The formation of large neoblasts in shocked zircon and their utility in dating impacts

Researchers have discovered large neoblasts (5–100 µm) in shocked zircon at the Sudbury impact structure, marking the first such finding outside South Africa's Vredefort Dome. These neoblasts, previously only documented in mafic melt beneath impact sheets, were identified in roof rocks of the Sudbury crater, enabling dating from its upper stratigraphy for the first time. Electron backscatter diffraction analysis revealed that large neoblasts likely formed through post-impact growth in shocked zircon within slowly cooling environments, unlike smaller neoblasts linked to high-pressure conditions. This discovery suggests that similar neoblasts in lunar zircon may indicate a major basin-forming event on the Moon around 4.33 billion years ago and opens potential for linking ex situ zircon in lunar breccias to specific impact structures, improving lunar cratering record calibration.

Kenny, G. G., Morales, L. F., Whitehouse, M. J., Petrus, J. A., & Kamber, B. S. (2017). The formation of large neoblasts in shocked zircon and their utility in dating impacts. Geology, 45(11), 1003–1006. https://doi.org/10.1130/g39328.1