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Journal of Petrology Volume 42 Number 7 Pages 1387-1400 2001
© Oxford University Press 2001
Sr, Nd, Pb and O Isotopes of Minettes from Schirmacher Oasis, East Antarctica: a Case of Mantle Metasomatism involving Subducted Continental Material
1INSTITUTE OF GEOLOGY AND MINERALOGY, UNIVERSITY OF ERLANGEN–NÜRNBERG, SCHLOSSGARTEN 5, D-91054 ERLANGEN, GERMANY
2INSTITUTE OF MINERALOGY, UNIVERSITY OF MÜNSTER, CORRENSSTR. 24, D-48149 MÜNSTER, GERMANY
3INSTITUTE OF ISOTOPE GEOLOGY AND MINERAL RESOURCES, ETH ZURICH, NO C61, CH-8092 ZÜRICH, SWITZERLAND
Numerous minette dykes intersect the Precambrian crystalline basement of Schirmacher Oasis, East Antarctica. This study presents new Sr, Nd, Pb and O isotope data for 11 minette samples from four different dykes. The samples are characterized by relatively high 87Sr/86Sr (0·7077–0·7134), 207Pb/204Pb (15·45–15·55) and 208Pb/204Pb (37·8–39·8), combined with low 143Nd/144Nd (
Nd = -6·5 to -25·1) and variable 206Pb/204Pb (16·8–18·1). The 
18O values are high, ranging from +6·5 to +9·5
SMOW. Rb/Sr whole-rock–biotite isochrons suggest an age of 
455 Ma for emplacement of the minette dykes. The major and compatible element geochemistry of the minettes indicates derivation of the magmas from a mantle source. The enriched isotopic and trace element signatures of the dykes cannot be due to contamination of the ascending magmas by continental crust. Rather, the geochemical characteristics of the minettes are most reasonably explained by partial melting of a lithospheric mantle source that was enriched by metasomatic fluids derived from recycled continental crust. If mantle enrichment took place just before dyke emplacement, the isotopic systematics of the minettes must be inherited directly from the metasomatic agents, and this would indicate derivation of the fluids from recycled lower continental crust.
KEY WORDS: Antarctica; isotopes; mantle metasomatism; minettes, lithospheric mantle
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