TY - JOUR
T1 - Rapid cooling of planetesimal core-mantle reaction zones from Mn-Cr isotopes in pallasites
AU - McKibbin, S. J.
AU - Ireland, T. R.
AU - Holden, P.
AU - O'Neill, H. St C.
AU - Mallmann, G.
N1 - Publisher Copyright:
© 2016 European Association of Geochemistry.
PY - 2016
Y1 - 2016
N2 - Pallasite meteorites, which consist of olivine-metal mixtures and accessory phosphates crystallised from silico-phosphate melts, are thought to represent core-mantle reaction zones of early differentiating planetesimals. Pallasite meteorites can be linked to five distinct planetesimals, indicating that they are default products of differentiation. However, their formation modes (deep, shallow, and impact environments) and age are still elusive. We have investigated the trace element and Mn-Cr isotopic signatures of Main-Group pallasite olivine, finding enhanced Mn, P and 53Cr/52Cr near crystal rims which indicates early ingrowth of radiogenic 53Cr∗ in silico-phosphate melts. Mn-Cr isotopic data corroborate previous Hf-W isotopic data, indicating an early metal-silicate separation event but additionally that rapid cooling generated silico-phosphate eutectic melts with high Mn/Cr within ∼2.5 to 4 Myr of Solar System formation. These melts formed before most known samples of planetesimal crusts (eucrite and angrite meteorites) and are among the earliest evolved planetary silicates. Additionally, Mn-rich phosphates in other, non-Main-Group pallasite meteorites suggest that core-mantle reaction zones are generic, datable features of differentiation.
AB - Pallasite meteorites, which consist of olivine-metal mixtures and accessory phosphates crystallised from silico-phosphate melts, are thought to represent core-mantle reaction zones of early differentiating planetesimals. Pallasite meteorites can be linked to five distinct planetesimals, indicating that they are default products of differentiation. However, their formation modes (deep, shallow, and impact environments) and age are still elusive. We have investigated the trace element and Mn-Cr isotopic signatures of Main-Group pallasite olivine, finding enhanced Mn, P and 53Cr/52Cr near crystal rims which indicates early ingrowth of radiogenic 53Cr∗ in silico-phosphate melts. Mn-Cr isotopic data corroborate previous Hf-W isotopic data, indicating an early metal-silicate separation event but additionally that rapid cooling generated silico-phosphate eutectic melts with high Mn/Cr within ∼2.5 to 4 Myr of Solar System formation. These melts formed before most known samples of planetesimal crusts (eucrite and angrite meteorites) and are among the earliest evolved planetary silicates. Additionally, Mn-rich phosphates in other, non-Main-Group pallasite meteorites suggest that core-mantle reaction zones are generic, datable features of differentiation.
UR - http://www.scopus.com/inward/record.url?scp=84969187763&partnerID=8YFLogxK
U2 - 10.7185/geochemlet.1607
DO - 10.7185/geochemlet.1607
M3 - Article
SN - 2410-339X
VL - 2
SP - 68
EP - 77
JO - Geochemical Perspectives Letters
JF - Geochemical Perspectives Letters
IS - 1
ER -