Partitioning of $ Fe_{2} %$ O_{3} $ in peridotite partial melting experiments over a range of oxygen fugacities elucidates ferric iron systematics in mid-ocean ridge basalts and ferric iron content of the upper mantle

Abstract Basalts and peridotites from mid-ocean ridges record fO2 near the quartz-fayalite-magnetite buffer (QFM), but peridotite partial melting experiments have mostly been performed in graphite capsules (~ QFM-3), precluding evaluation of ferric iron’s behavior during basalt generation. We perfor...
Ausführliche Beschreibung

Abstract Basalts and peridotites from mid-ocean ridges record fO2 near the quartz-fayalite-magnetite buffer (QFM), but peridotite partial melting experiments have mostly been performed in graphite capsules (~ QFM-3), precluding evaluation of ferric iron’s behavior during basalt generation. We performed experiments at 1.5 GPa, 1350–1400 °C, and fO2 from about QFM-3 to QFM+3 to investigate the anhydrous partitioning behavior of $ Fe_{2} %$ O_{3} $ between silicate melts and coexisting peridotite mineral phases. We find spinel/melt partitioning of $ Fe_{2} %$ O_{3} $ (%${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{spl}/\mathrm{melt}}%$) increases as spinel $ Fe_{2} %$ O_{3} $ concentrations increase, independent of increases in fO2, and decreases with temperature, which is consistent with new and previous experiments at 0.1 MPa. We find %${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}%$ = 0.63 ± 0.10 and %${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{cpx}/\mathrm{melt}}%$ = 0.78 ± 0.30. MORB $ Fe_{2} %$ O_{3} $ and $ Na_{2} $O concentrations are consistent with a modeled MORB source with $ Fe_{2} %$ O_{3} $ = 0.48 ± 0.03 wt% ($ Fe^{3+} $/ΣFe = 0.053 ± 0.003) at potential temperatures (TP) from 1320 to 1440 °C. The temperature-dependence of the %${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{spl}/\mathrm{melt}}%$ function alone allows ~ 40% of the variation in MORB compositions. If we allow %${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}%$ and %${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}%$ to also vary with temperature by tying them to spinel $ Fe_{2} %$ O_{3} $ through intermineral partitioning, then all the MORB data are within error of the model. Our model $ Fe_{2} %$ O_{3} $ concentration for the MORB source would require that the convecting mantle be more oxidized at a given depth than recorded by continental mantle xenoliths. Our result is supported by thermodynamic models of mantle with $ Fe^{3+} $/ΣFe = 0.03 that predict fO2 of ~ QFM-1 near the garnet-spinel transition, which is inconsistent with fO2 of MORB. Our results support previous suggestions that redox melting may occur between 200 and 250 km depth. Ausführliche Beschreibung

Autor*in:	Davis, Fred A. [verfasserIn] Cottrell, Elizabeth

Format:	E-Artikel
Sprache:	Englisch

Erschienen:	2021

Schlagwörter:	MORB Oxygen fugacity Experimental petrology Mantle petrology

Anmerkung:	© This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2021

Übergeordnetes Werk:	Enthalten in: Contributions to mineralogy and petrology - Berlin : Springer, 1947, 176(2021), 9 vom: 12. Aug.
Übergeordnetes Werk:	volume:176 ; year:2021 ; number:9 ; day:12 ; month:08

Links:	Volltext

DOI / URN:	10.1007/s00410-021-01823-3

Katalog-ID:	SPR044814178