Oxygen-isotope dating the Yilgarn regolith
The broad-scale distribution of δ18O values of kaolinite developed in weathering profiles in the Yilgarn Craton is interpreted as reflecting their age. As Australia progressively moved from a near-polar latitude in the Permian to lower latitude, with most translation during the past 60 Ma, the imprint of varying oxygen-isotope composition of meteoric water (rainwater and groundwater) has been preserved in weathering minerals such as clays and iron oxides. This correlation, namely δ18O values of kaolinite v. palaeo-latitude (and therefore, age), is well understood for eastern Australia. We have applied the same approach to samples widely spaced across the entire Yilgarn Craton and find that kaolinite from the majority of partially dissected weathering profiles displays Neogene δ18O ages. There are older profiles, some seemingly of pre-late Mesozoic age, and these are predominantly in the north and east of the craton. There is no evidence within the δ18O-derived age pattern for a northern older plateau and a younger southern plateau, at least in terms of their primary age of deep weathering as equated to planation. Instead, the difference between northern and southern areas is that the southern area is more dissected and displays more deeply stripped weathering profiles.
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