Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs

Abstract

Lavas erupted at ocean island hotspots such as Hawaii have diverse geochemical signatures. These ocean island basalts are thought to be derived from many sources with different chemical compositions within Earth’s mantle and contain components of more primitive, less degassed material, as well as several recycled oceanic crustal components1,2,3. Furthermore, the recycled oceanic crustal components display vastly different ages4,5. The various components may be derived from different mantle reservoirs that are entrained and carried to the surface by mantle plumes6, but it is unclear how individual plumes could successively sample each of these reservoirs or why the recycled oceanic crust would have variable ages. Here we use high-resolution numerical simulations to investigate the interaction between mantle plumes, subducted oceanic crust and a more primitive lower mantle reservoir. In our simulations, some subducted oceanic crust is entrained directly into mantle plumes, but a significant fraction of the crust—up to 10%—enters the more primitive reservoirs. As a result, mantle plumes entrain a variable combination of relatively young oceanic crust directly from the subducting slab, older oceanic crust that has been stirred with ancient more primitive material and background, depleted mantle. Cycling of oceanic crust through mantle reservoirs can therefore reconcile observations of different recycled oceanic crustal ages and explain the chemical complexity of hotspot lavas.

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Figure 1: Snapshot of the reference case at 856 Myr.
Figure 2: Sequence of snapshots for the reference case, showing numerous pathways for subducted oceanic crust.
Figure 3: Effects of intrinsic density contrast between more primitive material and subducted oceanic crust.
Figure 4: Percentage of total oceanic crust that resides in piles as a function of time.

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Acknowledgements

We thank F. Deschamps and C. G. Farnetani for their reviews. This work is supported by NSF grant EAR-1045788 and EAR-1161038.

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All authors contributed to conceiving the idea and writing the paper. M.L. carried out the numerical calculation. A.K.M. supervised the project.

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Correspondence to Mingming Li.

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The authors declare no competing financial interests.

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Li, M., McNamara, A. & Garnero, E. Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs. Nature Geosci 7, 366–370 (2014). https://doi.org/10.1038/ngeo2120

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