TY - JOUR
T1 - Lithium elemental and isotopic variations in rock-melt interaction
AU - Su, Ben Xun
AU - Zhang, Hong Fu
AU - Deloule, Etienne
AU - Vigier, Nathalie
AU - Sakyi, Patrick Asamoah
N1 - Publisher Copyright:
© 2014 Elsevier GmbH.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - Despite the occurrence of highly variable lithium (Li) elemental distribution and isotopic fractionation in mantle mineral, the mechanism of Li heterogeneity and fractionation remains a controversial issue. We measured Li contents and isotopic compositions of olivine and clinopyroxene xenocrysts and phenocrysts from kamafugite host lavas, as well as minerals in melt pockets occurring as metasomatic products in peridotite xenoliths from the Western Qinling, central China. The olivine xenocrysts in the kamafugites show compositional zonation. The cores have high Mg# (100×Mg/(Mg+Fe); 91.0-92.2) and Li abundances (5.63-21.7ppm), low CaO contents (≤0.12wt%) and low δ7Li values (-39.6 to -6.76‰), which overlap with the compositional ranges of the olivines in the melt pockets as well as those in peridotite xenoliths. The rims of the olivine xenocrysts display relatively low Mg# (85.9-88.2), high CaO contents (0.19-0.38wt%) and high δ7Li values (18.3-26.9‰), which are comparable to the olivine phenocrysts (Mg#: 86.4-87.1; CaO: 0.20-0.28wt%; Li: 12.4-36.8ppm; δ7Li: 18.1-26.0‰) and the silicate-melt metasomatized olivines. The clinopyroxene phenocrysts and clinopyroxenes in the melt pockets have no distinct characteristics with respect to the Li abundances and δ7Li values, but show higher and lower CaO contents, respectively, than the clinopyroxenes from silicate and carbonatite metasomatized samples. These features indicate that Li concentration and isotopic signatures of the cores of the xenocrysts recorded carbonatite melt-peridotite reaction (carbonatite metasomatism) at mantle depth, and the variations in the rims probably resulted from xenocryst-host magma interaction during ascent. Our results reveal that the interaction with carbonatite and silicate melts gave rise to an increase in Li abundance in minerals of peridotite xenoliths at mantle depth or during transportation. In terms of δ7Li, the carbonatite and silicate melts produced remarkably contrasting δ7Li variations in olivine. Based on the systematic variations of Li abundances and Li isotopes in olivines, we suggest that the δ7Li value of olivine is a more important indicator than that of clinopyroxene in discriminating carbonatite and silicate melt interaction agents with peridotites.
AB - Despite the occurrence of highly variable lithium (Li) elemental distribution and isotopic fractionation in mantle mineral, the mechanism of Li heterogeneity and fractionation remains a controversial issue. We measured Li contents and isotopic compositions of olivine and clinopyroxene xenocrysts and phenocrysts from kamafugite host lavas, as well as minerals in melt pockets occurring as metasomatic products in peridotite xenoliths from the Western Qinling, central China. The olivine xenocrysts in the kamafugites show compositional zonation. The cores have high Mg# (100×Mg/(Mg+Fe); 91.0-92.2) and Li abundances (5.63-21.7ppm), low CaO contents (≤0.12wt%) and low δ7Li values (-39.6 to -6.76‰), which overlap with the compositional ranges of the olivines in the melt pockets as well as those in peridotite xenoliths. The rims of the olivine xenocrysts display relatively low Mg# (85.9-88.2), high CaO contents (0.19-0.38wt%) and high δ7Li values (18.3-26.9‰), which are comparable to the olivine phenocrysts (Mg#: 86.4-87.1; CaO: 0.20-0.28wt%; Li: 12.4-36.8ppm; δ7Li: 18.1-26.0‰) and the silicate-melt metasomatized olivines. The clinopyroxene phenocrysts and clinopyroxenes in the melt pockets have no distinct characteristics with respect to the Li abundances and δ7Li values, but show higher and lower CaO contents, respectively, than the clinopyroxenes from silicate and carbonatite metasomatized samples. These features indicate that Li concentration and isotopic signatures of the cores of the xenocrysts recorded carbonatite melt-peridotite reaction (carbonatite metasomatism) at mantle depth, and the variations in the rims probably resulted from xenocryst-host magma interaction during ascent. Our results reveal that the interaction with carbonatite and silicate melts gave rise to an increase in Li abundance in minerals of peridotite xenoliths at mantle depth or during transportation. In terms of δ7Li, the carbonatite and silicate melts produced remarkably contrasting δ7Li variations in olivine. Based on the systematic variations of Li abundances and Li isotopes in olivines, we suggest that the δ7Li value of olivine is a more important indicator than that of clinopyroxene in discriminating carbonatite and silicate melt interaction agents with peridotites.
KW - Li isotopes
KW - Mantle metasomatism
KW - Mineral-host magma interaction
KW - Phenocrysts
KW - Xenocryst
UR - http://www.scopus.com/inward/record.url?scp=84919675189&partnerID=8YFLogxK
U2 - 10.1016/j.chemer.2014.04.005
DO - 10.1016/j.chemer.2014.04.005
M3 - Article
AN - SCOPUS:84919675189
VL - 74
SP - 705
EP - 713
JO - Chemie der Erde
JF - Chemie der Erde
IS - 4
ER -