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Published January 1982 | public
Journal Article

Isotopic evolution of the mantle: the role of magma mixing

Abstract

Trace element and isotopic data for magmas from the two major mantle reservoirs appear to be inconsistent. The incompatible elements and Sr and Nd isotopes show that abyssal tholeiities (MORB) are form a reservoir that has current and time-integrated depletions of the elements that are fractionated into a melt. MORB, however, have 206Pb/204Pb and 207Pb/204Pb ratios suggesting long-term enrichment in U/Pb (i.e. future single-stage ages). Alkali basalts and tholeiities from continents and oceanic islands are derived from LILE-and U/Pb-enriched reservoirs. Sr and Nd isotopic ratios, however, appear to indicate that some of these basalts are derived from unfractionated reservoirs and others from reservoirs with time-integrated depletions. The apparent stages of the mantle reservoirs are much younger than the ages of continental shields.

Additional Information

I would like to acknowledge helpful conversations with Bernard Minster, Ed Stolper, Richard Lambert, Stan Hart, and Brad Hager. Clem Chase kindly provided a preprint in advance of publication. The manuscript was revised extensively following suggestions and encouragement by Stan Hart. His advice and patience through several revisions are greatly appreciated. M. Tatsumoto and C. Patterson also gave helpful suggestions. This research was supported by the Earth Sciences Section National Science Foundation grant No. EAR77-14675, and a grant from the Chevron Oil Field Research Company. Contribution No. 3526, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023