Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Special demagnetising apparatus was constructed to study the stability of several samples of basic igneous rocks from three localities in eastern Australia, particular emphasis being placed on the reliability of the directions of NRM. The direction of primary magnetisation acquired when the rocks first cooled was determined for samples at all three sites. Mesozoic dolerite from Red Hill Dyke in southern Tasmania has little or no secondary magnetisation and the mean direction of NRM is representative of the Jurassic in Tasmania. There is no evidence of systematic error due to stress or shape, and therefore the direction of NRM is a reliable estimate of the direction of the geomagnetic field at the time of intrusion. Devonian Nethercote basalt from southern New South Wales can be divided into two distinct groups, one in which the NRM is completely unaffected in either direction or intensity by demagnetisation in peak alternating fields of up to 1000 oersteds, and the other in which secondary magnetisation completely masks any primary magnetisation that may be present. Tertiary basalts from southern New South Wales show a wide range of stability. The NRM consists of primary TRM and varying proportionate amounts of secondary magnetisation, which is almost certainly viscous and which was probably acquired in the present Earth's field. The stability shown by the three rock types makes it more probable that previous palaeomagnetic results, which span a long period from Devonian to Tertiary, form a reliable record of the geomagnetic field in Australia.The general effects of alternating demagnetising fields are also discussed and a comparison made between the theoretical predictions and the data obtained.

Field parties based on Mawson in Mac.Robertson Land, Antarctica, during the period from 1957 to 1959 used seismic and gravity methods to determine ice thicknesses on traverses extending 400 miles south from Mawson as far as the southern Prince Charles Mountains. The results confirmed the continental character of this part of Antarctica and showed an average inland ice thickness of about 6000 ft and reaching a maximum of 9271 ft. The maximum seismic velocity recorded in the ice was 12,780 ft/s reached at a depth of 680 ft. A westerly, sub-glacial extension of the northern Prince Charles Mountains was discovered; these, together with the eastern and southern Prince Charles Mountains, form a rim of igneous and metamorphic rocks enclosing a large sedimentary depression on three sides. The western limit of the depression was not explored. North of the sub-glacial range is a deep valley, an expression of a major tectonic event, separating the Framnes and northern Prince Charles Mountains.

Legacy product - no abstract available

1st edition Available from GSWA or as a GA Library resource

1st edition Available from GSWA or as a GA Library resource

1st edition Available as a product from NT Geological Survey or as a resource from GA Library