combining low temperature apatite thermochronology and cosmogenic isotope analysis in quantitative...

Combining low temperature apatite thermochronology and

cosmogenic isotope analysis in quantitative landscape

evolution studies

Roderick Brown, Hermione Cockburn, Barry Kohn, David Belton, David Fink, Andrew Gleadow

and Michael Summerfield

The University of MelbourneAustralian Nuclear Science & Technology OrganisationThe University of Edinburgh

Conceptual landscapeevolution models

Numerical landscape evolution models

van der Beek et al. (2002)

Numerical landscape evolution models

Numerical landscape evolution models

Southern Africa

Drakensberg Escarpment

Landsat ETM+ 321RGB Image

Drakensberg Escarpment, Sani Pass

Sani Top Photograph by Alastair Fleming

Apatite Fission Track Age

Estimated Palaeogeothermal Gradients

Atlantic Margin, Namibia

Gamsberg Escarpment, ASTER VNIR Image

Gamsberg Plateau, ASTER VNIR Image

Gamsberg EscarpmentPhotograph by Hermione Cockburn

Gamsberg EscarpmentPhotograph by Hermione Cockburn

Gamsberg Plateau Transect

Gamsberg Escarpment Transect

South Eastern Australia

South Eastern Australia, 300m DEM

Brown Mountain Transect

50 km

Denudation since 110 Ma

Denudation since 65 Ma

Apatite U-Th/He Ages

Paired Apatite FT & He Ages

Apatite FT & U-Th/He Ages

Age of continental rifting

ANTARES Detector Array, ANSTO, Australia

Conclusions

Measured denudation rates and chronologies for the Gamsberg, Drakensberg and Brown Mountain escarpments are incompatible with a steady, parallel retreat model

Combined thermochronologic and cosmogenic datasets are capable of quantifying passive margin escarpment retreat rates

A viable alternative model involves the establishment of an escarpment at a major inland drainage divide with moderate to low subsequent retreat rates