Correlated iron isotopes and silicon contents in aubrite metals reveal structure of their asteroidal parent body

Soumya Ray,Vinai K Rai,Laurence A J Garvie,Meenakshi Wadhwa

doi:10.1038/s41598-021-99160-9

Abstract

Iron isotopes record the physical parameters, such as temperature and redox conditions, during differentiation processes on rocky bodies. Here we report the results of a correlated investigation of iron isotope compositions and silicon contents of silicon-bearing metal grains from several aubritic meteorites. Based on their Fe isotopic and elemental Si compositions and thermal modelling, we show that these aubrite metals equilibrated with silicates at temperatures ranging from ~ 1430 to ~ 1640 K and likely sampled different depths within their asteroidal parent body. The highest temperature in this range corresponds to their equilibration at a minimum depth of up to ~ 35 km from the surface of the aubrite parent body, followed by brecciation and excavation by impacts within the first ~ 4 Myr of Solar System history.

Highlights

Iron isotopes record the physical parameters, such as temperature and redox conditions, during differentiation processes on rocky bodies
Force constants are measures of bond strengths and a higher force constant translates to stronger bonds, which in turn facilitates the enrichment of heavier isotopes
For ordinary chondrites (OCs), the δ56Fe of metal increases from H through L to LL, a temperature dependence related to petrographic grade is observed[21, 22]

Summary

Introduction

Iron isotopes record the physical parameters, such as temperature and redox conditions, during differentiation processes on rocky bodies. We report the results of a correlated investigation of iron isotope compositions and silicon contents of silicon-bearing metal grains from several aubritic meteorites Based on their Fe isotopic and elemental Si compositions and thermal modelling, we show that these aubrite metals equilibrated with silicates at temperatures ranging from ~ 1430 to ~ 1640 K and likely sampled different depths within their asteroidal parent body. The presence of delocalized electrons in Fe-metal facilitates shorter and stiffer metallic bonds, compared to the Fe–O bonds in silicates, which favors the enrichment of heavier Fe isotopes in the Fe-metal[19] This is consistent with the observation that metals from p allasites[9], enstatite c hondrites13, aubrites[13, 17], iron meteorites[20], and ordinary chondrites[21,22,23] are characterized by heavier Fe isotope compositions compared to coexisting silicates and sulfides. To our knowledge, there have been no studies that have investigated the potential correlation of Si content with Fe isotope fractionation in natural metallic samples that record metal-silicate equilibration

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Results

Conclusion