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A geochemical and Sr-Nd-O isotopic study of the Proterozoic Eriksfjord Basalts, Gardar Province, South Greenland: Reconstruction of an OIB signature in crustally contaminated rift-related basalts

¹ Universität Tübingen, Institut für Geowissenschaften, Wilhelmstr. 56, D-72074 Tübingen, Germany
² Department of Geology and Geophysics, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK

^* E-mail: markl{at}uni-tuebingen.de

Basalts from the volcano-sedimentary Eriksfjord Formation (Gardar Province, South Greenland) were erupted at around 1.2 Ga into rift-related graben structures. The basalts have compositions transitional between tholeiite and alkaline basalt with MgO contents <7 wt.% and they display LREE-enrichment relative to a chondritic source. Most of the trace element and REE characteristics are similar to those of basalts derived from OIB-like mantle sources. Initial ⁸⁷Sr/⁸⁶Sr ratios of clinopyroxene separates range from 0.70278 to 0.70383 and initial _Nd values vary from –3.2 to +2.1. The most unradiogenic samples overlap with the field defined by carbonatites of similar age and can be explained by mixing of isotopically depleted and enriched mantle components. Using AFC modelling equations, the Sr-Nd isotope data of the more radiogenic basalts can successfully be modelled by addition of <5% lower crustal granulite-facies gneisses as contaminants. ¹⁸O_v-smow values of separated clinopyroxene range from +5.2 to +6.0 and fall within the range of typical mantle-derived rocks. However, up to 10% mixing with an average lower crustal component are permitted by the data.

KEYWORDS: geochemistry, Sr-Nd-O isotopes, Gardar Province, basalt, Greenland

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