The influence of igneous processes on the chromium isotopic compositions of Ocean Island basalts
作者： P. Bonnand , R. Doucelance , M. Boyet , P. Bachèlery , C. Bosq
DOI: 10.1016/J.EPSL.2019.116028
关键词: Igneous differentiation 、 Partial melting 、 Basalt 、 Geochemistry 、 Mantle (geology) 、 Isotope fractionation 、 Peridotite 、 Geology 、 Rayleigh fractionation 、 Olivine
摘要: Abstract We present the first stable chromium isotopic data for a suite of ocean island basalts (OIB) in order to investigate Cr isotope fractionation during major igneous processes such as partial melting and fractional crystallisation. Twenty-one basaltic samples from Fangataufa Island (Tuamotu Archipelago, Pacific Ocean) have been analysed major- trace-element concentrations, Sr, Nd compositions. They define two distinct series: medium high-K calc-alcaline low medium-K calc-alcaline. The variations incompatible elements La Yb mostly result varying degrees mixed mantle source composed lithologies: garnet bearing peridotite recycled “fertile” component. component is also identified with Sr composition basalts. In contrast, compatible element contents Ni are governed by crystallisation mixture olivine, clinopyroxene spinel. this study characterised small −0.24 −0.17‰. Cr-poor on average lighter compositions compared Cr-rich ones. observed low-K series can be modelled Rayleigh model factor ( Δ 53 Crcrystals-melt) −0.010 ± 0.005‰. more limited than that lunar hypotheses may explain observation: change crystallising phases (cpx + spinel Earth Moon) and/or difference temperature oxygen fugacity between terrestrial primitive an −0.18 0.01‰, pristine xenoliths. Chromium isotopes therefore slightly fractionated melts depleted heavy isotopes. silicate xenoliths indicates could produce but resolvable shift up 0.05‰. covariation δ e 143 values explained processes: (i) lower liquids relative their sources (ii) produced degree experienced
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