Improvements in magnetic depth estimation: application of depth and width extent nomographs to standard depth estimation techniques

Flanagan, Guy; Bain, John E.

doi:10.3997/1365-2397.2013028

Cited by 8 publications

(4 citation statements)

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“…The former assumption may have limited applicability in relation to deeper basement sources as may be judged from the example cross-sectional model of Figure 2b. Flanagan and Bain (2013) also note depth errors as high as 40% when the assumption of infinite depth extent is made. When considering assessments of mid-to deep-crustal sources, the practical depth extent of potential sources is also restricted by the (assumed) limit of 30 km.…”

Section: Processing Techniquesmentioning

confidence: 91%

The deep crustal magnetic structure of Britain

Beamish

Kimbell

Pharaoh

2016

Proceedings of the Geologists' Association

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The deep crustal magnetic structure of Britain has not previously been described in a uniform manner. We provide a new assessment of the deep crustal magnetic bodies responsible for the long wavelength magnetic features. The study area contains deep crustal relics of the destruction of early Palaeozoic oceanic lithosphere along the Thor-Tornquist Suture and primarily the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Spectral decomposition is applied to a merged onshore and offshore magnetic anomaly data set. Thirty idealised basement bodies are compared with a representation of the subsurface obtained by a coarse 3D inversion of the data. The central area separating Laurentia and Avalonia, is largely characterised by an absence of high susceptibilities throughout the whole crustal volume. We find that the idealised basement bodies are largely consistent with relatively high susceptibility zones at depths in excess of 10 km. The zones of higher relative susceptibility are referenced to the tectonic-terrane framework of the area and possible geological explanations for the contrasts are reviewed. In the north, the Laurentian terranes are diverse, comprising crust first created in the Archaean (Hebridean Terrane), Palaeoproterozoic (Rhinns Terrane), Mesoproterozoic? (Midland Valley Terrane), Neoproterozoic (sub-Southern Upland rocks) and Ordovician. Magnetic anomalies further record the assembly of the Gondwanan (Eastern Avalonian) part of the country through Neoproterozoic and Ordovician (Tornquist) arc magmatism and accretion. The convergence zones between Laurentia, Avalonia and Baltica have all left a magnetic imprint, as has Variscan convergence to the south.

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Section: Processing Techniquesmentioning

confidence: 91%

The deep crustal magnetic structure of Britain

Beamish

Kimbell

Pharaoh

2016

Proceedings of the Geologists' Association

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“…Many methods of estimating the depth to basement from magnetic data rely on the simple assumption that the geometry of the causative source has an infinite depth extent (Flanagan and Bain, 2013). This assumption ignores the fact that the thickness of the magnetized layer will be depth limited by either the crust-mantle interface (the Moho) or the Curie temperature of the magnetic minerals, whichever depth is shallower (Wasilewski et al, 1979;Wasilewski and Mayhew, 1992;Lee et al, 2010;Salem et al, 2010;Flanagan and Bain, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…This assumption ignores the fact that the thickness of the magnetized layer will be depth limited by either the crust-mantle interface (the Moho) or the Curie temperature of the magnetic minerals, whichever depth is shallower (Wasilewski et al, 1979;Wasilewski and Mayhew, 1992;Lee et al, 2010;Salem et al, 2010;Flanagan and Bain, 2013). Within continental areas, the Moho and Curie isotherm are likely to be at great depth and hence the effect on depth-to-source estimates is small.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of depth to top of magnetic sources using the local-wavenumber approach in an area of shallow Moho and Curie depth — The Red Sea

et al. 2014

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The local-wavenumber method estimates the depth to a magnetic source based on the spectral content of a single anomaly assuming that the base of the magnetic body is at infinite depth. However, the "infinite-depth" assumption can lead to significant underestimation of the depth to the top of magnetic bodies, especially in areas where the depth to the bottom of the magnetic layer is not large compared to the depth to the top, as would occur in high heat-flow regions and thinned continental margins. Such underestimation of depths has been demonstrated in model studies and using real data with seismic and well control. We evaluated a modification to the local-wavenumber approach to estimate the depth to the top of magnetic sources assuming that the depth to the bottom of the magnetic sources is controlled by the Curie temperature or crustal thickness. We applied this new method to a simple model of a continental margin and to magnetic survey data over the central Red Sea where the Curie isotherm is shallow. The effective structural index of this finite depth extent model is found to increase continuously from the continent to the ocean as the depth to the magnetic basement increases and the depth to the bottom of the magnetic layer decreases. We have also discovered in this study that the local-wavenumber maxima correlate well with major seafloor spreading magnetic reversal epochs in the central Red Sea segment.

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Quantitative interpretation of magnetic anomalies from bodies approximated by thick bed models in complex environments

Eppelbaum

2015

Environ Earth Sci

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Improvements in magnetic depth estimation: application of depth and width extent nomographs to standard depth estimation techniques

Cited by 8 publications

References 0 publications

The deep crustal magnetic structure of Britain

The deep crustal magnetic structure of Britain

Estimation of depth to top of magnetic sources using the local-wavenumber approach in an area of shallow Moho and Curie depth — The Red Sea

Quantitative interpretation of magnetic anomalies from bodies approximated by thick bed models in complex environments

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