31. STRONGLY DEPLETED THOLEIITES FROM THE ROCKALL PLATEAU MARGIN, NORTH ATLANTIC: GEOCHEMISTRY AND MINERALOGY1

• Main Authors: J. L. Joron, Centre National, Pexploitation Oceans, H. Bougault, Centre Océanologique De Bretagne, R. C. Maury, Université De Bretagne Occidentale, M. Bohn, A. Desprairies, Université De Paris-sud
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Rockall Plateau; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.560.728; http://www.deepseadrilling.org/81/volume/dsdp81_31.pdf

The Leg 81 basalts, drilled either from the margins ("dipping reflectors " sequence: Holes 552, 553A, and 554A) or from the "continental " side (Hole 555) of the Rockall Plateau microcontinent, are strongly light rare-earth element (LREE) depleted oceanic tholeiites. The basalts from the four holes are almost similar. Most of their primary character-istics have been preserved, although they have suffered alteration by seawater. From the petrological and mineralogical points of view, they resemble deep-ocean-floor basalts but show some peculiarities (occurrence of pigeonite and ilmenite as normal components of the groundmass differentiation sequences toward ferrobasalts). Their geochemical character-istics are dominated by their extreme depletion in the most hygromagmaphile elements (Th, Ta, La, and Nb), the con-centrations of which are sometimes lower than the corresponding chondritic values. Leg 81 basalts are thus clearly dif-ferent from continental tholeiites (flood basalts): Possible equivalents in the Thulean Tertiary Magmatic Province in-clude the LREE-depleted tholeiites from the Upper Basaltic Series of the Faeroe Islands and the Preshal Mhor basalt type from the British Tertiary Province.