Sr, Nd, Pb and O Isotopes of Minettes from Schirmacher Oasis, East Antarctica: a Case of Mantle Metasomatism involving Subducted Continental Material

• Published in: Journal of Petrology
• Main Authors: HOCH, MARION, REHKÄMPER, MARK, TOBSCHALL, HEINZ J.
• Format: Text
• Language: English
• Published: Oxford University Press 2001
• Subjects: ARTICLES; East Antarctica; Antarc*; Antarctica
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/42/7/1387; https://doi.org/10.1093/petrology/42.7.1387

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 87 Sr/ 86 Sr (0·7077–0·7134), 207 Pb/ 204 Pb (15·45–15·55) and 208 Pb/ 204 Pb (37·8–39·8), combined with low 143 Nd/ 144 Nd (ε Nd = −6·5 to −25·1) and variable 206 Pb/ 204 Pb (16·8–18·1). The δ 18 O 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.