How old is the North Pole Dome impact, Western Australia?
C.L. Kirkland, J. Kaempf, T.E. Johnson, B.V. Ribeiro, A. Zametzer, R.H. Smithies, B.J. McDonaldShatter cones from the North Pole Dome in the Pilbara Craton, Western Australia, may provide a rare record of Archean bombardment, but their age is debated. We present integrated zircon, apatite, calcite, and muscovite geochronology from shocked rocks to address that question. Zircon shows a continuum from >3.4 Ga older equant grains to younger skeletal forms, with the concordant skeletal component yielding a weighted mean 207Pb/206Pb age of 3024 ± 7 Ma, interpreted to date recrystallization of older zircon during impact-related thermal-fluid activity. An impact age of ca. 3.02 Ga is the most parsimonious interpretation because zircon recrystallization and hydrothermal apatite growth are coeval; no recognized regional high-grade tectonothermal event between 3.4 Ga and 3.0 Ga can account for zircon (re)crystallization, and younger Proterozoic zircon Pb loss cannot record impact as it post-dates undeformed mica (1655 ± 27 Ma) in veins that cross-cut the shatter-cone fabric. Collectively, these data support the North Pole Dome crater as Earth’s oldest and only known Archean impact structure.