Palaeomagnetic results from the Palaeozoic basement of the southern Drummond Basin, central Queensland, Australia

Abstract

SUMMARY Palaeomagnetic results from the Theresa Creek Volcanics and the Middle Devonian (∼380 Ma) Retreat Batholith, located in the southern Drummond Basin, central Queensland, Australia, reveal up to three components of magnetization. Component 1 is characteristically of reversed polarity with a mean palaeopole at 64.0 ◦ S, 79.7 ◦ E( N = 7, A95 = 11.5 ◦ ), possibly reflecting a remagnetization event associated with the Middle Carboniferous Alice Springs Orogeny, is found in both units. A shallow to very shallow roughly north‐south direction, Component 2, was isolated in seven sites, predominantly within the Retreat Batholith, D = 345.8 ◦ , I =− 6.7 ◦ (α 95 = 10.1 ◦ , k = 36.8). The corresponding palaeomagnetic pole lies at 66.0 ◦ S, 290.7 ◦ E( A95 = 9.1 ◦ ). This pole is consistent with the Middle Devonian segment of Australia’s apparent polar wander path (APWP) and is thought to reflect a primary magnetization related to the emplacement and cooling of the batholith. Component 3 is found exclusively within the Theresa Creek Volcanics and is characterized by east‐west directions with moderate to steep inclinations, D = 62.4 ◦ , I = 59.5 ◦ (α 95 = 10.5 ◦ , k = 25.0). A consistent set of site level virtual geomagnetic pole (VGPs) yield a palaeopole at 4.1 ◦ N, 188.9 ◦ E( N = 9, A95 = 14.0 ◦ ). The presumed Middle Devonian age for the volcanics is at odds with this direction, with respect to the Australian Early to Middle Palaeozoic APWP, suggesting the characteristic direction found in the volcanics reflects an Ordovician or possibly Early Silurian magnetization age. A pre-Middle Devonian magnetization age for the Theresa Creek Volcanics is supported by a positive contact test between the volcanics and the hornfelsing Retreat Batholith as both units are characterized by stable magnetizations whose palaeopoles are dissimilar from each other and younger segments of Australia’s APWP.