How old is the North Pole Dome impact, Western Australia?

Abstract

Shatter 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.