ES1001 Flashcards
What is Earth’s geographical column?
om locality to locality around the world, geologists have pieced together a composite stratigraphic column that represents the entirety of Earth’s visible history
Relative vs. numerical age:
The age of one feature relative to another is known as its RELATIVE AGE. The age of a feature given in years is its NUMERICAL AGE
What is radioactive decay?
When isotopes undergo a conversion into a different element (Bonus point: In half life)
What is Geochronology?
We investigate the what, when, and how of planetary-scale of a process
What is a seismic wave?
Rupture of intact rock or frictional slip along a fault produces seismic waves (and earthquakes), these move outward in all directions
What density of rock will make p-waves travel at an increased velocity?
Denser rock, such as igneous
(Example: peridotite vs sandstone)
Do seismic waves travel faster or slower in solids? In comparison to liquids
They travel faster through solids
(Example: they move more slowly in liquid than solid rock)
Can s-waves go through liquid?
both P- and S-waves can travel through solids but only P-waves can travel through liquid
When do seismic waves refract?
Seismic energy as waves will reflect and/or refract when reaching the interface between two layers of rock of differing compositions and/or densities
Define a rock
(Like no seriously…)
A naturally occurring and consolidated material usually comprised of one or more mineral phases
What rock type is igneous
Something which directly crystallised form a liquid rock (melt)
What rock type is sedimentary
Bits of other rocks in one place
What rock type is metamorphic
Cooked rocks
Why do sedimentary rocks form at or near the Earth’s surface?
Cementation of grains and/or fragments derived from pre-existing rocks
Precipitation of minerals from water solutions
Growth of skeletal material in organisms
What is weathering
The processes that break up and corrode solid rock, eventually transforming it into sediment
Physical weathering breaks rocks into unconnected grains or chunks
Chemical weathering refers to the chemical reactions that alter or destroy minerals when rock comes into contact with water solutions or air
Fun fact!!
(Lemme have fun jeez… flip!!)
Sedimentary Rocks are sometimes made of dead things
How are metamorphic rocks formed?
A rock that forms when a pre-existing rock (igneous or sedimentary) is affected by changes in its physical or chemical environment
include variations in temperature (T) and pressure (P), these changes result in the growth of new minerals and textures
What is ‘plate tectonics’
The lithosphere is divided into 15-20 plates of varying sizes
The plates move relative to each other
Explain a ‘hot spot’
Isolated volcanic centres far away from plate boundaries, many lie at the end of a chain of extinct volcanic islands and seamounts known as a hotspot track
hot spot tracks are thought to be the result of plates moving over stationary plumes
Why do we study minerals?
They make up everything, the majority of Earth, any rock is an aggregate of two or more mineral grains.
Definition of a mineral
Aka the web of lies
A mineral is a crystalline, homogenous, inorganic solid with a defined chemical composition that occurs naturally
Explain the minerals crystal structure
Their building blocks (atoms, ions, molecules) are arranged in an ordered and repeated pattern.
The unit cell is the smallest unit that still has the full symmetry of the crystal structure of a material.
Repeating the unit cell over and over again forms a crystal.
The ordered atomic network within a crystal can be simple or fairly complex.
What is a mineraloid?
Some minerals are not (fully) crystalline. These are called mineraloids.
Explain why crystals SHOULD be homogenous
Following from the infinitely repeatable unit cell of the crystal structure, minerals should by definition be homogenous
What may be the cause of a non homogenous mineral?
Zonations and crystal defects
What are the examples of an organic ‘mineral’
Biominerals - formed by a living organism usually inorganic in composition may contain organic material
Amber - fossilised tree resin organic composition
What is a polymorph?
Minerals with the same composition but different crystal structure
What is coordination?
The number of direct neighbours that an atom/ion is bonded to in a crystal structure.
Typically we talk about cations and their surrounding anion-neighbours.
What is coordination?
the number of direct neighbours that an atom/ion is bonded to in a crystal structure.
Typically we talk about cations and their surrounding anion-neighbours.
What is a site?
A space in a crystal lattice that can be occupied by an atom/ion. It is typically named by its coordination.
What is compatibility?
Atoms/ions in a crystal lattice can be substituted by other elements, as long as their radius is similar.
Ideally, their charge would also be the same! If an element fits readily into a crystal structure, it is called compatible
Nesosilicates
Island silicates
Consist of isolated “islands” of [SiO4] 4– tetrahedrons.
Sorosilicates
Group silicates
Two SiO4-tetrahedrons can share one oxygen and form a group
Cyclosilicates
Ring silicates
When a SiO4-tetrahedron shares two of its oxygen corners, we can form rings
Inosilicates
Chain silicates
Like an unclosed ring, sharing two oxygen corners creates chains
Phyllosilicates
Sheet silicates
Sheets of Inosilicates
Tectosilicates
Framework silicates
What is ‘plate tectonics’?
The lithosphere is divided into 15-20 plates of varying sizes
The plates move relative to each other
Hot Spots?
Isolated volcanic centres far away from plate boundaries
Many lie at the end of a chain of extinct volcanic islands and seamounts known as a HOT SPOT TRACK
Hot spot tracks are thought to be the result of plates moving over stationary plumes
Defniton of a mineral?
A mineral is a crystalline, homogenous,
inorganic solid with a defined chemical
composition that occurs naturally
How d minerals have a crystalline structure?
Their building blocks (atoms, ions, molecules) are
arranged in an ordered and repeated pattern.
Aka repeating he UNIT CELL
What a a mineral which isnt fully crystalline?
Mineraloid
What is a polymorh?
Polymorphs are minerals with the same
composition but different crystal structure.
How do minerals form
crystallisation of a magma due to cooling effectively the same as freezing
Magma cools below its liquidus, and starts to crystallise minerals.
The mix of melt + minerals keeps on crystallising until it ”hits” the solidus, now all melt has solidified
- Elements
Pure elements, metals often called “native”…
usually bound by metallic (in metals) or covalent bonds
- Sulphides
Minerals that have sulphur as anion.
- Halides
Minerals with halogens (F, Cl, Br, I) as anion.
- Oxides/ Hydroxides
Minerals with oxygen and/or OH as anion.
- Carbonates
… with the carbonate ion (CO3) 2- as anion.
- Borates
… with the borate ion (BO3) as anion.
- Sulphates
with the sulphate ion (SO4) 2- as anion.
- Phosphates
… with the phosphate ion (PO4)
3- as anion.
- Silicates
Form 90% of Earths crust
Si and O as anions
Building silicates
SiO4 tetrahedredreon
1 Si with 4 O- atoms
Si4+ (+) 4o^2- makes [siO4]4^4-
Neosilicates - Island silicates
consist of isolated “islands” of [SiO4]4– tetrahedrons.
Since a mineral cannot be charged, we have to balance the quadruply-negative charge.
A charge balance can be achieved by throwing cations in the mix.
nesosilicates - island silicates EXAMPLE
Olivine
achieves charge balance by adding two divalent cations per [SiO4]4– island.
It can be either Mg2+ or Fe2+
→ (Mg,Fe)2SiO4
Sorosilicaties - group silicates
Two SiO4-tetrahedrons can share one
oxygen and form a group:
2 Si4+ + 7 O2- makes [Si2O7]6-
Sorosilicates-group silicates EXAMPLES
Zoisite
Cyclosilicates - ring silicates
When a SiO4-tetrahedron shares two of its oxygen corners, we can form rings
Depending on the number of rings, we get different molecular anions, with different charges…
But always a multiple of Si4+ + 3 O2- → [SiO3]2-
Cyclosilicates - ring silicates EXAMPLES
Tourmaline, Beryl
Inoslicates - chain silicates
Like an unclosed ring,
sharing two oxygen corners creates chains
2 Si4+ + 6 O2- → [Si2O6]4-
Inosiliictes - chain silcates EXAMPLES
Pyroxenes
have two slightly different cation-sites in their lattice
M2 (larger cation site)
M1 (smaller cation site)
e.g. Augite
Amphiboles … are complicated and have a lot of cation-sites, but are a common mineral
phyllosilicates - sheet silicates
Every SiO4-tetrahedron shares three of its corner oxygens
Si4+ + 1O2- + 3*½O2- = SiO2.5 = [Si4O10]4-
phyllosilicates - sheet silicates EXAMPLES
Micas
Tectosilicates
- framework silicates
Every SiO4-tetrahedron shares all four of its corner oxygens
Si4+ + 4*½O2- = SiO2 = [SiO2]0 - No charge!
Tectosilicates
- framework silicates EXAMPLES
Quartz
is a very happy chappy,
doesn’t need any cations
to charge balance and
therefore usually is very pure.
Formula: SiO2
Composition of a mineral
Heavy element = heavy mineral (duh)
Packing
More atoms = more dense
Like more socks = more dense suitcase
Relative estimates
Colour
colour as a result of interaction with (sun)light
(Sunlight = white light
contains all wavelengths of the visible spectrum)
Colour WARNING!
Small changes in a crystal
can change the way it interacts with light.
(e.g amethyst, quartz, citrine)
Streak colour?
We can powder” a mineral by grinding it
against a hard and
rough surface, like an
unglazed ceramic tile.
Transparency
Describes whether a material allows light
to pass through.
Lustre
How a mineral reflects
Just make up your own words
Twinning
Twinning describes the intergrowth of two
(or more) crystals of the same mineral
through a slight change in orientation of
the crystal lattice.
Double refraction
Technically the majority of transparent and translucent
minerals double-refract light;
CALCITE is so very slay that u can see double
Photo - Luminescence
In some minerals, absorbing (high-energy) light results in the emission of (visible) light.
Fluorescence
The light emission stops when the
high-energy light stops
Phosphorescence
The light emission can continue for some time after the excitation stops
Magmatism
Magnetite is magnetic
Taste
Salty stuffs
Halite tastes salty.
It is table salt after all.
Sylvite tastes salty, too,
but has a bitter aftertaste.
7 crystal system SHAPES
(teigan terms dw)
Cube
Chip
Matchbox
Pencil
Triangular prism
Flattened matchbox sidey-ways
Stack of cards pushed askew in two directions
7 crystal TERMONOLOGY
cubic
tetragonal
orthorhombic
hexagonal
trigonal
monoclinic
What is metamorphism
The mineralogical and
structural adjustment of solid rocks to physical
and chemical conditions that have been
imposed at depths below the near surface zones
of weathering and which differ from conditions
under which the rocks in question originated.
What are the key factors of metamorphism
The precursor rock
Pressure
Temp
Deformation
Where does the heatcome from within metamorphism
Conduction (mantel)
Advection (magma/hot fluid)
Radioactive decay ( U, Th, K etc)
Temps of 250 to >1000°C
Where does pressure come from with metamorphism
Overlying rock mass
Horizontal tectonic forces
Pressure= fore per unit
Lithostatic pressure = density x gravity x height
Why do newminerals grow?
More stable at better conditions
Determined by thermodynamics
Thus, thermodynamics determines which collection of minerals have thelowest energy for a particular rock composition, pressure and temp
Regional metamorphism
Due to burial
Occurs with deformation
Occurs over large areas
Called belts
Shows continental collision (therefore mountain ranges)
Occurs formulations to 10s of millions of years
Contact deformation
Localised heat sources
Occurs around large igneous intrusions (dominated by heating n cooling)
Occurs oversmaller areas
Area around the intrusion is called the contact aureole
Short-lived
Hydrothermal metamorphism
Ocean floor basalts interact with hot fluids
The basalt is metamorphosed
Impact metamorphism
This occurs when you drop a huge rock from space (meteorite) onto the earth.
¨ Enormous transient pressure and temperature changes
¨ Very short lived - seconds-days
¨ Also called shock metamorphism
¨ Pressure from the impact (force per unit area)
¨ Temperature from friction
Fault related metamorphism
Related to brittle or ductile deformation in faults and shear-zones
Intense deformation allows new minerals to grow
¨ Sometimes friction can provide additional heat
Commonly associated with hydrothermal metamorphism
Metamorphic rocks are classified in general on their
appearance
¨ This is controlled by:
Composition
P and T conditions
Deformation
Features of metamorphic rocks!
Inherited features
Eg bedding in metamorphosed sediments
Eg large igneous crystals from metamorphosed
igneous rocks
Features of metamorphic rocks!
Metamorphic features
Minerals of different sizes
Features of metamorphic rocks!
Metamorphic and deformation features
Distinct layers
Aligned grains (preferred orientation)
Folds
Metamorphic fabric and structure
Layering
Alternating layers of different compositions
May include inherited features such as bedding
Foliation
A planar feature in a rock defined by the preferential
orientation of mineral grains
Lineation
A linear feature in a rock defined by the preferential
orientation of mineral grains
Crenulations
Small scale folds
Porphyroblasts
Metamorphic rocks may have some garians that
are much bigger than the average grain size
Porphyroclasts
In FAULT related rocks they are metamorphic rocks may have some garians that are much bigger than the average grain size
Phenocrysts
The big grains in igneous rocks
Matrix
The finer-grained minerals that host the
porphyroblasts are collectively referred to as
“matrix”
Matrix minerals
Individual minerals are called “matrix minerals”
Using structure no foliation
No foliation
¨ Hornfels
¨ Granofels
Using structure with foliation/lineation
Foliation/lineation
¨ Slate
¨ Phyllite
¨ Schist
¨ Gniess
¨ Layered or banded gneiss & Migmatite
Using structure- intensely foliated
Intensely foliated and sheared rocks
¨ Mylonite
What is a metamorphic assemblages
Is those minerals that appear to co-exist stably in a rock
¨ i.e it is a list of minerals
AKA Christmas rock
Garnet-clinopyroxene(omphacite)-quartz
Metamorphic assemblages are important for constraining metamorphic grade (Pressure & Temperature)
What is a metamorphic facies
any two rocks with the same chemical
composition that are metamorphosed at the same P-T conditions will contain the same minerals in the same proportion
¨ This is governed by thermodynamics
¨ We can use common rock types to define broad P-T regions based on the mineral assemblage they contain
These broad P-T regions are called metamorphic facies
Metamorphic facies can also be determined using other
rock types such as metapelites
What are the 5 main metamorphic facies
¨ Greenschist facies
¨ Amphibolite facies
¨ Granulite facies
¨ Blueschist facies
¨ Eclogite facies
What is metamorphic evolution
As metamorphic rocks occur at the surface today, they
must also experience a period of cooling after
metamorphism
¨ We can divide the metamorphic evolution into parts based on whether T is increasing or decreasing
T increasing prograde
T highest peak
T decreasing retrograde
P-T pathways
The tall, elongated, clockwise path is characterised by deep burial and exhumation with limited heating
The shorter, rounder clockwise red path is represents both substantial burial and heating
What is a metamorphic zone (zonen)
In contact metamorphism there is a strong temperature gradient away from the intrusion
¨ This results in changes in mineral assemblages away from the intrusion
What is a metamorphic isograd?
Some regional metamorphic belts show a consistent change in minerals across them.
¨ The appearance of a key mineral can be mapped in as an isograd.
Each metamorphic zone is separatrated by an isograd
Whatis continental collision in metamorphism
The most important metamorphic environment
If metamorphism occurs when continental plates collide then ancient
metamorphic belts show us how and when the continents were assembled into their current configuration
Ocean subduction I metamorphism
If metamorphism occurs in subduction zone then some metamorphic belt tell us where old subduction zones were
Metamorphic - Diverent plate boundaries
Plates move apart
¨ This is where new oceans form if the process continues
Metamorphic - transform plate boundaries
Plates slide laterally
¨ May involve a component of extension (transtension) or compression (transpression)
Metamorphic- convergentplate boundaries
Plates collide
¨ If one or both of the plates is oceanic then subduction occurs
¨ If both are continental then continental collision occurs
Orogenesis
Building mountains
Mountains represent crust/lithosphere that has been thickened
¨ Sometimes to more than double its normal thickness
¨ Thickened crust is not stable, but occurs because of tectonic forces
Mountains are controlled by isostacy (the iceberg effect)
¨ The higher the mountain the thicker the crust/lithosphere
Examples of continental collision
Alps and himalayas
Regional metamorphism - With regards to subduction
Here we have subduction causing continental collision.
There is defm & thickening due to the applied stresses
Subduction zones and island arcs
Two types
Ocean-ocean
¨ Makes island arcs
¨ Eg Japan
Ocean-continent
¨ Makes continental volcanic arcs and mountains on the continental margins
¨ Eg the Andes
These may evolve into collision zones
Subduction metamorphism
Subduction involves high pressures. SO the rocks formed in subduction zones are blueschists and eclogites
During burial and heating the rock experiences prograde metamorphism. The prograde reactions release water which enters the hot mantle.
This water can initiate melting of the mantle: also melting of the slab
can occur
Metamorphic - volcanic arcs
The large input of magma heats and thickens the arc crust
Arcs are very hot environments
Get high T at relatively shallow depths
Very high temperatures common in the lower half of arc systems
High temperature-low pressure metamorphism due to magmatic heat
Explain the biosphere structure
Living organisms (biota) and non-living (abiotic) factors from
which they derive energy and nutrients
What are the two Geobiological energy sources?
Phototrophy and Chemotrophy
What is an autotroph
Primary Producers: build organic matter by fixing carbon
Provide most organic carbon for the biosphere
Cyanobacteria
What is a Heterotrophs
Cannot fix carbon to form their own organic compounds.
Consumes organic compounds/primary producers
Energy flow in ecosystems
The biosphere is an open system with regards to energy
→ energy flow upwards in a food pyramid is inefficient, and relies on
continued primary production
What is the residence time? (Equation)
Mass of substance
————————– = residence time (10^12kg/year = GtC) of carbon
Flux (in or out of)
