Comments on paper by K.D. Klitgord, “Sea-floor spreading: The central anomaly magnetization high”

Prévot, Michel; Lecaille, Alain

doi:10.1016/0012-821x(76)90168-0

Cited by 25 publications

(7 citation statements)

References 14 publications

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“…Because high magnetization is more concentrated in the outer fine-grained layers of the pillows, initial weathering causes an extremely rapid decrease in intensity resulting in a somewhat narrow (although broad as compared to the superimposed low of the present study) high directly over the axis (Klitgord et al, 1975;Klitgord, 1976). In contrast, Prevot and Lecaille (1976) have suggested that the central axial magnetic high is caused by variations in original rock chemistry and have shown this type of variation to be coincident with the central axial magnetic high in a portion of the FAMOUS area of the MAR. It is highly unlikely, however, that this type of variation in MORB chemistry has occurred on a world-wide scale.…”

Section: Axial Highscontrasting

confidence: 54%

“…Prevot and Lecaille (1976) have found that olivine basalts can be 2 to 3 times more magnetic than plagioclase-rich basalts due to the grain size of the magnetic minerals. However, significant rock chemistry variations would have to be very long-lived ( > 10 000 yr) in order to remain un-averaged through the thickness of the magnetized layer.…”

Section: Axial Highsmentioning

confidence: 98%

“…Variations in original rock chemistry have been called upon to explain variations in magnetic intensity in the FAMOUS area of the MAR (Prevot and Lecaille, 1976). Prevot and Lecaille (1976) have found that olivine basalts can be 2 to 3 times more magnetic than plagioclase-rich basalts due to the grain size of the magnetic minerals.…”

Section: Axial Highsmentioning

confidence: 98%

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Deep-Tow magnetics near 20°S on the East Pacific Rise: A study of short wavelength anomalies at a very fast spreading center

1990

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Abstract. Six Deep-Tow magnetic profiles across the axis of the East Pacific Rise [EPR] in two small areas between 19~ ' and 20~ were collected during the 1983 Protea 1 cruise of the R/V Melville. These near-bottom profiles are of extremely high resolution allowing the interpretation of very short wavelength features. We have inverted the magnetic field data to determine the rock magnetization distribution near the axis of this ultrafast speading center (162 mm yr t). The solutions reveal large amplitude (up to 35 A m -l) short wavelength (I-3 km) variations in magnetization. Specifically all crossings show a narrow (0.5 to 1.5 km) low in magnetization superimposed on a broader (2.5 to 4 km) high directly over the ridge axis. Four profiles in the northern area (19~ ' to 19'~33'S) also show symmetrical near-axis (within 4 km) lows which are remarkably continuous along strike. Explanations for the short-wavelength variations are discussed which fall into the following categories: (1) variations in the thickness of the magnetized layer, (2) variations in rock chemistry (e.g. alteration due to hydrothermal activity), and (3) paleofield intensity variations. None of the mechanisms discussed alone adequately explain the observed phenomena in the study area or on a world-wide scale. Further sampling and high resolution surveying will be required in order to accurately determine the relative importance of the mechanisms discussed.

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Section: Axial Highscontrasting

confidence: 54%

Section: Axial Highsmentioning

confidence: 98%

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Deep-Tow magnetics near 20°S on the East Pacific Rise: A study of short wavelength anomalies at a very fast spreading center

1990

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“…The source of the CAMH has been discussed at length in the published literature [ Klitgord , 1976; Tivey and Johnson , 1987; Gee et al , 1996, 2000; Schouten et al , 1999; Bowles et al , 2006]. While rapid alteration [ Gee and Kent , 1994] and geochemical variations [ Prevot and Lecaille , 1976] have all been discussed as possible sources of the CAMH, the most widely discussed explanation for the formation and distribution of the CAMH is the recent maximum in geomagnetic intensity and its modulation by crustal accretionary processes in young oceanic crust [ Schouten et al , 1999; Gee et al , 2000]. We investigate the relationship between the CAMH and crustal accretion in our study area by integrating our interpretation of the near‐bottom data with several other data sets including seismic data, backscatter data and multibeam bathymetry.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Central Anomaly Magnetization High documentation of crustal accretion along the East Pacific Rise (9°55′–9°25′N)

Williams¹,

Tivey

Schouten

et al. 2008

Geochem Geophys Geosyst

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[1] Near-bottom magnetic data collected along the crest of the East Pacific Rise between 9°55 0 and 9°25 0 N identify the Central Anomaly Magnetization High (CAMH), a geomagnetic anomaly modulated by crustal accretionary processes over timescales of $10 4 years. A significant decrease in CAMH amplitude is observed along-axis from north to south, with the steepest gradient between 9°42 0 and 9°36 0 N. The source of this variation is neither a systematic change in geochemistry nor varying paleointensity at the time of lava eruption. Instead, magnetic moment models show that it can be accounted for by an observed $50% decrease in seismic Layer 2A thickness along-axis. Layer 2A is assumed to be the extrusive volcanic layer, and we propose that this composes most of the magnetic source layer along the ridge axis. The 9°37 0 N overlapping spreading center (OSC) is located at the southern end of the steep CAMH gradient, and the 9°42 0 -9°36 0 N ridge segment is interpreted to be a transition zone in crustal accretion processes, with robust magmatism north of 9°42 0 N and relatively low magmatism at present south of 9°36 0 N. The 9°37 0 N OSC is also the only bathymetric discontinuity associated with a shift in the CAMH peak, which deviates $0.7 km to the west of the axial summit trough, indicating southward migration of the OSC. CAMH boundaries (defined from the maximum gradients) lie within or overlie the neovolcanic zone (NVZ) boundaries throughout our survey area, implying a systematic relationship between recent volcanic activity and CAMH source. Maximum flow distances and minimum lava dip angles are inferred on the basis of the lateral distance between the NVZ and CAMH boundaries. Lava dip angles average $14°toward the ridge axis, which agrees well with previous observations and offers a new method for estimating lava dip angles along fast spreading ridges where volcanic sequences are not exposed.

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“…1975; Klitgord 1976; Hussenoeder et al . 1996) or geochemical variations of the extrusive basalts and of the magnetic carrier (Prévot & Lecaille 1976) have been proposed to produce alternately high and low magnetized zones. Conversely, the systematic occurrence of the CAMH and of older ‘tiny wiggles’ has suggested a geomagnetic origin (Cande & Labrecque 1974; Cande & Kent 1992; Gee et al 1996), associated with geomagnetic field intensity fluctuations such as those revealed by archaeomagnetic data (McElhinny & Senanayake 1982).…”

Section: Introductionmentioning

confidence: 99%

NRM intensity of altered oceanic basalts across the MAR (21°N, 0-1.5 Ma): a record of geomagnetic palaeointensity variations?

Ravilly¹,

Horen

Perrin

et al. 2001

Geophysical Journal International

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Summary During cruise Tammar (May 1996) of R/V Nadir and submersible Nautile, 66 basaltic rock samples were collected along two long cross‐sections encompassing the oceanic crust between 0 and 1.5 Myr at the centre of the mid‐Atlantic ridge segment located at 21°N. This dense sampling provides a means to investigate natural remanent magnetization (NRM) variability with age using rock magnetic studies (high‐field and k–T experiments, palaeofield intensity determinations by the original Thellier method) together with the good geophysical and geological knowledge of this peculiar segment. NRM intensities range from 1.3 to 25.4 A m−1 but do not display any rapid exponential decay with age, as expected. Despite the scatter, they seem to present short‐wavelength variations consistent on both flanks of the two lines. Because of the relative uniformity in grain size (i.e. single domain, SD), ulvospinel content (i.e. x = 0.6) and amount of magnetic minerals in Tammar samples, the observed across‐axis NRM intensity variations may be due either to oxidation degree variations or to geomagnetic field intensity changes. Curie temperatures display no increase towards the flanks nor a clear relationship with NRM intensities, suggesting that oxidation degree is not the major process controlling the NRM variations. Half of the collected samples, either fresh or highly altered, provide good‐quality palaeointensity determinations. Depending on the alteration degree of samples, two major types of NRM/TRM diagrams are observed. For relatively fresh materials, only one line segment and the major part of NRM is used for field intensity calculations. For moderately or highly altered specimens, two line segments are observed with the first most probably corresponding to thermal demagnetization of the original remanence, and the second to the product resulting from chemical modification (i.e. inversion). Despite the difference in the amount of NRM that can be thermally demagnetized, samples of similar age but of different non‐stoichiometric degree give coincident palaeofield strengths. Palaeofield values, from 15 to 62 µT (i.e. VADM from 3.4 to 13.6 × 1022 A m2), are in good agreement with the global palaeointensity database, and display coherent short‐wavelength undulations with age, consistent (assuming a 1‐km‐wide neo‐volcanic zone and steady, symmetrical spreading) with the relative palaeointensity record deduced from sediment core analysis (Guyodo & Valet 1999). Comparison between NRM and field intensity variations with age reveals a remarkable coincidence between both signals, suggesting that the NRM intensities are more sensitive to the field intensity than to the alteration degree. These observations suggest that magnetic particles are titanomaghemites, generated during the initial magma cooling and storing a durable record of the geomagnetic field intensity. The type of remanence is either (1) a chemical remanent magnetization that closely mimics the properties of the initial NRM or (2) a thermoremanent magnetization (the maghemit...

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Comments on paper by K.D. Klitgord, “Sea-floor spreading: The central anomaly magnetization high”

Cited by 25 publications

References 14 publications

Deep-Tow magnetics near 20°S on the East Pacific Rise: A study of short wavelength anomalies at a very fast spreading center

Deep-Tow magnetics near 20°S on the East Pacific Rise: A study of short wavelength anomalies at a very fast spreading center

Central Anomaly Magnetization High documentation of crustal accretion along the East Pacific Rise (9°55′–9°25′N)

NRM intensity of altered oceanic basalts across the MAR (21°N, 0-1.5 Ma): a record of geomagnetic palaeointensity variations?

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