Multibeam sonar swath-mapping has revealed small submarine volcanic cones on the northeastern Lord Howe Rise (LHR), a submerged ribbon continent. Two such cones, aligned NNW and 120 km apart, were dredged at 23-24Degrees S. Water depth is about 1150 m nearby: the southern cone rises to 750 m and the northern to 900 m. Volcanic rocks dredged from the cones are predominantly highly altered hyaloclastites with minor basalt. The clasts are mostly intensely altered vesicular brownish glass with lesser basalt, in zeolitic, clayey, micritic or ferruginous cement. Lavas and hyaloclastites contain altered phenocrysts of olivine and plagioclase, and fresh clinopyroxene. The latter have compositions between acmite and Ti-augite, and match well clinopyroxene phenocrysts in undersaturated intraplate basanitic mafic lavas. Interbedded micrites in the volcaniclastics represent calcareous ooze that was deposited with (or later than) the volcanic pile. Foraminifera indicate that the oldest micrite is late Early Miocene (~16 Ma), and that the original ooze was deposited in cool water. Late Miocene to Pliocene micrites, presumed to be later infillings, all contain warm water forms. This evidence strongly suggests that both cones formed in pelagic depths in the Early Miocene. Ferromanganese crusts from the two cones are up to 7 cm thick and similar physically, but different chemically. The average growth rate is 3 mm/m.y.. Copper, nickel and cobalt content are relatively high in the north, but copper does not exceed 0.08 wt %, nickel 0.65% and cobalt 0.25%. The Mn:Fe ratio is high in the south (average 13.7) suggesting strong hydrothermal influence. Such small volcanic cones related to intraplate hotspot-type magmatism may occur in extensive fields like those off southern Tasmania. On Lord Howe Rise, the known small volcanic cones coincide with broad gravity highs in areas of shallow continental basement. The highs probably represent Neogene plume-related magmatism. The thick continental crust may dissipate and spread the magma widely, whereas plumes may penetrate thin oceanic crust more readily and build larger edifices. The correspondence of the ages derived from micropalaeontology and from extrapolating from nearby dated hotspot traces support such a genesis. Accordingly, gravity highs in the right setting may help predict fields of small volcanic seamounts.

This dataset contains polygon cadastral data and non-spatial attribute data for the Cocos (Keeling) Islands. Horsburgh Island and North Keeling Atoll are not included in this dataset.

Product no longer exists, please refer to GeoCat #30413 for the data

Product no longer exists, please refer to GeoCat #30413 for the data

Product no longer exists, please refer to GeoCat #30413 for the data

Product no longer exists, please refer to GeoCat #30413 for the data

This dataset contains point, line and polygon topographic and cultural data for the Cocos (Keeling) Islands. Coverage is of Home and West Islands. To view a sample of the data showing the ArcView legend click here.

We report the discovery of three submerged, living patch coral reefs covering 80 km2 in the southern Gulf of Carpentaria, Australia, an area previously thought not to contain coral bioherms. The patch reefs have their upper surfaces at a mean water depth of 28.6±0.5 m, and were consequently not detected by satellites or aerial photographs. The reefs were only recognised in our survey using multibeam swath sonar supplemented with seabed sampling and under water video. Their existence points to an earlier, late Quaternary phase of framework reef growth, probably under cooler climate and lower sea level conditions than today. Submerged reefs with surfaces between 20 and 30 m water depth occur in other regions of the Earth and existing bathymetry indicates they could be widespread in the Gulf. Many tropical regions that today do not support patch or barrier reefs for reasons similar to the modern Gulf, may have done so in the past, when environmental conditions were more suitable. Submerged reefs may provide an important refuge for corals during the next few decades when near-surface reefs are threatened by widespread coral bleaching due to warmer global sea surface temperatures.

Henson P.A., Gibson G.M., Debenham S., Kalinowski A., Barlow M. & McIntyre A. 2004. 3D structural model for the northern Leichhardt River Fault Trough and adjacent Lawn Hill Platform, Mt Isa. In: Barnicoat A.C. & Korsch R.J. eds. Predictive Mineral Discovery Cooperative Research Centre: Extended Abstracts from the June 2004 Conference. Geoscience Australia, Record 2004/9, 91-94.

Gibson G. M., Murphy B., Henson P. & Barlow M. 2004. Basement controlled basin architecture and fault geometries in the Mount Isa Western Succession. SEG 2004: Predictive Mineral Discovery Under Cover; extended abstracts. Centre for Global Metallogeny, University of Western Australia Publication, 33, p.419.