233-4 The Miralga impact structure, a new terrestrial analog for craters on early Earth and Mars

Session: Impact Cratering and the Evolution of Life

Presenting Author:

Authors:

Abstract:

Two recently published studies [1, 2] documented well preserved shatter cones in North Pole Dome, Pilbara Craton, Western Australia. These reveal the presence of a deeply eroded complex impact crater on the north flank of the dome, hosted mostly within 3.47 Ga greenstones. We named this crater the Miralga impact structure after consultation with the Nyamal traditional owners of the region [1]. Here, we discuss several noteworthy features and our ongoing studies of this new crater:

While the crater was initially suggested to be 3.47 Ga old and ~100 km wide [2], our work [1] revised its age to <2.71 Ga and its diameter to ~16 km. This revision was based in part on the occurrence of shatter cones in rocks as young as 2.77 Ga. In addition, the orientations of shatter cones in Miralga radiate conspicuously outward from a central point, which we infer to be the geographic point of impact at the center of the structure. This pattern is undisturbed by, and thus cross-cuts, regional faults that post-date 2.71 Ga. Shatter cones occur over a ~6.5 km wide circle that corresponds to an inferred apparent diameter of ~16 km.

Miralga contains the oldest shock-metamorphosed terrestrial rocks yet identified at 3.47 Ga. These include abundant basalts and cherts that experienced early seafloor hydrothermal alteration. The altered basalts contain especially abundant and finely preserved shatter cones, as well as the high-pressure phase TiO₂-II (indicates ≥12 GPa shock). Hydrothermally altered metabasalts are thus excellent recorders of shock metamorphism at outcrop and grain scale, useful features in the continuing search for Archean craters.

The basaltic, aqueously altered, Archean rocks of Miralga make it perhaps one of the best terrestrial analog sites for impact cratering on early Mars. This builds on decades of work establishing the Mars analog potential of early biosignature sites nearby, including the oldest well-established microbial stromatolites on Earth (3.48 Ga). Those fossils, along with other designated early life sites, are within the crater, potentially enabling future studies of shock metamorphism of biosignatures.

[1] Brenner A.R. et al. (2025) Science Advances. [2] Kirkland C.L. et al. (2025) Nature Communications.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8458

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