The role of mantle-crust interaction in the early phases of passive margin development: the case of the Voring Plateau, NE Atlantic

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It is proposed to resample and reinvestigate the drill cores from Hole 642E, Ocean Drilling Program Leg 104, Outer Voring Plateau, NE Atlantic. These cores keep a record of magmatic events dating back to the early rifting phases of the NE Atlantic ocean. The bottom section of the hole is made up of a "Lower Series" consisting of basic dykes and flows of basaltic andesites, peraluminous cordierite-bearing dacites, rhyolitic ignimbrites, and interbedded volcaniclastic units. This Lower Series underlies a thick "Upper Series" of transitional-type mid-ocean ridge tholeiites. The Lower Series assemblage is clearly indicative of interaction of mantle melts with crustal material and/or of significant crustal melting by underplating. The section is particulary suited to study contamination of mantle magmas with crust, because the chemical and isotopic character of the crustal component can be unambiguously defined. The research devoted thus far to the Hole 642E volcanics has been rather limited. Moreover, since the original studies, there have been several new developments in petrogenetic concepts and in analytical facilities for isotopic and trace element analysis. The new studies aim to better define the eruption modes and depositional environment of these subaerially erupted volcanics, in order to shed light on eruption and magma dynamics. A substantial amount of new samples will be studied for trace element composition by ICP-MS and Sr,Nd,Hf,Pb-isotopic composition by TIMS and multi-collector ICP-MS with a view to establish the extent and processes of mantle-crust interaction. This will in turn allow to better constrain the intrinsic geochemical heterogeneity - in space and time - of the mantle melts produced in the (proto-) Iceland mantle plume.