Rock magnetism and geophysical interpretation of the Black Hill Norite, South Australia

Rajagopalan, Shanti; Schmidt, P. W.; Clark, David

doi:10.1071/eg993209

Cited by 16 publications

(13 citation statements)

References 5 publications

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“…The directions of Phillips (2005) do not agree closely with others and appear to be too steep and northward. Rajagopalan et al (1993) suggest that the resultant magnetisation direction may be different for the CMP compared with the CNP and BHN, and our results support this too. Foss and McKenzie (2011) suggest the presence of a much higher Q, than found in paleomagnetic results, to reconcile their positive inclination directions for the CNP and BHN.…”

Section: Case Study: Black Hill Noritesupporting

confidence: 81%

“…The pattern of the anomalies in the area show an obvious negative to the north/north-east, which is opposite to the pattern observed for an induced anomaly in a local field of declination 8.3° and inclination -66.9°. This suggests a strong natural remanent magnetisation (NRM) which has been studied by many authors (e.g., Pratt et al 2012;Foss and McKenzie, 2011;Philips, 2005;Rajagopalan et al 1993), to constrain apparent polar wonder paths (APWP), for example .…”

Section: Case Study: Black Hill Noritementioning

confidence: 99%

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Recovery of Resultant Magnetization Vectors from Magnetic Anomalies

Hillan

Foss²,

Schmidt³

2013

ASEG Extended Abstracts

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Section: Case Study: Black Hill Noritesupporting

confidence: 81%

Section: Case Study: Black Hill Noritementioning

confidence: 99%

Recovery of Resultant Magnetization Vectors from Magnetic Anomalies

Hillan

Foss²,

Schmidt³

2013

ASEG Extended Abstracts

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“…• declination (Rajagopalan et al, 1993). Schmidt and Clark's (1997) Helbig analysis resulted in a direction within 22…”

Section: Example-black Hill Norite South Australiamentioning

confidence: 99%

Can we estimate total magnetization directions from aeromagnetic data using Helbig’s integrals?

Phillips

2005

Earth Planet Sp

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An algorithm that implements Helbig's (1963) integrals for estimating the vector components (m x , m y , m z ) of the magnetic dipole moment from the first order moments of the vector magnetic field components ( X , Y , Z ) is tested on real and synthetic data. After a grid of total field aeromagnetic data is converted to vector component grids using Fourier filtering, Helbig's infinite integrals are evaluated as finite integrals in small moving windows using a quadrature algorithm based on the 2-D trapezoidal rule. Prior to integration, best-fit planar surfaces must be removed from the component data within the data windows in order to make the results independent of the coordinate system origin. Two different approaches are described for interpreting the results of the integration. In the "direct" method, results from pairs of different window sizes are compared to identify grid nodes where the angular difference between solutions is small. These solutions provide valid estimates of total magnetization directions for compact sources such as spheres or dipoles, but not for horizontally elongated or 2-D sources. In the "indirect" method, which is more forgiving of source geometry, results of the quadrature analysis are scanned for solutions that are parallel to a specified total magnetization direction.

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“…The Black Hill Complex has not undergone later metamorphism and is only locally deformed. It is comprised of the Central (CNP), Cambrai (CMP), and the Black Hill (BHN) plutons, with lithologies from peridotites and troctolites to olivine gabbros and norites (Rajagopalan et al, 1993(Rajagopalan et al, , 1995. The axes of the magnetic anomalies associated with the plutons have varying azimuths, which could reflect different bulk magnetization directions.…”

Section: Geology and Geophysics Of Study Areamentioning

confidence: 99%

Microscale Magnetic Inversion of Remanent Magnetization Mineral Sources From the Black Hill Norite, South Australia

Lee

McEnroe

Pastore

et al. 2023

Geochem Geophys Geosyst

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Inverse modeling of regional‐scale aeromagnetic data is complicated due to the non‐uniqueness principle and interference of anomalies, especially with increased source‐sensor separation. This is why in situ data and constraints are required to create a reliable inversion model. However, these complications even exist when analysis is conducted at a microscale level with the magnetic mapping of a thin section. Here, we assess the impact of magnetic minerals on adjacent non‐magnetic minerals, specifically magnetite and ilmenite, respectively. The sample is from the Black Hill Norite, South Australia, which has been the focus of both paleomagnetic and geophysical modeling. Here, we conduct inverse modeling of all opaque minerals in the thin section. During post‐modeling, the opaque minerals are identified as magnetite or ilmenite using backscatter electron imaging for quantifiable classification. The results show that ilmenite will exhibit a magnetic intensity and direction when magnetite lamellae are present or when it is adjacent to a magnetite grain from which the ilmenite grain was oxy‐exsolved. We also assess the scale of interpretation by modeling the grains both as a singular volume (frustum) and as a series of smaller volumes (tabular arrays). It is shown that although the magnetic field generated by the frustums and the tabular arrays are quantitatively similar to the original measured magnetic field from the scanning magnetic microscope, the tabular array produces a closer fit to the modeled anomaly.

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Rock magnetism and geophysical interpretation of the Black Hill Norite, South Australia

Cited by 16 publications

References 5 publications

Recovery of Resultant Magnetization Vectors from Magnetic Anomalies

Recovery of Resultant Magnetization Vectors from Magnetic Anomalies

Can we estimate total magnetization directions from aeromagnetic data using Helbig’s integrals?

Microscale Magnetic Inversion of Remanent Magnetization Mineral Sources From the Black Hill Norite, South Australia

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