Transfer of Os isotopic signatures from peridotite to chromitite in the subcontinental mantle: insights from in situ analysis of platinum-group and base-metal minerals (Ojén peridotite massif, southern Spain)

José M. González-Jiménez*, Claudio Marchesi, William L. Griffin, Rosario Gutiérrez-Narbona, Jean P. Lorand, Suzanne Y. O'Reilly, Carlos J. Garrido, Fernando Gervilla, Norman J. Pearson, Karoly Hidas

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

Small (<5m) chromitite bodies in the Ojén peridotite massif (southern Spain) were formed when small fractions of volatile-rich melts, residual after kilometric-scale infiltration through the subcontinental mantle, reacted with Cr-rich pyroxenite enclosed in dunite. The Os isotopic compositions of accessory platinum-group minerals (PGM) and base-metal minerals (BMM, including sulfides and arsenides) in chromitite and the host peridotite have similar values and ranges of heterogeneity. The formation of chromitite, which involved partial melting, melt transport/pooling and melt-rock reactions, did not erase the original 187Os/188Os heterogeneity of the peridotite source. The distribution of Os model ages calculated for chromitite-hosted PGM-BMM mainly clusters at ~0.3Ga; minor peaks extend back to ~1.4Ga. Base-metal sulfides (BMS) hosted in peridotite show a relatively minor age peak at ~0.2Ga and two prominent peaks at ~0.6 and 1.2Ga. Independent geochronological data constrain the formation of chromitites at 21Ma ago, suggesting that these older model ages reflect the sourcing of Os from volumes of older subcontinental lithospheric mantle that underwent several episodes of melting and metasomatism since the Mesoproterozoic. We interpret the different distributions of 187Os/188Os and model ages in chromitite and peridotite as due to the combined control that mantle source heterogeneity, melting and melt/rock interaction processes exert on the Os-isotope composition of the parental melts of chromitite.

Original languageEnglish
Pages (from-to)74-85
Number of pages12
JournalLithos
Volume164-167
DOIs
Publication statusPublished - Apr 2013

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