Li-Sr-Nd isotope signatures of the plume and cratonic lithospheric mantle beneath the margin of the rifted Tanzanian craton (Labait) |
| |
| Authors: | Sonja Aulbach Roberta L Rudnick William F McDonough |
| |
| Institution: | (1) Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, USA;(2) Present address: Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada |
| |
| Abstract: | Lithium concentrations and isotopic compositions of olivine and 87Sr/86Sr and 143Nd/144Nd of coexisting clinopyroxene from peridotite xenoliths from the Quaternary Labait volcano, Tanzania, document the influence
of rift-related metasomatism on the ancient cratonic mantle. Olivines show negative correlations between Fo content and both
δ7Li and Li concentrations. Olivines in iron-rich peridotites (Fo85–87) have high Li concentrations (3.2–4.8 ppm) and heavy δ7Li (+5.2 to +6.6). In contrast, olivines in ancient, refractory peridotites have lower Li concentrations (∼2 ppm) and relatively
light δ7Li (+2.6 to +3.5). This reflects mixing between ancient, refractory cratonic lithosphere and asthenosphere-derived rift magmas.
A uniquely fertile, deformed, high-temperature garnet lherzolite, interpreted to be from the base of the lithosphere, has
a 87Sr/86Sr of 0.7029 and 143Nd/144Nd of 0.51286, similar to HIMU oceanic basalts. It provides the best estimate of the Sr–Nd isotope composition of the upwelling
mantle (i.e., plume, sensu lato) underlying this portion of the East African Rift, and is slightly less radiogenic compared
to previous estimates of the plume that were based on rift basalts. Although elevated δ7Li are not exclusive to HIMU source regions, the data collectively indicate that the plume beneath Labait has HIMU characteristics
in Sr, Nd and Li isotope composition.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
| |
| Keywords: | Lithium isotopes Strontium isotopes Neodymium isotopes East African Rift Plume Cratonic lithospheric mantle Tanzania |
| 本文献已被 SpringerLink 等数据库收录！ |
|
