JpGU-AGU Joint Meeting 2020

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[E] Poster

P (Space and Planetary Sciences ) » P-PS Planetary Sciences

[P-PS03] High-pressure phases in shocked meteorites: key to understanding impact events on parent asteroids

convener:Kishan Tiwari(Indian Institute of Technology Kharagpur)

Shocked meteorites, which are the products of collisions in between their parent asteroids, contain shock melt veins, which are pervasive localized zones of very high pressure, temperature, and frictional melting. Minerals entrained in and around such SMVs being subjected to such extreme conditions are transformed to high-pressure polymorphs and thus such shocked meteorites serve as unique natural samples to study the mechanism of such polymorphic transformations. Based on shock metamorphic features observed in olivine and plagioclase, produced at different P-T conditions, a shock stage classification system has been developed with highest shock stage, S6 corresponds to 75-90 GPa. But the pressure stability range established by static high-pressure experiments for the high-pressure polymorphs reported in shocked meteorites is much lower than that indicated by their corresponding shock stage. Such a large difference is mainly because such polymorphic transformations depend on kinetics of the reaction and the actual P-T-t path experienced by the mineral grains during the shock. Computational modeling and microscopic studies of shock front behavior and shocked samples indicate that interaction of shock waves with mineral grain of different shock impedance may result in pressure heterogeneity and localized spikes in temperature. Compositional and textural analyses of matrix portions in shocked meteorites have revealed that they have crystallized directly from the chondritic melt at high pressure. Thus, phase relations and mineral stability at different P-T conditions derived from static high-pressure experiments can be used to infer the crystallization pressure and shock pressure. Estimated shock pressure can be used to calculate shock velocity, impact velocity, and parent body size by using the Rankine-Hugoniot equation. So apart from transformation mechanisms, shocked meteorites can provide us with information about collision dynamics on their parent asteroids.