Ringwoodite Lamellae in Olivine from the L6 S6 Chondrite Tenham: Constraints on the Transformation Mechanism

1. Introduction High-pressure minerals, produced by shock metamorphism, are common in and around melt veins in highly shocked chondrites [1-8]. These minerals either crystallized from silicate melt in the shock-vein or formed by solid-state transformed from host-rock fragments entrained in the melt or along shock-vein margins [3]. The study of these high pressure minerals can give us a better understanding of the pressure and temperature conditions associated with shock meta-morphism. This abstract focuses on the solid-state transformation of olivine to ringwoodite and the formation of ringwoodite lamellae. Although high-pressure phase transformations in shocked chondrites can be used to infer shock conditions , their use to quantitatively calibrate shock pressure and duration should be done with caution. The pressure constraints that one can draw are limited by sluggish transformation kinetics. However, if one can estimate the conditions of transformation, transformation kinetic data can be used to constrain the duration of shock events [9-11]. In order to apply experimental kinetic data to nature, the transformation mechanisms must be the same in both cases. Recent observations of ringwoodite lamellae in partially transformed olivine near shock veins [10-12], have motivated us to look more closely at partially transformed olivine in Tenham. In this report we document the occurrence of ringwoodite lamellae in partially transformed olivine in Tenham, and discuss the likely transformation mechanism.