Preparations and analysis of a new set of grain-size fractions of nanodiamonds from Kainsaz

• Main Authors: Verchovsky, A. B., Fisenko, A. V., Semjonova, L. F., Wright, I. P.
• Format: Conference Object
• Language: unknown
• Published: 2009
• Subjects: The Pointers
• Online Access: https://oro.open.ac.uk/32355/; http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1908.pdf

Introduction: In this paper we present new results of our long-term project on investigations of meteoritic nanodiamonds using grain-size analysis. The main goal of the project is to identify and characterize nanodiamond populations with different origin. The idea that meteoritic nanodiamonds can be represented by more than one population has been discussed for long time, almost since their discovery. The pointers to multiple populations include variations in carbon isotopic composition during stepped combustion of the nanodiamonds and variations between samples from meteorites with different metamorphic histories. The latter suggests that the different nanodiamond populations have varying level of resistance to the parent body metamorphic alterations (grades and environment where it takes place). In other words, notwithstanding what could have been an initial homogeneity in the diamond ensemble, a certain separation between populations occurred in different parent bodies (or at different places within individual parent bodies) during metamorphism under natural conditions. Laboratory grains-size separation of the nanodiamonds by means of centrifugation show that carbon isotopic composition varies systematically with size of the diamond grains. The total range of carbon isotope variations significantly increased and the effect of metamorphism considerably enhanced in the size fractions compared to unseparated samples so that it became possible to create a model from which carbon isotopic compositions of the pure populations can be found. In an early stage of the investigations we identified only two populations for the bulk grain-size fractions of Efremovka, Krymka and Boriskino, though the stepped combustion data suggested that a third populations may also be present. Recently we developed centrifugation procedures that have allowed us to produce the coarsest fractions. Applying these procedures to nanodiamonds from Orgueil we were able to identify a third high-temperature population with relatively heavy carbon ...