Rock magnetic studies and a comparison between microwave and Thellier palaeointensities for Canadian Precambrian dykes

McArdle, Nick; Halls, H. C.; Shaw, John

doi:10.1016/j.pepi.2004.03.015

Cited by 23 publications

(6 citation statements)

References 26 publications

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“… Halls et al [2004] used the microwave technique [e.g., Shaw et al , 1996] to obtain a mean VDM value of 2.53 ± 0.93 × 10 22 Am 2 from twelve Matachewan dikes. McArdle et al [2004] reported similar VDM values from four Matachewan dikes.…”

Section: Discussionmentioning

confidence: 68%

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Смирнов

Tarduno

2005

J. Geophys. Res.

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[1] Thellier paleointensity determinations from two dikes of the Early Proterozoic ($2.46 Ga) Matachewan dike swarm (Canada) yield field values of 2.14 ± 0.18 and 9.81 ± 1.65 mT. Corresponding values of virtual axial dipole moment are very low (0.54 ± 0.05 Â 10 22 and 2.49 ± 0.42 Â 10 22 Am 2 , respectively) when compared with the modern field. The characteristic remanent magnetization (ChRM) was isolated over a narrow range of high unblocking temperatures ($520-580°C). Detailed rock magnetic analyses indicate that the ChRM is carried by nearly stoichiometric pseudo single domain magnetite. Scanning electron microscopy (SEM) reveals that the magnetite is in the form of fine intergrowths with ilmenite, formed by oxyexsolution during cooling. The high-temperature oxidation defined in the SEM images could have continued at temperatures below the Curie point of magnetite. In this case, the ChRM would be a thermochemical remanent magnetization (TCRM) rather than a thermal remanent magnetization (TRM). Estimates of the TCRM/TRM ratio show that the Thellier data could underestimate the true field value by a factor of 4 without violating experimental selection criteria. This uncertainty in TRM fidelity translates into a potential range of field values that spans that defined by the modern field ($8 Â 10 22 Am 2 ) and proposed low Precambrian levels ($2 Â 10 22 Am 2 ). Therefore understanding further how TCRM is acquired and records the field represents a major challenge if these and many other similar rocks are to be used in Thellier studies aimed at defining the strength of the Precambrian field.Citation: Smirnov, A. V., and J. A. Tarduno (2005), Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?,

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Section: Discussionmentioning

confidence: 68%

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Смирнов

Tarduno

2005

J. Geophys. Res.

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“… Selected Archaean/Proterozoic VDMs. 1, Pesonen & Halls (1983); 2, Yu & Dunlop (2001); 3, Thomas & Piper (1995); 4, Macuoin et al (2003); 5, Thomas (1993); 6, Yu & Dunlop (2002); 7, Shcherbakova et al (2004); 8, Shcherbakova et al (2006a); 9, Shcherbakova et al (2006b); 10, Shcherbakova et al (this paper); 11, Bergh (1970); 12, Sumita et al (2001); 13, Yoshihara & Hamano (2000); 14, Yoshihara & Hamano (2004); 15, McArdle et al (2004); 16, Smirnov & Tarduno (2005); 17, Tarduno et al 2007 and 18, Smirnov et al 2003. …”

Section: Discussionmentioning

confidence: 79%

Palaeointensity and palaeodirectional studies of early Riphaean dyke complexes in the Lake Ladoga region (Northwestern Russia)

Щербакова¹,

Lubnina

Щербаков³

et al. 2008

Geophysical Journal International

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S U M M A R YResults of palaeointensity and palaeomagnetic studies for the volcanic rocks of 1450 Ma, from Early Riphaean Baltic shield dyke complex sampled in Lake Ladoga region (Karelia, Northwestern Russia) are reported. Electron microscope observations, thermomagnetic and hysteresis measurements indicate the presence of single domain (SD) to pseudo-single domain (PSD) titanomagnetite (TM) with low Ti content as the main magnetic mineral. Stepwise alternating field (AF) and/or thermal demagnetization revealed a two-component natural remanent magnetization (NRM) for most of the samples. The characteristic remanent magnetization (ChRM) component was isolated between 440 and 590 • C. Note that the ChRM amounts to 95 per cent of the NRM intensity. The geographic position of the ChRM palaeopoles does not contradict the 'key poles' of the [1270; 1580] Myr time interval, testifying anticlockwise rotation of whole East Europe Craton between 1450 and 1500 Ma. Palaeointensity determinations were performed by Coe-modified Thellier procedure. 35 samples passed our palaeointensity selection criteria and show large linear segments on Arai-Nagata plots. The site mean virtual dipole moment (VDM) varies from 2.00 to 3.91 (× 10 22 A m 2 ). Based on these and other observations, we suggest that the Palaeo-and MezoProterozoic was dominated by low VDMs.

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“…The first field value was recorded by the Burakovka dikes from separated plagioclase crystals [ Smirnov et al , 2003] with the same age as the low VDM of the Matachewan dikes [ Macouin et al , 2003]. Two studies [ Halls et al , 2004; McArdle et al , 2004] were recently performed using microwave experiments. Interestingly the first one involves the 2.45 Ga Matachewan dykes and indicates a mean VDM of 2.5 ± 0.9 × 10 22 Am 2 which is in excellent agreement with the results of Macouin et al [2004] (2.8 ± × 0.9 × 10 22 Am 2 ).…”

Section: Integration Within the Existing Database And Discussionmentioning

confidence: 99%

Absolute paleointensity at 1.27 Ga from the Mackenzie dyke swarm (Canada)

Macouin

Valet

Besse

et al. 2006

Geochem Geophys Geosyst

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[1] Paleointensity studies have been conducted on 6 mafic dykes from the 1270 Ma Mackenzie swarm in the Slave Province (Canada). The mean direction of the characteristic magnetization coincides with results of an earlier study in which the primary origin of the magnetization was established on the basis of a contact test. High unblocking temperatures, magnetic mineralogy, and grain-size experiments suggest that the magnetization is dominated by pseudo-single domain or single domain grains of magnetite. Paleointensity experiments were conducted with a specially designed oven, using a revised version of the Thellier-Coe method. Thirteen successful determinations of paleointensity were obtained for 4 dykes. The paleofield estimates vary between 4.3 and 22.1 mT, yielding virtual dipole moments (VDMs) between 1.3 ± 0.2 and 4.5 ± 0.9 Â 10 22 Am 2 . These new results increase the number of low field determinations during the Precambrian, which largely dominate the database with an averaged field of 3.1 ± 2.5 Â 10 22 Am 2 . They also emphasize the importance of additional studies to understand the differences with the strong paleointensities obtained using new techniques.

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Rock magnetic studies and a comparison between microwave and Thellier palaeointensities for Canadian Precambrian dykes

Cited by 23 publications

References 26 publications

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Thermochemical remanent magnetization in Precambrian rocks: Are we sure the geomagnetic field was weak?

Palaeointensity and palaeodirectional studies of early Riphaean dyke complexes in the Lake Ladoga region (Northwestern Russia)

Absolute paleointensity at 1.27 Ga from the Mackenzie dyke swarm (Canada)

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