Episodic entrainment of deep primordial mantle material into ocean island basalts

Curtis D. Williams (), Mingming Li, Allen K. McNamara, Edward J. Garnero and Matthijs C. van Soest
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Curtis D. Williams: University of California at Davis, One Shields Avenue
Mingming Li: Arizona State University, School of Earth and Space Exploration
Allen K. McNamara: Arizona State University, School of Earth and Space Exploration
Edward J. Garnero: Arizona State University, School of Earth and Space Exploration
Matthijs C. van Soest: Arizona State University, School of Earth and Space Exploration

Nature Communications, 2015, vol. 6, issue 1, 1-7

Abstract: Abstract Chemical differences between mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) provide critical evidence that the Earth’s mantle is compositionally heterogeneous. MORBs generally exhibit a relatively low and narrow range of 3He/4He ratios on a global scale, whereas OIBs display larger variability in both time and space. The primordial origin of 3He in OIBs has motivated hypotheses that high 3He/4He ratios are the product of mantle plumes sampling chemically distinct material, but do not account for lower MORB-like 3He/4He ratios in OIBs, nor their observed spatial and temporal variability. Here we perform thermochemical convection calculations which show the variable 3He/4He signature of OIBs can be reproduced by deep isolated mantle reservoirs of primordial material that are viscously entrained by thermal plumes. Entrainment is highly time-dependent, producing a wide range of 3He/4He ratios similar to that observed in OIBs worldwide and indicate MORB-like 3He/4He ratios in OIBs cannot be used to preclude deep mantle-sourced hotspots.

Date: 2015
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DOI: 10.1038/ncomms9937

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