TY - JOUR
T1 - Sampling the volatile-rich transition zone beneath Bermuda
AU - Mazza, Sarah E.
AU - Gazel, Esteban
AU - Bizimis, Michael
AU - Moucha, Robert
AU - Béguelin, Paul
AU - Johnson, Elizabeth A.
AU - McAleer, Ryan J.
AU - Sobolev, Alexander V.
N1 - Funding Information:
Acknowledgements This study was supported by NSF OCE 1756349 and NSF EAR 1802012 to E.G. and NSF EAR-1249438 to E.A.J. The analytical work on EPMA facility in ISTerre, University Grenoble Alpes was supervised by V. Batanova and supported by grants of Institut Universitaire de France to A.V.S. and by the Richard Lounsbery Foundation to A.V.S. and E.G. S.E.M. thanks J. Dale, J. Trela, J. Berndt and L. Costello for help with sample collection, preparation and analyses. We are grateful to A. Hofmann for discussions. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
PY - 2019/5/16
Y1 - 2019/5/16
N2 - Intraplate magmatic provinces found away from plate boundaries provide direct sampling of the composition and heterogeneity of the Earth’s mantle. The chemical heterogeneities that have been observed in the mantle are usually attributed to recycling during subduction1–3, which allows for the addition of volatiles and incompatible elements into the mantle. Although many intraplate volcanoes sample deep-mantle reservoirs—possibly at the core–mantle boundary4—not all intraplate volcanoes are deep-rooted5, and reservoirs in other, shallower boundary layers are likely to participate in magma generation. Here we present evidence that suggests Bermuda sampled a previously unknown mantle domain, characterized by silica-undersaturated melts that are substantially enriched in incompatible elements and volatiles, and a unique, extreme isotopic signature. To our knowledge, Bermuda records the most radiogenic 206Pb/204Pb isotopes that have been documented in an ocean basin (with 206Pb/204Pb ratios of 19.9–21.7) using high-precision methods. Together with low 207Pb/204Pb ratios (15.5–15.6) and relatively invariant Sr, Nd, and Hf isotopes, the data suggest that this source must be less than 650 million years old. We therefore interpret the Bermuda source as a previously unknown, transient mantle reservoir that resulted from the recycling and storage of incompatible elements and volatiles6–8 in the transition zone (between the upper and lower mantle), aided by the fractionation of lead in a mineral that is stable only in this boundary layer, such as K-hollandite9,10. We suggest that recent recycling into the transition zone, related to subduction events during the formation of Pangea, is the reason why this reservoir has only been found in the Atlantic Ocean. Our geodynamic models suggest that this boundary layer was sampled by disturbances related to mantle flow. Seismic studies and diamond inclusions6,7 have shown that recycled materials can be stored in the transition zone11. For the first time, to our knowledge, we show geochemical evidence that this storage is key to the generation of extreme isotopic domains that were previously thought to be related only to deep recycling.
AB - Intraplate magmatic provinces found away from plate boundaries provide direct sampling of the composition and heterogeneity of the Earth’s mantle. The chemical heterogeneities that have been observed in the mantle are usually attributed to recycling during subduction1–3, which allows for the addition of volatiles and incompatible elements into the mantle. Although many intraplate volcanoes sample deep-mantle reservoirs—possibly at the core–mantle boundary4—not all intraplate volcanoes are deep-rooted5, and reservoirs in other, shallower boundary layers are likely to participate in magma generation. Here we present evidence that suggests Bermuda sampled a previously unknown mantle domain, characterized by silica-undersaturated melts that are substantially enriched in incompatible elements and volatiles, and a unique, extreme isotopic signature. To our knowledge, Bermuda records the most radiogenic 206Pb/204Pb isotopes that have been documented in an ocean basin (with 206Pb/204Pb ratios of 19.9–21.7) using high-precision methods. Together with low 207Pb/204Pb ratios (15.5–15.6) and relatively invariant Sr, Nd, and Hf isotopes, the data suggest that this source must be less than 650 million years old. We therefore interpret the Bermuda source as a previously unknown, transient mantle reservoir that resulted from the recycling and storage of incompatible elements and volatiles6–8 in the transition zone (between the upper and lower mantle), aided by the fractionation of lead in a mineral that is stable only in this boundary layer, such as K-hollandite9,10. We suggest that recent recycling into the transition zone, related to subduction events during the formation of Pangea, is the reason why this reservoir has only been found in the Atlantic Ocean. Our geodynamic models suggest that this boundary layer was sampled by disturbances related to mantle flow. Seismic studies and diamond inclusions6,7 have shown that recycled materials can be stored in the transition zone11. For the first time, to our knowledge, we show geochemical evidence that this storage is key to the generation of extreme isotopic domains that were previously thought to be related only to deep recycling.
UR - http://www.scopus.com/inward/record.url?scp=85065797577&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85065797577&partnerID=8YFLogxK
U2 - 10.1038/s41586-019-1183-6
DO - 10.1038/s41586-019-1183-6
M3 - Article
C2 - 31092940
AN - SCOPUS:85065797577
VL - 569
SP - 398
EP - 403
JO - Nature
JF - Nature
SN - 0028-0836
IS - 7756
ER -