The tectonic link to southwest Australian paleovalley evolution

[摘要] Traces of major paleovalley networks in the southwestern Australia Yilgarn Craton are potentially the oldest geomorphological features within the landscape today. The paleovalleys are visible as a string of large saline lakes (e.g. Lake Grace) that cut across geological provinces within the craton, and abruptly cut off at the Yilgarn Craton’s south boundary where they cannot be traced into the Albany Fraser Orogen. A multi‐resolution valley bottom flatness (MrVBF) map of southwestern Australia highlights distinguishing features of the dendritic to sub‐dendritic paleovalley network. Landscape features change over time as a result of changes in climate, sea level, geological and tectonic processes. Australia is currently tectonically stable and the climate in southwestern Australia is arid to semi‐arid. However, the paleovalleys in southwestern Australia do not resemble typical geomorphological features expected from an arid climate. Some of the paleovalley morphology do not conform with expected morphology of large rivers. We obtained magnetic data to a 30 m resolution which shows major geological structures of underlying Precambrian rocks not visible at the surface, due to extensive and deep cover. We found some correlations between unusual paleovalley features on the MrVBF map when compared with several linear magnetic anomalies that have likely shaped the paleovalley morphology visible today. We also conducted a literature review to determine potential links to paleovalley morphology from initial valley incision until current taking into consideration changes in plate dynamics and climate for the last 300 Ma. Glacially‐related diamictite deposits with striated clasts are in the base of some paleovalleys in the eastern Yilgarn Craton, and similar diamictite deposits are in basins that were active during the Gondwanan Permo‐Carboniferous glaciation and surround the Yilgarn and Pilbara cratons. Original paleodrainage directions from some valleys in the western Yilgarn Craton suggest drainage towards the north from Antarctica indicating that the large paleovalleys once extended southward over the Albany Fraser Orogen. There is ~4.5 km thick sediment deposition into the Bremer Sub‐basin during the basin’s initial rifting and opening phase during the Late Jurassic which indicates there was a large amount of weathering and erosion from the margins of the basin. The remnants of large paleovalleys in the Albany Fraser Orogen may have been removed when Bremer Sub‐basin opened. The southern margin of the Yilgarn Craton would have been uplifted as part of rift development between Australia and Antarctica. Therefore, the paleovalleys within the Yilgarn Craton may have continued to drain northward. Recent relaxing and subsidence of the southern margin of Australia has led to the flattening of the Yilgarn Craton, where some parts of the Yilgarn craton drain internally into a string of large playa lakes.

[发布机构] CSIRO

[效力级别] Quaternary Environments [学科分类] 地球科学(综合)