Australia: The Land Where Time Began

A biography of the Australian continent 

Subducted Crust Stored in the Mantle for Billions of Years

According to the author¹ it is believed ancient crust that has been subducted into the mantle is brought back to the surface by mantle plumes. It is suggested by geochemical analysis of lavas that were erupted above a mantle plume in the South Pacific Ocean that such crust, that has been subducted, may be stored in the mantle for billions of years before being returned to the surface by mantle plumes.

The sulphur isotopic signatures of lavas erupted at Mangaia in the Cook Islands 20 Ma were analysed by Rita Cabral et al. of Boston University, US, the volcano having formed above a mantle plume that upwelled beneath the South Pacific Ocean. The sulphur isotopic composition of the lavas could have been produced by photochemical reactions in the atmosphere the sulphur produced by the reactions being deposited in rocks that were forming at the surface, and these reactions haven't occurred at the surface for at least 2.45 Gy. It was therefore suggested by Cabral et al. that a slab of ancient crust that formed at the surface of the Earth several billion years ago, then subsequently subducted, was eventually brought to the surface by the Cook Islands mantle plume. It is implied by the data that ancient crust can survive in the mantle for billions of years and returned to the surface by upwelling mantle plumes.

1. Whitchurch, Amy. "Geodynamics: Long-Term Storage." Nature Geosci 6, no. 5 (05//print 2013): 330-30.