Transcript MAGNETIC HISTORY OF THE MOON AND MARS

MAGNETIC HISTORY OF
THE MOON AND MARS
Stan Cisowski and Mike Fuller,
HIGP-SOEST,
University of Hawaii, Honolulu,
Hawaii.
Research topic for fun - essentially
talk given at AGU December 2003
Observations
Moon
Site magnetometer surveys
Sub-satellite magnetometers surveys
Satellite surveys - Lunar prospector
Electron reflectance experiment
Apollo returned samples
Lunar meteorites
Mars
Satellite magnetometer surveys
Electron reflectance experiment
Martian meteorites
Apollo Magnetometer Site
Surveys
Dyall, Parkin and Sonnett, 1970
Sub-satellite magnetometer
surveys
Coleman et al., 1973
Reiner Gamma type swirls
Apollo: Returned samples - mare
basalts, breccia and soil
Rock magnetism
Paleomagnetism
Implications for Lunar magnetism
Rock magnetism
a)
Fe in basalt,
b)
FeNi Melt breccia
and
c)
Superparamagetic
Fe in Soil
Nagata et al., 1972
Mare basalts
Melt breccias
Regolith Breccias
Shock Magnetization and
Demagnetization
Cisowski et al., 1973
More Shock Effects
Cisowski et al., 1973
17km/s Flying plate impact into
basalt (Srnka et al., 1979)
Shock Magnetization
Impact Induced Field changes
Lunar Basalts Paleointensity
Summary
Cisowski and Fuller, 1986
Lunar paleointensity Linear f(t)
Lunar paleointensity data
300
250
Int IRMs
Int ARM
Int. microtesla
200
Int KTT
150
100
50
0
5
4
3
2
Age (By)
1
0
Lunar Paleointensity log f(t)
Lunar paleointensity
1000
Int KTT
Int ARM
Int IRMs
Int microtesla
100
10
1
4
3
2
Age (By)
1
0
Abundance and Distribution of Iron on the
Moon
Lucey, Taylor and Malaret (1995)
On to Mars.
Martian meteorites
Viking - soil analysis
Crustal anomaly model
Paleomagnetism of ALH84001
High resolution SQUID observations
Weiss et al., 2002
Magnetite in Martian meteorite ALH84001
Fine magnetite in carbonate
Transmission electron microscope image showing oriented elongated magnetites
(M) and regions containing periclase (P) in carbonate in ALH84001 (Barber and
Scott, 2002).
Paleomagnetism of ALH84001
Soft -reversed
Soft magnetization
Hard magnetization
AF Demagnetization of NRM
AF DEMAGNETIZATION
CHARACTERISTICS
Demagnetization of IRMs
Mars Crustal Magnetic Anomalies
Comparison between terrestrial and martian crustal anomalies
Comparison between
Models for Martian Crustal
Magnetic Anomalies
Magnitude and Occurrence
Sea floor spreading (Connerney et al,1999),
Terrane accretion (Fairen et al, 2001)
Igneous model (Hammer and Brachfield 2003)
Hydrothermal alteration of igneous rocks
(Harrison 2001, Solomon et al., 2003)
Magnetic phases invoked
Magnetite, Pyrrhotite, Hematites,
Hemo-ilmenties, Maghemite
Magnetization of Martian Crust
• Modeling suggests crust locally magnetized in southern
hemisphere to ~20 km with intensity ~10 A m-1
(Connerney, Nimmo, Parker).
• Intensity of magnetization acquired by rocks depends on
1. Magnitude of Martian field.
2. Mechanism of magnetization.
3. Magnetic material
Outline of Model
In southern highlands:
When dense CO2 atmosphere present and water is stable,
weak acid forms and Fe-rich carbonate deposited in crust.
Continued growth of crust from magmatic intrusions
causes siderite decomposition forming single-domain
magnetite. Locally ~1% carbonate forms to depth of ~20 km
and is converted to 0.5% SD magnetite.
Earth-like field from dynamo induces intensity of
magnetization of up to 10 A m-1 prior to 4.0 Gyr.
SD magnetite stable over 4 Gyr due to subsequent lack
of water, as in ALH84001.
Suggested Origin of Single-Domain Magnetite in Martian crust
during Noachian (Hydrology after Clifford & Parker 2001)