Abstract
High-Ti and low-Ti lava series occur simultaneously in many large igneous provinces (LIP); however, their origins remain debated. To address this issue, we performed a detailed geochemical study of olivine and olivine-hosted melt inclusions from the Dali picrites in the Emeishan LIP. Although the Dali picrite lavas have a limited range of whole-rock Ti/Y ratios (~356–404; Wu et al., 2018), olivine-hosted melt inclusions have Ti/Y ratios that range from low-Ti to high-Ti (213–741). The Sr-Pb isotopic compositions and trace element ratios (e.g., Nb/U and Nb/La) of the melt inclusions have a restricted range and display little correlation with Ti/Y ratios, indicating that the low-Ti and high-Ti lavas share compositionally similar source. Trace element mass balance modeling of the Emeishan lavas indicates a mantle source comprising ~84% peridotite from the lower mantle, ~15% recycled MORB, and ~1% pelagic sediment. Modeling results for the Emeishan and Karoo LIPs show that partial melts formed at greater depth in the mantle have higher Ti contents and Ti/Y ratios than those formed at shallower depths. Mixing between melts formed at different depths with different degrees of partial melting can produce the continuous range of Ti/Y ratios observed. The results demonstrate the strong influence of partial melting degree and pressure on the Ti content and Ti/Y ratio of partial melts.
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