New ⁴⁰Ar/³⁹Ar dating of the Antrim Plateau Volcanics, Kalkarindji, Australia: clarifying an age for the eruptive phase of Kalkarindji

The Kalkarindji flood basalt province of northern Australia erupted in the mid-Cambrian. Today the province consists of scattered volcanic and intrusive suites, the largest being the Antrim Plateau Volcanics (APV) in Northern Territory. Accurate dating of Kalkarindji has proved challenging with previous studies focused on minor volcanics and intrusive dykes in Northern Territory and Western Australia. These previously published data, corrected to the same decay constants, range from 512.8-509.6 ± 2.5 Ma [2σ], placing Kalkarindji in apparent synchronicity with the Cambrian Stage 4-5 biotic crisis at 510 ± 1 Ma. This study utilises ⁴⁰Ar/³⁹Ar dating of basalts from the APV to accurately date the major volcanic eruptions in this province. Results yield an age of 508.0-498.3 ± 5.5 Ma [2σ], indicating the APV is younger than the intrusives. These dates allude to a relative timing discrepancy, where intrusive activity in the North Australian Craton preceded the eruption of the APV as the last magmatic activity in the region. The determination of these largest eruptions to be later than 510 Ma, effectively disassociates Kalkarindji lavas from being a major cause of the 510 Ma biotic crisis, but cannot definitely discount any deleterious effects on the fragile Cambrian ecosystem.