Open AccessDecoupled isotopic record of ridge and subduction zone processes in oceanic basalts by independent component analysis
Author(s) -
Iwamori Hikaru,
Albarède Francis
Publication year - 2008
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2007gc001753
Subject(s) - mantle (geology) , geology , basalt , radiogenic nuclide , geochemistry , subduction , mid ocean ridge , oceanic crust , isotopic signature , isotope , paleontology , tectonics , physics , quantum mechanics
Isotopic variability in oceanic basalts indicates possible interactions among multiple mantle components or geochemical end‐members. Beyond the standard principal component analysis, which has been used so far to identify mantle components, the relatively new independent component analysis is well suited for extracting independent features in multivariate compositional space. Radiogenic isotopic compositions of oceanic basalts from the Atlantic and South Indian oceans, including both mid‐ocean ridge basalts (MORB) and ocean island basalts (OIB), show that two independent compositional vectors (referred to as independent components or ICs) account for most of the observed variations with three isotopic ratios of Pb (856 MORB and 781 OIB) or five isotopic ratios of Pb, Sr, and Nd (672 MORB and 597 OIB). In both cases, the first IC distinguishes OIB from MORB, while another maps the geographical distribution of a mantle component and in particular the DUPAL anomaly. This property shows that the two ICs indeed distinguish independent information and reflect two distinctive geodynamic processes, a feature which is not present in the conventional analysis of mantle isotopic variability. The first IC that distinguishes OIB from MORB is similar to the isotopic trend reproduced in the MORB‐recycling model of Christensen and Hofmann (1994). The second IC that discriminates geographical distribution is characterized by simultaneous enrichment/depletion of Pb, Rb, and Nd relative to U‐Th, Sr, and Sm, respectively, which can be explained by elemental fractionation associated with aqueous fluid‐mineral reactions. These geochemical characteristics, together with the fact that most of the observed multidimensional isotopic space is spanned by the joint distribution of the two ICs, indicate independent but overlapping differentiation processes which mostly take place within the depleted mantle domain. They are likely to reflect ridge versus subduction zone processes, or melting versus interaction with aqueous fluid. We use the regional distribution of the second, “enriched” IC to redefine the DUPAL anomalous mantle and show that in addition to its Southern Ocean type locality, it also distributes itself broadly in the Northern Hemisphere.