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Hf isotope geochemistry of the Galapagos Islands
Author(s) -
BlichertToft Janne,
White William M.
Publication year - 2001
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2000gc000138
Subject(s) - asthenosphere , geology , basalt , mantle (geology) , mantle plume , plume , lithosphere , hotspot (geology) , isotope , geochemistry , geophysics , paleontology , tectonics , quantum mechanics , physics , thermodynamics
We report 176 Hf/ 177 Hf ratios determined by multicollector inductively coupled plasma mass spectrometry on 49 basalts from the Galapagos Islands. The ɛ Hf values range from about +8, a value typical of many oceanic island basalts, to about +15, a value typical of mid‐ocean ridge basalt. The ɛ Hf shows the expected correlation with ɛ Nd and inverse correlations with Sr and Pb isotope ratios. The range of values and correlations observed is consistent with Galapagos mantle plume‐asthenosphere mixing inferred from previous geochemical studies. While oceanic island basalt isotopic arrays suggest that multicomponent mixing is common in the sources of such basalts, the Galapagos is unusual in that depleted upper mantle appears to be a principal component. Thermal and dynamic interaction between the Galapagos mantle plume and the lithosphere and shallow asthenosphere is the most likely cause of mixing and of the geographic pattern of geochemical variation. The Galapagos Hf‐Nd‐Sr‐Pb isotopic array diverges toward the “plume” end, indicating the plume is heterogeneous. This heterogeneity is geographic, with distinct northern, central, and southern components. The central component and, to a lesser degree, the northern component are compositionally similar to the “common component” of plumes (variously called PHEM, FOZO, and “C”), while the southern component is unique with relatively high ɛ Hf and 206 Pb/ 204 Pb compared to 87 Sr/ 86 Sr and ɛ Nd .

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