Tectonic geography of the lower Roper Group, McArthur Basin, Northern Australia using detrital geochronology and shale geochemistry

Abstract

The informally termed greater McArthur Basin, covers a wide extent of Northern Australia. The basin spans the Mesoproterozoic and preserves within its sedimentology, evidence for the tumultuous events that surround the basin during its formation. LA-ICP-MS detrital zircon U–Pb, Lu–Hf and REE data presented here provide new constraints on the lower Roper Group and reveal temporal and provenance variations that illustrate the evolution of the basin. Here we attempt to elucidate the rifting of Laurentia from the Australian cratons and identify a provenance change as a consequence.

The maximum depositional age of the Munyi Member of the upper Roper Group has been constrained to 1530 ± 45 Ma whereas grains of the Hodgson Sandstone, Jalboi Formation and Arnold Sandstone of the lower Roper Group suggest maximum depositional ages of 1591±90 Ma, 1580±66 Ma and 1633±89 Ma, respectively. The Crawford Sandstone preserved an age of 1766 ± 82 Ma. As well as using U–Pb in zircon, we also look at Rb–Sr isotopes within glauconite to further constrain the depositional history of the Crawford sandstone. These data yielded an age of 1284 ± 51 Ma, too young to reflect a depositional age, and we therefore suggest it instead reflects a resetting event; the intrusion of the Derim Derim dolerite (ca. 1313 Ma).

Age variations up-stratigraphy suggest a subtle change from older, Paleoproterozoic sources to additional input from younger sources, as we transition from the lower Roper into the Upper Roper Group. Older formations record age peaks that are consistent with rocks of the Tanami Region and Aileron Province. Overlying Crawford and Jalboi Formations show derivation from a ca. 1700 Ma source, with a minor 2500 Ma peak, both of which are consistent with southern sources, specifically the Aileron and Arunta Region. The Arnold and Hodgson Sandstones both have detritus with dominant ca. 1780 Ma age peaks, consistent with southern sources.

We suggest that the provenance variation initially records the exhumation and exposure of the Tanami Region as a result of intracratonic rifting and widespread 1.5–1.4 Ga magmatism. The increase in abundance of1860–1650 Ma detritus suggests uplift of the Arunta region.