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What does temperature of rock explain? But does it do a poor job of explaining?
formation of plutonic (intrusive) rocks; volcanoes
What is the most common tectonic setting that mafic/basaltic magmas form?
mid-ocean ridges (divergence between 2 oceanic crusts) + hot spots in oceanic crust
Why is magma M/B at mid-ocean ridges?
b/c the source of the magma is the mantle, which is mafic-ultramafic in composition
Are only mafic rocks (basalt, gabbro, diorite) found at these places?
No, but mafic rocks are the majority
3 processes help make magmas more felsic...
fractional crystallization, assimilation, + magma mixing
Characteristics of Hawaii - shield volcano
broad, low angle slopes
eruption style is effusive, not explosive
3 Properties of stratovolcanoes?
higher angle slopes;
more explosive eruptions;
range of lava compositions
as plate is subducted, more magma is generated
younger magmas mix w/ older magmas to change composition
the type of magma/lava determines: (4)
what is erupted;
style of eruption;
frequency of eruption;
flowing cloud of hot ash + cinders;
eventually becomes welded tuff
Forming calderas (4 step cycle)
1. Bulge in surface created by magma chamber
2. Crust thinned over magma chamber (ground surface cracks in ringlike fractures)
3. Tephra columns erupt from fractures + collapse into ash and pumice flows
4. surface crust collapses as magma is depleted forming caldera
Flood/Plateau Basalt; example?
...the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava
Economic importance of igneous rocks
metals; igneous activity is a conduit for more dense material to move from the mantle to the crust
What is the cause/tectonic setting of flood basalts?
unknown; none active today, but many ancient ones
vertical section of igneous rock w/ sills and/or dikes radiating from it;
thought to be an old magma chamber feeding a volcano
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