10:45 AM - 11:00 AM
[BCG07-07] Impact-induced magmatism on early Earth
Keywords:Asteroid impact crater, Impact tsunami deposits, Early Earth
Our survey has revealed the presence of “impact tsunami deposits” at the boundary of the MBCM and the Apex Basalt. They are ~1-40 m thick, extending at least 20 km along the strike in the Marble Bar area. They contain numerous fragments (<5 mm size) of stony meteorites, together with various-sized (<1 mm to ~10 m), generally angular-shaped, fragments and blocks of the MBCM. We have also discovered ~15-40 m thick “impact tsunami deposits” underlying the Apex Basalt at ~80 km SE of Marble Bar. Numerous fractures (mostly perpendicular to the bedding planes, and many extending to 100s of meter into the underlying Duffer Formation), the dislocations and rotations of the MBCM in ~cm to ~100 m scales, as well as the “impact tsunami deposits”, were most likely created by an asteroid impact. Our survey has provided evidence that the ~3km-thick Apex Basalt represents the crater-filing komatiite/basalt lavas that were generated by the sudden decompression-melting of the mantle peridotites, triggered by a giant impact, and that the Mt. Edgar Batholiths (~3.46-3.43 Ga in ages), which intruded in the crater, probably represent the rebound of the older continental crust and the products of partial melting of the mantle peridotite and oceanic crust.
Our investigations suggest that the greenstone-granite complexes (“granite dome complexes”) that characterize the geology of the East Pilbara district may represent 8 or more craters created by impacts of asteroid bodies 10-30 km in diameter during the Archean. Consequently, the magmatism and tectonics of early Earth may have been dictated by gigantic asteroid impacts, rather than by the plume- and/or plate tectonics.