Midterm Flashcards
What does the world geology mean? Why is it important?
Geo = earth
Ology = the study of
Therefore geology is the study of the earth.
It is important for energy and natural resources, solving environmental problems, building cities and highways, and predicting and preventing natural disasters.
What is the fundamental principle of the concept of uniformitarianism, and what does it mean? What is the timescale of the earth measured in?
The present is the key to the past. This means that the processes that we see shaping th earth today are the same as the processes that shaped the earth millions of years ago. Geological time is meausred in billions of years.
When when did the Big Bang occur?
~14 billion years ago
What theory is generally excepted as correctly explaining the formation of the solar system? Describe it.
The Nebular theory - 5 billion years ago. A nebular made up of hot gasses - mainly hydrogen and helium. The nebular cloud contracted under gravity and began rotating. The rotating instigating central pedal force, which caused elements to concentrate in the centre. Gravitational energy converted to thermal energy. This became the sun. The other, heavier elements began to fuse together into planets and moons, which continued to rotate around the sun.
Explain how the earth was formed, and what layers formed.
Formed by rock collisions. The heavier elements (Fe, Mg) migrated inwards and became the core. The lighter elements (oxygen rich elements) migrated outwards and formed a very thin crust. The middle area between the crust and the core is called the mantle. In the process, gasses escaped and formed the atmosphere.
Describe the names and the layers of the world.
- Lithosphere (“sphere of rock”)
- the crust AND the upper most mantle - split into plates that move over top of the asthenosphere - Asthenosphere (“weak sphere”)
- liquid - due to unequal heat distribution in the earth convection currents occur here, the lithosphere rides on top of them, in CONTINENTAL DRIFT - Core
- very dense and under extreme heat, intense pressure keeps the core a solid - Ni, Fe
What causes more geological activity, convergent or divergent boundaries?
Convergent boundaries
What is a divergent boundary?
Occurs when plates move apart due to tensional stress. This allows for upwellling of material in the mantle, forming ridges and rifts. It is the cause of SEA-FLOOR SPREADING.
What is a convergent boundary?
The primary cause of geological activity. Occurs when denser, oceanic plate descends below lighter, continental plate. This is known as SUBDUCTION, and it forms a trench. The denser, oceanic plate reaches far enough into the asthenosphere that it begins to melt. Sometimes, this allows for melted magma to protrude and form a volcano, which eventually erodes into sediment. It is at convergent boundaries that earthquakes and volcanoes often form.
What is subduction?
The descent of the denser oceanic lithosphere beneath the lighter, continental lithosphere.
What does Pangaea mean? What evidence is there to support it?
Pan = all, Gaea = earth
- Fit of the continents
- South America and Africa fit together at a depth of 900 meters (at the continental shelf) - Fossil evidence
- Fossils match across continents (ex. Mesosaurus fossils found in East S.A. and South Africa) - Rocks and Structures
- ex. Appalachian mountains and Scandinavian mountains form a continuous chain - Paleoclimatic Similarities
- ex. finding coal in ancient tropical swamps in places that are now glaciated; finding striations from glaciers in tropical areas today
What are the 4 spheres of the earth? How do they interact?
Earth is a dynamic system of interacting spheres.
- Geosphere - the earth and rock sphere
- Hydrosphere - the sphere of water
- Biosphere - the sphere of life, ranging from the hydrosphere, slightly into the atmosphere
4, Atomsphere - thin and tenuous sphere of gases, producing weather and climate
Where are new rock types mainly produced at?
Converging boundaries
Explain the rock cycle, beginning at magma.
Magma crystallizes to form igneous rock, igneous rock is weathered, transported, and deposited to form sediment, which is cemented to form sedimentary rock, sedimentary rock undergoes metamorphisis to form metamorphic rock. Metamorphic rock melts to form magma. Metamorphic rock can become sediment by weathering, as can sedimentary rock. Igneous rock can also undergo metamorphisis under heat and pressure to form metamorphic rock.
What are minerals? How many are there? How many are common in the earth’s crust? How are they produced?
Minerals are inorganic substances formed by nature that combine together to form rocks. Their elemental composition, chemical structure, and bonding determine the properties that the mineral will have. There are 4700 known minerals, but only about 20 are predominant in the earth’s crust.
What type of mineral is the most abundant?
Silicates
What are silicates? What is their structure, and elemental composition?
Silicates are composed of Silicon and Oxygen, covalently bonded to each other to form tetrahedrons (SiO4)4-. Because oxygen is an anion, and therefore negatively charged, metal cations such as Fe2+ and Mg2+ can ionically bond. This ionic bonding is weaker than the overall covalent bonding, which usually results in a spot of weakness along the mineral, which becomes the cleavage point.
What is the composition of a dark silicate?
Ferromagnesian - therefore with Fe and Mg within the silicate tetrahedra.
What are the four ferromagnesian silicates? Describe their bonding, and cleavage?
- Olivine
- single tetrahedra, covalently bonded, with Fe2+ and Mg2+, no cleavage - Pyroxene
- single chains of tetrahedra, with metals between them, cleavage is 2 at 90 degrees - Amphibole
- double chains of tetrahedra, with metals between them, cleavage is 2 not at 90 degrees (60 and 120) - Biotite (black mica)
- sheets of tetrahedra with metals between them, cleavage is basal/platy
What are the four non-magnesian silicates? Describe them.
- Muscovite (white mica)
- perfect basal cleavage, often used for muscovy window glass - Feldspar
- strongly bonded 3D network of silica tetrahedra
a. Orthoclase (K feldspar) with potassium, cleavage is 2 at 90 degrees.
b. Plagioclase (Ca/Na feldspar) with calcium in mafic rocks and sodium in felsic rocks, cleavage is 2 at 90 degrees. - Quartz
- very strong, purely covalent silica tetrahedra, has a hardness of 7, can form crystals with sufficient space in nature. (SiO2)
Name the two types of non-silicate minerals, and describe them.
- Carbonates (CO3)2-
a. Calcite (CaCO3) - used in cement and limestone
b. Dolomite (MgCaCO3) - Evaporites
a. Halite (NaCl) - table salt
b. Gypsum - plaster and drywall
Name the metallic, non-silicate type of mineral.
Ores of metals
- Hematite/Magnetite (Fe)
- Sphalerite (Zn)
- Pyrite/Chalcopyrite (Cu)
- Galena (Pb)
Where are igneous rocks? Where does the name come from? Which types of minerals are in igneous rocks?
Igneous = fire
Igneous rock crystallizes from molten SILICATE magma, which is formed deep in the earth under high temperatures and pressures.
What are the two options for magma at the site of a volcano? What type of rock does each location of formation form? Typically what are the textures of this rock?
- Intrusive - forms plutonic rock - texture tends to be PHANERITIC
- Extrusive - forms volcanic rock - texture tends to be either PYROCLASTIC, APHANITIC, OR GLASSY, due to quick cooling, or quenching by air or water.
Does flowing lava tend to be mafic or felsic? How about lava that violently erupts to form glassy textures or pyroclastic material?
Mafic = flowing, hot, runny
Felsic = more viscous, violently erupts
Viscosity is directly dependent on the silica content of the parent magma
What types of rocks are formed by felsic magma? How much silica does it contain, and what minerals form the rocks?
- Granitic rock - phaneritic texture
- Rhyolite - aphanitic texture
Minerals - quartz, biotite, orthoclase, Na-rich plagioclase
70% silica content, therefore very viscous
What type of rock does intermediate magma tend to produce? What percent of it is silica?
- Diorite - phaneritic
- Andesite - aphanitic
Minerals - amphibole, plagioclase
60% silica
What type of rock does mafic magma produce? What minerals are in the rock? What is it’s silica content?
- Gabbro - phaneritic
- Basalt - aphanitic
Minerals - Ca-rich plagioclase, pyroxene
50% silica
What type of rock does ultramafic magma produce? What are the minerals in it? What percent of silica is it?
- Peridotite
Minerals - pyroxene
40% silica content
Where is basalt found?
In the upper oceanic crust and on volcanic islands - the most abundant rock in the crust
Where is gabbro found?
In the lower oceanic crust
Where is peridotite found?
The main rock of the upper mantle
Name the four types of intrusive bodies, and their characteristics.
- Dyke - discordant, tabular
- Sill - concordant, tabulat
- Laccolith - concordant, bulge
- Batholith - discordant, bulge
What about Bowen’s reaction series is continuous? What is discontinuous? How does it work?
Ferromagnesian silicates are discontinuous, non-ferromagnesian silicates are continues.
Bowen’s reaction series states that heavier minerals have a higher melting point, and precipitate from the melt first. Lighter minerals precipitate from the melt last. This is how lighter rocks can be produced from mafic magma, as the mafic magma becomes felsic.
Out of olivine and pyroxene, which precipitates first?
Olivine, then pyroxene
Which mineral is left over after most of the magma melt has precipitated out?
Quartz - this is how granite can be formed from ORIGINALLY BASALTIC MAGMA
Why do volcanoes occur? What two things can lava do upon extrusion?
Gas builds up in the magma chamber, causing pressure that needs to be released. Lava can either flow down the side, or blow through the top.
What is extrusive, mafic magma also known as? What are its physical characteristics like?
Basaltic magma - it is hot and runny, and runs quietly downthe volcano before hardening
What is extrusive, felsic magma also known as? What are its physical characteristics?
Rhyolitic magma - it tends to be cooler and more viscous, tends to erupt violently and form pyroclastic material such as tuff and breccia
What are the two types of magma?
- Pahoehoe - made of hotter, runnier, mafic magma which hardens to form a coiled, “ropy” texture
- Aa - made of cooler, slower, felsic magma - tends to be “blocky” in texture
What are pillow lavas?
Pillow lavas resemble pillows and are formed underwater when magma either flows into the water, or exits through tube ends. The texture is typically GLASSY, from quenching or quick cooling by the water.
What is a Nuee Ardente? Where does the name comes from, and what is it also known as?
Nuee Ardente = glowing cloud - also known as a PYROCLASTIC FLOW
These are extremely destructive, and occur when a cloud of gas, hot ash, and magma races down a volcano - they can wipe out a whole city at once.
What is pyroclastic material, and what are some examples?
Pyroclastic material = fire fragments
Formed by magma ejected into the air. Can range from fine ash, to streamlined bombs, to large blocks.
What is a lahar?
A lahar is pyroclastic material, mixed with snow, mud, rain, and ice.
What is the most common type of volcano? What is it made up of?
A composite cone - made up of pyroclastic material as well as lava flows - medium in size with a crater
Describe the three types of volcanoes, and their compositions.
- Shield volcano - very large, ranging in hundreds of km, has a caldera at the top, much wider than it is tall - and made up of successive lava flows
- Cinder cone - very small, with a crater, made mainly of pyroclastic material
- Composite cone - medium sized, made of pyroclastic material and lava flows
What is the difference between a crater and a caldera? How is a caldera formed?
Crater < 1 km
Caldera > 1 km
Calderas are formed by the collapse of the underlying magma chamber as it empties
What leads the magma to the caldera or the crater?
A conduit or pipe
What are fissure eruptions? What do they form?
Fissure eruptions occur when magma flows out of fissures in the crust, plateaus are formed by the magma that flows from the fissure
Where do volcanoes tend to occur?
They tend to occur at convergent boundaries at subduction zones, where denser, oceanic lithosphere melts to form basaltic/gabbro rich mafic magma
What type of magma does melted oceanic lithosphere generate?
Basaltic magma
Around what geological structure do subduction zones and volcanoes tend to occur?
Around the Pacific Ring of Fire
What is a seamount?
A location in which and underwater volcano produces basaltic magma which flows out onto the sea floor
What is an intraplate volcano and what causes it?
An intraplate volcano occurs in the middle of a continent/lithospheric plate - it is caused by deep mantle plumes which protrude
What are the two types of weathering that forms sedimentary rock?
- Mechanical
- frost wedging, sheeting, biological - Chemical
- hydrolysis, dissolution, oxidation
What is mechanical weathering also known as?
Disintegration
What is chemical weathering also known as?
Decomposition
What is the relationship between mechanical and chemical weathering?
They work together to enhance erosion - mechanical weathering increases surface area for chemical weathering to work on
Describe the types of mechanical weathering.
- Frost wedging - water enters rock fractures as a liquid, it expands 9% as it freezes splitting the rock apart
- Sheeting - occurs when material is unloaded from a batholith, allowing for rock expansion, as the rock expands slabs break off
- Biological activity - vegetation grows roots in rock fractures - the roots grow and expand, splitting rock apart
Describe the three types of chemical weathering, and their effects on the rock.
- Dissolution - CO2 + H2O —> H2CO3
- this carbonic acid dissolves some rocks, making them stable at surface conditions - Oxidation - ferromagnesian rocks have metals which react with oxygen in the atmosphere forming metal oxides, rust, and CLAY MATERIALS
- Hydrolysis - occurs when K+ in orthoclase is replaced by hydrogen, because hydrogen is much smaller, it causes collapse of the mineral, forming clay