STARDUST II - Spatial and Temporal Assessment
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New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico
Timms, N.E.; Pearce, M.A.; Cavosie, A.J.; Rae, A.S.P.; Wheeler, J.; Wittmann, A.; Ferrière, L.; Poelchau, M.H.; Tomioka, N.; Collins, G.S.; Gulick, S.P.S.; Rasmussen, C.; Morgan, J.V.; IODP-ICDP Expedition 364 Scientists (2019). New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico. Contrib. Miner. Petrol. = Beitr. Mineral. Petrol. 174(5): 38. https://dx.doi.org/10.1007/s00410-019-1565-7
In: Contributions to Mineralogy and Petrology = Beiträge zur Minerologie und Petrologie. Springer: Heidelberg; Berlin. ISSN 0010-7999; e-ISSN 1432-0967
Accessory mineral geochronometers such as apatite, baddeleyite, monazite, xenotime and zircon are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity-impact processes. To date, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and a U–Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoid from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired core from the International Ocean Discovery Program Hole M0077A preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1)?=?~?{1¯11}{1¯11}, and shear direction (?1)?=??, and less commonly with the mode K1?=?{130}, ?1?=?~?<522?>?. In some grains, {130} deformation bands have formed concurrently with the deformation twins, indicating dislocation slip with Burgers vector b?=??can be active during impact metamorphism. Titanite twins in the modes described here have not been reported from endogenically deformed rocks; we, therefore, propose this newly identified twin form as a result of shock deformation. Formation conditions of the twins have not been experimentally calibrated, and are here empirically constrained by the presence of planar deformation features in quartz (12?±?5 and?~?17?±?5 GPa) and the absence of shock twins in zircon (
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STARDUST II is a project funded by the INTERREG III A programme (France/Walloon Region/Flanders
French-Flemish subprogramme) of the European Community's Regional Development Fund.
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