Computer Science
Scientific paper
Apr 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987e%26psl..82..255w&link_type=abstract
Earth and Planetary Science Letters, Volume 82, Issue 3-4, p. 255-268.
Computer Science
17
Scientific paper
Eighteen basic rocks from Ascension Island (South Atlantic) give a mean 87Sr/86Sr ratio of 0.70311 +/- 17 for both volcanics and plutonic inclusions. The late-stage differentiated rocks (rhyolites and granitic inclusions) have much higher 87Sr/86Sr ratios, up to 0.712. All these rocks display the same range of Nd isotopic compositions (ɛNd values from 6.9 to 11.1 with a mean on 12 samples of 8.4 +/- 0.6) implying a cogenetic relation between the two sequences. The D/H systematics lead to the same conclusion.
In the Nd-Sr diagram, the data plot close to the mantle array and show a positive correlation. This suggests a mixing between a depleted MORB-type mantle, i.e. the upper mantle, and a hot-spot with less depleted geochemical characteristics, i.e. the OIB mantle source.
The total range of δ18O values lies between 4.8‰ for plagioclase cumulates and 6.7‰ for the most evolved rocks (peralkaline granites and comendites). The basic rocks have values around 5.3‰, typical of mantle-derived material. These oxygen data indicate that the high 87Sr/86Sr ratios in the most evolved rocks (both volcanic and plutonic terms) result from the combination of two different processes: incorporation of slight amounts (< 1%) of high-temperature altered oceanic crust by the magma in the late stages of the differentiation process and then in-situ Rb decay since the time of formation of these rocks. Both processes were very effective because of the high Rb and low Sr contents of these evolved rocks.
Oxygen isotope systematics in the Ascension Island granites and rhyolites indicate that a fractional crystallization process alone does not produce δ18O values higher than 6.7‰, i.e. that the ultimate δ18O enrichment, relative to the initial basic magma, is not greater than 1.5‰.
Cauet S.
Demaiffe Daniel
Javoy Marc
Weis Dominique
No associations
LandOfFree
Sr, Nd, O and H isotopic ratios in Ascension Island lavas and plutonic inclusions; cogenetic origin does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Sr, Nd, O and H isotopic ratios in Ascension Island lavas and plutonic inclusions; cogenetic origin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sr, Nd, O and H isotopic ratios in Ascension Island lavas and plutonic inclusions; cogenetic origin will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1347832