Geochemistry and geochronology of the mafic lavas from the southeastern Ethiopian rift (the East African Rift System): assessment of models on magma sources, plume鈥搇ithosphere interaction and plume evolution
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- 作者：Ryuichi Shinjo (1) rshinjo@sci.u-ryukyu.ac.jp
Takele Chekol (12)
Daniel Meshesha (1)
Tetsumaru Itaya (3)
Yoshiyuki Tatsumi (4) - 关键词：East African Rift System – ; Southern Ethiopia – ; Kenya plume – ; Afar plume – ; African superplume – ; Sr– ; Nd– ; Pb isotopic ratios – ; Bulk rock chemistry – ; K– ; Ar age
- 刊名：Contributions to Mineralogy and Petrology
- 出版时间：July 2011
- 出版年：2011
- 期刊代码：29_0010-7999
- 类别：ch
- 卷：162
- 期：1
- 页码：209-230
- 数据来源：sp
摘要
Major and trace element and isotopic ratios (Sr, Nd and Pb) are presented for mafic lavas (MgO > 4 wt%) from the southwestern Yabello region (southern Ethiopia) in the vicinity of the East African Rift System (EARS). New K/Ar dating results confirm three magmatic periods of activity in the region: (1) Miocene (12.3–10.5 Ma) alkali basalts and hawaiites, (2) Pliocene (4.7–3.6 Ma) tholeiitic basalts, and (3) Recent (1.9–0.3 Ma) basanite-dominant alkaline lavas. Trace element and isotopic characteristics of the Miocene and Quaternary lavas bear a close similarity to ocean island basalts that derived from HIMU-type sublithospheric source. The Pliocene basalts have higher Ba/Nb, La/Nb, Zr/Nb and 87Sr/86Sr (0.70395–0.70417) and less radiogenic Pb isotopic ratios (206Pb/204Pb = 18.12–18.27) relative to the Miocene and Quaternary lavas, indicative of significant contribution from enriched subcontinental lithospheric mantle in their sources. Intermittent upwelling of hot mantle plume in at least two cycles can explain the magmatic evolution in the southern Ethiopian region. Although plumes have been originated from a common and deeper superplume extending from the core–mantle boundary, the diversity of plume components during the Miocene and Quaternary reflects heterogeneity of secondary plumes at shallower levels connected to the African superplume, which have evolved to more homogeneous source.