GEOL 1 Lecture Notes - Lecture 7: Oceanic Crust, Partial Melting, Peridotite

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19 Oct 2020
Department
Course
Professor
Jeff Koo
Geol 1
Physical Geology
Spring 2019
4 Units
Bowen’s Reaction Series
Shows temperature from low to high
High temperature-first minerals to crystalize
Low temperature- that can stay liquid
Gold has a very low melting point- similar to quartz- the last things that crystalizes
How do we make different rocks? - the mantle comes up
- Kind of the same thing
Partial melting: melt part of the rock,
and fractional crystallization: big thig of magma and cool it down and you start crystalizing
from the top-down
Partial melting: as a rock heats up and begins to melt, Bowen’s reaction series operates from the
bottom up. The most silica-rich end of the rock’s composition begins melting first
What’s the bottom line? Magma tends to be more silica-rich than the parent rock that it was
generated from
Let’s look at compostions:
Peridotite: 45% silica, rich in FE, Mg, Ca
Basalt/ gabbro: 50% silica, rich in Fe, Mg, Ca
Andesite/ diorite: 60% silica,
Starting with the mantle: peridotite: 45% silica, rich in Fe, Mg, Ca partially melts along rising
plumes in convection cells in the mantle
- The mantle is made of peridotite
Basalt/ gabbro: 50% silica, rich in Fe, Mg, Ca- it forms oceanic crust- and eventually bump into
another oceanic crust and gets subducted back in
Now we have oceanic crust: eventually it subducts under other oceanic crust
There, partial melting occurs (remember adding water?)
Basalt/ Gabbro: 50% silica, rich in Fe, Mg, Ca
Andesite/ diorite: 60% silica, mix of cations
Now we have a volcanic arc: typically, these are andesitic volcanoes
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