How does the core differ from the rest of Earth's layers composition wise?
The core has no silicate minerals. Outer/inner core.
-Outer consists of liquid iron alloy.
-Inner core is solid iron alloy. Solid because of its pressure keeps atoms locked tightly.
What is the core made of ?
Fe and Ni ( Iron and nickle)
What is the mantle made of
-silicate minerals, mostly olivine
-ultramafic rock called peridotite which is dark and dense/ silicate minerals
-Soft but mostly solid
What is the crust made of ?
-Variety of rocks that differ in composition, silicate minerals, many different kinds
-Typically, upper continental crust is less mafic than oceanic crust so it is less dense
What physical property defines the asthenosphere
-Ductile, which means its hot with low pressure
- mushy
What physical property defines the lithosphere
-Rigid/ Brittle
-Little bit of mantle, little bit of crust
What is the lithosphere
-Outer shell composed of rock that cannot flow easily, consisting of the crust plus uppermost cooler part of mantle=lithospheric mantle.
-Oceanic lithosphere
-Continental lithosphere: thicker
What is the asthenosphere
Under lithosphere, occurs where temperature reaches 1280 degrees C, rock begins to soften and flow
Alfred Wegner's hypothesis of continental drift?
What was his evidence?
What were the problems with this hypothesis?
Hypothesis= continents move over surface of earth / super continent Pangea all fitting together
-animals/fossils
- But continents cant plow through oceanic crust and solid mantle
Harry Hess's hypothesis of seafloor spreading?
How did he resolve the issues of Alfred Wegner's hypothesis?
-High ridges in middle of ocean with a high heat flux creating new oceanic crust
Where is crust created? Where is it destroyed?
Created- Mid Ocean Ridges
Destroyed- Old ocean floor sinks into the mantle ( trenches)
How old is oceanic crust? What happens to it eventually (i.e. why is oceanic crust relatively young (no more than 180 million years old) in comparison to continental crust (up to 4.2 billion years old)***
Oceanic is new crust pushing up and old crust being pulled apart.
What are the three driving forces to plate movement?
Ridge push- because the lithosphere of M.O.R lies at a higher elevation than that of the adjacent abyssal plains ( honey in water). Lith moves away from ridge axis, new hot asthenosphere roses to fill gap.
Slab pull- oceanic plate starts to sink, graduall
How fast do plates move? (have a concept of what appropriate velocity rates look like)
Relative plate velocity- comparison between plate rates
Absolute plate velocity- from space/fixed location
Know the difference between active and passive margins
Passive margins- transition from continental to oceanic crust with no plate boundary
Active margin- two plates meet and interact
Divergent Boundaries:
How does magma form here?
Oceanic Divergen boundaries?
What do these boundaries look like ( mid ocean ridges)
Magma- hot mantle rock rises to fill rift zones. When rock rises, a decrease in pressure causes hot mantle rock to melt and form magma.
What happens as oceanic lithosphere cools and moves away from spreading center?
Mantle ( not crust) gets thicker with age, mantle becomes more dense, lower elevation
Do volcanoes occur in divergent boundaries?
What kind of igneous rocks created in divergent boundaries?
Earthquakes?
-Form volcanic islands which occur when the plates move apart to produce gaps which molten lava rises to fill.
-Basalt: dark, fine-grain, high density igneous rock
-shallow earthquake activity
Convergent Boundaries
More dense crust subducts under less dense crust. Creates trench. Shallow and deep earthquakes. Magma rises into volcano.
What is subduction? How does magma form in subduction zones?
Plate that subducts squeezes water out from fractures in the cracks of subducting plates. Minerals drive water out.
Oceanic-Oceanic
-More dense subducts
-Trench
-Volcano/Magma
What determines which plate will subduct in Convergent boundaries?
Density
What geographic feature marks a convergent boundary?
Earthquakes present?
Volcanoes?
Trench. Deep and shallow earthquakes. Yes volcanoes.
What igneous rocks in convergent boundaries?
What type of land formation is made at oceanic-oceanic convergent boundaries?
Convergent plate boundary
(ocean-ocean). Andesite & diorite is
characteristic (basalt & gabbro are also found;
rhyolite is rare) (e.g. the Caribbean)
Oceanic-Convergent boundaries:
Volcanism? What igneous rocks?
Why doesn't continental crust subduct?***
Continental crust is less dense.
Andesite & diorite are characteristic. Rhyolite &granite are common. Basalt is less common (e.g. the Andes)
Continental-Continental:
What happens when continental lithosphere collides?
Volcanoes/Earthquakes?
Mountains are formed
No/minimal volcanoes
Shallow earthquakes
Transform boundary:
Volcanoes/Earthquakes?
Hot Spot volcanism: What is happening here? *****
What kind of igneous rock?
Many shallow earthquakes but no volcanoes.
What are the three main types of rocks?
Igneous
Sedimentary
Metamorphic
Igneous Rocks:
What defines an igneous rock?
Result of magma cooling and crystalization
What controls how magma forms?
Pressure, temperature, water content, chemical composition
What environments do we produce magmas?
...
What are two criteria we use to classify igneous rocks?
Texture and Composition
Texture:
What governs the texture of the igneous rock( what are the two main cooling environments for magma and how does this effect crystal growth?
...
Texture:
Intrusive vs. Extrusive
Aphanitic vs. phaneritic vs. porphyritic
Intrusive: when magma solidifies underground
Extrusive: when magma freezes above ground when in contact with atmosphere or ocean.
Porphyritic- 2 rates of cooling- slow cooling followed by fast cooling.
Aphanitic- fine grained
Phaneritic- course grained
Composition:
What is it?
Chemical composition governs which minerals are allowed to form, therefore the minerals we see in an igneous rock tell us about the chemical composition of the rock
4 compositional groups
ultramafic
mafic
intermediate
felsic
What is the chemistry of each compositional group?
The more felsic, the more increase in silica and the more decrease in Fe and Mg
Which minerals belong in which category?***
Olivine- ultramafic/mafic
Understand how we evolve magmas:
What is Bowen's reaction series?
What is fractional crystallization and how does it work?
-Bowen determined that specific minerals form at specific temperatures as a magma cools. mafic minerals crystalise first, settle out
-remaining magma gets increasingly silica rich
-Fractional cryst.= transition from liquid to solid, minerals form and take
Where does each type of igneous rock form in the context of plate tectonics? (e.g. basalts and gabbros can form at divergent boundaries and so on...)
-Felsic rocks form primarily at convergent, continental volcanic arcs
- Intermediate rocks form primarily at convergent volcanic arcs
-Mafic igneous rocks are dominant at ocean ridges and where oceanic hot spots erupt (such as Hawaii). Mafic rocks can be
Seafloor spreading
o Magnetic stripes
o Heat flow
o Seafloor topography
Why add water when forming magma?
water breaks bonds between atoms
lowers melting temperature
where do we generate magma?
hotsopts
divergent boundaries
subduction zones
Crystalization
Mafic minerals crystallize first, settle out
Remaining magma gets increasingly Si-rich
Create intermediate and felsic magmas
Minterals
discontinuous - form specific temperatures and compositions
Continuous ( plagioclase) take different elements in as a chemelion, adjusts what it wants to evolve into