Coupled Hf–Nd–Pb isotope co-variations of HIMU oceanic island basalts from Mangaia, Cook-Austral islands, suggest an Archean source component in the mantle transition zone
التفاصيل البيبلوغرافية
العنوان:
Coupled Hf–Nd–Pb isotope co-variations of HIMU oceanic island basalts from Mangaia, Cook-Austral islands, suggest an Archean source component in the mantle transition zone
Although it is widely accepted that oceanic island basalts (OIB) sample geochemically distinct mantle reservoirs including recycled oceanic crust, the composition, age, and locus of these reservoirs remain uncertain. OIB with highly radiogenic Pb isotope signatures are grouped as HIMU (high-μ, with μ = 238U/204Pb), and exhibit unique Hf–Nd isotopic characteristics, defined as ΔeHf, deviant from a terrestrial igneous rock array that includes all other OIB types. Here we combine new Hf isotope data with previous Nd–Pb isotope measurements to assess the coupled, time-integrated Hf–Nd–Pb isotope evolution of the most extreme HIMU location (Mangaia, French Polynesia). In comparison with global MORB and other OIB types, Mangaia samples define a unique trend in coupled Hf–Nd–Pb isotope co-variations (expressed in 207Pb/206Pb vs. ΔeHf). In a model employing subducted, dehydrated oceanic crust, mixing between present-day depleted MORB mantle (DMM) and small proportions (∼5%) of a HIMU mantle endmember can re-produce the Hf–Nd–Pb isotope systematics of global HIMU basalts (sensu stricto; i.e., without EM-1/EM-2/FOZO components). An age range of 3.5 to 3 Gyr and implies that OIB chemistry can be used to test geodynamic models.
