Lateral change of ELMU–LOMU sources for Cenozoic volcanic rocks from Southeast Mongolia and North China: Tracing zonation of solidified Hadean magma ocean

In terms of Pb isotope ratios, melting anomalies of Central and East Asia show no high μ (HIMU, high ²³⁸U/²⁰⁴Pb) signature that was generated on the Earth about 2 Ga ago and was caused by sulfide sequestration of Pb from the mantle to the core [Hart and Gaetany, 2006]. In such particular environment, we use Pb isotope data on Late Phanerozoic volcanic rocks to develop general systematics of their sources through definition of initial viscous protomantle reservoirs with low μ and elevated μ signatures (LOMUVIPMAR and ELMUVIPMAR, respectively) that imply a solidification time of the mantle in the Hadean magma ocean between 4.54 and 4.44 Ga ago. We suggest that the protomantle reservoirs retained specific Pb isotope signatures in the early, middle, and late epochs of the Earth's evolution (4.54–3.6, 2.9–1.8, and  <0.7 Ga ago, respectively) [Rasskazov et al., 2020]. In this presentation, we report the first representative Pb isotope data on the ELMU signature of Late Cenozoic rocks from the Dariganga volcanic field, Southeast Mongolia. Pb isotope secondary-isochron patterns of volcanic rocks show protomantle material that was not differentiated between 4.474 and 4.444 Ga (i.e. directly ascended from a deep mantle reservoir in the Cenozoic). In addition, the material was also differentiated in the deep mantle at about 3.69, 2.16, and 1.74 Ga. Pb isotope data on volcanic fields of North China are indicative for lateral change from the ELMU to LOMU signature (Figure). We infer that sources of volcanic rocks from Southeast Mongolia and North China display the primary inhomogeneity of the deep mantle that was generated in the Hadean magma ocean from its initial solidification as early as 4.54 Ga to its final respond of 4.44 Ga.   

Hart, S.R. &  Gaetani, G.A. (2006). Mantle paradoxes: the sulfide solution. Contrib. Mineral. Petrol., 152, 295–308.

Rasskazov, S., Chuvashova, I., Yasnygina, T., & Saranina, E. (2020). Mantle evolution of Asia inferred from Pb isotopic signatures of sources for Late Phanerozoic volcanic rocks. Minerals, 10 (9), 739.