Rare earth patterns in shergottite phosphates and residues

Abstract

Leaching experiments with 1M HCl on ALHA 77005 powder show that rare earth elements (REE) are concentrated in accessory phosphate phases (whitlockite, apatite) that govern the REE patterns of bulk shergottites. The REE patterns of whitlockite are typically light REE depleted with a negative Eu anomaly and show a hump at the heavy REE side, while the REE pattern of apatite (in Shergotty) is light REE enriched. Parent magmas are calculated from the modal compositions of residues of ALHA 77005, Shergotty, and EETA 79001. The parent magmas lack a Eu anomaly, indicating that plagioclase was a late‐stage crystallizing phase and it probably crystallized before the phosphates. The parent magmas of ALHA 77005 and Shergotty have similar REE patterns with a subchondritic Nd/Sm ratio. However, the Sm/Nd isotopics require a light REE depleted source for ALHA 77005 (if the crystallization age is <600 m.y.) and a light REE enriched source for Shergotty. Distinct Nd and Sr isotopic signatures may suggest different source regions for shergottites.