Lecture 2 SS Meteorites Flashcards
Protoplanetary discs
proplyds
are discs of gas and ‘dust’ around embryonic stars
Dust condenses in the cloud
evidence : little pieces trapped in meteorites inbetween other minerals
Formation of Solids in solar nebula
The first native elements and minerals begin to condense
Chemical phases
A ‘phase’ is a solid (s), liquid (l) or gas (g).
Liquids and gases may mix, but solids generally do not.
Therefore a rock is made of several solid phases, minerals
Periodic Table
not the best way to classify elements for Earth scientists ? (that is chemical classification)
lanthanides
rare earth elements added on to PT
Siderophiles
iron loving elements
Fe, Co, Ni, Ir, Pt, Au
Lithophiles
silicate loving elements
in mantle / crust / solid part of earth silican dominated
Si, O, Li, Uranium (nuclear fuel)
Chalcophiles
copper loving
early metal ore elements
Silver, (Gold), Zink, Mercury ; Lead, Sulphur, Copper
Atmophiles
prefer to be in earths atmosphere
Nitrogen, H, Oxygen, Carbon, F), (Cl), (Br), (I), + inert gases.
Geochemical Classification
instead of periodic table
high to low temp., as temp lower, elements with lower condensation temps appear
Geochemical Classification Order
- Refractory siderophiles - s
- Refractory oxides
- Iron-Nickel .
- Magnesium silicates -
- Alkali metals, Na & K.
- Volatile chalcophiles
- Mineral-bound O & OH
- Ice mineral elements,
- Permanent gases,
high to low temo
highest temp Geochgemical Classification 1,
Refractory siderophiles - metals condensing above the condensation point of Fe-Ni alloys. These include W, Os, Ir & Re and have extremely low cosmic abundances.
these are rare in the SS, governed by iron nickel alloys
Geochgemical Classification 2
Refractory oxides - primarily elements and their oxides which form the minerals such as corundum, perovskite and spinel.
Geochgemical Classification 3
Iron-Nickel metal alloys (including small amounts of Co, Cu, Au, Pt, Ag.
Geochgemical Classification 4
Magnesium silicates - primarily elements and their oxides which form olivines etc.
Geochgemical Classification 5
Alkali metals, Na & K. (loweer melting points, form rathere late)
Geochgemical Classification 6
Volatile chalcophiles
even lower temp
Geochgemical Classification 7
Mineral-bound O & OH
minerals that contain water in the form of OH, structure bound in materials like clay
Geochgemical Classification 8
Ice mineral elements, which comprise water ice, ammonia, methane etc.
Geochgemical Classification 9
Permanent gases, i.e. H2, He, Ne.
gas form
Cosmic Dust
continually entering earths atmosphere
about one micron in size
spherical, composed of many little grains
Minerals in Cosmic Dust
minerals in them are silicates such as : Olivine var. forsterite Mg2SiO4
Pyroxene var. enstatite MgSiO3
but also Corundum Al2O3, Spinel MgAl2O4, Perovskite Ca2Al2SiO7
these minerals form at high temp in solar nebula
high temperaturee condensates
Metallic iron condenses a bit lower
Iron Sulphide FeS
Olivine MgFeSiO4
CAIs calcium-aluminium inclusions
great significance, has the oldest things we can find in solar system
in special meteorites “Allende Meteorites”
CAIs have yielded the oldest radiometric age measured, 4.56 Ga. They have given us the age of the first solid materials in the Solar System
now older meteorite was found in australia, older than our solar system7Ga years old
Age of the Solar System
4.56 Ga. (billion)
Early Gaseous Molecules found in Meteorites
H2, N2, O2, CO, CH4, NH3
Solid Gas Hydrates
(clathrate hydrates) deform, similar to beeswax
small quantities in meteorites
do occur on earth (deep marine)
Planetisimal def
something smaller than a planet
precursors of planets, formed from the accretion of particles of dust, gravel-sized rocks, gas hydrates and gaseous molecules
formation of planetisimals
used to believe: Components condense with decreasing T to form onion-skin layered spheres…
however process is actually more energetic: these are smashed by further impacts, which may be more catastrophic the larger the planetisimals become. They will re-accrete by impacts at lower velocities but have a more homogenous composition
impacts , energetic process, not just smooth going
Early Chemical Zonation of The SS
as objects form they attract each other( gravity), start to move, collisions, rebound
sun
hot region- ricj in iron Fe-Mg Silicates and oxides
rocky planetisimals
cold region- lumps of gas hydrates and snowflakes
very cold region- icy comets coated in graphite (C) and silicon carbide (SIC)
Comets represent
primordial solar nebula compositions
has a long tail with materials that heat up
OOrt cloud
Comets comprise the Oort Cloud, the outer limits of the solar system.
icy material that was once blown away by solar winds but eventually comes around to planetary region and can be observed
Other debris from the solar nebula was long ago blown away by stellar winds
Meteorite Allende
primitive meteorite
early elements
organic chem in meteorites more comnplex
circular objects in meteorites
They contain CHONDRULES and are called CHONDRITES (chondrites is the roup of chondrules)
Chondrites
contain an homogenous mix of primordial elements, minerals and rocks
undifferentiated, got high to low temp things
represent the geochemical composition of the primordial Earth
are clearly made of particles sticking together
Planetary Differentiation
Planetary Differentiation: segregation of matter into discrete reservoirs universal process ( all planetary bodies) have a denser core differentiation was underway between 2 & 10 Myrs of the condensation of the first solids ( very early!)
Composition of terrestial planets
- All have metallic iron at center, different proportions
universal concept of mass surrounded by a mantle
In the colder, lower velocity areas of the outer Solar System, chunks of stable gas hydrates will collide and readily stick together, with snowflakes and other ice particles (and a substantial amount of ‘rocky’ material too).
gas giant planets begin to accrete
Meteors
what we see in the sky
meteorite formation process
what arrives and we can pick up
derived from asteroids, Moon, Mars. → enter Earth’s magnetic field at 11.2 kms-1
hypeervelocity objects, travel very fast, atmosphere acts a s a shield
Fusion crust
Meteorites
generate a thin crust where minereals are fused, outside shape on a meteorite → fusion crust
dragged away when passing thru atmosphere so inside doesnt eeven heat up as much
Iron Meteorites
dominated by iron
5% of meteorites found
Stony Iron Meteorites
rare, distinctive, 1.5%
stone (silicate) and iron
Stony Meteorites
93%
dominated by silicate materials
Chondrites
85%
contain chondrules
(NB 3.6% of chondrites are C, H, N & O -bearing; “carbonaceous chondrites”)
Achondrites
7%
- do not contain chondrules
stony meteorites which do not contain chondrules.
•they are similar to terrestrial igneous rocks of basic composition; basalts, dolerites, gabbros
•they are (mostly) too old to be derived from the Earth
•derived from differentiated asteroids
* a small % come from Mars or the Moon!
Iron Meteorites
dominantly composed of Ni-Fe alloys, but also some crystallised minerals
show exsolution textures; widmanstätten structure
structure cubic shapes, crossing over
derived from the cores of differentiated bodies eveen asteroids
Stony Iron Meteorites: Mesosiderites
contain iron, Ca-pyroxene, plagioclase + glass
•have a brecciated texture
•welded together after a series of impacts
Stony Iron Meteorites: Pallasites
contain iron and olivine (peridot)
might represent exact boundary of core and mantle (bcs metallic from core and olivine from mantle!)
•represent core-mantle boundaries of differentiated asteroids
stony iron meteorite (iron and silicate)
Phase Diagrams mission
CHanges in mineral phases are generally driven by changes in temperature (T) and Pressure (P)
Triple Point
if a rock has all three minerals in it it has to be at the point where they all meet and coexist,
equilibrate / equilibrium coexist
Gibbs Phase Rule
- rule about degree of freedom F= C - P +2 F: variance, degree of freedom C: number of components present P: number of phases present The number 2 represents the variables that may affect the system ie Temp and Pressure
fixed phase diagrams
no degree of freedom ex.
example at triple point: F= C is 1 and P is 3 because number of phases (3colours) +2 =0
this means no degrees of freedom, invariant point
triple point 3 phases coexits neither temp of pressure can change otherwise phases change
unfixed phase diagrams and variant lines
- ex if F=1
UNVARIANT LINE - 2 phases may coexist but if 1 variable changes it cannot be maintained
DIVARIANT LINE
-1 phase can exist at equilibrium P and T can be changed and situation is maintained until boundary is reached and would plot in different phase field
Ice and Water Vapour Phase diagram
one component system , all H20 , all same formula (ex. silica)
System definition
an arbitrary limited physical-chemical entity
can be defined as widely or specifically required
closed system
no material added or taken away, ideal lab situation
open sytsme
naterlay added or taken away, constantly changing, in natura example
liquidus
curved line between liquid and liwuid+solid field called “liquidus”
line on phase diagram where all temp above are liquid
solidus
all temp below solidus will be solid
solidzs and liquidus have
meet at pure end members
they have single melting and freezing point
Melting / point/ range
crystal will start to freeze at its liquidus temp and only completely solid at solidus temp
The Lever Rule
estimates the solidified proportions of solids and liquids
Melting
the reverse of crystallization is melting
adding heat when you melt
you remove heat when you crystallize
Effect of water in a phase diagram
if we have a wet system we reduce required melting temp
Importance of Equilibrium in nature
if it is not maintained the system is open
can be disequilibrium and an open system or a closed system
Zoning
represent changes in temp and pressure through cracks
