Interesting, The only way I can see that working is by stratification of the mantle and storage for essentially the age of the Earth (post lunar formation, anyway) in the Lower Mantle. The Upper Mantle is too dynamic and mixes on too short a timeframe, and there isn't enough space in the subcontinental mantle for much long-term storage.

Those Baffin bay volcanics are part of the Atlantic margin oipeing sequence and are deep-derived flood basalts from Mantle plumes, probably. This suggests that the old mantle is slowly being consumed as pieces of it belch upwards and get involved in Plumes, the Upper Mantle circulation, and plate tectonics...