a liquid outer core and solid inner core. It is mostly iron and some nickel.
What is meant by congruous dissolution? What is meant by incongruous dissolution?
Dissolution is the process whereby a mineral dissolves in a solvent as a result of the freeing up of its ions (i.e. transformation of the compound into free ions). The most important solvent in nature is water, and the minerals which dissolve most readily or easily are the halides, nitrates, carbonates and sulfates. Dissolution is therefore an important process in the weathering of limestones (made predominantly of calcite) and evaporites (which consist of halides and sulfates). Essentially, these acid solutions in the soil environment attack the rock minerals, the bases of the system, producing neutralization products of dissolved constituents and solid particles. Two general types of reactions occur: congruent and incongruent Congruent dissolution: the transferring from a solid to a liquid of the same substance Incongruent dissolution: dissolution of a mineral with decomposition or reaction in the presence of a liquid, converting one solid phase into another
What do the terms siderophile, atmophile, lithophile and "incompatible element" mean? Why are some elements (Uranium is a good example) more incompatible than others? The slides at the end of lecture 4, discussed in class, are the best reference for these questions.
Goldschmidt found that most elements have greater affinity for 1/3 minerals: silicates, sulfides, and metals, groups according to their preferred host phases Siderophile: iron-loving chemical elements form a dense metallic phase Atmophile: atmosphere-loving gaseous elements that concentrates in the atmosphere Lithophile: Rock-loving chemical elements, form a light silicate phase ....
What is the difference between gabbros and granite?
Granites are felsic, relatively light in color Gabbros are mafic, generally darker in color
Why does mica (muscovite, biotite) exhibit such perfectcleavage?
In sheet structures, each tetrahedron shares three of its oxygen ions with adjacent tetrahedra to build stacked sheets of tetrahedra. Cations may be inter-layered with tetrahedral sheets. If the bonds between some of the planes of atoms or ions in a crystal are weak, the mineral can be made to split along those planes. Muscovite, a mica sheet silicate, breaks along smooth, lustrous, flat, parallel surfaces, forming transparent sheets less than a millimeter thick. Mica's excellent cleavage results from weakness of the bonds between the sandwiched layers of cations and tetrahedral silica sheets.
Explain the principle of "uniformitarianism."
In the eighteenth century, James Hutton advanced this key historic principle of geology that can be summarized as "the present is the key to the past". Hutton's concept holds that the geological processes that we see in action today have worked much in the same way throughout geological time. The principle of uniformitarianism does not mean that: -all geologic phenomena are slow(some of the most important processes happen as sudden events) -we have to observe geologic phenomena to know that they are important in the current Earth system(ex: in recorded history, humans have never witnessed a large meteorite impact, but we know they have occurred many times in the geologic past)
What are the major differences between the 8 planets of our solar system?
Inner planets: MVEM, relatively small, composed mostly of rock, have few or no moons Outer planets: JSUN, mostly huge, gaseous, ringed, have many moons. Much less dense than the inner, rocky planets. Earth is the densest planet and is the only terrestrial planet with plate tectonic. Saturn is least dense. It would float on water! Jupiter most massive planet BY FAR, then saturn trails it Jupiter has strongest gravitational attraction at its surface Farther from sun= colder, except when greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere
What are the names of the planets and their relative distances from the sun?
Mercury (57.9 km), Venus (108.2 million km), Earth (149.6 million km), Mars (227.9 million km), Jupiter (778.3 million km), Saturn (1,427.0 million km), Uranus (2,871.0 million km), Neptune (4,497.1 million km)
The mantle
Made up of Si and O, like the crust, but contains more Fe and Mg which form ultramafic rocks. Olivine and pyroxene are abundant in the mantle. Mantle contains the lower portion of the lithosphere, asthenosphere, and mesosphere. Heat convection causes plate tectonics to move.
Why does mantle rock (peridotite) melt during extension or rifting of the lithosphere and what is the composition of the magma that is produced? What is a geotherm? How does melting depend on the relative positions of the geotherm and melting curves.
Mantle rock melts during extension of rifting in the lithosphere due to a process called decompression melting. As pressure decreases, so does the melting temperature of rocks. Hence, as peridotite rises closer and closer to the surface during rifting or extension, it melts due to lower pressures. A geotherm is the curve that describes how Earth's temperature increases with depth. The geotherm is left of the melting curve, so the rock is solid. When rock starts at depth A and ascends to depth B, it crosses the melting curve, so rock starts to melt.
How are mineral phase diagrams useful in interpreting metamorphic rocks? How might the P-T (pressure-temperature) histories of blueschist and greenschist rocks have differed?
Metamorphism generally is characterized by changing conditions of pressure and temperature, and the history of these changes is called a metamorphic P-T path. The P-T path can be a sensitive recorder of many important factors that influence metamorphism—such as the sources of heat, which change temperatures, and the rates of tectonic transport, which change pressures. Looking at the mineral phase diagram in the textbook, one can see the different metamorphic fades. They are groupings of rocks of various mineral compositions formed under different grades of metamorphism from different parent rocks. It is determined that blueschist rocks have formed in areas of high pressure and low temperature, near subduction zones. Whereas, greenschist rocks have formed in more low to intermediate environments with both low pressure and temperature.
What is the difference between a pyroclastic flow and a lava flow? How does SiO2 content factor into these differences? Where are pillow basalts formed? How are shield and strato-volcanoes distinguished in terms of eruptive styleand general structure?
Pyroclastic flow: form of eruption that occurs when hot ash, dust, and gases are ejected in a glowing cloud that rolls downhill at high speeds. The solid particles are buoyed up by the hot gases, so there is little frictional resistance. STYLE OF FLOW ONLY. Lava flow: Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock. Higher viscosity means that there is a higher silica(Si02) content. The higher the viscosity, the more resistant the magma is to flow; high-viscosity is cement like and slower due to more friction. This means that lava flow has more silica content than pyroclastic flow. Higher viscosity also tends to trap gases and increase the explosivity. Pillow basalts: Pillow basalt is a volcanic igneous rock that forms when lava of basaltic composition's erupted underwater. The rapid cooling of the lava by cold water on all sides forms the pillow-shaped bodies, which can then break open and extrude more of the hot lava from inside. Strato Volcanoes comprise the largest percentage (~60%) of the Earth's individual volcanoes and most are characterized by eruptions of andesite and dacite - lavas that are cooler and more viscous than basalt. These more viscous lavas allow gas pressures to build up to high levels (they are effective "plugs" in the plumbing), therefore these volcanoes often suffer explosive eruptions. Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. For this reason these volcanoes are not steep (you can't pile up a fluid that easily runs downhill). Eruptions at shield volcanoes are only explosive if water somehow gets into the vent, otherwise they are characterized by low-explosivity
Approximately what percentage of the Earth's surface area is composed of sedimentary rocks? Approximately what percentage of the crust is composed of sedimentary rocks? Why does this difference exist?
Sedimentary rocks make up 75 percent of the rocks at the earth's surface, but only 5% of the Earth's crust.
Give examples of common silicate minerals. Which exhibit silicate tetrahedra in 3Dnetworks, sheets, single and double chains, and in isolation.
Six classes of Silicates based on tetrahedra linkage: Isolated, Single chain, Double chain, Sheet, Framework. Isolated tetrahedra: Tetrahedra are linked by cations -ie tetrahedra are isolated from each other. Olivine: important upper mantle mineral (dominant mineral in peridotite). Cleavage plane of Olivine: 1 plane Single-chain silicates: 2 oxygen atoms in each tetrahedra are shared with adjacent tetrahedra to form chains. Pyroxenes: class of minerals important in Igneous (volcanic) and metamorphic rocks). Tend to have a stubby/equiaxed morphology(structure/form). Cleavage plane: 2 planes at 90 degrees. Double chain silicates: Two chains link by sharing an oxygen on every other tetrahedra. Amphiboles: class of mineral (similar to pyroxenes) important in igneous and metamorphic rocks. Tend to have acicular(needle like) morphology. Cleavage plane: 2 planes at 60 and 120 degrees. Sheet silicates: Layered structure with interlayer cations - layers are weakly bonded (Van der Waals). Micas and clays: Have platy morphology. Micas break (cleave) easily along the layers. Types of micas: Muscovites and biotites. Cleavage plane: 1 plane Three-dimensional framework silicates: Each oxygen atom in a tetrahedra is shared with an adjacent tetrahedra forming an infinite framework. Quartz and feldspars: Very common silicate minerals. Major components of Granite.
What are the similarities and/or differences between solar elemental abundance and that observed in meteorites? What are the major differences between the composition of the whole Earth and crust? What processes have given rise to these differences?
Solar elemental abundance is about 99% hydrogen and helium. Composition of meteorites led Emil Wielchert to realize how the Earth is layered by density. When Wiechert turned to the solar system, and in particular, to meteorites, he knew that some meteorites are made of a mixture of two heavy metals, iron and nickel, and that these elements are relatively abundant throughout our solar system. Yet, when looking at the composition of the Earth, only 8 elements, make up 99% of Earth's mass. In fact, about 90% of the Earth consists of only four elements: iron, oxygen, silicon, and magnesium(iron and oxygen are the most abundant). With regards to Earth's crust, it is almost half oxygen, with the rest being mainly silicon, aluminum, iron, magnesium, calcium, and other elements. The different compositions of Earth's layers are primarily due to the work of gravity(ex: looking at how the core of the Earth is almost entirely iron, with some nickel and other elements-this is due to gravity and changes in pressure).
Explain the following stratigraphic principles: 1) Original horizontality, 2) superposition, 3) faunal succession, and 4) cross-cutting relations.
Stratigraphic principles help scientists to interpret strata(layers in rocks) 1) Principle of original horizontality: States that sediments are deposited under the influence of gravity as nearly horizontal beds. Folds and tilts are younger than the rocks themselves. 2) Principle of superposition: A younger layer cannot be deposited beneath an existing layer. Thus, in a sedimentary sequence, the OLDEST will be on the BOTTOM and the YOUNGEST will always be on the TOP. This is only if the rock is undisturbed, meaning rocks that are still flat and level. 3) Principle of faunal succession(fossil succession/change): Specific groups of fossils follow, or succeed, one another in the rock record in a definite order. Once you know the order, you can find the relative ages and correlate rocks in different parts of the world based on the fossils present. 4) Principle of cross-cutting relations: Anything that cuts through a rock, must be younger than the rock. a. Ingenous intrusion: an ingenious rock melts its way into existing rocks. Is younger than the rock it has intruded(cut across). Pre-existing rock will undergo CONTACT METAMORPHISM. b. Faults: are younger than the rock they displace c. Erosion: layers that get cut are older than the erosion
What event in an igneous rock's history is dated by the K-Ar method?
The K/Ar dating technique is generally used to date volcanic rocks, minerals, and ash, that range from 500,000 years old to billions of years; half-life of potassium-40 is 1.3 billion years. The method in general is used to date igneous rocks by dating the age of crystallization...
What are the basic differences between oceanic and continental crust? Explain qualitatively the concept of lithospheric plates. What are the three major types of plate boundaries?
The continental crust is thicker, yet is less dense than the oceanic crust and thus, the crust floats like buoyant rafts on the denser mantle. The continental crust is made of mainly granite and granodiorite. Oceanic crust is thiner and more dense than continental crust; it is mostly made of basalt. The lithosphere is not a continuous shell; it is broken into about a dozen large plates that move over Earth's surface at rates of a few centimeters per year. Each plate is a rigid unit that rides on the asthenosphere, which also is in motion. The forces that push and pull the plates around the surface come from the heat engine in Earth's solid mantle. Driven by internal heat, hot mantle material rises where plates separate. The litho- sphere cools and becomes more rigid as it moves away, eventually sinking into the mantle under the pull of gravity at boundaries where plates converge. The convecting mantle and its overlying mosaic of litho- spheric plates constitute the plate tectonic system. The three major types of plate boundaries are divergent, convergent, and transform boundaries. Divergent boundary: A boundary between lithospheric plates where two plates move apart and a new lithosphere is created. Convergent boundary: A boundary between lithospheric plates where the plates move toward each other and one plate is recycled into the mantle. Transform-fault boundaries: A plate boundary at which the plates slide horizontally past each other and lithosphere is neither created nor destroyed.
The core
The innermost layer and has a liquid outer core and solid inner core. It is mostly iron and some nickel.
Rhyolitic lava
The lava type that is the richest in silica, erupts at the lowest temperatures, and is the most viscous.
Explain how radioactive isotopes can be used to date geologic materials, and what you need to know or measure to date successfully.
The rate of radioactive decay is measured by the isotope's half-life—the time required for one-half of the original number of parent atoms to transform into daughter atoms. We must know the initial amount that was present in a rock to calculate the isotopic age. Radioactive isotopes make good clocks because the half-life does not vary with temperature, chemistry, pres- sure, or other changes that can accompany geologic pro- cesses on Earth or other planets. So when atoms of a radio- active isotope are created anywhere in the universe, they start to act like a ticking clock, steadily altering from one type of atom to another at a fixed rate.
Erosion
The set of processes that loosen soil and rock and move them to the spot where they are deposited as sediment.
The lithosphere
The strong, upper 100 km of the Earth. The lithosphere are the tectonic plates we talk about in plate tectonics. Cool, rigid, brittle, wants to break Regulates amount of energy entering/leaving Earth
Metamorphism
The transformation of preexisting solid rocks under the influence of high pressure and temperature.
What are the two basic types of characteristics used to distinguish igneous rock?
The two basic types of characteristics used to distinguish igneous rock is texture and composition. Texture refers to the size of the mineral grains in the rock. Composition is often determined by what the minerals actually are. Extrusive rocks form when magma erupts at the surface, rapidly cooling to fine ash or lava, developing tiny crystals. The resulting rock(seen in basalt) is finely grained or has a glassy texture. Intrusive igneous rocks crystallize when molten rock intrudes into unmelted rock masses in Earth's crust. Large crystals grow during the slow cooling process, producing coarsely grained rocks, seen in granite samples.
What is the composition (name) of typical volcanic rocks erupted at a) divergent plate boundaries, b) an island arc where two oceanic-plates meet, c) a convergent boundary where the volcanic arc is on a continent?
The type of volcanic rocks erupted at divergent boundaries are igneous rocks, more specifically basalt, gabbro, and peridotite. The type of rocks erupted at an island arc are andesite, basalt, dacite, and rhyolite. At a convergent boundary, granite batholiths are common along with the same rocs as an island arc.
Why is the K-Ar method more useful for dating older rocks than the C14 method?
Those that decay rapidly, such as carbon-14, can only be used to date younger rocks. Isotopic dating is possible only if a measurable num- ber of parent and daughter atoms remain in the rock.Carbon-14 is especially useful for dating fossil bone, shell, wood, and other organic materials in sediments less than a few tens of thousands of years old. Carbon is an essen- tial element in the living cells of all organisms. As green plants grow, they continuously incorporate carbon into their tissues from carbon dioxide in the atmosphere. When a plant dies, it stops absorbing carbon dioxide. At that moment, the amount of carbon-14 in relation to the stable carbon isotopes in the plant is identical to that in the atmosphere. We can, however, estimate this absolute age by comparing the amount of carbon-14 left in the plant material with the amount in the atmosphere at the time the plant died. Hence because the C14 can only be used to date younger rocks, the K-Ar method's ability to date older rocks is more useful in that instance. K-Ar method: Potassium-argon dating, abbreviated K-Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar).
Given a schematic geologic cross-section, work out or unravel the geologic history (that is, be prepared to unravel the geologic events from a sample cross-section). What is an unconformity, angular unconformity, and non-conformity?
Unconformity: a surface between two rock layers in a stratigraphic succession that were lid down with a time gap between them Angular unconformity: where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further orogenic activity. Non-conformity: A nonconformity exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock.
How is CO2 an important part of the weathering process?
Variability in the atmosphere's concentration of carbon dioxide leads to corresponding variability in the rate of weathering. Higher levels of carbon dioxide in the atmosphere lead to higher levels in the soil, which increases the rate of weathering. As discussed in Chapter 15, carbon dioxide, a greenhouse gas, makes Earth's climate warmer and thus promotes weathering. Weathering, in turn, converts carbon dioxide into bicarbonate ions and so decreases the amount of carbon dioxide in the atmosphere. This decrease in carbon dioxide eventually results in a cooler climate. In this way, the weathering at the surface of a feldspar grain is linked to the causes of global climate change. As more and more carbon dioxide is used up through weathering and the climate cools, weathering decreases again. As weathering decreases, the amount of carbon diox- ide in the atmosphere builds up again, and the climate warms, thus completing the cycle.
At shallow depths and low temperatures, mud lithifies to become shale. As this shale is buried, metamorphism changes its mineralogy and texture. List in increasing grade of metamorphism, the rock types that form.
We refer to the metamorphic rocks formed under the lower temperatures and pressures of shallower crustal re- gions as low-grade rocks and the ones formed at the higher temperatures and pressures of deeper zones as high-grade rocks. As the grade of metamorphism changes, the mineral assemblages within metamorphic rocks also change. Order of increasing grade of metamorphism/rock types: Low-grade: greenschists Intermediate-grade: amphibolites High-grade: granulites slate forms from shale, it is the lowest grade metamorphic rock shale will become - with increasing temperatures it recrystallizes to become phyllite - with even higher temps and pressures than those that phyllite forms at, it will become schist (different types of schist depending on combo of temp and pressure) - If schist is subjected to high enough temps its constituents become more mobile and the rock will recrystallize as gneiss
What is the fundamental building block of the silicate minerals? Sketch it.
[SiO4]4− tetrahedron
Fault
a planar fracture or distcontinunity in a volume of rock across which there has been significant displacement as a result of rock-mass movement
What is an ophiolite sequence? What is a turbidite? Where do both of these deposits form?
ophiolite sequence: an ophiolite sequence is an unusual assemblage of rocks, characteristic of the seafloor but found on land, consisting of deep-sea sediments, submarine basaltic lavas, and mafic igneous intrusions. The assemblage comprises fragments of oceanic crust that were transported by seafloor spreading and then raised above sea level and thrust onto a continent in a later episode of plate collision. Turbidite: A bed formed as a result of deposition from a turbidity current is called a turbidite. It's a graded bed of sand, silt, and mud deposited by a turbidity current on the abyssal plain.
