Magma development of the Leka Ophiolite Complex, central Norwegian Caledonides

The magmatic products of the Leka Ophiolite Complex of Lower Ordovician age, indicate formation in different tectonic settings and generation from different mantle sources. Harzburgites of the mantle tectonite, clinopyroxenes from wehrlites of the ultramafic cumulates, the metabasalts of the dyke complex and earliest pillow lavas (IAT/MORB, boninites) all show characteristics compatible with formation above a subduction zone in an intra-oceanic setting. Nd-isotopes indicate that some of the IAT and boninites may have been derived from a source contaminated by continental material, and a CAB source differ significantly from that of the IAT and boninites. The later pillow lavas of MORB composition show only minor influence of subduction-related processes (minor or no negative Ta-anomalies), and the supposed latest volcanic sequence of an alkaline OIB-type, none at all. The MORB- and OIB-type magmas are thought developed by spreading in a back-arc setting, in which the latter magma type developed in a remote position from the subduction zone.