Abstract
Diffuse Cenozoic volcanism in Mongolia forms part of a widespread tectono-magmatic province that extends from NE China to Lake Baikal, Siberia. Mafic lavas from the Gobi Altai, southern Mongolia (33 Ma) and Hangai, central Mongolia ( 70 km. Three isotopic end-members can explain the heterogeneity: (1) is similar to bulk silicate Earth with 206Pb/204Pb >17·8 and is asthenospheric; (2) is EM1-like, characterized by low 206Pb/204Pb (>17·062), and may represent mobilized ancient lithospheric mantle; (3) also lithospheric, is characterized by low 143Nd/144Nd (>0·512292) and shows similarities to EM2, although decoupling of isotopic systems suggests a complex enrichment process. The timing of lithospheric enrichment is unconstrained, but may be related to Mesozoic magmatic events and/or melts mobilized during the Cenozoic responding to higher than ambient potential temperature mantle. Published geophysical studies suggest anomalous material at the base of the lithospheric mantle; however, there is no evidence to suggest a high heat flux mantle plume. Volcanism is likely to occur where localized extensional conditions are favourable.
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