|Title||The stable strontium isotopic composition of ocean island basalts, mid-ocean ridge basalts, and komatiites|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Amsellem E., Moynier F., Day JMD, Moreira M., Puchtel I.S, Teng F.Z|
|Type of Article||Article|
|Keywords||barberton komatiites; Bulk silicate earth; continental-crust; early Earth; element; Geochemistry & Geophysics; he-3/he-4 ratios; iceland mantle plume; Kilauea Iki; Komatiites; magmatic differentiation; Mid-ocean ridge basalts; ocean island basalts; solar-system; south-atlantic; Sr isotopes; sr-isotope; systematics|
The radiogenic Rb-87-Sr-87 system has been widely applied to the study of geological and planetary processes. In contrast, the stable Sr isotopic composition of the bulk silicate Earth (BSE) and the effects of igneous differentiation on stable Sr isotopes are not well-established. Here we report the stable Sr isotope (Sr-88/Sr-86, reported as delta Sr-88/86, in parts per mil relative to NIST SRM 987) compositions for ocean islands basalts (OIB), mid-ocean ridge basalts (MORB) and komatiites from a variety of locations. Stable Sr isotopes display limited fractionation in a OIB sample suite from the Kilauea Iki lava lake suggesting that igneous processes have limited effect on stable Sr isotope fractionation ( +/- 0.12 parts per thousand over 20% MgO variation; 2sd). In addition, OIB (delta Sr-88/86 = 0.16-0.46 parts per thousand; average 0.28 +/- 0.17 parts per thousand), MORB (delta Sr-88/86 = 0.27-0.34 parts per thousand; average 0.31 +/- 0.05 parts per thousand) and komatiites (delta Sr-88/86 = 0.20-0.97 parts per thousand; average 0.41 +/- 0.16 parts per thousand) from global localities exhibit broadly similar Sr stable isotopic compositions. Heavy stable Sr isotope compositions (delta Sr-88/86 > 0.5 parts per thousand) in some Barberton Greenstone belt komatiites may reflect Archean seawater alteration or metamorphic processes and preferential removal of the lighter isotopes of Sr. To first order, the similarity among OIBs from three different ocean basins suggests homogeneity of stable Sr isotopes in the mantle. Earth's mantle stable Sr isotopic composition is established from the data on OIB, MORB and komatiites to be delta Sr-88/86 = 0.30 +/- 0.02 parts per thousand (2sd). The BSE delta Sr-88/86 value is identical, within uncertainties, to the composition of carbonaceous chondrites (delta Sr-88/86 = 0.29 +/- 0.06 parts per thousand; 2sd) measured in this study.
|Short Title||Chem. Geol.|