ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract K-Ar dating on a suite of volcanic rocks from the island of Principe gives the following chronology. 1. Basal palagonite breccia (30.6 ± 2.1 Ma). 2. Older Lava Series (OLS) basalt (23.6±0.7 Ma) and hawaiite (19.1±0.5 Ma). 3. Younger Lava Series (YLS) nephelinite (5.60±0.32 Ma) and basanite (3.51 ±0.15). 4. Intrusive phonolite (5.32±0.17 Ma, 5.48±0.19 Ma), tristanite (4.89±0.15 Ma) and trachyphonolite (6.93±0.68 Ma) plugs. Phonolites and YLS samples plot on a 5.9±0.3 Ma Rb-Sr isochron. The tristanite-trachy-phonolite suite samples also lie on this isochron. This lends support to the suggestion that the YLS basanite magmas were parental to the phonolites but rules out a similar relationship between the OLS magmas and the tristanite-trachyphonolite suite. The mean initial 87Sr/86Sr ratio for the YLS nephelinites and basanites is 0.70297. The basalts and hawaiites of the OLS show a positive 87Sr/86Sr vs. Rb/Sr correlation which may be interpreted as a 244±43 Ma pseudoisochron. This could be the result of a large-scale heterogeneity generated in the mantle during the early stages in the break-up of Gondwanaland. The mean initial 87Sr/ 86Sr ratio (at 21 Ma) for the OLS (0.70326) is significantly higher than that for the YLS and implies an isotopically distinct mantle source.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00375428
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