TY - JOUR
T1 - Li-Sr-Nd isotope signatures of the plume and cratonic lithospheric mantle beneath the margin of the rifted Tanzanian craton (Labait)
AU - Aulbach, Sonja
AU - Rudnick, Roberta L.
AU - McDonough, William F.
PY - 2008/1
Y1 - 2008/1
N2 - 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 δ7 Li (+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.
AB - 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 δ7 Li (+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.
KW - Cratonic lithospheric mantle
KW - East African Rift
KW - Lithium isotopes
KW - Neodymium isotopes
KW - Plume
KW - Strontium isotopes
KW - Tanzania
UR - http://www.scopus.com/inward/record.url?scp=36448949037&partnerID=8YFLogxK
U2 - 10.1007/s00410-007-0226-4
DO - 10.1007/s00410-007-0226-4
M3 - Article
AN - SCOPUS:36448949037
SN - 0010-7999
VL - 155
SP - 79
EP - 92
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 1
ER -