Antarctic Meteorites - Emporia State University

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Transcript Antarctic Meteorites - Emporia State University

Molly Reardon
ES 567 Final Project
Spring 2010
http://www.emporia.edu/earthsci/
amber/go340/students/reardon/
I am a graduate student at Emporia State University
in Earth Science. This project was for my gemstone
course, www.emporia.edu/earthsci/amber/go340,
and includes:
 Introduction
 Historic review
 Meteorite concentration mechanism & areas
 Collecting methods
 Shipping & analysis
 Origins
 Classification
 Conclusions & references
For comments or questions,
[email protected]

Meteorites are rock and gemstones too!
There is not one generally accepted definition for
“gemstone”, however, they all have something
unique about them. In the case of meteorites,
their origin is what sets them apart from other
gems we’ve studied in this course.

What is a meteorite?
- It’s a fragment of a space rock that lands on Earth as the
result of a collision or impact between two parent rocks.
- Some have lunar or Martian origins, but most originate from
the asteroid belt.
- Meteoritic events that are witnessed are called a “fall”, while
meteorites that are stumbled upon are called a “find.”
- Meteorites are usually named after the person who
discovered them or after the closest town or geographic
landmark.

Why are Antarctic Meteorites significant?
- More meteorites have been found here than on any other
continent.
- A special concentrate mechanism exists to explain why so
many different meteorites are found on the ice.
- Antarctica is an amazing place to talk about and study!
- In the early 1970’s, at a Meteoritical Society meeting,
http://www.meteoriticalsociety.org/, Japanese scientists
described finds of 9 different kinds of meteorites in one area
in Northeastern Antarctica.
- Until this point, meteorites concentrated in one location have
always been from the same fall.
- Meteorites found on the ice by expeditions dating back to
1911 were not realized to be significant. It was unknown
these rocks were parts of much larger “strewn fields”.
-
American scientist, William Cassady recognized the
significance of the Japanese find and conducted more
research. Eventually his proposals were accepted by the
National Science Foundation and he founded the ANSMET
program.
- Thousands of years ago, meteorites fell to earth and became
embedded in the Antarctic Ice.
- As the glacial ice flowed downstream from the interior of the
continent to the coastal regions, it carried embedded rocks
and debris with it.
- Sometimes the ice encounters a barrier or stagnation point,
such as a mountain range or a subsurface ridge. When ice
stops flowing at stagnation points, it evaporates or ablate.
- The rocks and debris embedded in the ice at these stagnation
points will gradually make their way to the surface as the ice
they are contained in ablates.
- We are then left with a concentration of rocks in one location;
most of which come from varying sources and started their
downward journey at different times. (See image on next
slide)
 Image depicts the
concentration mechanism
responsible for meteorite
strewn fields on the
Antarctic Continent.
Image obtained from:
http://curator.jsc.nasa.go
v/antmet/index.cfm
The image to the right shows
known concentration fields along
the Western edge of the
Transantarctic Mountains.
The Transantarctic Mountains
act as a barrier to the ice that is
flowing from the interior of the
continent (North East) to the
coastal areas (South West).
The region depicted on the map
is the predominant area of study
for the ANSMET program.
Image obtained from:
http://meteorites.wustl.edu/lunar/
ansmet_locations.htm
N
- To determine potential collection points and concentration
areas, ANSMET scientists study the US Geologic Survey's
archive of aerial and satellite photos of Antarctica in Reston,
Virginia.
- They are specifically looking for direction of ice flow marked
by crevasse fields and potential boundaries such as
mountains and subsurface ice ridges.
-
These areas are distinguishable on satellite and aerial photos
by variations in pattern and color of the ice.
- Once on the ice, the scientists branch out to potential areas of
interest and set up a field camp.
- The field seasons occur during the Austral Summer, between
October and February of each year. The climate is too harsh
to be outdoors during the winter months. Summertime
temps can range from -55F up to 0F. Summertime has the
added benefit of 24/7 sunlight. So scientists can work round
the clock!
Image right shows typical
field camp occupied by
ANSMET participants.
Image obtained from:
geology.cwru.edu/
~ansmet/living/index.html
- Depending on location, meteorite searches conducted on foot
or skidoo.
- Skidoos used to cover large areas of open ice where only a
few rocks are present.
- On-foot searches conducted in glacial moraines where many
rocks are present, and distinguishing between earth rocks
and meteorites requires a closer look. A typical method is 56 people to be spread out over 30-40 meters and to search
ground in a series of sweeps.
Image obtained from:
http://geology.cwru.edu/
~ansmet/collecting/index.html
- If a rock is suspected to be a meteorite, it is put into
collection kit
- The kit contains “sterile bags to put the meteorites in,
numbered tags to label them with, tape to close and seal the
bags, a notebook to take down any distinguishing features of
the sample, and some scissors to cut the tape.”
(http://geology.cwru.edu/~ansmet/collecting/index.html)
This image obtained from:
http://geology.cwru.edu/
~ansmet/collecting/index.html
- Once the rocks are collected from the ice, the shipment
processes begins.
- The rocks are kept frozen and packaged into coolers that are
shipped to the Antarctic Meteorite Curation labs at the
Johnson Space Center (JSC) in Houston, Texas
- At the labs, the rocks are carefully thawed and cracked open
for study.
- The JSC classifies and assigns a name and number to the
rock. Then they write a short description which is published
in the Bi-Annual Antarctic Meteorite Newsletter, found here:
http://www-curator.jsc.nasa.gov/antmet/amn/amn.cfm
 The
JSC classifies meteorites based on
composition.
 There are three main origins of meteorites
found on earth:
- Lunar
- Martian
- Asteroid Belt

Lunar
- A lunar meteorite is “a rock found on earth that was
“ejected from the Moon by the impact of an asteroidal
meteoroid or possibly a comet. ”
(http://meteorites.wustl.edu/lunar/moon_meteorites.htm)
- By testing suspected meteorites for chemical compositions,
isotope ratios, minerals, and textures, comparisons can be
made to moon rocks collected on Apollo missions.
- Lunar meteorites found on Earth contain a fusion crust
which is evident on the outside of the rock. This crust
formed with deceleration through Earth’s atmosphere.
- One example of using chemical composition to determine
origins of the rock is with the lunar meteorites that are
classified as “feldspathic breccias.” These rocks are rich in
aluminum and calcium which is indicative of the mineral
anorthite. The lunar highlands area is composed of this
mineral, which is not known to be present on
other planets or our asteroid belt.


This is a lunar meteorite found in the MacAlpine Hills area of
Antarctica in 1989.
The cube in the lower left is 1cm X 1cm. Note the fusion
crust on the outside of the rock.
Image obtained from:
http://meteorites.wustl.edu/
lunar/moon_meteorites.htm

Martian
- A Martian meteorite is a rock that originated on Mars and
as the result of some sort of celestial impact, has been
ejected into the solar system and landed on Earth.
- Of the tens of thousands of meteorites that have been
found on Earth, only a small fraction (less than 40) have
been identified as originating from Mars.
- The isotope ratios in the Martian rocks are what typically
separates these meteorites from other Earthly rocks.
- A previously unknown type of martian meteorite was
discovered by ANSMET scientists in 2003. For more info,
see:
www1.nasa.gov/home/hqnews/2004/jul/HQ_04232_meteo
rite.html

The Martian rock below was discovered in the Allan Hills area
of Antarctica in 1977. Through isotope ratio testing and
examining the igneous interior, this was determined to be a
Martian sample. Cube in lower right is 1cm X 1cm.
Image obtained from:
http://www2.jpl.nasa.gov
/
snc/alha1.gif

Asteroid Belt
- Asteroids are small planetary bodies that orbit our sun
within the asteroid belt and pass between Jupiter and Mars.
Occasionally, asteroids collide and rock remnants from the
impact get pulled into the Earth’s atmosphere and fall to
the ground.
- Meteorites with asteroid belt origins are the most common
type found on Earth.
- The chemical composition of meteorites from the asteroid
belt fall into one of three categories: Carbonoceous,
Silicates, and Metallics. The presence of a fusion crust and
chemical composition are what sets asteroid belt meteorites
apart from Earthly rocks.

This is a typical rock from the asteroid belt. Dimensions are
approx 5cm X 5cm. This is a stone meteorite classified as a
chondrite (see next slide), and does contain trace amounts of
nickel iron.
Image obtained from :
http://curator.jsc.nasa.gov/
antmet/amn/AMNJul97/
PetDes.htm#GRO95551

Meteorites are classified into three main
groups
- Irons
- Stony Irons
- Stone

Irons
- Irons originate in the differentiated core of a planetary
body and have extremely high densities.
- They contain varying amounts of nickel-iron masses.
- They are subdivided into three groups hexahedrites,
octahedrites, and ataxites which are differentiated by
the amount of nickel in each.
- Iron Hexadedrite: A type of iron meteorite made entirely of
kamacite (a nickel-iron alloy) and named for its cubic
(hexahedral) crystal structure. Contains 4.5% - 6.5 % nickel
-
Iron Octahedrite: Octahedrites contain 6.5% – 13%
nickel. Image right obtained from
http://curator.jsc.nasa.gov/antmet/amn/
AMNAug96/PetDes.htm#GRO95522
The tiny cube in lower right is 1cm X 1cm
-Iron Ataxites: Made almost entirely of taenite (a
nickel-iron alloy) with a loose chemical structure.
Contains 16% - 30% nickel

-
-
Stony Irons
These rocks are a combination of mantle-rock and
nickel iron that have been fused together by impact.
Stony Irons contain two subgroups called mesosiderites
and pallasites.
Mesosiderites: contain equal parts of
metallic nickel-iron and silicate.
Image obtained from:
http://curator.jsc.nasa.gov/antmet/
samples/petdes.cfm?sample=ALHA81
208
Pallasites: contain olivine crystals of peridot
quality in an iron-nickel matrix. You can see
the olivine suspended in the iron-nickel in
this image.
Image obtained from:
http://curator.jsc.nasa.gov/antmet/
samples/petdes.cfm?sample=
ALHA81208

Stones
- These rocks are the most abundant type of meteorite
found. They have been known to come from the Moon,
Mars, and the asteroid belt.
- These rocks are suspected to have formed 4.56 billion
years ago, after the formation of the sun.
- Stone meteorites consist of two subgroups: chondrites
and achondrites.
 Chondrites: contain "chondrules," which
are gaseous inclusions that formed
during the solar nebula. This image is a
close-up under polarized light of an
ordinary chondrite. You can see the gaseous chondrule
inclusions in the rock. Image obtained from: http://curator.jsc.
nasa.gov/antmet/samples/petdes.cfm?sample=ALH82110
Achondrites: This is a stone meteorite
that contains no chondrules. Image is a
close up of a Martian Achondrite found
on Antarctica. Image obtained here:
http://curator.jsc.nasa.gov/antmet/
samples/petdes.cfm?sample=
ALHA77005
- Although meteorites are not typically associated
with aesthetically pleasing gemstones, they are
being cut and fashioned using the cabochon style.
Their unique origins set them apart from other
gems with the exception of moldavite!
- Meteorites provide a glimpse into planetary
geology and the possible formation of our solar
system. These gemstones are extremely valuable
for their geologic significance.
-
Because of the concentration mechanism on the
Antarctic Ice and the proven success of meteorite
finds, it’s imperative that this research
continues and that some specimens
are preserved as gems!
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www.antarcticconnection.com/antarctic/science/meteorites.s
html
geology.cwru.edu/~ansmet/
www-curator.jsc.nasa.gov/antmet/index.cfm
www-curator.jsc.nasa.gov/antmet/amn/amn.cfm
www.gi.alaska.edu/ScienceForum/ASF7/744.html
nineplanets.org/meteorites.html
www.emporia.edu/earthsci/amber/go340/syllabus.htm
www.bwsmigel.info/GEOL.115.ESSAYS/Gemology.Meteorites.
html
wapi.isu.edu/geo_pgt/Mod05_Meteorites_Ast/mod5.htm
Cassady, W. A. 2003. Meteorites, Ice, and Antarctica.
Cambridge University Press.