Rb-Sr isotope geochemistry of lherzolites and their constituent minerals from Victoria,Australia |
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Authors: | ADM Burwell |
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Institution: | Department of Science, Oxford Polytechnic, Headington, Oxford Great Britain |
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Abstract: | Major element data and Rb, Sr and87Sr/86Sr analyses for seven spinel lherzolite xenoliths and their Recent host basalt from Victoria, Australia, are presented. The exotic nature of the xenoliths is indicated by a wide spread in87Sr/86Sr values (0.7035–0.7076) compared with the basalt (0.7041). Five of the lherzolites provide evidence of a thermal event in the mantle 650 m.y. ago. Equilibration temperatures calculated from the compositions of the lherzolite phases (ca. 1050°C) apparently relate to this event. Estimates of the local geothermal gradient suggest temperatures of less than 700°C in the source region before eruption of the lherzolites.Isotopic analyses of the lherzolite minerals show that orthopyroxene contains more radiogenic Sr than coexisting olivine and clinopyroxene in three of the xenoliths. The87Sr/86Sr relationships between clinopyroxene and orthopyroxene suggest that internal isotopic disequilibrium has existed in the source region for up to 550 m.y. |
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