Low absolute paleointensity during Late Miocene Noma excursion of the Earth’s magnetic field

Okayama, Kazuhiro; Mochizuki, Nobutatsu; Wada, Yutaka; Otofuji, Yo–ichiro

doi:10.1016/j.pepi.2018.12.006

Cited by 7 publications

(4 citation statements)

References 50 publications

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“…The weakest paleointensity flow accompanies an excursion‐like direction (flow A3‐20 at 1,365 m altitude) (Ahn et al., 2020). Similar paleointensity variations were observed by other studies (e.g., Ferk & Leonhardt, 2009; Okayama et al., 2019). We consider that the successive lavas of AALIP with short eruption intervals enabled the observation of PSVs.…”

Section: Discussionsupporting

confidence: 90%

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Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Yoshimura

Yamazaki

Yamamoto

et al. 2020

Geochem Geophys Geosyst

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Information on the history of Earth's magnetic field is essential for understanding the geodynamo evolution, and variations in the intensity of the geomagnetic field in the past (paleointensity) are fundamentally important for constraining numerical geodynamo models. Despite a long history of research, there is still controversy about the long-term trend of time-averaged virtual (axial) dipole moment (V(A)DM): for example, the possibility of a stronger paleointensity during the Cretaceous Normal Superchron (

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Section: Discussionsupporting

confidence: 90%

“…N spec /N try : the ratio of the number of accepted specimens to the total number of specimens. studies (e.g., Ferk & Leonhardt, 2009;Okayama et al, 2019). We consider that the successive lavas of AALIP with short eruption intervals enabled the observation of PSVs.…”

Section: 1029/2020gc009341mentioning

confidence: 99%

Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Yoshimura

Yamazaki

Yamamoto

et al. 2020

Geochem Geophys Geosyst

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“…It is common practice to prolong the second hold duration to allow a similar amount of alteration to occur in a specimen that has presumably undergone some thermal stabilisation. Some examples of first (second) heat hold durations are: 30 (60) minutes (Tsunakawa and Shaw, 1994), 10 (20) minutes (Yamamoto et al, 2003), 24 (48) minutes (Yamamoto and Hoshi, 2008), 20-35 (30-45) minutes (Mochizuki et al, 2011), 15 (30) minutes (Yamamoto and Yamaoka, 2018), and 30 (40) minutes (Okayama et al, 2019).…”

Section: The Shaw Methodsmentioning

confidence: 99%

Improvements to the Shaw-Type Absolute Palaeointensity Method

et al. 2021

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Palaeointensity information enables us to define the strength of Earth’s magnetic field over geological time, providing a window into Earth’s deep interior. The difficulties in acquiring reliable measurements are substantial, particularly from older rocks. Two of the most significant causes of experimental failure are laboratory induced alteration of the magnetic remanence carriers and effects relating to multidomain magnetic carriers. One method that has been claimed to overcome both of these problems is the Shaw method. Here we detail and evaluate the method, comparing various selection criteria in a controlled experiment performed on a large, non-ideal dataset of mainly Precambrian rocks. Monte Carlo analyses are used to determine an optimal set of selection criteria; the end result is a new, improved experimental protocol that lends itself very well to the automated Rapid 2G magnetometer system enabling experiments to be carried out expeditiously and with greater accuracy.

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“…In the course of these assessments, it has been pointed out that the ARM correction is effective not only for correcting thermal alterations but also for correcting remanence anisotropy and compensating for possible magnetostatic interactions among magnetic domains. With this as background, the TS method has been applied to old igneous rocks in Africa (Ahn et al., 2016; Yoshimura et al., 2020), China (Yamamoto, Tsunakawa, et al., 2007), French Polynesia (Mochizuki et al., 2011; Yamamoto, Ishizuka, et al., 2007; Yamamoto & Tsunakawa, 2005), Hawaii (Singer et al., 2019; Yamamoto & Yamaoka, 2018), Japan (Kato et al., 2018; Mochizuki et al., 2013; Okayama et al., 2019; Tsunakawa et al., 2009; Yamamoto et al., 2010), Korea (Ahn & Yamamoto, 2019), Louisville seamount (Yamazaki & Yamamoto, 2014), New Zealand (Mochizuki et al., 2006), and archeological materials in Japan (Kitahara et al., 2018, 2021). Although LTD treatments are not necessarily included, the TS method has also been applied to Precambrian rocks (Lloyd, Biggin, et al., 2021; Thallner, Biggin, & Halls, 2021, Thallner, Biggin, McCausland, & Fu, 2021), partly with consideration for different sets of selection criteria (Lloyd, Paterson, et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature

Yamamoto

Tauxe

Ahn

et al. 2022

Geochem Geophys Geosyst

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Absolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory‐induced thermoremanent magnetization (Lab‐TRM). Plots of NRM unblocking versus Lab‐TRM blocking from API experiments often exhibit nonideal curvature, which can result in biased estimates. Previous work showed that curvature can increase with age; however, selection criteria designed to eliminate such behavior yielded accurate estimates for two‐year‐aged specimens (70.3 ± 3.8 μT; N = 96 specimens out of 120 experiments). API can also be estimated in coercivity space. Here, we use the Tsunakawa‐Shaw (TS) method applied to 20 specimens aged in the laboratory field of 70.0 μT for 4 years, after acquisition of zero‐age (fresh) Lab‐TRM in the same field. Selection criteria for the TS experiment also yielded accurate results (68.5 ± 4.5 μT; N = 17 specimens). In thermal API experiments, curvature is related to internal structure with more single domain‐like behavior having the least curvature. Here we show that the fraction of anhysteretic remanent magnetization demagnetized by low‐temperature treatment was larger for samples with larger thermal curvatures suggesting a magnetocrystalline anisotropy source. We also tested experimental remedies that have been proposed to improve the accuracy of paleointensity estimates. In particular, we test the efficacy of the multi‐specimen approach and a strategy pretreating specimens with low field alternating field demagnetization prior to the paleointensity experiment. Neither yielded accurate results.

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Low absolute paleointensity during Late Miocene Noma excursion of the Earth’s magnetic field

Cited by 7 publications

References 50 publications

Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Improvements to the Shaw-Type Absolute Palaeointensity Method

Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature

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