Palaeomagnetic, rockmagnetic and magnetic fabric results are presented for a Carboniferous (Visean to Westphalian) succession of felsic, mainly ignimbritic, volcanic and volcaniclastic rocks from the Rocky Creek Block of the northern Tamworth Belt, southern New England Orogen. Detailed thermal demagnetization of 734 samples from 64 sites has shown three groups of magnetic components with low (LT: up to 300 degrees C), intermediate (IT: 300 to 600 degrees C) and high (HT: mainly 500 to 680 degrees C) unblocking temperature ranges. Analysis and interpretation of component directions have established well-defined primary magnetization results fro 29 sites and evidence for four magnetic overprint phases.The overprints are of widespread (a,c) or localized (b,d) occurrence and are attributed to: a mid_tertiary weathering event (a: mainly LT); or to fluid movements (b,c,d) associated with either Late Cretaceous opening of the Tasman Sea (b: mainly HT); or to thrusting during the Middle Triassic main phase of the Hunter_Bowen Orogeny (c: mainly IT); or to latest Carboniferous - Early Permian formation of the Bowen-Gunnedah-Sydney Basin system (d: IT,HT). Rockmagnetic (Lowrie-Fuller test, IRM acquisition, Lowrie-test, low- and high-temperature susceptibility cycling) and palaeomagnetic analyses indicate predominance of magnetite carriers with main unblocking temperatures ranging from 400 to between 500 and 580 degrees C, and less prevalent presence of hematite carriers with unblocking temperature ranges generally up to 640 degrees C and for some sites up to 680 degrees C. Multidomain (MD-) magnetite is prevalent in the volcaniclastic rocks. Most of the volcanic rocks with well-defined primary magnetization components show evidence for single domain (SD-) magnetite with no, or only limited, presence of MD-magnetite. See paper for remainder of abstract

Interpretation of magnetic field data is complicated by the presence of remanent magnetization and benefits from palaeomagnetic and rock magnetic studies. Additionally, the planning of palaeomagnetic sampling sites and mapping of the distribution of magnetizations recovered in palaeomagnetic studies benefits from inspection of magnetic field imagery. These inter-relationships between magnetic field interpretation and palaeomagnetic studies are particularly important in Australia, where deep weathering and extensive cover by younger formations commonly lead to the magnetic field data being the most complete and detailed source of information for basement-related geological mapping and mineral exploration, and where there are few opportunities for direct palaeomagnetic sampling. For the assistance of both magnetic field interpreters and palaeomagnetists, we have developed a database tool to document and interrogate this relationship. We have started to populate the database, and are planning the facilities required to make the database available as an interactive, web-based resource. The key objectives are to facilitate interpretation of magnetic field data, increase reliability in developing deep drilling targets from magnetic field interpretation, and to better establish the spatial range of magnetizations related to igneous, metamorphic, thermal, alteration and mineralization events. Our intention is to establish a widely used, interactive, minimally-moderated resource rather than a more definitive but possibly less useful one. We envisage that the data base will grow primarily through public contributions, and will also be the forum for debate and speculation regarding Australian magnetization events. We believe that this model is appropriate for wider, global application.

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Abstracts for Workshop organised jointly by the Australian Geological Survey Organisation, CSIRO Division of Exploration and Mining, and the Research School of Earth Sciences ANU. Workshop held on May 3rd and 4th at AGSO.

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part 3<br><br>Please report any errors or omissions regarding this publication to: <a href="mailto:reference.library@ga.gov.au?subject=Document error">Geoscience Australia Library</a>

part 1<br><br>Please report any errors or omissions regarding this publication to: <a href="mailto:reference.library@ga.gov.au?subject=Document error">Geoscience Australia Library</a>