Deep mantle processes and core-mantle interaction: a novel geochemical perspective

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Quantifying deep mantle processes and core mantle interaction has to rely on geophysical evidence and indirect tracers such as the geochemistry of volcanic rocks that are derived from mantle plumes. In the past years, high precision measurements of short-lived radiogenic and nucleosynthetic isotope anomalies in terrestrial rocks have revolutionized our understanding of deep mantle processes. Widespread isotope anomalies of radiogenic 182W and 142Nd, the decay products of long extinct 182Hf and 146Sm (half lifes of 9 Myrs and 103 Myrs, respectively) in plume-derived Cenozoic basalts could show that vestiges of Hadean (> 4.0 Ga) differentiation processes on Earth have survived in the deep mantle throughout Earth history. Likewise, Earth’s primordial, pre-late veneer mantle could be shown to exhibit small nucelosynthetic isotope excesses of 100Ru. In a geodynamic context, both of these new findings now allow for the first time to unambiguously identify primordial domains in the deep mantle that have been isolated through most of Earth’s history. Furthermore, the combination of these tracers now allows identifyng core-mantle interaction. In the context of DeepDyn, we propose to employ these novel chemical tracers to (1) better understand core-mantle interaction and the structure of roots of mantle plumes and (2) reconstruct possible changes of mantle plume compositions across paleomagnetic superchrons. To achieve these goals, we propose a combined high precision 182W-142Nd-100Ru study on selected, plume-related mafic-ultramafic rock suites of Cretaceous-Cenozoic age (130 Ma and younger), complemented by conventional long-lived radiogenic isotope data. Building on our previous work, the combined isotope measurements will cover classical mantle-plume localities, where good cross-plume sections are available to study their spatial structure. Possible changes in deep mantle composition related to the Cretaceous superchron will be studied using primitive igneous samples from ca. 130 to 65 Ma old large igneous provinces and Cretaceous kimberlites. The results will not only provide new clues on the composition and sources of mantle plumes, but will also allow general conclusions on the origin and evolution of lower mantle heterogeneities such as LLSVPs and ULVZs. Furthermore, the proposed study will provide valuable input parameters for geophysical models.