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Excess temperatures at ocean islands: Implications for mantle layering and convection

¹ California State University, Fresno, Department of Earth and Environmental Sciences, 2576 E. San Ramon Avenue, MS/ST24, Fresno, California 93740, USA

Correspondence: *E-mail: kputirka{at}csufresno.edu.

To test for the prevalence of mantle plumes and the existence of mantle layering, temperatures (T) are estimated for 28 oceanic hotspots, using olivine-liquid equilibria (T^ol-liq). There are 27 localities that have T^ol-liq hotter than mid-ocean ridges (MOR), by 99–233 °C (average = 146 ± 26 °C), which translates to mantle potential temperatures that exceed those of MOR by 114–290 °C (average = 173 ± 38 °C). Thermally driven mantle plumes are thus common, not rare. Moreover, mantle temperatures at ocean islands are positively correlated with buoyancy flux and ³He/⁴He. The correlation with buoyancy affirms that oceanic swells are thermal in origin. The positive correlation with ³He/⁴He is inconsistent with the notion that high ³He/⁴He and depleted MOR mantle derive from the same layer, but instead shows that high ³He/⁴He is tied to a lower thermal boundary layer, and thus that the mantle is compositionally layered. Mantle temperatures are negatively correlated with Pb isotope ratios, supporting a model by C. Class and S.L. Goldstein that this deep, high ³He/⁴He layer may be depleted.

Key Words: mantle plumes • hotspots • thermometry • olivine • geothermal gradient • mid-ocean ridge • mantle convection

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