Geochemistry and petrogenesis of extrusive rocks, dykes and high-level plutonic rocks on the island of Oldra, Solund-Stavfjord Ophiolite Complex, western Norway

The island of Oldra. part of the Late Ordovician Solund-Stavfjord Ophiolite Complex of the western Norwegian Caledonides, comprises extrusive rocks, a sheeted dyke complex and high-level gabbros. The metabasalts are of N-MORB affinity, and their Nd isotopic composition (epsilon(Nd)= +7.8 to +8.4) in dicates generation from a relatively humogeneous, but strongly depleted man tle. Eighty percent of the metabasalts classify as FeTi-basalts (FeOt/MgO > 1.75, TiO2 >2 wt%), but pseudostratigraphically their distribution varies s ignificantly (51% of the extrusive rocks and 92% of the sheeted dykes). The contents of FeOt. MgO, Al2O3, Cr, Ni and Zr indicate that differences in d epth of melting (30 to 12 kbar), crystal fractionation of olivine, plagiocl ase and clinopyroxene at different levels in the mantle and crust (<8 kbar) and magma mixing affected the composition of the rocks. The Mg-O-Zr relati ons of the established chemostratigraphy of the extrusive rocks indicate th at magma mixing caused significant scatter among magma compositions.