mag
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the Murrindal, Vic, 1996 VIMP Survey (GSV3060) survey were acquired in 1995 by the VIC Government, and consisted of 15589 line-kilometres of data at 200m line spacing and 80m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Australia 85 magnetic declination (variation D) isomagnetic chart 1985.0 epoch 1:10M
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A detailed study to estimate magnetic bottom depths under north Queensland has been made using the continent-wide high-resolution airborne total magnetic intensity (TMI) data of Australia (a source dataset for the World Digital Magnetic Anomaly Map, WDMAM). Magnetisation of the lithosphere is generally assumed not significant below the Moho crust/mantle boundary due to compositional changes. However, in regions of high temperatures in the lower crust, this bottom-depth of magnetisation may be significantly above the Moho depths due to temperatures in excess of the Curie-point isotherm of the dominant magnetic mineralogy. This study uses modelling of the azimuthally averaged log of the power spectrum of TMI data to determine bottom depths. Two methods are considered and compared: slope-fitting and automated fitting of full spectral data. Several issues in successfully using these methods have been addressed, such as magnetisation type, size of data window, location of spectral peak, sensitivities of the spectral parameters and the choice of optimisation algorithm. The TMI data have an initial grid resolution of 80 m, with an appropriate IGRF removed. These data are reduced to the pole, upward continued 1 km, sub-sampled to a 1 km grid spacing and a first order polynominal trend removed prior to the spectral analysis. Calculated magnetic bottom depths are compared both with published data on the depth to Moho and with other model interpretations of the area including heat flow modelling.
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Legacy product - no abstract available