Paleointensity and Rock magnetism of Martian nakhlite meteorite MIL03346: Small Scale Magnetization of the Martian Crust
Abstract
The existence and duration of the martian magnetic dynamo are key parameters for assessing Mars' early habitability and for understanding the dynamics of its deep interior.
While the martian dynamo is not active today, crustal remanent magnetism shows that Mars once was able to sustain a dynamo magnetic field. The canonical scenario suggests that it had ceased by about 4 Ga. However, recent data from the InSight and MAVEN mission showed that magnetizations in young volcanic terrains may be much stronger than predicted from crustal field modeling using orbital data. This leads to the possibility of a longer-lived dynamo and motivates the measurement of younger martian meteorites to understand the surface magnetic field environment. Here we present the first rock and paleomagnetic study of 6 mutually oriented samples from the martian Nakhlite meteorite MIL03346, which is exceptionally well suited for paleomagnetic measurements. Its age is well known (1368 ± 83 Ma) and the magnetic mineralogy is dominated by magnetite, a common mineral in Earth rocks. Furthermore, MIL03346 has not been subjected to significant aqueous alteration, or shock pressure or temperature, which could have reset the remanent magnetization. We analyzed the samples using first order reversal curves (FORC), alternating field magnetization of natural (NRM), anhysteretic (ARM), and isothermal remanent magnetizations, and magnetic microscopy using a quantum diamond microscope (QDM). The bulk of the NRM is carried by large (>10μm) Ti-magnetite crystals that are in the multidomain size range of magnetite. In contrast, rock magnetic analysis shows that the crystals have a high coercivity and are in a domain state close to single domain. Fine exsolution lamellae of ilmenite can be found in the host magnetite and alter the domain-state. AF demagnetization of the NRM reveals two distinct directions. A weak terrestrial isothermal overprint is removed by weak AF fields while an extraterrestrial high coercivity component is stable to 70 mT. ARM paleointensities of 4 interior samples reveal a strong 5.1±1.5 μT paleofield, even larger than the 2000 nT measured by InSight. These results provide further evidence for stronger than expected, small scale crustal fields on Mars.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMGP015..03V
- Keywords:
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- 1594 Instruments and techniques;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1595 Planetary magnetism: all frequencies and wavelengths;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 5734 Magnetic fields and magnetism;
- PLANETARY SCIENCES: FLUID PLANETS;
- 5443 Magnetospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS