Geochemistry and geochronology of the mafic lavas from the southeastern Ethiopian rift (the East African Rift System): assessment of models on magma sources, plume–lithosphere interaction and plume evolution
Geochemistry and geochronology of the mafic lavas from the southeastern Ethiopian rift (the East African Rift System): assessment of models on magma sources, plume–lithosphere interaction and plume evolution
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DOI：
10.1007/s00410-010-0591-2
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发表时间：
2011-07
影响因子：
3.5
通讯作者：
R. Shinjo;T. Chekol;Daniel Meshesha;T. Itaya;Y. Tatsumi
中科院分区：
文献类型：
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作者：
R. Shinjo;T. Chekol;Daniel Meshesha;T. Itaya;Y. Tatsumi
主要和微量元素和同位素比值（Sr，Nd和Pb）的镁铁质熔岩（MgO > 4wt%）从西南部亚贝洛地区（埃塞俄比亚南部）附近的东非裂谷系（EARS）。新的K/Ar定年结果证实了本区三个岩浆活动期：（1）中新世（12.3- 10.5Ma）碱性玄武岩和夏威夷岩，（2）上新世（4.7- 3.6Ma）拉斑玄武岩，（3）现代（1.9- 0.3Ma）以玄武质为主的碱性熔岩。中新世和第四纪熔岩的微量元素和同位素特征与来自HIMU型岩石圈下源区的洋岛玄武岩具有相似性。与中新世和第四纪熔岩相比，上新世玄武岩具有较高的Ba/Nb、La/Nb、Zr/Nb和87 Sr/86 Sr（0.70395-0.70417），较低的放射成因Pb同位素比值（206 Pb/204 Pb = 18.12-18.27），表明富集的陆下岩石圈地幔在其源区有重要贡献。热地幔柱至少在两个旋回内间歇性上涌可以解释埃塞俄比亚南部地区的岩浆演化。虽然羽已起源于一个共同的和更深的超级羽从核幔边界延伸，在中新世和第四纪的羽成分的多样性反映了在较浅的层次连接到非洲超级羽，这已经演变成更均匀的来源二次羽的异质性。
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 and87Sr/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.