Paleointensity and Rock Magnetism of Martian Nakhlite Meteorite Miller Range (MIL) 03346: Evidence for Intense Small Scale Crustal Magnetization on Mars

1Michael Volk,1Roger Fu,2Anna Mittelholz,3James M.D. Day
Journal of Geophysical Research Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006856]
1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, 02138
2Institute of Geophysics, ETH Zuerich, 8092 Zuerich, Switzerland
3Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093‐0244 USA
Published by arrangement with John Wiley & Sons

The martian dynamo’s strength and duration are essential for understanding Mars’ habitability and deep interior dynamics. Although most northern volcanic terranes were likely emplaced after the martian dynamo ceased, recent data from the InSight mission show stronger than predicted crustal fields. Studying young volcanic martian meteorites offers a precise, complementary method to characterize the strength of the martian crustal field and examine its implications for past dynamo activity. We present the first rock and paleomagnetic study of nine mutually oriented samples from the martian Nakhlite meteorite MIL 03346, which is well‐suited for paleomagnetic analysis due to its well‐known age (1368 ± 83 Ma) and lack of significant aqueous, thermal, and shock overprinting. Rock magnetic analysis, including quantum diamond microscope (QDM) imaging, showed that the natural remanent magnetization (NRM) is carried by Ti‐magnetite crystals containing µm‐scale ilmenite exsolution lamellae, which can accurately record ancient magnetic fields. Demagnetization of the NRM revealed a high coercivity magnetization interpreted to date from the age of eruption based on its intensity, unidirectionality, and a passing fusion crust baked contact test. Paleointensities of four samples reveal a 5.1±1.5 µT paleofield, representing the most reliable martian paleointensity estimates to‐date and stronger than the 2 µT surface fields measured by InSight. Modeling shows that the observed fields can be explained by an older sub‐surface magnetized layer without a late, active dynamo and support a deeply buried, highly magnetized crust in the northern hemisphere of Mars. These results provide corroborating evidence for strong, small scale crustal fields on Mars.

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