Mn-Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution

• Main Authors: Göpel, Christa, Birck, Jean-Louis, Galy, Albert, Barrat, Jean-Alix, Zanda, Brigitte
• Other Authors: Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Department of Earth Sciences Cambridge, UK, University of Cambridge UK (CAM), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de recherche pour le développement IRD : UR206-Centre National de la Recherche Scientifique (CNRS), ANR-08-BLAN-0260,T-Tauri.Chem.,La Chimie du disque solaire T-Tauri(2008)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: EARLY SOLAR-SYSTEM; CHROMIUM ISOTOPE SYSTEMATICS; UNGROUPED CARBONACEOUS CHONDRITE; PARENT BODY; TAGISH LAKE; MN-53-CR-53 CHRONOMETRY; PROTOPLANETARY DISK; ALLENDE INCLUSIONS; CORE FORMATION; CHRONOLOGY; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Tagish; Tagish Lake
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01164061; https://doi.org/10.1016/j.gea.2015.02.008

International audience Cr isotopic compositions have been measured on carbonaceous chondrites (CC): Tafassasset, Paris, Niger I, NWA 5958, NWA 8157 and Jbilet Winselwan. In bulk samples, the Cr-54/Cr-52 ratios (expressed as epsilon Cr-54) range from 0.93 to 1.58 epsilon units. These values are in agreement with values characteristic for distinct petrologic types. Despite this 54 Cr heterogeneity, the variability in the Cr-54/Cr-52 ratios (expressed as epsilon Cr-53) of 0.2 epsilon units and the Mn/Cr ratios is consistent with the previous finding of an isochron in the Mn-Cr evolution diagram.The Mn/Cr ratio in CC corresponds to variable abundances of high-T condensate formed and separated at the beginning of the solar system, thus the canonical Mn-53/Mn-55 ratio can be defined. Based on a consistent chronology for U-Pb and Mn-Cr between the earliest objects formed in the solar nebula and the D'Orbigny angrite we define a canonical Mn-53/Mn-55 ratio and epsilon Cr-53(i) of 6.8 x 10(-6) and -0.177, respectively.The internal Mn/Cr systematics in Tafassasset and Paris were studied by two approaches: leaching technique and mineral separation. Despite variable epsilon Cr-54 values (up to >30 epsilon) linear co-variations were found between epsilon Cr-53 and Mn/Cr ratio. The mineral separates as well as the leachates of Tafassasset fall on a common isochron indicating that (1) cooling of the Tafassasset's parent body occurred at 4563.5 +/- 0.25 Ma, and that (2) Cr-54 is decoupled from the other isotopes even though temperatures >900 degrees C have been reached during metamorphism. In the case of Paris, the leachates form an alignment with a Mn-53/Mn-55 ratio higher than the canonical value. This alignment is not an isochron but rather a mixing line. Based on leachates from various CM and CI, we propose the occurrence of three distinct Cr reservoirs in meteoritic material: PURE54, HIGH53 and LOW53 characterized by a epsilon Cr-53 and epsilon Cr-54 of 0 and 25,000, -2.17 and 8, and 0.5 and -151, respectively. ...