A magnetic study of the serpentinization process at Burro Mountain, California

Lienert, Barry R.; Wasilewski, P. J.

doi:10.1016/0012-821x(79)90095-5

Cited by 31 publications

(18 citation statements)

References 21 publications

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“…This result confirms previous magnetic studies of serpentinized peridotites, which showed no correlation between NRM and Is (Lienert and Wasilewski, 1979;Nazarova and Gorodnitsky, 1990). On the other hand, the large content of magnetite in our samples (> 1%) (Krammer, 1990) should create intensive magnetostatic interaction between ferromagnetic grains.…”

Section: The Nrm Value and The Degree Of Serpentinizationsupporting

confidence: 94%

Serpentinized peridotites as a possible source for oceanic magnetic anomalies

Nazarova

1994

Mar Geophys Res

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Abstract. New data acquired on the slow spreading MidAtlantic Ridge during several Legs of the Ocean Drilling Programme (ODP) give evidence that, in many places, serpentinized peridotites constitute the upper oceanic crust in the vicinity of rift valley. This discovery contradicts the classical view on the formation of oceanic crust at the ridge axis, which postulates that only basalts constitute the upper oceanic crust.The magnetic properties of 5 7 samples of such serpentinized peridotites, collected at five ODP sites in the Atlantic Ocean, have been analyzed in order to examine the origin and evolution of their natural remanent magnetization (NRM). All samples are characterized by NRM (average value about 3.5 A/M) comparable with NRM of altered oceanic basalts. Average Q-ratio (NRM to induced magnetization ratio) was about 2.The results reported here give evidence that serpentinization is a complex and irregular process. The local concentration of magnetite is determined by magnetostatic interaction between magnetic grains rather than volume concentration of magnetite. This local concentration, which represents the degree of serpentinization, affects the NRM value. The domain structure of magnetite grains developed during serpentinization is controlled by the degree of serpentinization.Experimental data show that original remanence of serpentinites exposed in the upper oceanic crust may contribute to the oceanic magnetic anomalies. In particular, serpentinites with magnetite of pseudodomain size represent a very probable source for magnetic anomalies. It is however unlikely that such ODP serpentinites systematically contribute to the oceanic magnetic lineations.

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Section: The Nrm Value and The Degree Of Serpentinizationsupporting

confidence: 94%

Serpentinized peridotites as a possible source for oceanic magnetic anomalies

Nazarova

1994

Mar Geophys Res

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“…The magnetic particles are in the PSD-MD range, so the remanence is controlled predominantly by the concentration of magnetite. In contrast, no apparent relationship exists between NRM and M s (Figure 9(f)), which is consistent with other research (Lienert et al, 1979;Nazarova, 1994). This indicates that ongoing serpentinization gives rise to the development of maghemite and hematite.…”

Section: Figuresupporting

confidence: 90%

Mechanism of magnetic property changes of serpentinites from ODP Holes 897D and 1070A

Liu

ZhaoXia

Duan

2015

Sci. China Earth Sci.

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Serpentinites have great implications for the oceanic crust, subduction zones, island arc magmatism activity, and the formation of nickel ore deposits. To further determine the mechanism of magnetic property changes of serpentinites, samples from ODP Holes 897D and 1070A were investigated by integrating both magnetic and non-magnetic methods. Detailed rock magnetic results demonstrate that magnetite prevails in the entire serpentinite section, while maghemite is present in the upper and altered parts. The concentration of Fe in the fresh peridotite is inhomogeneous; nonetheless, the magnetic properties are generally determined by the serpentinization process. The formation and state of the magnetite depend on the fracture conditioning and fluid activities which are controlled by the serpentinization process. By comparing these two holes, we found that the production of magnetite is consistent with the serpentinization process; serpentinization is a multi-stage process which involves early high-temperature serpentinization and later low-temperature oxidation. As the serpentinization continues, the fine magnetic particles become coarser, combined with the formation of new SP particles, and the later low-temperature oxidation leads to the maghemitization of the magnetites. The duration of oxidation also contributes to the differences of remanent magnetization between these two holes. These results greatly improve our understanding of the magnetic enhancement during the serpentinization process, and provide constraints on the interpretation of the paleomagnetic and aeromagnetic anomalies in this area. magnetite, maghemite, serpentinization, ODP Holes 897D, 1070A Citation: Su K, Liu Q S, Jiang Z X, et al. 2015. Mechanism of magnetic property changes of serpentinites from ODP

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“…The variation of NRM intensity is related to the degree of serpentinization (Moody 1976;Lienert & Wasilievski 1979). The magnetic susceptibility (measured with Molspin equipment) has a mean value of 0.8-1 • 10 -2 SI.…”

Section: Magnetic Mineralogymentioning

confidence: 99%

New constraints on the bending of the Gibraltar Arc from palaeomagnetism of the Ronda peridotites (Betic Cordilleras, Spain)

Feinberg

Saddiqi

Michard

1996

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The study of 210 cores (15 sites) from the Ronda peridotites (Sierra Bermeja and Sierra Alpujata, Alpujarride nappe complex, Betic zone), and from the granites intruding these peridotites and their country rocks shows the occurrence of two stable antipodal directions of magnetization ( D = 46°, I = 47°, α 95 = 6.6). The reverse polarity high-temperature component, only found in peridotites, is carried by hematite, while the normal polarity intermediate-temperature component is carried by magnetite in the peridotites, and by sulphides in the granites. Negative fold tests point to a late magnetization. The acquisition of remanence is attributed to the post-metamorphic cooling of the Alpujarrides, bracketed between 23 and 18 Ma by isotopic and stratigraphic data. Structural data and the homogeneity of the in situ mean palaeomagnetic directions preclude significant tilting of the massifs after their magnetization. The observed declination is interpreted as the result of a post-metamorphic, 46° ± 8° clockwise rotation of the Ronda massifs around a vertical axis. These results are compared with those from the Beni Bousera peridotites (southern branch of the Gibraltar Arc). In the latter massif, a c. 74° ± 11° anticlockwise rotation has been documented, and dated from the time of cooling of the peridotite unit. Therefore the opposite rotations of the Spanish and Moroccan massifs occurred rapidly during Early Miocene. A tectonic model involving extensional collapse with preferential displacement towards the Atlantic free-margin is favoured.

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A magnetic study of the serpentinization process at Burro Mountain, California

Cited by 31 publications

References 21 publications

Serpentinized peridotites as a possible source for oceanic magnetic anomalies

Serpentinized peridotites as a possible source for oceanic magnetic anomalies

Mechanism of magnetic property changes of serpentinites from ODP Holes 897D and 1070A

New constraints on the bending of the Gibraltar Arc from palaeomagnetism of the Ronda peridotites (Betic Cordilleras, Spain)

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