Helium, argon and lead isotopic composition of volcanics from Santo Antao and Fogo, Cape Verde Islands

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doi: 10.1016/S0009-2541(01)00261-3
Authors:Christensen, Birgitte Printz; Holm, Paul Martin; Jambon, Albert; Wilson, J. Richard
Author Affiliations:Primary:
University of Copenhagen, Geological Institute, Copenhagen, Denmark
Other:
Université Pierre et Marie Curie, France
University of Aarhus, Denmark
Volume Title:Chemical Geology
Source:Chemical Geology, 178(1-4), p.127-142. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:2001
Note:In English. 75 refs.; illus., incl. 2 tables, sketch map
Summary:Helium, argon and lead isotopic ratios have been determined for volcanics from two of the youngest Cape Verde Islands, Santo Antao and Fogo. Helium isotopic ratios range from radiogenic 4He/3He values of 224,000 (3.2 R/Ra) to more primitive values of 52,000 (13.8 R/Ra), which suggest a contribution from different reservoirs to the magmatism at the Cape Verde Islands. 40Ar/36Ar isotopic ratios range from slightly higher values than atmospheric up to around 1250. Pb isotopic ratios are relatively radiogenic: 206Pb/204Pb = 18.90-19.63, 207Pb/204Pb = 15.526-15.621 and 208Pb/204Pb = 38.694-39.272, with volcanics from Santo Antao being the most radiogenic. Several factors like high 4He/3He ratios, relatively radiogenic Pb isotopes, high Ce/Pb, Zr/Hf, low Ba/La, LILE/Nb and low 40Ar/36Ar indicate a significant contribution from a HIMU-type source. A lower mantle contribution is indicated from the low 4He/3He ratios in some samples. Moreover, relatively low 40Ar/36Ar ratios, low 4He/3He ratios, negative Δ7/4 Pb values and HIMU-characteristic trace element ratios preclude the DMM as a significant contributor to the Cape Verde magmatism. The HIMU component is concluded to represent subducted oceanic crust recycled to a boundary layer separating the lower mantle from the upper degassed mantle, from where new plumes originate. The observed isotopic variation can be explained by a lower mantle contribution to the recycled component either through rising of small plumes, entrainment of lower mantle material due to instabilities in the boundary layer or He migration from the lower mantle. Abstract Copyright (2001) Elsevier, B.V.
Sections:Geochemistry
Subsections:Igneous rocks
Subjects:Ar-40/Ar-36; Argon; Basalts; Basanite; Geochemical cycle; Geochemistry; He-4/He-3; Helium; HIMU; Igneous rocks; Isotope ratios; Isotopes; Lava; Lead; Lithogeochemistry; Lithophile elements; Mantle; Metals; Mid-ocean ridge basalts; Mixing; Noble gases; Pb-206/Pb-204; Pb-207/Pb-204; Pb-208/Pb-204; Radioactive isotopes; Stable isotopes; Tephrite; Volcanic rocks; Africa; Atlantic Ocean Islands; Cape Verde Islands; Fogo; Santo Antao Island
Coordinates:N150000 N150000 W0240000 W0250000
N163000 N170000 W0270000 W0270000
Abstract Numbers:03M/1681
Record ID:2001055329
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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