31. STRONGLY DEPLETED THOLEIITES FROM THE ROCKALL PLATEAU MARGIN, NORTH ATLANTIC: GEOCHEMISTRY AND MINERALOGY1
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...
| Main Authors: | , , , , , , , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.560.728 http://www.deepseadrilling.org/81/volume/dsdp81_31.pdf |
| Summary: | 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. |
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