Magnetic Mineralogy in Lunar Mare Basalts and Implications for Paleointensity Retrieval.
Saved in:
| Title: | Magnetic Mineralogy in Lunar Mare Basalts and Implications for Paleointensity Retrieval. |
|---|---|
| Authors: | Jung, Ji‐In1 (AUTHOR) jiinjung@stanford.edu, Tikoo, Sonia M.1,2 (AUTHOR), Váci, Zoltán3 (AUTHOR), Krawczynski, Michael J.3 (AUTHOR), Solheid, Peat4 (AUTHOR), Burns, Dale H.2,5 (AUTHOR), Vailionis, Arturas5,6 (AUTHOR) |
| Source: | Journal of Geophysical Research. Planets. Sep2025, Vol. 130 Issue 9, p1-20. 20p. |
| Subject Terms: | Iron-nickel alloys, Paleomagnetism, Lunar surface, Moon, Observations of the Moon, Magnetic transitions |
| Company/Entity: | Apollo program (U.S.) |
| Abstract: | Lunar paleomagnetic studies have identified multidomain metallic Fe–Ni alloys as the dominant magnetic contributors in mare basalts. Here, we explore the low‐temperature magnetic behavior of standard samples for a suite of opaque minerals that occur within mare basalts (single‐domain and multidomain Fe, wüstite, ulvöspinel, iron chromite, ilmenite, and troilite). We compare the observed low‐temperature behaviors to those of several Apollo mare basalt samples (10003, 10044, 10020, 10069, 10071, 12009, 12022, 15597). Notable magnetic transitions were detected at < ${< } $30 K (ilmenite), 60–80 K (chromite, troilite), and 100–125 K (ulvöspinel, chromite). We also investigated the effects of low‐temperature cycling on mare basalt remanence and observed that only grains with coercivities < ${< } $20–40 mT were cleaned. This suggests a minimal impact of diurnal temperature cycling at the lunar surface on the retrieved lunar paleointensity values. Using comprehensive electron microscopy techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), x‐ray diffraction, and transmission electron microscopy (TEM), we further examined magnetic phases within four Apollo 11 mare basalt samples. Our findings revealed the presence of Fe grains (one to 10 μm in diameter) associated with troilite contain sub‐grains ranging in size from tens to hundreds of nanometers in some samples. These grains, which fall within the single‐domain to multi‐domain range as observed in their first‐order reversal curves, might have the potential to retain high coercivity components and thereby effectively record an ancient dynamo field. Plain Language Summary: Scientists have been interested in the origin of magnetism recorded in the volcanic rocks brought back from the Moon during the Apollo and Chang'e missions. Originally, iron grains were believed to be the primary carriers, but two questions remained. First, the iron grains observed may be too large to effectively retain magnetic information. Second, previous studies investigating the low‐temperature magnetic behavior of lunar volcanic rocks suggested that the mineral magnetite might also be present; if true, this would raise the possibility that rocks acquired magnetization during impact events long after their formation. Here, we conducted detailed rock magnetic experiments and microscopy analyses to reexamine the magnetic minerals in lunar volcanic rocks. Our results revealed two important findings: (a) We discovered very small, < ${< } $100 nm particles of iron that are well suited for recording magnetic signals. (b) Contrary to earlier suggestions, we found no evidence of magnetite. Instead, the low‐temperature behavior is explained by the mineral ulvöspinel. Additional low‐temperature experiments revealed that temperature fluctuations at the lunar surface due to day/night cycles are unlikely to significantly alter the magnetism recorded. Overall, these findings suggest that Moon rocks contain minerals capable of preserving a stable record of the Moon's original magnetic field. Key Points: Mixtures of multidomain to single domain Fe–Ni grains are the main magnetic carriers in Apollo mare basalts; magnetite is not presentLunar diurnal temperature cycling does not demagnetize mare basalts enough to affect standard paleointensity calculationsHigh coercivity Fe–Ni grains within lunar mare basalts permit retention of ancient field records, such as from a dynamo [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of Geophysical Research. Planets is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | GreenFILE |
| Abstract: | Lunar paleomagnetic studies have identified multidomain metallic Fe–Ni alloys as the dominant magnetic contributors in mare basalts. Here, we explore the low‐temperature magnetic behavior of standard samples for a suite of opaque minerals that occur within mare basalts (single‐domain and multidomain Fe, wüstite, ulvöspinel, iron chromite, ilmenite, and troilite). We compare the observed low‐temperature behaviors to those of several Apollo mare basalt samples (10003, 10044, 10020, 10069, 10071, 12009, 12022, 15597). Notable magnetic transitions were detected at < ${< } $30 K (ilmenite), 60–80 K (chromite, troilite), and 100–125 K (ulvöspinel, chromite). We also investigated the effects of low‐temperature cycling on mare basalt remanence and observed that only grains with coercivities < ${< } $20–40 mT were cleaned. This suggests a minimal impact of diurnal temperature cycling at the lunar surface on the retrieved lunar paleointensity values. Using comprehensive electron microscopy techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), x‐ray diffraction, and transmission electron microscopy (TEM), we further examined magnetic phases within four Apollo 11 mare basalt samples. Our findings revealed the presence of Fe grains (one to 10 μm in diameter) associated with troilite contain sub‐grains ranging in size from tens to hundreds of nanometers in some samples. These grains, which fall within the single‐domain to multi‐domain range as observed in their first‐order reversal curves, might have the potential to retain high coercivity components and thereby effectively record an ancient dynamo field. Plain Language Summary: Scientists have been interested in the origin of magnetism recorded in the volcanic rocks brought back from the Moon during the Apollo and Chang'e missions. Originally, iron grains were believed to be the primary carriers, but two questions remained. First, the iron grains observed may be too large to effectively retain magnetic information. Second, previous studies investigating the low‐temperature magnetic behavior of lunar volcanic rocks suggested that the mineral magnetite might also be present; if true, this would raise the possibility that rocks acquired magnetization during impact events long after their formation. Here, we conducted detailed rock magnetic experiments and microscopy analyses to reexamine the magnetic minerals in lunar volcanic rocks. Our results revealed two important findings: (a) We discovered very small, < ${< } $100 nm particles of iron that are well suited for recording magnetic signals. (b) Contrary to earlier suggestions, we found no evidence of magnetite. Instead, the low‐temperature behavior is explained by the mineral ulvöspinel. Additional low‐temperature experiments revealed that temperature fluctuations at the lunar surface due to day/night cycles are unlikely to significantly alter the magnetism recorded. Overall, these findings suggest that Moon rocks contain minerals capable of preserving a stable record of the Moon's original magnetic field. Key Points: Mixtures of multidomain to single domain Fe–Ni grains are the main magnetic carriers in Apollo mare basalts; magnetite is not presentLunar diurnal temperature cycling does not demagnetize mare basalts enough to affect standard paleointensity calculationsHigh coercivity Fe–Ni grains within lunar mare basalts permit retention of ancient field records, such as from a dynamo [ABSTRACT FROM AUTHOR] |
|---|---|
| ISSN: | 21699097 |
| DOI: | 10.1029/2025JE009030 |
