Dipole/quadrupole family modeling of paleosecular variation

McFadden, P. L.; Merrill, Ronald T.; McElhinny, M. W.

doi:10.1029/jb093ib10p11583

Cited by 210 publications

(222 citation statements)

References 21 publications

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“…All new VGPs obtained on this study yield lesser colatitudes (maximum value is 28.3º) than generally adopted 45º cut-off angle (Johnson et al, 2008). We obtained S F =16.0 with S U =25.5 and S L =8.1 (upper and lower limits respectively) which reasonably agree to the model G of McFadden et al (1988McFadden et al ( , 1991 fit to the McElhinny and McFadden (1997) and Johnson et al (2008) databases for the last 5 Myr (Fig. 8b and 9).…”

Section: Resultssupporting

confidence: 73%

“…A simple method to estimate the PSV consists in observing of the angular standard deviation (ASD) of virtual geomagnetic poles (VGPs) for a given locality. Several combinations of dipole and non-dipole components predict the ASD characteristic of PSV with latitude (McFadden et al, 1988(McFadden et al, , 1991Lawrence et al, 2006;Johnson et al 2008)). Johnson et al (2008) reported a detailed synthesis of a new generation of paleomagnetic data compilations.…”

Section: Introductionmentioning

confidence: 99%

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Paleomagnetic and rock-magnetic survey of Brunhes lava flows from Tancitaro volcano, Mexico

Peña

Goguitchaichvili

Monroy

et al. 2009

GeofInt

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ResumenEste estudio presenta los resultados paleomagnéticos del Volcán Tancitaro, (perteneciente al Campo Volcánico Michoacán Guanajuato), en el oeste de México, como una contribución a la base de datos de promediados en el tiempo del campo global. Se realizó el estudio paleomagnético y de magnetismo de roca en once flujos de lava. Se colectaron 120 núcleos orientados en el volcán Tancitaro y sus áreas aledañas. Todos los sitios fueron previamente fechados por 40 Ar (Ownby et al., 2007,) y van desde 793 ka hasta el presente. Se realizaron experimentos de magnetismo de roca, curvas de susceptibilidad e histéresis magnética y en la mayoría de los casos la remanencia magnética fue por la presencia de titanomagnetita pobre en Titanio con estructura magnética de pseudodominio simple. Ocho de los once flujos de lava dieron polaridad normal, mientras que los tres restantes produjeron paleodirecciones inconsistentes y no se tomaron en cuenta para el análisis y se debió probablemente por efectos de rayos. La paleodirección principal obtenida de los ocho flujos es Inc=39.5º, Dec= 356.4º, k=29, α 95 =9.1º lo cual corresponde a la posición del polo con Plat=84.4º, Plong=219.9º, K=33 y α 95 =8.5º. Esta dirección es prácticamente consistente con la paleodirección esperada del Plio Cuaternario, derivada del polo de referencia para el Craton Norteamericano. La variación paleosecular coincide con otros estudios de la misma latitud y con modelos estadísticos recientes. La inclinación media cae dentro de la incertidumbre del Eje Dipolar Geomagnético más 5% de contribuciones cuadrupolares. AbstractThis study presents paleomagnetic results from Tancitaro volcanism in the Michoacan Guanajuato Volcanic Field, western Mexico, as a contribution to the time averaged field global database. Detailed paleomagnetic and rock-magnetic studies were carried out on eleven independent lava flows; 120 oriented, standard paleomagnetic cores were collected from Tancitaro volcano and surrounding areas. All sites were dated by means of 40 Ar-39 Ar (Ownby et al., 2007) as originating from 793 ka to present. Rock-magnetic experiments included continuous susceptibility and hysteresis measurements. Remanence is carried mostly by Ti-poor titanomagnetite of pseudosingle-domain magnetic structure. Eight out of eleven flows yield normal magnetic polarities while three sites yielded inconsistent paleodirections most probably due to lightning. Mean paleodirection from eight flows is Inc=39.5°, Dec=356.4°, k=29, α 95 =9.1° which corresponds to a pole position with Plat=84.4°, Plong=219.9°, K=33 and A 95 =8.5°, practically undistinguishable from expected Plio-Quaternary paleodirections, for the North American Craton. Paleosecular variation is compatible with other studies at the same latitude bands and with recent statistical models. The mean inclination falls within the uncertainties of the Geomagnetic Axial Dipole plus 5% quadrupolar contributions.

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Section: Resultssupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Paleomagnetic and rock-magnetic survey of Brunhes lava flows from Tancitaro volcano, Mexico

Peña

Goguitchaichvili

Monroy

et al. 2009

GeofInt

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“…Our model for the Gaussian coefficients is also different in concept from that proposed by MCFADDEN et al (1988), who introduced the dipole and quadrupole families of spherical harmonic coefficients. The dipole family includes all coefficients in which the degree and order differ by odd numbers, while their quadrupole family includes those whose degree and order differ by an even number.…”

Section: Discussionmentioning

confidence: 99%

Rates of change of the Earth's magnetic field measured by recent analyses.

Harrison

Huang

1990

J. geomagn. geoelec

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The availability of accurate representations of the Earth's magnetic field for the past 25 years allows us to study the typical rates of change of the field as a function of the degree of the spherical harmonic. It is shown that there is a general increase in the relative rate of change as the degree of harmonic is increased. The analysis was only carried out to degree eight harmonics, because knowledge of the rate of change of the higher degrees is poor. If the projected rate of change continues in the same manner for higher degrees, then it is predicted that harmonics of, say, degree 14 will change at a rate of about 6% per year. This will mean that it should be easy to determine whether harmonics higher than degree fourteen originate in the core or whether they are caused by crustal magnetization. Although westward drift of the field does not necessarily tell us about motions of the core fluid at the core mantle boundary, it is probably true that these motions depend on the same parameters as those used to determine the westward drift. Since the westward drift depends on the longitudinal gradient of the component of field under consideration, it generally depends more on the higher orders of harmonic within each degree than on the lower orders, all other things being equal. In fact, not all other things are equal, because it is shown that in general the power in the higher orders of harmonic is less than the power in the lower orders. Another important factor in determining longitudinal motions is that it is the field at the core mantle boundary which is important, not the field at the Earth's surface. This results in the higher degrees being relatively more important than at the surface of the Earth. But because of the longitudinal differentiation, it turns out that in order to determine a major portion of the longitudinal drift it is necessary to have information about harmonics up to about degree 20. Therefore, with knowledge only of degrees eight or less, we really know rather little about longitudinal motions. Evidence for secular acceleration was found. Not surprisingly, the average rate of secular acceleration

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“…More recently, McFadden et al (1988) proposed Model G in which harmonics belonging to the dipole family (i.e., ge or h7 with £ + m = odd) and quadrupole family (t + m = even) are decoupled in the generation of the 616 M. KoNo geodynamo, and, as a consequence, the angular variance of the VGPs can be written as the sum S2 = A2A2 + B2,…”

Section: Introductionmentioning

confidence: 99%

“…For instance, the form of Eq. (2) was deduced from the analysis of a field model for 1965 (McFadden et al, 1988), but recently it was pointed out (Hulot and Gallet, 1996) that this cannot match even the field of recent past (e.g. 1800), and so justification for using Eq.…”

Section: Introductionmentioning

confidence: 99%

Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients.

Kono¹

1997

J. geomagn. geoelec

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Expressions are derived for the magnetic field directions produced by randomly varying Gauss coefficients. This approach was pioneered by Constable and Parker (1988), and followed by Kono and Tanaka (1995) and Kono and Hiroi (1996). The present treatment is a sequel to the latter two. The basic assumption is that the magnitude of the axial dipole component is much larger than all the other terms: equatorial dipoles or nondipole components. It is also assumed that, in a sufficiently long time interval, Gauss coefficients, g' and h7 , behave as independent random variables that have the first and second moments defined. General expressions are obtained for the field directions (inclination I and declination D). Paleosecular variation (PSV) of field directions is formulated as latitude dependences of statistical parameters (the means and variances) of inclination and declination.It is possible to derive a family of PSV models by specifying the statistical nature of individual Gauss coefficients, i.e., assigning means and variances to them. In this paper, we describe a "homogeneous background model" (HBM), which consists of a large axial dipole component (g°) and other harmonics that have zero mean and variances decreasing exponentially with the degree of the harmonic. This model is too homogeneous to reproduce observed latitudinal variation of secular variation, but is quite useful to identify the harmonics that have effect that is larger than produced by the HBM. Comparison with paleomagnetic data obtained from volcanic rocks of 0-5 Ma ages (Quidelleur et al., 1994) shows that it is necessary that the mean of ga must be about 5% of the mean of go, and that g2 (or h2) should have about three to four times as large an effect as suggested by the HBM. The former conclusion is consistent with the result of Constable and Parker (1988), while the latter conclusion substantiates the similar conclusion obtained by Kono and Tanaka (1995) by the analysis of the scatter of the virtual geomagnetic poles (VGPs).

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Dipole/quadrupole family modeling of paleosecular variation

Cited by 210 publications

References 21 publications

Paleomagnetic and rock-magnetic survey of Brunhes lava flows from Tancitaro volcano, Mexico

Paleomagnetic and rock-magnetic survey of Brunhes lava flows from Tancitaro volcano, Mexico

Rates of change of the Earth's magnetic field measured by recent analyses.

Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients.

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