EESA06H3 Lecture Notes - Extrusive Rock, Viscosity, Silt

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Published on 15 Apr 2013
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Slide 1
Equadore
The Galapagos Islands (finches and Darwin)
Hot spots
Islands are the tip of an iceburg of a submerged plateau
right at the head of the island group
movement of the Nazca plate east
They then erode (dead volcanoes) and have flat tops below sea level
They become Guyotx: a flat topped dead volcano as part of a hot spot trail
About 40 hotspots mostly in oceanic plates
In terms of the islands age two things were found:
-Age of the rocks on the hotspot island compared to those aroundthe ocean florr? They are
much younger
The youngest island down the trail you have extinct volcanoes eventually going below sea
level, systematic ageing of the rocks as you move away from the hotspots
Orientation of the hotspot = gibes the direction of plate movement
hotspots play a key role in plate tectonic theory
hOTSPOTS ARE COMPOSED OF SMALLER SPOTS
Bathymetric – A map that shows water dense
3 million years old islands
Fluid basalt – shield volcano
bumps as a result of magma hitting water (Phreato(water) magmatic erruptions)
You can tell it is a young landscape because there is no vegetation or plants
Image: Eroded remnant of and old volcano (dark rock daggaring upward) actively collapsing
Image: Layers of pyroclastic ash
Image: Cynercone volcano (pointing upward like a cone, ash blows out around the rim) Coarse
ash sometimes referred to as Scoria
Beach turtle tracks: Trace Fossil -> the track of an organism
Prickley Pair Cactus with ropey lava being colonized by green things. They are large b/c they
have adapted to their environment
Predation: to eat something, what is eating the cactus? It grows its stem for survival. Eaten
by giant tortoises
Blue Footed booby? Nostrils are pushed forward right under its eyes so it wont die from
water air pressure
1859 Darwin published the origin of species
Spent five weeks in the Galapogos for a five year voyage
Tortoise habitat destroyed cause they were used as food for long voyages and they were
killed off by livestock (goats killing vegetation), feral cats and rats
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Rocks and Minerals:
The rock cycle
Magma procude a board class of rocks -> Igneous(born of fire) rocks -> Intrusive igneous
rocks that will cool at depth, a lot of them get extruded at the surface -> as a result of
weathering we produce sediments that get deposited in layers in the ocean over time getting
burried from a soft sediment to something which is cemented, these might form successions
that are many km thick, some containing fossil material. But all have unique characteristics
Both igneous and sedimentary rocks can be changed by heat and pressure such that the new
rock (metamorphic) is completely different fro mthe parent sedimentary or igneous rock
Lithification: to turn a sediment into rock
Compaction : to squeeze water/air out of something
Cementation
Difference between rocks and minerals
A rock is made out of different minerals (naturally formed, consolidated material composed of
grains of one or more minerals)
A mineral is a naturally occurring, inorganic, crystalline solids that has a definite chemical
composition. They are the building blocks of rocks
Crystalography: study of different mineral types and crystal sizes
4500 different types of minerals known as silicates: minerals based on silicon and oxygen
Quartz
Olivine – dominant mineral in the mantle
Feldspars - crust
Pyrocenes
Mica
Clay minerals such as kaolinite, montmorillonite
Diagram – Isolated silicate structures and their effects on magma viscosity
single chains, double chains, sheets, and framework
relationship between complex minerals and stiff magmas
This aggregation property of the circuit minerals controls the viscosity of the magmas
Quartz is the key mineral to thicken magma and there is very little in basalt
Basic Rocks – Lack silica or have little
Acidic Rocks – In regard to a much higher content of quartz (granite, andesite)
Same mineral can have different colour versions
Streak – If you rub the mineral you get a streak (chalk)
Hardness goes from Talc to Diamond
fingernails are 2.5 knife blade 5.5 steel 6.5
Terminology used to describe mineral shapes
Sedimentary Environments
Locations where sediments accumulate
Abisil plain: deep plains
Range f environments in which sediments accumulate
Each environment produces a distinct type of sediment
Rift Basin Diagram
Associated with evaporates
builds up water, then rift dries out
Rock salt common component of rift basins
mOST OIL AND GAS ACCUMULATES FROM ROCKS FROM CONTINENTAL SHELF
ORIGIN
cross bedding produces sandstones
Sedimentary Rocks
Conglomerate (cemented gravel), Sandstone(cemented sand), Shale Mudstone (cemented silt)
Form of sediment grains eroded from rock and transported by water, ice or air
Compacted, cemented – lithified
Classic rocks
Some are made of broken fossils, particularly limestone (bioclastic limestone)
Some sediments are due to the evaporation of seawater CaCO3, calcium carbonate
Lithification
Note: We find little voids/white spaces: pores – its in these little open spaces that water oil and
gas accumulates
^ that is how sediment turns into rock through lithification
Organic rock typically Sale
Anticlinal trap
Most of the worlds major oil and gas deposits occur in the thick sediment fills between
continental shelves (ancient and modern)
Metamorphic Rock
Pressure
As you move from 00 down you are getting deeper into the earths crust
we go through different zones where distinct mineral types appear as a result of the rock being
cooked
if we can identify the minerals we could put the metamorphic rock into those zone
Metamorphic Facies
Most metamorphic rocks are folliated (banded) layers are often extensively deformed
Common Metamorphic rocks Low grade to = Slate, phyllite, schist, gneiss = high grade
Typical rates of defamation, 3,4,5,6 cm a year the rate which plates move
Stretched pebble conglomerate = individuals pebbles were stressed out through heat and
pressure
Canadian shiled is dominated by metamorphic rocks, old, hard, metamorphic rocks
Igneous either Extrusive(the devils rocks) rocks or Intrusive
The texture or grain size of the igneous rock.
Phaneritic – Coarse grained
Aphanitic – Rock cooled quickly, crystals didn't have time to grow so they are small
They are intrusive because they cooled slowly underground (p)
Fine grained ones are extrusive (a)
Obsidian – glass looking crystal, arrowheads made out of them
Basic dark coloured rocks dominated by olivine
Silica dominates lighter coloured rock
By using 2 system of reference you can pigeon hole each ingeous rock
fine = extrusive
coarse = cools on ground, intrusive
Granite is typical of continental (less dense than salt cause it has more silicone)
and basalt is typical oceanic crust
Pluton – broad body of rock cooling underground (named after Pluto)
Dikes (vertical intrusions of igneous rock) vs sills

Document Summary

Islands are the tip of an iceburg of a submerged plateau. Right at the head of the island group. They then erode (dead volcanoes) and have flat tops below sea level. They become guyotx: a flat topped dead volcano as part of a hot spot trail. About 40 hotspots mostly in oceanic plates. In terms of the islands age two things were found: The youngest island down the trail you have extinct volcanoes eventually going below sea level, systematic ageing of the rocks as you move away from the hotspots. Orientation of the hotspot = gibes the direction of plate movement. Hotspots play a key role in plate tectonic theory. Bathymetric a map that shows water dense. Bumps as a result of magma hitting water (phreato(water) magmatic erruptions) You can tell it is a young landscape because there is no vegetation or plants. Image: eroded remnant of and old volcano (dark rock daggaring upward) actively collapsing.