Term
| Why does melting take place beneath the axis of a mid-ocean ridge? Explain the process. |
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Definition
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Term
| What factors influence the viscosity of magma. |
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Definition
- Silica Content
- Temperature
- Volatile Content
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Term
| Use a P/T Diagram to explain the mechanism responsible for forming magma at a divergent margin. What type of magma is erupted at this type of plate edge and why? |
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Definition
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Term
| Use a P/T Diagram to explain the mechanism responsible for forming magma at a convergent margin. What type of magma is erupted at this type of plate edge and why? |
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Definition
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Term
| Describe the way magmas are products in subduction zones. |
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Definition
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Term
| How are basalt and gabbro different? |
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Definition
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Term
| How are basalt and gabbro similar? |
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Definition
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Term
| What is the silica content of a felsic magma? |
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Definition
>64%
66-76% by the readings in the book |
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Term
| What is the silica content of an Intermediate magma? |
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Definition
52-64%
52-66% by the book |
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Term
| What is the silica content of a mafic rock? |
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Definition
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Term
| What is the silica content of an ultra-mafic rock? |
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Definition
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Term
| What is the eruption temperature for a felsic rock? |
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Definition
700-800°C - by our lab manual
600-900°C by in-class powerpoint |
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Term
| What is the eruption temperature for an Intermediate rock? |
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Definition
800-1000°C by our lab manual
1050° by in-class powerpoint
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Term
| What is the eruption temperature for a Mafic rock? |
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Definition
1000-2000°C - by lab manual
1160°C by in class powerpoint |
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Term
| What is the eruption temperature of an Ultra-mafic rock type? |
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Definition
>1200°C
1250°C by in-class powerpoint |
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Term
| What is the relative viscosity and relative explosive potential of felsic rock? |
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Definition
| Felsic rocks have high silica content and a lower eruption temperature which gives them a relatively high viscosity and high explosive potential because it does not flow easily and will trap gases - the internal pressure of all the high pressure gas stuck will cause the most violent eruptions. |
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Term
| What is the relative viscosity and relative explosive potential of an intermediate rock? |
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Definition
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Term
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Definition
| and adjective that refers to the occurance of felsic minerals such as feldspar and quartz in igneous rocks. Also known as silicic due to the high content of silica. |
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Term
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Definition
| refers to igneous rocks that have a composition between that of felsic and mafic. |
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Term
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Definition
refers to igneous rocks that contain abundant mafic minerals, minerals with a relatively high proportion of MgO, and FeO or Fe2O3.
ma - stands for magnesium
-fic stands for iron (from the latin ferric) |
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Term
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Definition
| describes igneous rocks that are very low in silica content and rich in iron and magnesium content. |
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Term
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Definition
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Term
| How does the silica content affect viscosity of magma? |
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Definition
Higher silica content = higher viscosity
Lower silica content = lower viscosity
Silica tends to polymerize, meaning it tends to link up and form long chain-like molecules whose presence slows down the flow. |
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Term
| How does the temperature affect viscosity of magma? |
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Definition
Higher Temps has a lower viscosity
Lower Temps have a higher viscosity
Because thermal energy breaks bonds and allows atomes to more more easily.
Felsic magmas can remain liquid at temps of only 650-800C, whereas ultramafic may reach temps of 1300C. |
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Term
| How do crystals affect viscosity of magma? |
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Definition
More crystals = higher viscosity
crystals slow down the flow. |
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Term
| How does the presence of volatiles affect viscosity of magma? |
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Definition
Gases reduce viscosity
High silica holds back gas bubbles and can have a counter effect on viscosity.
Magmas containing more volatiles are less viscous than dry magmas because the volatile atoms also tend to break apart bonds. |
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Term
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Definition
| The process in which only part of a rock melts to form a magma that then moves away. |
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Term
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Definition
<The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve.>
The process of assimilation takes place when rocks fall into the magma and then partially melt or when heat from the magma partially melts the walls of the chamber. |
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Term
| Fractional Crystallization |
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Definition
| A process in which magma changes composition as it cools because formation and sinking of crystals preferentially remove certain atoms from the magma. |
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Term
| How does magma differ from Lava? |
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Definition
| magma refers to the melt that exists below the Earth's surface, where lava refers to the melt that has erupted from a volcano at the surface of the earth. |
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Term
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Definition
| When lava erupts at the Earth's surface and freezes in contact with the atmosphere or the ocean, then the rock it forms is called extrusive igneous rock. This implies that the rock extruded from (flowed or exploded out of) a vent in a volcano. |
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Term
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Definition
| If magma freezes underground, the rock it forms is called intrusive igneous rock, implying that the magma pushed or intruded into preexisting rock of the crust. |
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Term
| Why do some volcanic eruptions consist mostly of lava flows, whereas others are explosive and have no flow? |
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Definition
| Which type of eruption occurs depends largely on a magma's composition and volatile content. Mafic lavas tend to have low viscosity and spread in borad, thin flows. Volatile-rich felsic lavas tens to erupt explosively and form thick ash deposits. |
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Term
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Definition
a nearly vertical, wall-like tabular intrusion.
Tabular intrusion cuts across rock that does not have layering. In places where tabular intrusions cut across rock that has layering, dikes are defined as intrusions that cut across layering. |
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Term
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Definition
a nearly horizontal, tabletop shaped tabular intrusion.
Tabular intrusion cuts across rock that does not have layering. In places where tabular intrusions cut across rock that has layering, sill are defined as intrusions that are parallel to layering. |
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Term
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Definition
| an intrusion that starts to inject between layers but then domes upward, creating a blister-shaped intrusion. |
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Term
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Definition
| irregular or blob-shaped intrusions that range in size from 10's of meters across to tens of kilometers across. |
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Term
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Definition
the intrusion of numerous plutons in a region which produces a vast composite body which makes an immense mass of igneous rock that may be several hundred kilometers long and over 100km wide
note: batholiths do not extend all the way to the base of the crust. they are probably only a few Km to ~10km thick.
example: Sierra Nevada Mountains of California |
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Term
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Definition
| a process during which magma assimilates wall rock, and blocks of wall rock break off and sink into the magma. |
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Term
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Definition
| If a stoped block does not melt entirely, but rather becomes surrounded by new igneous rock, this is called a xenolith. |
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Term
| A rock made of a solid mass of glass, or of tiny crystals surrounded by glass, has a glassy texture. Rocks with this texture are ____________. |
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Definition
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Term
| Rocks that consist of mineral crystals that intergrow when the melt solidifies, and thus fit together like pieces of a jigsaw puzzle have an interlocking texture. Rocks with an interlocking texture are called ________________. |
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Definition
| Crystalline Igneous Rocks |
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Term
| Melts that exist below the Earth's surface are known as ___________. |
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Definition
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Term
| Melt that has erupted from a volcano at the surface of the Earth is known as ___________. |
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Definition
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Term
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Definition
| molten rock (liquid rock) |
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Term
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Definition
| melting as a result of a decrease in pressure. If the pressure affeting hot mantle rock decreases while the termperature remains unchanged, a magma forms. This type of melting occurs where hot mantle rock rises to shallower depths in the Earth, because pressure decreases toward the surface and rock is such a good insulator that it doesnt lose much heat as it rises. |
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Term
| The change in temperature with depth can be expressed on a graph by a curving line called the ______________. |
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Definition
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Term
| The rate of change in temperature with depth is known as ______________. |
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Definition
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Term
| According to the Bowen's reaction series, ___________, ________ crystallize first as magma's cool. |
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Definition
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Term
| According to the Bowen's reaction series, what minerals crystallize last? |
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Definition
| Quartz, muscovite, k-feldspar |
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Term
| According to the Bowen's reaction series, what minerals will you never find together? |
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Definition
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