Paleogeothermal gradients in Australia

key to 4-D lithosphere mapping

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    Empirical paleogeotherrns constructed from geothermobarometry of deep-seated xenoliths and garnet ± chromite concentrates from basalts, lamproites and kimberlites around Australia reveal regions of different paleogeothermal signatures. Differences between the tectonically young eastern areas and the cratonic western part of the Australian continent correspond to those shown on a large scale by long-wavelength magnetic data. which integrate the total magnetic signature from the lithospheric column where temperatures are below the Curie Point. Surface heat-flow measurements may not reflect deeper geothermal gradients and model-dependent extrapolations to lower crust and mantle depths must be used cautiously. In eastern Australia, where xenolith data are available (coinciding with the basaltic provinces), there is a remarkably consistent geotherm, which is independent of the age of the basaltic volcanism. This inflected (advective) geotherm is higher than conventional ocean basin geotherms and reflects thermal perturbation associated with volcanic episodes. It records the thermal state at the time of the particular volcanic activity, and decays towards a conductive geotherm with a relaxation time of 40-50 m.y. Data from the eastern craton margin (in South Australia and western New South Wales) indicate significant changes in the thermal state through time, while Archaean and Proterozoic areas in Western Australia reflect typically low geotherms. Knowledge of a robust geotherm for a specific lithospheric column can be used to construct a realistic distribution of rock types with depth. This lithospheric column provides constraints for the geologically meaningful interpretation of geophysical data and for placing geochemical and mantle process information in a spatial context.

    Original languageEnglish
    Pages (from-to)63-72
    Number of pages10
    JournalAGSO Journal of Australian Geology and Geophysics
    Issue number1
    Publication statusPublished - 1997

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