The principal objective of the remanent anomalies data base project is to promote the detection and correct treatment of remanent magnetization effects in the interpretation of magnetic field data. A key concern with the current status of magnetic field interpretation is that remanent magnetization effects often go undetected, or even if recognised may be ignored. The consequences of this are twofold – that spatial parameters of models derived from the magnetic field data are incorrect, and that information about geological processes related to the magnetization goes unnoticed. The objective of this project is to achieve a fundamental change in magnetic field interpretation from the present situation in which the existence of remanent magnetization is generally ignored, to one which standardly and correctly addresses its effects. We aim to achieve this objective with a threefold approach – to collect and disseminate information about the distribution of magnetizations recovered from Australian rocks, to develop and distribute tools for recovery of magnetization direction from interpretation of magnetic field data, and to provide education about the acquisition of magnetization by rocks, relationships between magnetization and its magnetic field expression, and about methods to correctly include remanent magnetization effects in magnetic field interpretation.
Senior Research Scientist, CESRE
Research Projects Officer, CESRE
Postdoctoral Fellow, CESRE
The remanent anomalies database project is a collaborative undertaking, primarily with Geoscience Australia which is the custodian of most of Australia’s regional aeromagnetic datasets and provides that primary data through GADDS (geophysical anomaly data delivery system). This project also includes collaboration with many State Geological Surveys which are responsible for regional geological interpretation and mineral prospectivity mapping.
The remanent magnetic anomalies database is a spatial database that contains information about anomalies recognised as being in large part due to a remanent magnetization directed other than in the present geomagnetic field direction. The database optionally includes a geo-located image of the anomaly for display and comparison with other spatial information in a GIS, and optional provision of the magnetic field data itself. Ideally the proposition that the anomaly is due at least in part to remanent magnetization is supported by investigation of the magnetization direction by suitable analytic methods, and/or by inverse modelling to recover estimates of both the spatial model and its accompanying magnetization. This supporting information, if available, can be recorded in linked databases of magnetization analyses and models. Magnetizations and rock magnetic properties critical for constraining magnetization directions and assigning those directions to geological events, are recorded in associated databases of rock magnetic and palaeomagnetic studies. In general there may be no direct relationship between a magnetic anomaly and any rock magnetic or palaeomagnetic study (particularly so if the source of the magnetic anomaly is buried), but nevertheless these direct measurements should be referenced wherever they are available. The palaeomagnetic database is developed from a previous global database, the Australian component of which has been updated as part of this project. Duplication of information in different databases is to be avoided wherever possible, and it is our intention to replace these ancillary palaeomagnetic and rock magnetic databases with live links to more fundamental databases whenever these become available – in particular, replacing the rock magnetic database with links to a new national magnetic properties database currently under development by Geoscience Australia. The remanent anomalies database is a joint project between CSIRO and Geoscience Australia, and is being developed in collaboration with various state geological surveys. We intend that this will be a lightly moderated database to which interested parties will be able to contribute, so that the future population of the database will become a community exercise. The database can be accessed through the Auscope portal – a utility that will be available in the long term, and which is already a resource for access and interrogation of diverse forms of spatial earth-science data. Figure 1 shows the anomalies and paleomagnetic survey sites currently available in the database.
Magnetic map of Australia
(Click to access anomaly database)