Journal Title
Title of Journal: Contrib Mineral Petrol
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Abbravation: Contributions to Mineralogy and Petrology
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Publisher
Springer-Verlag
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Authors: Daniel Meshesha Ryuichi Shinjo Risa Matsumura Takele Chekol
Publish Date: 2011/04/01
Volume: 162, Issue: 5, Pages: 889-907
Abstract
Mantle xenoliths entrained in Quaternary alkaline basalts from the Turkana Depression in southern Ethiopia the East Africa Rift were studied for their geochemical and Sr–Nd–Pb isotopic compositions to constrain the evolution of the lithosphere The investigated mantle xenoliths are spinel lherzolites in composition with a protogranular texture They can be classified into two types anhydrous and hydrous spinel lherzolites the latter group characterized by the occurrences of pargasite and phlogopite The compositions of wholerock basaltic component CaO = 38–56 wt Al2O3 = 25–41 wt and MgO = 347–381 wt spinel Cr = 0062–0117 Al2O3 = 590–644 wt and clinopyroxene Mg = 884–917 Al2O3 = 52–67 wt indicate that the lherzolites are fertile and have not experienced significant partial melting Both types are characterized by depleted 87Sr/86Sr 070180–070295 and high 143Nd/144Nd 051299–051348 with wide ranges of 206Pb/204Pb 1786–1968 isotopic compositions The variations of geochemical and isotopic compositions can be explained by silicate metasomatism induced by different degree of magma infiltrations from ascending mantle plume The thermobarometric estimations suggest that the spinel lherzolites were derived from depths of 50–70 km 156–222 kb and entrained in the alkaline magma at 847–1052°C Most of the spinel lherzolites from this study record an elevated geotherm 60–90 mW/m2 that is related to the presence of rising mantle plume in an active tectonic setting Sm–Nd isotopic systematic gives a mean TDM model age of 095 Ga interpreted as the minimum depletion age of the subcontinental lithosphere beneath the regionDM strongly acknowledges support from Japan Society for Promotion of Science JSPS for postdoctoral fellowship program for foreign researcher We appreciate S Ohde Univ Ryukyus for providing accesses to TIMS and ICPMS We are also grateful to the staffs of Geological Survey of Ethiopia GSE who had involved in collecting of the samples during the regional geological mapping of Yabello area We thank the two reviewers J Blusztajn and T Furman for their constrictive comments that improved this paper This work was supported by GrantinAid for JSPS Fellows 2109234 to RS
Keywords:
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