The duration of the Strangways Event in central Australia: Evidence for prolonged deep crust processes

Protoliths of the Strangways Metamorphic Complex (SMC) in the Arunta Region of central Australia are dated to the 1810–1800 Ma Stafford magmatic event by SHRIMP U–Pb dating of relict igneous zircon within granulite-facies metamorphic rocks. Detrital zircons preserved in associated metasediment have a provenance age spectrum similar to that in the Lander Package sedimentary rocks which are widespread in the region. The onset and duration of granulite-facies metamorphism is recorded differentially across the SMC depending on lithology, varying mechanisms of metamorphic zircon crystallisation, and the specific P–T–t paths of individual rocks in different sectors of the complex. The earliest recorded thermal process is partial melting in the Kanandra Granulite at 1734 ± 3 Ma; zircon ages indicate that melts at Edwards Creek (1716 ± 3 Ma) and Coles Hill (1708 ± 6 Ma) formed later. Overgrowths indicate renewed metamorphic zircon precipitation in the Kanandra Granulite, probably from fluids, as late as ca. 1690 Ma. A 50-Myr continuum of metamorphic zircon ages, from ca. 1740 to 1690 Ma, is recorded in a single rock at Utnalanama and attributed to prolonged solid-state metamorphic zircon formation. The Strangways Event was not a transient and discrete process with a single age. There is evidence for prolonged residence at granulite-facies conditions, with both discrete crystallisation events, and prolonged crystallisation responses, in different locations. Termination of the high-grade metamorphism coincided with local extension indicated by the intrusion of a dolerite dyke swarm at 1689 ± 8 Ma. The Strangways Event coincides with the segment between prominent bends B0 and B1 of the Australian Palaeomagnetic Polar Wander Path, relating the thermal process to major direction changes in the movement of the north Australian plate. The geographic distribution of high-grade metamorphism within the SMC, shallow-crust emplacement of magmas in the Tennant Region, and a low-temperature Ar isotope record in the Tanami Region, is consistent with effects propagating northwards from a plate boundary south of the SMC.