Evolution of the Ancient Martian Dynamo as Recorded by the ALH 84001 Meteorite
Abstract
While the unique Martian meteorite ALH84001 has been the subject of several previous paleomagnetic studies, key questions about the origin of its magnetization and its implications for the history of the Martian dynamo remain unanswered. Among the unresolved issues are the non-unidirectionality of magnetization in carbonate globules, which is potentially indicative of a prolonged period of remanence acquisition in a time-varying magnetic field, and the nature of magnetization in chromite grains, which may record Martian surface fields at 4.4 Ga.
In this study, we take advantage of the micron-scale resolution of a quantum diamond microscope (QDM) to build on the results of past paleomagnetic studies of ALH84001. We first assess the unidirectionality of carbonate magnetization both among and within individual globules by both upper continuation of magnetic field maps and direct modeling of the micrometer-scale magnetism. We also characterize the magnetic properties of chromite grains, which have been difficult to study using other magnetic field imaging systems due to their small size and proximity among grains. Preliminary results including the magnetic imaging of 24 discrete carbonate grains and alternating field demagnetization to 30 mT suggest that the carbonates carry a unidirectional magnetization while the magnetizations of the chromites are randomly oriented. This may suggest that the Martian dynamo was weak during the initial crystallization of ALH84001, but was strong by the time the carbonates formed in the 4.0-3.9 Ga interval. We will pursue further demagnetization and paleointensity experiments to confirm and quantify the inferred Martian surface field intensities.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGP12A..08S
- Keywords:
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- 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 1595 Planetary magnetism: all frequencies and wavelengths;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS