Proterozoic mafic–ultramafic intrusions in the Arunta Region, central Australia: Part 2: Event chronology and regional correlations

Abstract

The Arunta Region in central Australia records multiple Proterozoic crustal processes over a 1500-million-year period. The timing of mafic–ultramafic magmatism in this evolution is constrained by SHRIMP U–Pb dating of zircon, which is a primary phase in mafic–ultramafic intrusions across the region. The earliest mafic magmatism was part of the 1810–1800 Ma Stafford Event, and a second episode is recognised during the 1790–1770 Ma Yambah Event. Zircon overgrowths in some of these early intrusions record metamorphism during the Strangways Event, a regionally pervasive metamorphic episode whose termination at ca. 1690 Ma coincided with intrusion of dolerite dykes. Gabbro intrusion during the ca. 1640 Ma Liebig Event is related to the geologically distinct Warumpi Province in the south of the region. There is no record of mafic magmatism during the ca. 1590 Ma Chewings Event. Later systems include the ca. 1130 Ma alkaline-ultramafic Mordor Complex; and basaltic bodies are components of the Irindina Province which experienced high-grade metamorphism during the Palaeozoic. The dating associates mafic–ultramafic magmatism with each of these events, which suggests that repeated extensional systems are an important aspect of the tectonic evolution. The example of routinely obtaining zircon for dating from mafic and even ultramafic intrusions, using an integrated approach of field and geochemical criteria to guide sampling, opens the possiblility of dating mafic–ultramafic intrusions elsewhere. Direct dating of mafic–ultramafic magmatism permits its significance in Proterozoic event systems to be evaluated directly, free of assumed or conjectural timing correlations with the felsic plutons that are more often studied for age control.