Widespread magmatic activities on the angrite parent body at 4562 Ma ago

Naoji Sugiura,Keizo Yanai,Akiko Miyazaki

doi:10.1186/bf03351858

Abstract

Abstract Mn-Cr chronology of four quenched angrites showed that they formed nearly at the same time (4562 Ma) on the surface of the parent-body. Based on the chemical compositions, the cosmic ray exposure ages, and considerations on the thermal history of an achondrite parent-body, we suggest that the four angrites formed on top of a shallow magma ocean on the angrite parent body.

Highlights

IntroductionThe Pb-Pb age of D’Orbigny was initially reported to be 4557 ± 1 Ma: (Jagoutz et al, 2003) and nearly identical with those of LEW86010 and Angra dos Reis (4557.8 Ma: Lugmair and Shukolyukov, 1998)
Age determination of angrites is important because the angrites LEW86010 and Angra dos Reis are used as an anchor for connecting Pb-Pb absolute ages (4557.8 ± 0.5 Ma, Lugmair and Galer, 1992) and Mn-Cr ages (53Mn/55Mn = (1.25±0.07)×10−6, Lugmair and Shukolyukov, 1998) and because igneous activities on the angrite parent body are yet poorly understood.Recently, several new angrites were found
Based on the chemical compositions, the cosmic ray exposure ages, and considerations on the thermal history of an achondrite parent-body, we suggest that the four angrites formed on top of a shallow magma ocean on the angrite parent body

Summary

Introduction

The Pb-Pb age of D’Orbigny was initially reported to be 4557 ± 1 Ma: (Jagoutz et al, 2003) and nearly identical with those of LEW86010 and Angra dos Reis (4557.8 Ma: Lugmair and Shukolyukov, 1998). We report Mn-Cr ages of four angrites measured by secondary ion mass spectrometry (SIMS). Petrology of NWA1670 has been reported by Mikouchi et al (2003) These four angrites appear to have cooled more rapidly than LEW86010 and Angra dos Reis. They are called as “quenched angrites” by Mikouchi et al (2003). The synthetic sample contains ∼0.34 wt% Cr2O3 and ∼0.92 wt% MnO which were determined by EPMA (JEOL JXA-8800)

Results

Discussion

Conclusions