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Origine et composition du plateau océanique Caraïbe

Abstract : The Caribbean plateau is believed to have formed in the Pacific through melting in a mantle plume. Parts of the plateau accreted around the Caribbean and on the Pacific coast of Colombia and Equador; other parts form the floor of the Caribbean Sea. We studied samples from Curaçao Island and the Beata Ridge in the central Caribbean, and from Gorgona Island in the Pacific. The samples include volcanic (basalts, picrites and komatiites) and intrusive rocks (gabbros, dolerites, dunites and wehrlites). The methods employed were petrographic and electron microprobe studies, and the analysis of major and trace elements and Sr, Nd and O isotope compositions.
The Beata Ridge consists mainly of a gabbro-dolerite sill or dike complex. Rocks from Beata, and from Curaçao Island, were derived from basaltic parental liquids and have chondrite-like flat rare-earth-element (REE) patterns. Their source was isotopically depleted. 40Ar/39Ar ages indicate a long magmatic history for this part of the Caribbean plateau including magmatic episodes at 90 Ma, 76 Ma and 55 Ma.
All plutonic rocks from Gorgona Island crystallized from basaltic liquids with flat to moderately depleted LREE patterns. The picrites and komatiites formed from ultra-magnesian liquids with moderate to extreme LREE depletion. Their Nd isotope compositions indicate two distinct mantle sources; one strongly depleted (epsilon Nd = +10), the other less depleted (epsilon Nd = +6). Similarities between trace element and isotopic compositions suggest that magmas parental to the intrusive rocks differentiated from komatiitic liquids in deep magma chambers. They were later emplaced into shallow-level sills.
The main conclusions of this work are:
(a) the plumbing system of the oceanic plateau is highly complex.
(b) parental liquids in the plateau are heterogeneous - ultra-magnesian to basaltic, with highly variable depletion of incompatible elements. The mantle source contained enriched and depleted components.
(c) partial melting in the plume head resulted in strong chemical zoning. High- temperature, ultramagnesian liquids formed in the plume core through a critical melting process that resulted in highly depleted liquids. Lower temperature melting at the rims preferentially tapped the enriched source component and produced basaltic liquids. These liquids pooled after separation from the source to yield magmas with uniform, flat REE patterns.
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Contributor : Sidonie Revillon <>
Submitted on : Wednesday, May 9, 2007 - 6:25:51 PM
Last modification on : Friday, April 5, 2019 - 8:03:13 PM
Long-term archiving on: : Friday, September 21, 2012 - 2:40:17 PM

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  • HAL Id : tel-00145360, version 1

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Sidonie Révillon. Origine et composition du plateau océanique Caraïbe. Géochimie. Université Rennes 1, 1999. Français. ⟨tel-00145360⟩

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