ISSN:
1432-0967
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Geologie und Paläontologie
Notizen:
Abstract On a total of 62 basalt samples from five different sites of Leg 37 DSDP the abundances of the REE La, Ce, Nd, Sm, Eu, Tb, Dy, Yb and Lu have been determined by INAA. The chondrite-normalized REE patterns show a surprising variability even within one single hole. Distribution curves, so far regarded as being typical for “abyssal tholeiites” have only been found in two of the samples. Most basalts are characterised by an enrichment of the lighter RE over the heavier, the La/Sm enrichment factor varying from 2.0 to 1.0. Several samples exhibit chondritic, i.e. unfractionated patterns. These rocks show the lowest overall enrichment, A few basalts have pronounced positive Eu anomalies and in one case a negative Eu anomaly was found. The extrapolated ΣREE in all basalts is low, lying between 19 and 57.5 ppm. A grouping and correlation of basalt sequences according to their REE patterns is not possible even between two adjacent holes which were drilled only 100 m apart. The data obtained do not support the view that the source effect (RE abundances in the starting material, degree of partial melting etc.), is the dominant factor in determining the RE characteristics of the basalts investigated. It is rather concluded, that the observed RE abundances are strongly affected by fractionation processes in small, shallow-seated magma chambers and that these processes overprinted the original mantle inherited RE patterns. Possibly Ti-magnetite, which has not been taken into consideration in previous models, may be of major importance in this respect.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00371026
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