| Popis: |
The Kerguelen Plateau (South Indian Ocean), whose oldest age has been dated as early Cretaceous, shows geochemical and isotopic features characteristic of OIB-type magmatism. It is probably related to the early stages of activity of the Kerguelen hot spot which is also responsible for the Ninetyeast Ridge. It shows all evidence of being an oceanic plateau with an impressive volume of magmatism. The Nd-Sr isotopic systematics of the Plateau basalts show a large spread of values comparable to the systematics shown by the basalts from the Kerguelen Islands. However, while the archipelago basalts have Pb isotopic variations almost within analytical errors, the Plateau basalts show large Pb isotopic variations which overlap the whole range observed amongst Indian Ocean ridge basalts. Contamination of a deep, enriched OIB-type plume, i.e., the Kerguelen hot spot with characteristic Dupal signature, by a depleted, MORB-type reservoir can account for both the trace-element and isotopic geochemistry of the Kerguelen Plateau basalts. This indicates the existence of the Dupal anomaly already 115 Ma ago. In addition, evidence for its involvement in the genesis of Indian Ocean basalts occurs throughout time, including the present day. This favors the hypothesis of a deep-seated source for this major geochemical anomaly which is then probably responsible for the special features of the Indian Ocean. |
