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The Sudbury structure is a mineralized impact crater that hosts different families of orecontrolling shear zones with poorly known orogenic affinities. Discriminating whether these deformation events relate to the 1.85 Ga crater modification stage or later regional tectonism, that collapsed the impact structure, is important both for crustal and mineral exploration studies. We have combined underground mapping with isotopic and microstructural analysis of titanite and host minerals in a benchmark ore-controlling mylonitic shear zone of the mining camp, the Six Shaft Shear Zone from the Creighton Mine. Three growth stages of chemically and microstructurally-characterised titanite grains were identified related with the pre-, syn and late deformation stages. In-situ U-Pb age dating of the syndeformational grains demonstrates that a shearing event took place at 1645 ± 54 Ma during the Mazatzalian-Labradorian orogeny (1.7-1.6 Ga). This event led to the plastic deformation and local-scale remobilization of primary Ni-Cu-PGE sulphides in Creighton Mine (Sudbury, South Range). The adopted novel petrochronological approach can reveal the age significance of syn-deformational processes and holds promise for the untangling of complex syn-orogenic processes in Precambrian terranes globally.

Identifying and dating large impact structures is challenging, as many of the traditional shock indicator phases can be modified by post-impact processes. Highly robust accessory phases, such as zircon, while faithful recorders of shock wave passage, commonly respond with partial U-Pb age resetting during impact events. Titanite is an accessory phase with lower Pb closure temperature than many other robust chronometers, but its potential as indicator and chronometer of impact-related processes remains poorly constrained. In this study, we examined titanite grains from the Sudbury (Ontario, Canada) and Vredefort (South Africa) impact structures, combining quantitative microstructural and U-Pb dating techniques. Titanite grains from both craters host planar microstructures and microtwins that show a common twin-host disorientation relationship of 74° about <102>.In the Vredefort impact structure, the microtwins deformed internally and developed high and low-angle grain boundaries that resulted in the growth of neoblastic crystallites. U-Pb isotopic dating of magmatic titanite grains with deformation microtwins from the Sudbury impact structure yielded a 207 Pb/ 206 Pb age of 1851 ± 12 Ma that records either the shock heating or the crater modification stage of the impact event. The titanite grains from the Vredefort impact structure yielded primarily pre-impact ages recording the cooling of the ultra-high temperature Ventersdorp event but domains with microtwins or planar microstructures show evidence of U-Pb isotopic disturbance. Despite that the identified microtwins are not diagnostic of shock-metamorphic processes, our contribution demonstrates that titanite has great potential to inform studies of the terrestrial impact crater record.

The post-impact orogenic evolution of the world class Ni-Cu-PGE Sudbury mining camp in Ontario remains poorly understood. New temporal constraints from orecontrolling, epidote-amphibolite facies shear zones in the heavily mineralised Creighton Mine (Sudbury, South Range) illuminate the complex orogenic history of the Sudbury structure. In situ U-Pb dating of shear-hosted titanite grains by LA-

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