Geology Module 2
Radiometric Time Scale
- based on the natural radioactivity of chemical elements in some of the rocks - a more recent development borrowed from the physical sciences and applied to geologic problems
2 layers in the upper mantle and crust:
1. lithosphere 2. asthenosphere
By counting positive and negative orientations of the magnetic field on either side of a mid-ocean ridge, geologists have found that the Earth's magnetic field has switched nearly _____ times in the last ______ years
30, 5 million
About 30 million years ago, sedimenrary rocks were intruded by ______ magma. Define
Basaltic magma (comes from deeper in the Earth than granitic magma, so is hotter and more fluid and can rise to the surface before cooling and turning to rock). Basalt is a fine-grained, dark-coloured commonly black rock
How is dating rocks by radioactive isotopes difficult in the lab?
The principal difficulty lies in measuring precisely very small amounts of isotopes
The branch of science where we determine the age of a rock unit based on fossil content is called: ___________.
biostratigraphy
Step 6. Entire region undergoes uplift and erosion, as evidenced by...
by the tilted sedimentary sequence A (original horizontality) and erosion surface.
Geologists recognize many different types of granitic rocks, depending on their mineral and chemical composition. Technically, most of the granitic rocks in the Coast Mountains are _______ and ______
granodiorite and tonalite they have been raised to the surface while the overlying cover rocks have been eroded away.
In minerals, the combination of internal order (crystalline nature) and chemistry result in a set of physical properties that help us distinguish between minerals, including such characteristics as ______ (how the mineral grows), _______ and/or _______ (how the mineral breaks), ______ (how the mineral interacts with light) and _______ (a function of the strength of the bonds in a mineral).
habit - how it grows cleavage and/or fracture - how it breaks colour - how it interacts with light hardness - strength of the bonds
Low grade rocks have been subjected to:
lower temperatures and temperatures
When a mineral crystallizes, the start of the geologic clock, the amount of the _____ is at a maximum.
parent
If a concordant layer of igneous rock in a sequence of layered sedimentary rocks was emplaced as lava, it is ______ than the units below and ______ than the units above
younger, older
If a concordant layer of igneous rock in a sequence of layered sedimentary rocks was emplaced as sill, it is ______ than the units below and ______ than the units above
younger, younger
Geo History Activity Answer Key (pg. 20) from oldest to youngest
...
Web reading: Geologic Time...
...
The 4.6 billion long history of the Earth has been subdivided into four eons. Each eon are subdivided into _____, which are again subdivided into ______ and further into _____ and further into ______.
Eron - eras - periods - epochs - stages
Why do most igneous rocks in Southwestern B.C not contain fossils?
Igneous rocks crystallize from magma, which contains no life
The lithosphere plates of the Earth moves because of the ______ in the mantle
convection
The upper part of the earth (____, _____ and _____) can be envisioned as a giant recycling machine; matter that makes up rocks is neither created nor destroyed, but is redistributed and transformed from one rock type to another.
mantle, crust and surface
Lithosphere
the brittle, outermost layer that includes the uppermost mantle and the crust
The earth can be divided into 4 zones:
the crust, the mantle, the outer core, the inner core
Define Rocks:
Rocks are naturally occurring, solid, aggregates (mixtures) of minerals and mineraloids.
There are two types of crust: 1. 2.
1. the oceanic crust (mainly basalt and gabbro) 2. the continental crust: (a large range of rocks)
Geologists estimate the Earth to be ___ billion years old
4.6
Eras
broad spans based on the general character of life that existed during these times
Siwash Rock, a vancouver landmark, is a pillar of resistant volcanic rock that is part of a _____
dyke (that was intruded into the sandstone)
The evidence of the seas' former presence is, in part, the...
fossil forms of marine life that accumulated with the bottom sediments
rocks that have been buried deeply and subject to high grade metamorphism (like the second, lower image) can then be brought back to lower pressures and temperatures and as a result, the mineralogy changes to reflect that change. You may come across the term "_______" and "________" to refer to metamorphism that occurs under increasing and decreasing pressure and temperature conditions respectively.
prograde, retrograde
The ________ clock has become an extremely useful and efficient tool in dating the important episodes in the recent prehistory and history of man, but because of the relatively short half-life of _______, the clock can be used for dating events that have taken place only within the past 50,000 years.
radiocarbon carbon-14
Periods
shorter spans based partly on evidence of major disturbances of the Earth's crust
A sill is _________ than both overlying and underlying sedimentary rocks
younger
Define plate tectonics:
A generally accepted theory based on the hypothesis that a small number of plates "float" on the plastic upper mantle and move more or less independently of one another. Plates grind against each other like ice floes in a river. Much of the dynamic activity is concentrated at the periphery of plates, which are propelled from the rear by seafloor spreading and pulled from the front by subduction. Continents are part of plates and move with them, like logs frozen on ice floes.
Define a mineral (including the 5 common characteristics)
A mineral is a naturally occurring (1), solid (2), inorganic (3) substance that is crystalline (4) and has a well defined (characteristic) chemical composition (5).
Define the "chemical composition" of a mineral:
A mineral's composition is not necessarily exactly the same, but it does vary within well defined limits. Although the atoms and modules are arranged in an ordered way, under certain pressure and temperature conditions, different elements can substitute into a crystal structure. What this ultimately means is that we cannot rely on chemical composition alone to identify or classify a mineral.
Dyke:
A sheet-like body of igneous rock that cuts across the layered, folded, or other structures of the surrounding rock (compare with sill).
_________ data often relies upon the occurrence of certain minerals or materials being present, whereas ______ relies upon the ability to determine relationships between rock units. The two methods are most powerful when used in tandem, as uncertainties exist in both methods.
Absolute time, relative time
Smaller plates
Arabian Plate Philippine Plate Cocos Plate Caribbean Plate
In 1928, the Englishman ___________ introduced a theory in which both the continents and the crust beneath the great oceans are moving
Arthur Holmes
Most trilobites that lived during Cambrian time died without leaving any remains. However, some of them were buried and preserved under sediments shortly after death. Today they can be found as fossils. If we find one we know the sediment was deposited in ______ time
Cambrian
The oldest period of the Phanerozoic eon is called:
Cambrian
Trilobites were very common at the ocean bottom from ______ time
Cambrian (542-488 million years ago)
About 3 million years ago, volcanoes began to erupt along a line extending from southern BC to northern California. Since then, thousands of eruptions have produced the __________ volcanic belt.
Cascade including Mount St. Helens, Mount Rainier, Mount Hood, Mount Baker, Mount Garibaldi
3 Eras of Phanerozoic Eon (most recent to oldest)
Cenozoic Mesozoic Paleozoic
Metamorphic Rocks: Like igneous and sedimentary rocks, they can tell us about conditions of formation by looking at texture, but they can also tell us about _____.
Change
3 Periods of Mesozoic Era
Cretaceous (144 Ma) Jurassic (206 Ma) Triassic (248 Ma)
The outer shell, or _____ of the Earth is about ______ km thick and consists of:
Crust 5-250 km thick A mosaic of seven large plates and a number of smaller ones that float independently of one another on the Earth's mantle.
Step 2. Granite (G), a granitic batholith, is emplaced (from below) into D. Evidence is the inclusion of .....
D in G (at a large scale) with some evidence provided by the nature of the contacts where the edges show G squeezing into D.
Part 2 (of the module)
Earth Structure, Plate Tectonics, and the Tectonics of SW British Columbia
Age of the Earth. So far, scientists have not found a way to determine the exact age of the Earth directly from Earth rocks because...
Earth's oldest rocks have been recycled and destroyed by the process of plate tectonics
The 7 large plates:
Eurasian Plate African Plate Australian-Indian Plate Antarctic Plate Pacific Plate North American Plate South American Plate These are all much bigger than the largest continents
Such recurring events as mountain building and sea encroachment, of which the rocks themselves are records, comprise units of...
Geologic Time (even though the actual dates of the events are unknown) Like the broad units of time B.C. and A.D, geologists have done the same thing to geologic time by dividing the Earth's history into Eras (broad spans based on the general character of life that existed during these times), and Periods (shorter spans based partly on evidence of major disturbances of the Earth's crust.)
The Coast mountaints extend from Vancouver's North Shore nearly 1000 km to the Yukon and Alaska, and much of it consists of ______ rock (formed mainly of interlocking crystals of ______ and ______)
Granitic (feldspar and quartz - the 2 most common minerals in the Earth's crust)
Erosion of the Coast and Cascade mountains has exposed _______ and _______ rocks that formed deep in the Earth's crust more than 100 million years ago
Granitic and Metamorphic
There has not yet been observed any __________ era rocks on earth, most likely because it was too hot for rocks to form during the ______ era
Hadean
The 4,600 million years that the Earth has existed can be divided into four eons (from oldest to present)
Hadeon, Archean, Proterozoic and Phanerozoic
The ancient historian _____ in the 5th century B.C., made one of the earliest recorded geological observations.... What was it?
Herodotus After finding fossil shells far inland in what are now parts of Egypt and Libya, he correctly inferred that the Mediterranean Sea had once extended much farther to the South.
Stratigraphy
How layers of sediments, sedimentary rocks vary in age and thickness toward depth
Cycle: Liquid (molten) rock material solidifies at depth or at the earth's surface to form ______ ROCKS.
IGNEOUS
Principle of Uniformitarianism
"the present is the key to the past". In other words, the physical processes that presently are at play on Earth are the same as those that have shaped it during the past.
William Smith, a civil engineer was responsible for much of the realization that fossils represent past life. He noticed that fossils changed, and when a certain type disappeared, it never returned. This principle is known as:
- The Principal of Faunal Succession or - The Law of Fossil Succession *this work was revolutionary, and the basis for the work of such notables as Charles Darwin 50 years later
say we are out and about, and we find rocks that are folded and faulted, and possibly new minerals have grown (metamorphic) We can interpret that ....
- The rocks were deeply buried - The rocks were subjected to elevated temperatures and pressures - The rocks have subsequently been uplifted and brought to surface. - The specific minerals can be used to interpret the pressure and temperature conditions.
Relative Time Scale:
- based on the sequence of layering of the rocks and the evolution of life - highlights events in the growth of geologic science itself
Igneous rocks: 3 conclusions we can make if we find igneous rocks with interlocking crystals (quartz, feldspar)
- bigger crystals indicate a longer time to cool - we interpret these rocks formed at a deeper location - at some point, the rocks were uplifted to the surface and exposed
Other patterns Wegener found to support his hypothesis of continental drift
- fossils of the reptile cynoghanthus and mesosaurus and lystrosaurus found in South American and Africa, fossils of the plant glossopteris in all southern continents and india - traces of Ice Ages found in South American, South Africa, Australia and India
Radioactive decay is a spontaneous process in which an ______ (the parent) loses particles from its nucleus to form an isotope of a new element (the daughter). The rate of decay is conveniently expressed in terms of an isotope's _______
- isotope - half-life (or the time it takes for one-half of a particular radioactive isotope in a sample to decay)
How is the rock record skewed in its representation of environments for igenous rocks?
- not all environments or conditions are commonly preserved in the rock record. - e.g. any place where erosion takes place, such as mountain tops, erodes to form sedimentary rocks but this environment ins't preserved (it is eroded!) - so, we see a lot of sedimentary rocks that represent ocean environments and less that represent terrestrial environments
In a cross-section through a sequence of sedimentary layers, the lowermost layer is the ________ while the uppermost is the ________. This rule is valid for both loose sediments and hard sedimentary rock, however this rule is valid only when:
- oldest, youngest - the sediments are oriented more or less in the same way as they were deposited. If a sedimentary rock is faulted or folded, layers of old sediments may be put above younger sediments.
Carbon 14 age dating can only be used:
- on organic materials - only for recent times (~50,000 years or less)
4 conclusions of sedimentary rocks:
- rocks formed of fragments of other rocks - We note that these rocks are layered (unless layering has been disturbed after the sediment is deposited through salt/crystal growth or tidal flats organic activity) - We can look at the rock fragments and interpret where the rocks originated. - We can also interpret that these rocks formed through weathering, erosion, transportation and deposition in a near-surface environment (rivers, lakes, oceans).
What does it mean when sedimentary layering is tilted?
- sediments are never deposited in tilted layering - the tilting of the layering probably occurred much later than the deposition and consolidation of the sediments - the tilting tells us that the crust has been rotated subsequent to the consolidation of the sediments (the crust has been deformed)
Hutton first proposed formally the fundamental principle used to classify rocks according to their relative ages:
- that each layer represented a specific interval of geologic time - wherever uncontorted layers were exposed, the bottom layer was deposited first and was, therefore, the oldest layer exposed; each succeeding layer, up to the topmost one, was progressively younger
Igneous rocks: 3 conclusions we can make if we find volcanic rocks (basalt, volcanic ash)
- the fine grained nature tells us the rocks cooled quickly - we can interpret that an eruption took place - at some point in the past volcanoes were nearby
Radioactive age dating methods can only be used if... (3 criteria):
- the rock contains minerals of material that contain the appropriate elements - either enough time has elapsed to measure the change - not too much time has elapsed to measure the change such that the appropriate material is gone
Your focus in your reading and activities should be on the following
- types and characteristics of earth materials (minerals, rocks, surficial deposits) - the underlying principles of geological time - methods used to interpret age relationships - methods used to interpret past environments ensure you can define the terms to know by the end of the module (add any terms that you didn't add throughout the module)
This Flash module focuses on relative age dating methods and will address:
- what is a relative age and what is an absolute age? - how can relative ages of sedimentary rocks be determined? - what can the contact relationship between a sedimentary and an igneous rock tell us about the relative ages of the rocks? - what can the contact relationship between a sedimentary rock and the underlying unit tell us about the relative age relationship between the sedimentary rock and the underlying unit? - what can fossils tell us about the age of a rock? - what is stratigraphy? - the geological time scale
Subduction is responsible for:
-compression and thickening of crustal rocks, the rise of mountains, volcanic eruptions, and earthquakes (hallmarks of Canada's Pacific margin) -scraping off of island chains, large submarine volcanoes (seamounts) and mud deposits on the ocean floor of the down-going oceanic plates at the edge of the continent
It is by applying uniformitarianism principles that we interpret history from rocks. Uniformitarianism does not mean everything occurred at the same rate. As we observe, Earth processes occur at a variety of rates. Some processes are catastrophic in nature (meteor impact, floods, hurricanes), whereas others are slow and gradual (erosion of mountains). Uniformitarianism allows us to recognize that they are both gradual and catastrophic processes.
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Module 2 PDF document: Minerals:
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On a time scale of years or even centuries, the Earth appears essentially static and unchanging, but looks can be deceiving. For on the longer time scale, that of geological time, the Earth is dynamic and undergoes profound change. For example, the landscape of BC today bears little resemblance to that of 50 million years ago. What caused our landscape to change so much?
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Relative Age Flash Module Summary...
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Step 4. Volcanic Intrusions (H) occur (these cut across D, G and A
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Step 9. F (Dyke and volcano) is somewhat ambiguous; we would need to understand the relationship with the sediments located further south to know exactly when it was formed in the sequence. It formed after the uplift (step 5/6 -cross cutting relationships, erosion evidence), but since there is no physical connection between the glacial and river sediments shown, we cannot know which formed first.
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Vancouver, City on the Edge pp 14-33
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We will now focus on what the contact relationships between different rocks can tell us about the relative ages of the rocks. The red circle * shows an area where young sedimentary rocks have been formed on top of old high-metamorphic rocks...
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Flash Module, Relative Age Dating http://ansatte.uit.no/kku000/webgeology/webgeology_files/english/geol_time_eng.html
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4 facts of the geological history of a simple horizontally layered sedimentary rock:
1) the sediments were deposited in horizontal layers 2) the sediments were buried under younger sediments 3) because of the increasing temperature and pressure during burial, the sediments underwent lithification - a sedimentary rock was formed 4) later, uplift and erosion have brought the rocks to the surface
4 components of Earth's 'system'
1. Atmosphere: the gaseous envelope around the Earth 2. Hydrosphere: both solid and liquid componenets 3. Geosphere: solid Earth, the rocky mass which makes up the bulk of the Earth 4. Biosphere: the realm affected by life
5 steps in the geologists role:
1. Collects data - make observations, describe, measure, identify. 2. Determines relationships - place objects in a sequence using a few logical principles. 3. Determine dates and rates - when did something happen and how long did each process take? 4. Determines causes - uses observations and scientific principles to interpret why/how something happens. 5. Builds interpretation - the "story" *the rocks, which are classified by their origin into igneous, sedimentary and metamorphic, hold the key. the composition, including fossils and textures hold clues to the conditions under which the rock formed. If a particular rock is present, we interpret that a particular set of conditions existed. We look at the relationships between rock bodies to interpret timing.
Two examples using the principles of correlation in fossils at different scales
1. Correlation of rock units in a small area 2. Large region in the Southwestern US
3 layers of the geosphere
1. Crust (outer most layer, up to 100 km thick) 2. Mantle (middle layer, between ~100 Km to 2900 km) 3. Core (innermost layer, between 2900-6378 km).
Module 2 objectives:
1. Describe the origin and general physical characteristics of the three rock types.1. 2. Distinguish between relative and absolute time 3. Cite and describe the underlying principles and key methods of relative and absolute dating. 4. Interpret the geological history of a region from visual representations of rock relationships (photos and diagrams) 5. Describe the layered structure of the Earth, outlining the physical properties and key processes associated with each 6. Explain the basic principles and processes involved in plate tectonics. 7. Describe the key differences between continental and oceanic plates and how these differences influence plate interaction 8. Describe the geological setting of southwestern BC in plate tectonic terms, identifying evidence (processes and features) for particular types of plate interactions. 9. Begin to relate the evidence captured in the rock record of southwestern BC to its geological history.
Absolute time refers to the specific time an event occurred, usually measured in years before present (1950). What do these abbreviations mean to express dates? 1. Ga - 2. Ma - 3. Ka - 4. B.P. -
1. Ga - billions of years before present 2. Ma - millions of years before present 3. Ka - thousands of years before present 4. B.P. - Before Present
Several areas where metamorphism is common:
1. In subduction zones: as the oceanic plate descends into the mantle, both the sediments and the basalt floor are subjected to high pressure and low to high temperature conditions. Fluids may play an important role chemically change the rocks' composition. 2. Adjacent igneous intrusions - contact metamorphism, where cooler (country) rocks are altered by contact with a hot igneous intrusion, is another common type of metamorphism. This type of metamorphism commonly produces a 3. At spreading centres (mid-ocean ridge): Fluids play an important role in hydrothermal alteration associated with magma emplacement on the sea floor at mid-ocean ridges. 4. Contact (thermal) metamorphism of country rocks during igneous intrusion or beneath thick flows.
Two categories of igneous rocks are commonly delineated according to origin:
1. Intrusive (plutonic) rocks crystallize at depth. These rocks are brought to the surface through mountain building activity and erosion of overlying rocks. 2. Extrusive (volcanic and pyroclastic rocks) rocks crystallize after the magma reaches the earth's surface. We can witness these rocks forming at sea-floor spreading ridges and other rift zones, volcanic arcs (above subduction zones) and at hot spots (intraplate volcanism)
Your focus on module 2:
1. Note the terms relevant to plate tectonics in the "Terms to Know" page and ensure that you understand their definitions by the end of the module 2. To get a general overview of the subject material and its relevance to understanding SW BC/Vancouver geology, re-read pages 14-33 of Vancouver, City on Edge 3. Scan the web pages of Module 2, Part 2 4. Read through the Module, The Earth's Interior 5. Your major reading in Part 2 is the Plate Tectonics Module. A reading guide will be posted. Concentrate on identifying the following: - the composition and properties of Earth's layers - the underlying principles of plate tectonics - aspects of southwestern BC's tectonic setting 6. Return to Module 2, Part 2 Web Pages in course web site, and re-read the web pages in the module. The topics covered include the Rock Cycle and one "Think about it" question. 7. Complete the geological history activity and submit it by Thursday, January 29, 11:55 PM.
The Phanerozoic eon can be divided into 3 eras:
1. Paleozoic (542 million years ago to 248) 2. Mesozoic (248 million years ago to 65) 3. Cenozoic (65 million years ago to present)
1. essentially no fossils: _________ 2. "old life"": ___________ 3. "middle life": _________ 4. "recent life": ___________
1. Precambrian 2. Paleozoic 3. Mesozoic 4. Cenozoic
Two scales that are used to date the episodes of the Earth and measure the age of the Earth:
1. Relative Time Scale 2. Radiometric Time Scale
3 subject areas geologists use to understand how the Earth works:
1. The Rock Record: the evidence for understanding how the Earth works comes from the materials we study- minerals, rocks and sediments. We call this the rock record. 2. Geologic time: From observations and scientific study, we understand that what we see today did not appear overnight - processes take time. Some processes happen rapidly (storms, earthquakes, meteor impact) and some take a long time (the time it takes for mountains to form or erode, the movement of a river in a floodplain or development of a delta). These concepts relate to Geologic Time. 3. Plate Tectonics: Large scale earth movements driven by the internal heat engine described in the movie "The Restless Planet" have shaped and continue to shape the planet. The interactions between large blocks of the earth's crust drive the smaller scale changes we see. These concepts relate to late tectonics. These 3 subjects work together because, the theory of plate tectonics had its origin in the evidence contained in the rock record. Piecing the theory together involved relative and absolute age dating principles and an understanding of how to interpret processes from the rocks
Most radioactive isotopes have rapid rates of decay (that is, short half-lives) and lose their radioactivity within a few days or years. Some isotopes, however, decay slowly, and several of these are used as geologic clocks. List the Parent Isotopes and corresponding daughter products that are commonly used to determine the ages of ancient rocks (and their currently accepted half-life values)
1. Uranium - Lead (4.5 billion years) 2. Thorium - Lead (14 billion years) 3. Rubdium - Strontium (48.8 billion years) 4. Potassium - Argon (1.25 billion years) 5. Samarium - Neodymium (106 billion years)
Readings:
1. Vancouver City on the Edge: pp 14-33 (first) 2. Module 2 course pages 3. Web reading: geological time: http://pubs.usgs.gov/gip/geotime/contents.html (second - noting any unfamiliar terms, and any historical figured mentioned) Online movie: (scroll down to #10, click on VOD icon). (third) http://www.learner.org/vod/vod_window.html?pid=321 - Flash Module: relative age dating (fourth) 4. Flash modules on Earth's interior and plate tectonics (Part 2) (5th, and the absolute virtual dating activity)
1. The simple relationship between parent and daughter elements is complicated by things such as... 2. Therefore, most commonly we see "absolute" radiometric age dates bracketed by:
1. accuracy of measurements, geologic heating events that may "reset" the amount of a parent element, loss of a daughter element 2. an error (plus or minus a certain number of years)
3 types of boundary between crustal plates that are moving in relation to each other
1. collision zones: plates moving towards one another 2. spreading axes: plates moving away from each other 3. lateral movement: plates can move parallel to each other
the plate is eventually subducted under a __________ (1). In the trench of the subduction zone, at relatively shallow depths, high pressure - low-high temperature _________ (2) of the plate and its sediment cover occur. As the plate travels deeper, high temperature conditions cause partial ______ (3) of the crustal slab. Fluid intrusion plays a key role in partial melting (the lighter silica-rich materials melt and rise up through the overlying rock). As the partial melt rises, and intrudes into the ________ (4) plate, the surrounding country rock is contact-__________(5) at high temperature conditions. This melt is either driven to the surface as __________ (6), or crystallizes at depth to form ________ (7).
1. continental plate 2. metamorphism 3. melting 4. continental 5. metamorphosed 6. volcanic eruptions 7. plutonic igneous rocks
1. ___________ - where two plates moving toward one another meet; 2. ___________ - where two plates move apart; and 3. _________ - where two plates slide past one another. 4. In addition, there is a unique type of tectonic situation called a "______" which occurs in the middle of plates and operates over long time scales.
1. convergent boundaries 2. divergent boundaries 3. transform 4. hot spot
1. At the mantle-core boundary, the material of the mantle is heated, which results in a density ________ of the material. 2. The hot and ___ material in the lower part of the mantle moves upwards, while the colder and _____ material in the upper part moves downward 3. The mantle material moves in more or less circular patters which are called ____________.
1. decrease 2. light, heavier 3. mantle convection cells
1. The velocity of a seismic wave is dependent on the _______ of the rock is passes through 2. As a result of the velocity change, the wave is reflected/refracted at the boundary between 2 rock types. The wave that travels to the _____ level in the crust returns to the surface later than waves that are reflected at ____ levels. 3. The travel time of the wave from the source down to where it is reflected and back up to the microphone can be used to calculate:
1. density 2. deepest, higher 3. the depth of boundary where the wave was reflected.
Driving from Vancouver to Squamish traverses these rocks 1. _______ of the North Shore mountains and Stawamus Chief 2. and ancient metamorphosed sedimentary and ________ at Britannia beach
1. granites 2. volcanic rocks
_______ (1) rocks form at sea floor spreading ridges. Fluid intrusion of these rocks, both during and after formation, results in some low grade ______ (2). As the rocks cool, and more magma is introduced from below, the plate is forced away from the spreading ridge, and acquires a ________ (3) cover. The stripes represent changes in _______ (4) over time.
1. igenous 2. metamorphism 3. sediment 4. magnetic polarity
2 main types of rock at Caulfield Park:
1. light-coloured granitic rocks consisting mainly of crystals of the minerals quartz and feldspar 2. dark-banded metamorphic gneiss which contains feldspar and black hornblende
Nicolas Steno/Niels Steensen formed these 2 principles of relative age dating:
1. principle of original horizontality: sediments are deposited in a horizontal or near horizontal attitude 2. principle of superposition: in a vertical succession, the rocks deposited at the bottom are the older than the rocks on top
The top of the ophiolite sequence consists of fine grained, ocean ______ (1) (cherts, lime mudstones, etc.). Below this are _______(2), which form when hot magma is extruded onto the ocean floor. These rocks are often extensively altered by interaction with seawater
1. sediments 2. pillow basalts
1. The rate at which magma cools has has a fundamental effect on the _______ (size and arrangement of the minerals) of an igneous rock 2. Molten magma that cools slowly has ______ and _______ crystals than rapidly cooling magma
1. texture 2. distinct, larger
1. The southwest coast of British Columbia lies at the boundary of two great crustal plates: 2. The 2 plates are converging at a rate of about ____
1. the oceanic juan de fuca plate and the much larger, continental North American Plate 2. 4cm/year *They meet head-on about 200km off the coast; there the Juan de Fuca plate begins its slow descent beneath Western BC.
Sedimentary rocks in plate tectonics: The Parent rock undergoes _______ (1) by chemical and/or physical mechanisms into smaller particles. These particles are _________ (2) by ice, air or water to a region of lower energy called a sedimentary basin. ________ (3) takes place as a result of a lowering of hydraulic energy, organic biochemical activity or chemical changes (e.g., solubility). Once deposited, the sediments are slowly __________ (4) (turned into rock) through ________ (5) (decrease in rock volume due to weight of overlying sediment) and ________ (6) (chemical precipitation in pore spaces between grains which "glues" the rock together. The primary mineralogical and textural characteristics of the rock can be modified as the sediments are buried deeper in the earth's crust and undergo an increase in both temperature and pressure. These low pressure, low temperature changes are termed ___________ (7).
1. weathering 2. transported 3. deposition 4. lithified 5. compaction 6. cementation 7. diagenesis
1. Igneous rocks: the mineral composition and the texture of the rock (the size and arrangement of the grains) help us interpret.... 2. Molten material that is located beneath the surface is called ____, whereas molten material that flows onto the earth surface is called ____.
1. where the rock formed and under what conditions 2. magma, lava
The distance from the Earth's surface to its core is more than 6000 km, but modern technology does not allow us to drill more than to about ____ km down through the crust.
15
Today, scientists agree that the crust is divided into about ____ larger and smaller _____ plates, both ____ and ____
20 larger and smaller continental and oceanic
Fossil content, as well as lithology, are important in these correlations. In certain cases, the presence of specific fossils known as _____ Fossils are diagnostic of a specific time interval.
Index
Ancient rocks exceeding ______ billion years in age are found on all of Earth's continents. They are not from any sort of "primordial crust" but are lava flows and sediments deposited in shallow water, an indication that...
3.5 Earth history began well before these rocks were deposited
In Western Australia, single zircon crystals found in younger sedimentary rocks have radiometric ages of as much as ____ billion years, making these tiny crystals the oldest materials to be found on Earth so far.
4.3
The results show that the meteorites, and therefore the Solar System, formed between _______billion years ago. The best age for the Earth comes not from dating individual rocks but by considering the Earth and meteorites as part of the same evolving system in which the isotopic composition of lead, specifically the ratio of lead-207 to lead-206 changes over time owing to the decay of radioactive uranium-235 and uranium-238, respectively.
4.53 and 4.58
The Rock Cycle is a concept authored by:
James Hutton it depicts the interrelationships between igneous, sedimentary and metamorphic rocks
Between the years of 1785 and 1800 _____ and ________ advanced the concept of Geologic Time and strengthened the belief in an ancient world
James Hutton and William Smith
Sea floor spreading has further been conclusively confirmed by evidence of changes in the Earth's __________.
Magnetic field (at regular intervals, theEath's magnetic north pole and south pole switch places) Progressing further away from the mid-ocean ridge, geologists fund parallel bands of alternating positive and negative orientations of magnetic minerals in the rocks in the sea flow. This pattern can reveal when the various lava flows crystallized
Sedimentary rocks around the world have distinct assemblages of fossils that change vertically through the rock succession, that is, through time. Dinosaurs are found in ______ rocks.
Mesozoic.
Changes in temperature, pressure, and/or rock or fluid chemistry can cause igneous and sedimentary rocks to recrystallize to form ________ ROCKS
Metamorphic
The boundary between the crust and the mantle is called:
Mohorovic discontinuity (Moho) *the boundary represents an abrupt change in the velocity of seismic waves
In the mid-1600's Bishop Ussher, using the genealogy presented in the Bible, calculated that the Earth was created on October 23, 4004 BC. They believed that the Earth was once covered by an all encompassing Ocean which gradually receded. Those who believed this were called:
Neptunists (from Neptune, the God of the ocean)
Vancouver is near the boundary of the westward-moving ________ plate and the smaller ________ plate.
North American Juan de Fuca
P-waves can travel through liquids, however they are refracted at the boundaries between different zones they are traveling through which creates a zone where P-waves are never registered, _____
P-wave shadow zone
Alfred Wegener's hypothesis of continental drift is based on the idea that all of the continents were once joined together in a giant supercontinent which he called _______.
Pangaea
6 Periods of Paleozoic Era
Permian (290 Ma) Carboniferous Devonian Silurian Ordovician Cambrian (543 Ma)
_______, the study of rocks and their origins, is the formal process by which we resolve the interrelationships expressed in the rock cycle.
Petrology
4 Eons (most recent to oldest)
Phanerozoic (Precambrian) Proterozoic (2500 Ma) Archean (3850 Ma) Hadean (>3850 Ma)
Intrusive (_____) igneous rocks
Plutonic: crystallize at depth. These rocks are brought to the surface through mountain building activity and erosion
James Hutton (1727-1797) and John Playfair did not ascribe to the Neptunist viewpoint, and instead recognized that rocks form by a variety of processes. In contrast to the Neptunist, they were known as _________ - a term derived from the God of fire, meant to contrast their belief with that of the Neptunists. Their experience and observations that igneous rocks formed by cooling of very hot fluids.
Plutonists
Rocks that formed prior to Cambrian (i.e. during Proterozoic and Archean) are commonly referred to as ____________
Precambrian
Rocks that formed prior to Cambrian (i.e. during Proterozoic and Archean) are commonly referred to as ____________
Precambrian rocks
A fundamental principle used by geologists to reconstruct past events is the _______________
Principle of Uniformitarianism
2 Periods of Cenozoic Era
Quaternary (1.8 Ma) Tertiary (65 Ma)
_______ defines time in order as compared to other events, whereas______ defines the time in terms a known, measurable time scale.
Relative, absolute (time)
Metamorphic rock:
Rocks that have formed from pre-existing rocks by changes in mineral content and structure under high temperature, pressure and stress within the Earth's crust
Part 1 (of Module 2):
Rocks, Minerals and Geological Time concepts related to the rock cycle, geological time, stratigraphic principles and interpreting geological history from rock sequences
Best known example of 2 crustal plates moving laterally in relation to each other
San Andreas Fault in California (forms the boundary between the North American plate and the Pacific plate)
Nevertheless, scientists have been able to determine the probable age of the ________ and to calculate an age for the Earth by assuming that the Earth and the rest of the solid bodies in the _______ formed at the same time and are, therefore, of the same age.
Solar system
Define seafloor spreading:
The process whereby oceanic crust is produced by convective upwelling of magma along midoceanic ridges. Oceanic crust moves away from the ridges at rates of 1 to 10 cm per year
One way heat is transferred is by conduction. Define.
The single atoms above the heat source vibrate faster and faster. The energy that makes the atoms vibrate is transferred to the colder neighboring atoms, which then start to vibrate faster and faster, transferring heat from one atom to another
Stratigraphic correlation
The stratigraphy on one outcrop / drill core is correlated to the stratigraphy on a different outcrop / drill core
Crosscutting:
a body of rock or sediment cuts across a second body and is thus younger. Crosscutting commonly results from injection of magma or fluidized sediment along fractures in older rocks.
Define: terranes:
a distinctive fault-bounded body of rocks, thought to have been accreted, or added, to a continent at some time in the geological past.
Volcanic rock:
a finely crystalline or glassy igneous rock that crystallizes from magma on the Earth's surface. It is eiher ejected explosively during a volcanic eruption or extruded as lava
For convenience, geologists commonly group adjoining beds that possess similar or related features (including fossils) into a single, more conspicuous unit called...
a formation
Metamorphic Rocks in Plate Tectonics: Metamorphic rocks are formed where:
a parent rock, called the protolith, is subjected to changes in pressure, temperature or chemistry (such as addition of fluids).
A disconformity is a surface in a sedimentary sequence that represents:
a pause in sediment deposition
Foliation
a planar fabric in metamorphic rock, generaly produced by the alignment of minerals under directed stress
Define faults:
a plane or zone within the Earth along which rocks have moved past one another
Hutton's discovery, though elementary today, was a major breakthrough in scientific reasoning by establishing:
a rational bases for relative time measurements (however, unlike tree-ring dating, no precise rate of deposition can be determined for most of the rock layers. Therefore, the actual length of geologic time represented by any given layer is usually unknown or, at best, a matter of opinion).
cross cutting relationships:
a structure (e.g., a fault) or rock unit such as an igneous intrusion, that cuts across another rock unit (or structure) is younger than the rock unit it disrupts.
Granitic rock:
a term loosely applied to any light-coloured medium to coarse grained igneous rock consisting mainly of quartz and feldspar. Geologists discriminate many different types of granitic rocks on the basis of the types of feldspar and the amount of quartz, i.e. granite, granodiorite and tonalite.
Continental crust is composed of:
a variety of rock types, and include large proportions of crystalline igneous and metamorphic rocks. It is thicker than oceanic crust, and less dense
Asthenosphere
a weak, plastic region, thought by most scientist to be capable of flow, within the upper mantle.
If we measure the amount of the P and D, or the amount of each relative to one another (ratio - P/D), and we know the rate of decay (through laboratory measurements), we can determine the _______.
absolute age
An oceanic spreading ridge is an area of rifting where two oceanic plates are being forced apart by:
addition of new magma from below.
The mathematical expression that relates radioactive decay to geologic time is called the
age equation
When two oceanic plates drift apart, a body of melt rises form the mantle and crystallises into new sea floor along mid-ocean ridges. Therefore
an ocean can grow wider, with the oldest rocks further away and the youngest closest to the mid-ocean ridge
The _________ is positioned below the lithosphere mantle, a few percent of which is _______.
asthenosphere molten, which makes it much weaker than the lithosphere mantle
Sedimentary Rocks: form...
at or near the earth's surface
Layers of rocks
beds
Hutton believed that the present is the key to the past. In contrast to _________, this approach is called ________
catastrophism uniformitarianism
Video: Geologic time: Minerals which contain radioactive isotopes act like _____ inside of rocks. Clocks which are reset when a rock is.... Before geologists learned to measure the absolute ages using radioactive isotopes, they could only establish relative ages using the common sense logic of:
clocks, formed or metamorphosed superposition, original horizontality, cross-cutting relationships (they knew one rock performed before another, but not absolute ages)
Layers of sedimentary rock that have been deposited without interruption are called __________ layers
conformable
Alfred Wegener introoduced the hypothesis of ________ in 1915
continental drift
Conduction is a very slow mechanism to transfer heat. A much more efficient mechanism is: __________
convection
The earth's magnetism is caused by:
convectional currents in the outer liquid core
When two lithospheric plates move towards each other, ________ are formed in the collision zone, either with volcanic arcs or mountain ranges with volcanic activity alongside
deep sea trenches
The fossil content of a sediment/sedimentary rock can be used to determine its:
depositional age
The major divisions of the Geologic Time Scale are based on:
differences in fossil content
Igneous Rocks in Plate Tectonics Igneous rocks form by:
direct crystallization of minerals from a magma melt on the surface of the Earth and at depth.
Once more the sea-level rises - more sediments are deposited. The break in sedimentation and the subsequent erosion resulted in a surface called a ____________. Note that the layers above it are:
disconformity parallel to the layers below the disconformity
A _____ cuts the structures (i.e. the layering) of the sedimentary rock. __________ relationships like this provide a useful tool for relative dating rocks
dyke cross-cutting relationships
On this figure * magma forces itself up along fractures in a sedimentary rock (on the seafloor). Magma that crystallizes in a vertical fracture form an intrusive body called a ______...
dyke...
Dyke vs. sill
dyke: sheet-like volcanic intrusions that cut older rocks sills: intrusions that are parallel to the layers in sedimentary or metamorphic rocks.
How an angular unconformity is formed:
e.g. 1. old gneisses are overlain by much younger sedimentary rocks 2. The crust is deformed - the rocks are folded 3. Then, the upper parts of the rock-complex is eroded 4. sea level is rising 5. new sediments are deposited at the ocean bottom. The sediments undergo diagenesis and transform to sedimentary rocks. The boundary between the folded sedimentary rocks and the horizontally layered sedimentary rocks is called an angular unconformity.
Collision of the juan de fuca plate and the North Americna plate and the subduction of one beneath the other causes:
earthquakes on the west coast and are also responsible for the chain of active volcanoes at our doorstep. They also create and modify out landscape. The Coast Mountains are rising at rates of up to a few mm/year. The uplift prevents the rugged mountains from being leveled in the face of continuous erosion by streams, glaciers and landslides.
The processes that move sediments (wind, water, gravity) can be ______ or ______, so this leads to a natural sorting of materials and the creation of time horizons between events. _______, which you will read about later in this module, are an example of cyclic sedimentation in glacial lakes and some fjords.
episodic, cyclic Varves
the first thing you need if you want to carry out a seismic survey is an energy source (i.e. ________). The energy source sets off a seismic wave. The wave propagates in all directions away from the source.
explosives
the parent element (P) decays to a daughter (D) element at a measurable rate. This decay follows an ________ curve.
exponential
In general _____ igneous rocks have a finer grained texture than _______ igneous rocks
extrusive intrusive
All of BC, with the exception of the Rocky Mountains and the Interior Plains of Northeartern BC consists of a complex mosaic of terranes that successively collided with, and became a part of, the growing North American continent. Each terrane (far-traveled crustal segments) comprises a unique assemblage of ricks, and each is separated fro neighboring terranes by _____
faults
Shearing forces created by the Juan de Fuca plate sliding past the base of the overlying North American Plate cause the metamorphic minterals to align as they grow, giving many of these rocks a conspicuous layering, or ______.
foliation
The term "____" is often used to indicate the extent to which a rock has been altered and the conditions of metamorphism
grade
Rhyolite and Granite are rocks with the same composition; both are high in ____ and are _____ coloured. ______ form at or near the surface whereas ______ form at depth.
high in silica light coloured rhyolites- at or near the surface granite- forms at depth
High grade rocks have been subjected to:
high pressures and temperatures
Oceanic crust has a ________ density than the thicker continental crust. Therefore, the oceanic crust will always be driven:
higher beneath the continental crust
Commonly, sediments are deposited on the ocean floor in __________ layers. As time goes by, more and more sediments are deposited on the ocean floor. New sediments are always deposited ______ of older ones.
horizontal new= on top, old = bottom
inclusions:
if a rock unit contains a fragment of another rock type, the fragment is interpreted to have formed first, and was incorporated into the younger unit when it formed.
When _______ rocks crystallize, the newly formed minerals contain various amounts of chemical elements, some of which have radioactive isotopes. These isotopes decay within the rocks according to their half-life rates, and by selecting the appropriate minerals (those that contain potassium, for instance) and measuring the relative amounts of parent and daughter isotopes in them, the date at which the rock crystallized can be determined. Most of the large _____ rock masses of the world have been dated in this manner.
igenous
Interweaving the relative time scale with the atomic time scale poses certain problems because only certain types of rocks, chiefly the _______ variety, can be dated directly by radiometric methods. But these rocks do not ordinarily contain ________. _______ rocks are those such as granite and basalt which crystallize from molten material called "magma".
igenous fossils igneous- crystallized from magma
At higher temperatures, metamorphic (or any other rock type) rocks may be partially or fully melted, and crystallization of this melt will create ____ rocks. Uplift and erosion can expose all rock types at the surface, re-initiating the cycle.
igneous
The geothermal gradient shows how the temperature _____ towards depth. The melting temperature also increases towards depth as a consequence of the increase in pressure, which is why the ____ core is solid
increases, inner
The density of the material in the Earth ______ towards depth
increases, as a result of the increase in pressure
William Smith's hobby of cataloging fossil shells from rocks led to the discovery that certain layers contained fossils unlike those in other layers. Using these key, is _______ fossils as markers, Smith could identify:
index fossils a particular layer of rock wherever it was exposed.
intrusive relationships:
intruding rocks must be younger then the rocks they intrude
Module 2 focuses on...
investigating key fundamental principles of geology, which we will then apply to Vancouver. These topics include rocks and geological time, Earth structure & plate tectonics, and the application of these concepts to southwestern British Columbia and the Lower Mainland.
The core consists of _____. The outer core is ____ while the inner core is _____.
iron, liquid, solid
The ages of Earth and Moon rocks and of meteorites are measured by the decay of long-lived radioactive _______ of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements. These dating techniques, which are firmly grounded in physics and are known collectively as ____________, are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to rehomogenize its radioactive elements.
isotopes radiometric dating
A concordant layer of igneous rock in a sequence of layered sedimentary rocks may have been emplaced either as ____ or as a ____
lava, sill
Most sedimentary rocks have obvious: ______, a natural consequence of differential settling of materials that are of different masses and shapes.
layering
S-waves cannot travel through: Therefore, they stop when they arrive at the:
liquids outer core therefore, the distance from the Earth's surface to the mantle/outer core boundary (which is 2900 km), can be calculated on the basis of the size of the S-wave shadow zone
The minerals break down into smaller grains or ions in solution, which are transported and deposited as sediments in another location. The sediments are ________ (turned to a rock by processes like compaction or cementation), and _______ ROCKS form.
lithified sedimentary
1. The rigid and mechanically strong part of the earth (the crust and the lithosphere mantle) is called the _____________, and it contains a number of large plates that move relative to each other, called.. 2. It rests on top of the ___________
lithosphere, plate tectonics asthenosphere
Basalts and gabbros are rocks of the same composition; both are low in ____ and are ____ coloured.
low in silica dark coloured
In a sequence of sedimentary rocks, the lowest unit is the ________ and the highest unit is the ___________, provided that the sequence has:
lowest = oldest highest = youngest hasn't been disturbed by tectonic processes
Convection in the ______ is responsible for most of the transfer if heat from the hot core to the surface of the earth
mantle
The oldest rocks in the Vancouver area occur at the surface in the Coast Mountains north of Vancouver and in the Cascade Mountains. They are what geologists call ________ rocks.
metamorphic rocks: rocks that were originally sedimentary or igneous in origin, for example mudstone or basalt, but that have been subjected to high temperatures and pressures deep within the Earth.
Sea floor spreading has been confirmed, as the age of the oceanic crust increases proportionally with distance from the __________.
mid-ocean ridge
Oceanic crust forms at __________ and is composed of _______ rocks
mid-oceanic ridges (oceanic spreading centres), less hick and composed of mafic rocks (ophiolite sequences)
A rock can be composed of one or more minerals; we call rocks composed of one mineral "________". Provide 2 examples.
monomineralic Quartzite - a metamorphic rock composed of quartz alone Limestone
Heat is always transferred from hot to cold material. In the interior of the Earth, heat is transferred from the hot inner core towards the cold surface; this heat transfer is responsible for...
most geological activity (plate tectonics, volcanic activity)
If two continental plates collide, what happens?
niether will be driven down into the mantle, but folding and thrusting will occur and complicated geological structures will form
The boundary between the sedimentary rock and the underlying gneiss separates rocks that are not conformable. This type of boundary is called a _____________
nonconformity
The contact between crystalline basement rocks and an overlying unit of layered sedimentary rocks is called a ____________
nonconformity
A volcanic rock is __________ than the sedimentary rocks above
older
Caulfield Park in West Vancouver shows some of the ______ rocks in Vancouver.
oldest. These rocks formed deep within the Earth under very high temperature and pressure. Since then, they have been elevated tens of kilometres by Earth's forces, and the overlying rocks have gradualy eroded away.
The characteristic assemblage of rocks which form at spreading ridges is called an _______ sequence. The typical rock types are illustrated below, and include:
ophiolite ocean sediments, mafic extrusive and intrusive igneous rocks, and ultramafic rocks
The sedimentary rock is built up of conformable layers (i.e. ....)
parallel layers that have been deposited essentially without interruption
conformable layers
parallel layers that have been deposited essentially without interruption
minerals provide valuable clues as to the .....
physical and chemical conditions that were present when a rock formed thus, by looking at the minerals in a rock, we gain major insights into the conditions of formation
Crustal plates move because the mantle on which they rest is...
plastic (somewhat akin to toffee or silly putty) Plumes of super-heated mantle rock rise deep within the Earth, move laterally approximately parallel to the Earth's surface, becoming cooler in the process, and then sink back down towards the Earth's core (this process is termed convection, is driven by heat produced through the decay of radioactive elements in the Earth)
It was not until the 1960s that the theory of ______ became accepted by scientists and Wegener gained the status of the father of _____
plate motion (plate tectonics)
Convection itself drives the slow, inexorable movement of plates at the Earth's surface, a process called:
plate tectonics
_______________has a huge influence on the type of metamorphism and the types of structures we see in a region.
plate tectonics
Sedimentary rocks in plate tectonics: Sedimentary rocks form from:
pre-existing rock particles - igneous, metamorphic, or sedimentary
Lava tends to crystallize rapidly so any crystals seen in a lava formed _______ to eruption and were carried to the surface
prior
At Vancouver, crustal rocks 15-30 km below the surface are estimated to have temperatures of 300-400 degrees celcius. At these depths, the rocks are subject to great pressure due in part to the weight of overlying rock and they behave more like _____. Under these conditions, sedimentary and volcanic rocks undergo minteral, physical and chemical changes and slowly become _______ rock.
putty than solid rock. metamorphic rock.
When light waves passes from air to glass (and from glass to air) the waves are ________. Commonly, not all is ______, and some is _______. http://ansatte.uit.no/kare.kullerud/webgeology/webgeology_files/english/earthsinterior.html
refracted (1,2), reflected (3) Seismic waves behave in a similar way when they pass from one type of rock to another - the waves are reflected and refracted
Saying one rock is younger than another is using ______ age
relative
2 ways to understand history: First, we determined _____ ages of rock formations and geologic structures and then used these ages to construct a sequence of events through time Then, using _____ dating, we determined the abolute timing of these events, and measure the rates of geologic change
relative radiometric age dating techniques
Biostratigraphy is a _______ age dating method
relative (because we have no way to assign a specific date based on the fossil or groups of fossils alone)
If you can prove that one rock is older than another rock, you have carried out a _______________
relative age determination
Radiometric dating refers to the age determination based on the:
relative amount of radioactive material in minerals or organic matter
The upper part of the mantle is composed of rocks that have the same mechanical strength as crustal rocks. This part of the mantle is often called the:
rigid mantle or the lithosphere mantle
The theory of plate tectonics had its origin in the evidence contained in the....
rock record - most notably the similarities in rocks and fossils in disparate parts of the world. How geologists pieced this together involves relative and absolute dating principles and an understanding of how to interpret processes from the rocks.
The rocks that form the foundation of downtown Vancouver and most of the Fraser Lowland are:
sandstone, mudstone and conglomerate that formed 70-40 million years ago during and after the time of the dinosaurs They overlie and are younger than the metamorphic rocks described above and were deposited by rivers flowing off ancient coastal mountains. They have not been subjected to the high temperatures and pressures of the older rocks because they were never buried deep in the Earth.
In 1962, The American Harry Hess introduced the theory of ______________.
sea floor spreading
Most ________ rocks such as sandstone, limestone, and shale are related to the radiometric time scale by bracketing them within time zones that are determined by dating appropriately selected igneous rocks
sedimentary
Step 3. Units G+D are uplifted and eroded. ______ Sequence A is deposited on top of G and D, and is therefore younger (superposition, erosional relationship).
sedimentary (sandstone and mudstone)
An angular unconformity is the boundary between an underlying unit of __________ rocks that have been....... and an overlying unit of ________
sedimentary rocks that have been tilted or folded and an overlying unit of more flat-lying sedimentary rocks.
Continuing with the history of the same angular unconformity... Now, the sea-level is sinking (and the land is rising), so _______ stops, and instead the upper parts of the crust is _______.
sedimentation stops exposed to erosion
The mantle consists of _____ minerals
silicate
Magma that forces itself laterally in between two layers of sedimentary rock form a _____
sill...
The material of the mantle is not liquid, but is very ductile. The mantle convection is therefore a very _____ process.
slow
Metamorphic rocks from by the ___________ recrystallization of pre-existing rocks
solid state they form where pre-existing rocks (sedimentary, igneous or metamorphic) have been subjected to changes in pressure and temperature
Some of the terranes originated in equatorial areas and travelled thousands of kilometres before reaching their current resting places. As they docked with North America, the terranes were:
squeezed, folded, and split apart along faults, forming mountain ranges and eroded by rivers, glaciers, and gravity, all of which work to lower the land
Step 1 (oldest): The unit represented by D, metamorphic rocks, is the oldest. The first geo-event that took place is the formation of D. We know these are the oldest because: • They are included within the granite (G), so they must be older. • The dykes (F, H) cut across all occurrences • The fault (E) cuts across the unit. • The sediments (A) rest on top of D (________)
superposition
Step 7. Ice Age sediments, C, are deposited on top of tilted sedimentary sequence A (_______).
superposition
Step 8. Fraser River Sediments, B, are deposited on top of Ice Age Sediments C (________).
superposition
Define crystalline
the atoms are arranged in an orderly manner; this pattern results in a natural symmetry. The crystalline forms and the internal symmetry have their origin in the bonding relationships between the atoms and molecules that comprise the mineral.
nonconformity
the boundary that separates rocks that are and are not conformable the boundary between relatively young sedimentary rocks and the underlying crystalline rocks (metamorphic or magmatic rocks), which are much older.
Igneous Rocks form from...
the crystallization of a molten mineral melt - can take place within the earth and at or near the earth's surface.
The evidence of the pre-existence of mountain ranges lies in the nature of ___________
the eroded rock debris
If metamorphic rocks were created at great depth in the Earth's crust, why are they found today at the surface?
the metamorphic rocks have been slowly uplifted from the depths at which they formed by mountain-building processes. As the Coast and Cascade Mountains rose of a period of tens of millions of years, erosion stripped kilometres or rock from the mountains, eventually exposing their roots. Imagine the forces needed to elevate so vast an area of the crust!
The Radiometric Time Scale began with the discovery of.... by...
the natural radioactive decay of uranium in 1896 by Henry Becquerel
Subduction:
the process by which one crustal plate descends beneath another
Define convection
the slow, lateral and vertical cycling of mantle material beneath the crust, mainly due to variations in temperature within the Earth
Define radioactivity
the spontaneous change of one element to another by way of loss or gain of a high energy charged particle
The stratigraphy of a sedimentary sequence is a description of...
the various units of the sequence. The description may include sediment type, age, fossil content, thickness, etc.
Define Geologic Time
the vast span of time that defines how old the earth is... 4.5 billion years old or more
In an angular unconformity, below the unconformity, the sedimentary layering has been ____________. Above the line, the layering is _________.
tilted horizontal
Dendrochronology
time measurement based on the science of tree rings
Cyclic sedimentation: some environments exhibit a regular pattern of sedimentation. For example, glacial lakes undergo a yearly variation in sediments, with dark organic rich material deposited in winter, and lighter coarser material in the summer. These layered pairs are called ______, which may be used to determine:
varves may be used to determine the length of time a lake persisted
depending on how thick (______) the magma is, the resultant eruption may be explosive or be exuded as more liquid lava flows. Regardless of which type, the molten mineral material cools _____.
viscous rapidly
Extrusive (__________) igneous rocks We can witness them forming at...
volcanic and pyroclastic: crystallize after the magma reaches the earth's surface form at sea-floor spreading ridges and other rift zones, volcanic arcs, and hot spots
The magma that reaches the surface crystallizes to form a ________ rock
volcanic rock
It is more difficult to decide the relative ages of magmatic bodies that are oriented parallel to the sedimentary layering. In that case, we first ahve to decide whether the magmatic body formed as a _______________ at the surface or as a _________ at depth.
volcanic rock at surface or a sill at depth.
The most well known locations where igneous rocks form are ______, which bring ____ to the surface.
volcanoes, magma
Cycle cont:Uplift and exposure of rocks at the Earth's surface destabilizes the mineral structures of these intrusive (plutonic) rocks, causing them to break down via various forms of _______.
weathering
About 180 million years ago, the North American Plate began to separate from Europe along a rift that eventually developed into the Atlantic Ocean. Since then, the North American plate has moved slowly but steadily _________, colliding with and overriding oceanic plates composed mainly of _______. This collision process is termed: ______
westward basalt subduction
In addition to fossils, age of ocean crust away from mid oceanic ridges, magnetic patterning away from mid oceanic ridges, this pattern got geologists thinking about plate tectonics/contintental drift:
where volcanoes occur most of the volcanoes on the surface form a pattern of linking chains
A volcanic rock is ________ than the sedimentary rocks below
younger
Igneous rocks that cross-cut structures in sedimentary rocks are _________ than the sedimentary rocks
younger
In Stanley Park, as you walk south to third beach, the rocks get
younger! Because the rocks are inclined to the South. At Prospect Point, the rocks are late Cretaceous in age (about 70 million years old), and at third beach they are Tertiary in age (about 60-50 million years old) The sandstone was deposited by ancient rivers and streams that carried their sandy load from a nearby mountain range to the sea.