EESA06H3 Lecture Notes - Lecture 7: Schist, Metamorphic Facies, Batholith

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8 Aug 2016
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EESA06 Lecture 7 Page 1
EESA06 Lecture 7
Galapos Islands – in Equador, hotspots
- Hotspot trails – old dead volcanoes, flat tops (from erosion), below seas level, dead volcano
- Hotspots – majority occur on oceanic plates
- Relative Ages of islands: the youngest island above the hotspot, eventually go under sea level,
systematic aging of the rocks as you go down the trail
- Gives us a clue of plate movement
- Bathymetric – map that shows water depths
- Islands after 3 million years become completely submerged
- Phreatomagmatic – water + volcanic activity, violent releases
- Geologists like this area because there is No vegetation = young landscape, still actively evolving
- Barrel Cactus are the pioneer/first plants grow in cracks of lava,
oPrickly pear cactus another pioneer plants, eaten by giant tortoises, evolution of long
wooden stems to avoid being eaten
oBlue footed booby – bird with nostrils underneath eyes, due to evolution
- Aa lava (rocky), pohoehoe lava (ropey)
- Pyroclastic layers of ash that falls on the
land that blows out underwater, think of a
‘snow avalanche’ that happens under
water - laminated sediments
- Scoria – large pieces of burnt rock found
around cinder cones
- Trace fossil – track of organism, like
footprints, turtle tracks to lay eggs
Rocks and Minerals: Clues to Ancient Environments
-Lithification – to turn a sediment into rock
-Compaction – to squeeze water and air
out of something
Differences Between Rocks and Minerals
-Rock – is a naturally formed consolidated material, composed of grains of one or more minerals
-Mineral – is a naturally occurring, inorganic, crystalline solid that has a definite chemical
composition. They are the building blocks of rocks.
- Igneous rocks – to be born of fire, extrusive and intrusive
- Crystallography – the study of different shapes of crystal and diagnostic diff mineral types
Minerals 4,500 different types but
- The most important group are the silicate minerals containing silicon and oxygen and accounts
for 90% of all minerals. Few minerals dominate ex:
oQuartz – (silica = SiO2 = silicon plus oxygen)
oOlivine (Mg, Fe SiO4) – mantle
oFeldspars (largest subgroup, shiny field crystals, common in shield rocks, composite soil,
semi-precious stones) - crust
oPyroxenes (ex: augite)
oMica
oClay minerals such as kaolinite, montmorillonite – result of weather of other minerals,
electrical properties, dictate whether soil is fertile or not
Silicate Structure and its effects on magma viscosity
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EESA06 Lecture 7 Page 2
- According to how tetrahedron are assembled
- Isolated silicate structure – found in basalts
- Single Chains, Double Chains, Sheets and Framework
- Controls the thickness of magma, rocks we find, shape of
volcano etc.
- Quartz is the key mineral that thickens magma (less in basalt)
- Basic rocks lack silica, Acidic rocks have higher concentration of
quartz (Ex: Granite, Andesite, more than 50% is quartz)
How do we identify different minerals?
- Color – most noticeable by least accurate
- Streak – color when mineral group to a fine powder on streak plate
oEx: hematite – red/brown
oSilicate minerals do not streak
- Hardness (scratchability)
oMoh’s hardness scale (1-10)
Talc (very soft) = 1
Diamond = 10
Sedimentary Environments
- Locations where sediments accumulate
- Highest mountains to deepest oceans
- Different environments – produces diff type of sedimentary
rock
- Continental Shelf – shallow sea floor
- Slope – going down into deep sea
- Abyssal Plane – deep sea
Grand Canyon – Metaphoric rock layer covered by sedimentary rock
- Tells us about Fossils, plate movement
Rift Basin
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