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We measured the natural remanent magnetization (NRM) and rock magnetic properties of 57 sediment samples and 38 basalt samples from Tūranganui Knoll on the Hikurangi Plateau collected at Site U1526 during International Ocean Discovery Program Expedition 375. NRM was measured on all samples before and after either progressive alternating field or thermal demagnetization. Principal component analysis was conducted to provide estimates of the characteristic remanent magnetization direction. Rock magnetic observations include measurements on select samples of the bulk magnetic susceptibility, susceptibility versus heating for Curie temperature assessment, magnetic hysteresis, backfield for coercivity of remanence determinations, isothermal remanent magnetization, and first-order reversal curves.
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Preliminary Characterization of Submarine Basalt Magnetic Mineralogy Using Amplitude‐Dependence of Magnetic Susceptibility
Abstract The past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non‐destructive method that utilizes the amplitude‐dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock‐magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude‐dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude‐dependence should ideally be demagnetized either using alternating fields or via finely‐spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples.
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- PAR ID:
- 10488870
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 25
- Issue:
- 2
- ISSN:
- 1525-2027
- Subject(s) / Keyword(s):
- paleomagnetism magnetic susceptibility alternating field demagnetization thermal demagnetization IODP Expedition 391
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023GC011222
