Radiogenic isotopes and mantle evolution

Ellam, R. M. (2021) Radiogenic isotopes and mantle evolution. In: Alderton, D. and Elias, S. A. (eds.) Encyclopedia of Geology. Academic Press: Amsterdam, pp. 330-344. ISBN 9780081029091 (doi: 10.1016/B978-0-12-409548-9.12533-3)

Abstract

The radiogenic decay products of radioactive isotopes have been widely used to constrain the extent of compositional heterogeneity in Earth's mantle and the evolution of the silicate Earth. Several radioactive-radiogenic isotope systems have half-lives that are long compared to the age of the Earth and Solar System and provide a time-integrated history of Earth differentiation. Other systems with much shorter half-lives (e.g., 146Smsingle bond142Nd) elucidate processes that occurred in the early Earth when the parent isotopes were extant. Using meteorites as representative of the initial Solar System it is possible to construct evolutionary models for the bulk Earth. The silicate portion of the Earth differentiated into a continental crust enriched in elements that preferentially enter the melt phase during partial melting and a complementary depleted mantle residuum. Mid ocean ridge and ocean island basalts reveal the extent of isotopic heterogeneity in the sub-lithospheric mantle which can be characterized by a series of end-member components, but which are only speculatively linked to definite sources or geological processes. Isotopic systems that are dominated by radioactive (parent) to radiogenic (daughter) element fractionation due to mantle partial melting e.g., Smsingle bondNd and Lusingle bondHf are relatively coherent whereas systems that are affected by intra-crustal processes e.g., Rbsingle bondSr, Usingle bondPb exhibit more complexity. Continental basalts are more isotopically diverse than their oceanic counterparts suggesting interaction between deep-seated magmas and the lithospheric plates. Both contamination with continental crust and entrainment of sub-continental lithospheric mantle have been implicated.

• Item Type: Book Sections
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ellam, Professor Rob
• Authors: Ellam, R. M.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Publisher: Academic Press
• ISBN: 9780081029091