首页|Oxidized mantle sources of HIMU- and EM-type Ocean Island Basalts
Oxidized mantle sources of HIMU- and EM-type Ocean Island Basalts
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NSTL
Elsevier
Oxygen fugacity (fO2) is a fundamental variable in igneous petrology with utility as a potential tracer of recycled high Fe+3/EFe surficial materials in the sources of mantle-derived lavas. It has been postulated that ocean island basalts (OIB) have elevated fO2 relative to mid-ocean ridge basalts (MORB) owing to higher average Fe+3/EFe in their source regions. To examine this issue, trace-element systematics of olivine grains are reported from OIB lavas with HIMU (high-??; Mangaia, Canary Islands), enriched mantle (EM; Samoa; Sa??o Miguel in the Azores Islands) and depleted MORB mantle (DMM; Pico in the Azores Islands) Sr-Nd-Pb-Os isotope signatures, in order to constrain the fO2 of each magmatic system. Despite sampling distinct mantle reservoirs based on radiogenic isotope systematics, these OIB suites show similar fO2, ranging from +0.8 to +2.6 AFMQ, with an average of +1.5 ?? 0.8 AFMQ, largely higher than MORB using the same oxybarometry method at +0.6 ?? 0.2 AFMQ. The studied OIB show no correlation between fO2 and bulk rock isotopic ratios or calculated parental magma compositions. The lack of correlations with isotopic signatures likely results from radiogenic isotope signatures being hosted in volumetrically minor trace element enriched mantle lithologies, while Fe+3/EFe ratios that act as the primary control on fO2 are controlled by the volumetrically dominant mantle component. Higher fO2 in many OIB relative to MORB implies that they sample a uniformly high Fe+3/EFe plume source mantle that may be the result of either a common oxidized oceanic crust-rich reservoir parental to many modern plume lavas, or preservation of un-degassed and oxidized mantle domains formed shortly after core formation.
NSTL
Elsevier
