4:15 PM - 4:30 PM
[SCG52-10] The upper mantle heterogeneity revealed by Pb-Sr-Nd isotopic compositions of petit-spot basalts, NW Pacific plate
Keywords:petit-spot, Sr-Nd-Pb isotope, mantle heterogeneity, carbonatite magma, alkaline basalt
Enriched Mantle 1 (EM-1), one of the principal mantle endmember components, is characterized by low 143Nd/144Nd and 206Pb/204Pb, relatively low 87Sr/86Sr, and high 207Pb/204Pb and 208Pb/204Pb for a given value of 206Pb/204Pb, represented by lava from the Pitcairn hotspot. Previous studies reported the EM-1-like Sr-Nd isotopic signature of petit-spot basalts, but the isotopic composition of petit-spot basalt is obviously distinguished from EM-1 in OIB by its unradiogenic lead isotopic ratios, especially 208Pb/204Pb. In addition, a distinct positive correlation between 143Nd/144Nd and Ba/Nb is reported, indicating that the trace-element ratio preserves the information of petit-spot magma source. Although the contribution of carbonatite melt to the magma source of petit-spot basalt has been ever suggested, this correlation between the trace-element and the isotopic composition would be helpful to recognize the source mantle.
In this study, nine samples were strategically selected and analyzed to investigate the genesis of the EM-1 component beneath the NW Pacific petit-spot. To discuss the relationship between Pb-Sr-Nd isotopes and trace-element compositions of the petit-spot basalts, we measured the samples with elevated Ba/Nb ratio, which was expected to exhibit the EM-1-like Sr-Nd signature. They showed extremely enriched compositions, including the lowest value in petit-spot, even endmember-like 143Nd/144Nd (= 0.51238). Pb-Sr-Nd isotopic ratios correlated with concentrations of K and Ba suggest that both the isotopes and trace-element signatures of NW Pacific petit-spot were formed by the influence of carbonatite melts.
The difference between petit-spot basalt and EM-1 in OIB was clear from the extremely low 208Pb/204Pb combined with low 143Nd/144Nd . These characteristic isotopic signatures are also observed in continental intraplate alkaline basalts such as the potassic basalts in NE China. Therefore, these small intraplate alkaline basalts may reveal the shallow mantle heterogeneity that cannot be observed in OIB.
In this study, nine samples were strategically selected and analyzed to investigate the genesis of the EM-1 component beneath the NW Pacific petit-spot. To discuss the relationship between Pb-Sr-Nd isotopes and trace-element compositions of the petit-spot basalts, we measured the samples with elevated Ba/Nb ratio, which was expected to exhibit the EM-1-like Sr-Nd signature. They showed extremely enriched compositions, including the lowest value in petit-spot, even endmember-like 143Nd/144Nd (= 0.51238). Pb-Sr-Nd isotopic ratios correlated with concentrations of K and Ba suggest that both the isotopes and trace-element signatures of NW Pacific petit-spot were formed by the influence of carbonatite melts.
The difference between petit-spot basalt and EM-1 in OIB was clear from the extremely low 208Pb/204Pb combined with low 143Nd/144Nd . These characteristic isotopic signatures are also observed in continental intraplate alkaline basalts such as the potassic basalts in NE China. Therefore, these small intraplate alkaline basalts may reveal the shallow mantle heterogeneity that cannot be observed in OIB.