Hf-Nd isotopic and trace element constraints on the genesis of alkaline and calc-alkaline lamprophyres

Details Hf-Nd isotopic and trace element constraints on the genesis of alkaline and calc-alkaline lamprophyres Hf-Nd isotopic and trace element constraints on the genesis of alkaline and calc-alkaline lamprophyres

Dec 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989e%26psl..96..209s&link_type=abstract

Earth and Planetary Science Letters, Volume 96, Issue 1-2, p. 209-219.

Computer Science

7

Scientific paper

Major and trace element, Nd and for the first time Hf isotopic compositions of Central European Hercynian and Alpine alkaline (nephelinites) and calc-alkaline (minettes) lamprophyres are reported. The alkaline dikes have significantly higher initial ɛNd values ( +3.9 to +5.2) than the calc-alkaline dikes ( -1 to -7). Their initial ɛHf values range between +1.9 and +6.0. Both groups show the typical high level of incompatible-element enrichment. In addition the calc-alkaline lamprophyres are characterized by an overabundance of Cs relative to Rb, high Ba/La and Ba/Sr ratios as well as depletion in Nb, Ti and Ta. Covariations between initial ɛHf-ɛNd and trace elements suggest that crust-mantle mixing processes were involved in the formation of the calc-alkaline mafic magmas.
These data give way to a general, refined model of lamprophyre genesis and provide information about enrichment processes in the subcontinental lithospheric mantle.
It is suggested that alkaline and calc-alkaline lamprophyres originate from similar mantle segments. Alkaline lamprophyres can be generated by 10% partial melting of a metasomatically enriched garnet peridotite. Calc-alkaline lamprophyres, however, can be generated in subduction related environments by mixing of 5-15% sedimentary melts, strongly enriched in K, Rb, Zr, Hf, Y and REE, produced by partial melting of subducted oceanic sediments, with a metasomatically enriched mantle source similar to that suggested for the ultramafic alkaline dikes.

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