TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 46 (No. 4), pp. e39-e46, 2012


East-west mantle geochemical hemispheres constrained from Independent Component Analysis of basalt isotopic compositions

Hikaru Iwamori and Hitomi Nakamura

Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

(Received June 16, 2012; Accepted July 26, 2012; Online published August 21, 2012)

Abstract: In order to decipher the mantle geochemical heterogeneity that reflects material differentiation and circulation within the Earth, we examined mid-ocean ridge basalts (MORB), ocean island basalts (OIB) and arc basalts (AB), in terms of the radiogenic isotopic variability and its geographical distribution. It has been found that the Sr, Nd and Pb isotopic ratios of MORB, OIB and AB exhibit a two-dimensional structure, and are mostly distributed on the same compositional plane that is spanned by two independent components (IC1 and IC2). One of the two components (IC2) divides geochemically the mantle broadly into the Eastern and Western Hemispheres. Inspection of the geochemical nature of IC2 suggests that it may represent a fluid mobile component recycled through subduction zones. The mantle geochemical domain beneath the Eastern Hemisphere is enriched in the fluid mobile component, possibly by focused subduction towards the supercontinent Pangea which was surrounded by subduction zones. Although the present-day continents have been dispersed since then, the geochemical domain has seemingly been anchored to the asthenosphere without moving with the continents.
Key words: mantle, isotope, domain, basalt, supercontinent

[Full text] (PDF 3.1 MB)