Iron Meteorites
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Transcript Iron Meteorites
Iron Meteorites
Introduction to the wonderful world
of Iron Meteorites
What do we know?
Earth’s core is made of Fe
So asteroids must have formed cores
Indirect
evidence: HED meteorites - no metal,
but…segregated?
Meteorites that contain no metal but show
evidence of presence of metal
Relationship between achondrites and iron
meteorites
Differentiated asteroids also have achondrites
“-Philes”
Various elements like to partition
themselves:
Siderophiles – affinity for metal
Chalcophile – affinity for sulfides
Lithophile – rock (silicate o oxide)
I <3 metal
Core formation scavenges siderophile
elements
IE: Iron, nickel, platinum, cobalt etc
Achondritic meteorites derived by partial
melting must be depleted of the
siderophile elements in mantle
Siderophile elements make up most of iron
meteorites
Crystallization of Irons
Liquid film as opposed to
molten beads sinking
Evidence: loss of metal
sulfides
Process:
Forms kamacite or taenite
Depends on weight percent
and temperature
Widmanstatten pattern
Fe/Ni rich minerals
Widmanstatten pattern
Structural Classification
•Hexahedrites: Neumann lines, striations, all kamacite, mostly
featureless
•Octahedrites: 6-17% Ni, Kamacite and taenite, Widmanstatten
Om, Of
pattern, Largest y most diverse = Ogg, Og,
and Off groups
•Ataxites: microscopic Widmanstatten pattern, mostly teanite
•Anomalous: usually fine grained, cm sized crystals
Hexahedrites
Octahedrites
Ataxite and Anomalous
Chemical Classification
Separated by groups
I-IV
Subgroups
Belong to a limited
range of structural
classes
Correlation b/t band
width and chemical
grouping, etc
Chemical v. Structural
Classification
Solidification of Cores
Variable because of
process of solidification to
form cores
Certain elements
increase while others
decrease
Trends can be used to ID
types of iron meteorites
From fractional
crystallization: solid
separates from liquid
Problem: localized
differentiation
Loose ends
Variation of Widmanstatten pattern
widths : phase diagram
Silicate Inclusions – impacts o
incomplete melting?
Isochrones: Use radioactive elements to
date iron meteorites
Pallasites
The Prettiest of Them All
Stony-irons
Composed of olivine crystals enclosed in metal
Attractive :-D
Olivine tends to be Mg rich
Extension if IIIAB
Eagle Station (KY) meteorite
Iron-rich olivines, metals w/ composition unlike other
groups, differing oxygen isotope compositions
Pallasites
Mesosiderites
‘messys’ - accidents
1:1 ratio of metals and silicates
Mostly pyroxene and plagioclase
No olivine
Similar to HEDs
Limited range of abundances
From 2 differentiated asteroids colliding?
Messys
The End
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