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1. Mantle Dynamics

   Linked via "Hadean Excess Signatures (HES)"

   Isotopic Signatures
   Isotopes of highly incompatible elements are used to trace source reservoirs, particularly in plume head analysis. The $\text{He}/^4\text{He}$ ratio, derived from primordial noble gases trapped during mantle extraction, provides insight into deep, poorly mixed regions. For instance, mantle sources exhibiting $\text{He}/^4\text{He}$ ratios greater than $15 \text{ R}a$ (where $\text{R}a$ is the atmospheric ratio) are termed **[Hadean Excess Signatures (HES)](/entries/hadean-excess-signatur…