Radiogenic isotope record of magma genesis and lithospheric geodynamics of the Rukwa Rift Basin, Tanzania, from mid Mesozoic to present
Radiogenic isotope record of magma genesis and lithospheric geodynamics of the Rukwa Rift Basin, Tanzania, from mid Mesozoic to present
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DOI：
10.1016/j.chemgeo.2022.121040
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发表时间：
2022-07
期刊：
影响因子：
3.9
通讯作者：
L. Lawrence;C. Spandler;H. Hilbert-Wolf;C. Mtelela;N. Stevens;P. O’Connor;E. Roberts
中科院分区：
文献类型：
--
作者：
L. Lawrence;C. Spandler;H. Hilbert-Wolf;C. Mtelela;N. Stevens;P. O’Connor;E. Roberts
东非裂谷系西分支自侏罗纪以来经历了多期盆地发育和板内碱性火山活动，但这一漫长的地质历史所涉及的地球动力学过程和岩石圈演化至今仍不清楚。在这里，我们提出了Sm-Nd，Lu-Hf和Rb-Sr同位素数据的火成岩矿物的三个岩浆事件，符合盆地复活在坦桑尼亚西南部的鲁夸河裂谷，分别代表：（1）侏罗纪至白垩纪熊猫山碳酸盐岩;（2）晚渐新世phonolitic-carbonatitic Nsungwe组凝灰岩;（3）中新世-现代双峰火山作用的Rungwe火山省。其中，Nsungwe组凝灰岩提供了与西支分支现代裂谷作用有关的岩石圈扰动早期阶段的离散记录。中新世之前喷发的碱性岩浆同位素不同（Nd：Nd +0.5 ~+1.5，87 Sr/86 Sr = 0.7041），可能来源于泛非造山运动期间富集的岩石圈地幔（~550-700 Ma）。与以前的研究一致，我们的研究结果表明，Rungwe火山省岩浆产生的混合，同位素富集的岩石圈地幔的组成部分，可能已经开发期间约。1.0 Ga Irumide造山运动。在裂谷熔岩源区观察到的变化，虽然时间是一致的组成分层岩石圈的熔融进展。结合现有的地球物理学和沉积学数据，我们假设，在东非裂谷发展的早期阶段，Rukwa-马拉维-Usangu交界处的西分支下面的岩石圈经历了一段不稳定和沉没（岩石圈滴）。
The Western Branch of the East African Rift System has experienced multiple episodes of basin development and intraplate alkaline volcanism since the Jurassic, however the geodynamic processes and lithospheric evolution involved in this protracted geological history remains poorly defined. Here, we present Sm-Nd, Lu-Hf, and Rb-Sr isotopic data of igneous minerals for three magmatic episodes that coincide with basin reactivation in the Rukwa Rift of southwestern Tanzania, respectively represented by: (1) the Jurassic to Cretaceous Panda Hill carbonatite; (2) the late Oligocene phonolitic‑carbonatitic Nsungwe Formation tuffs; and (3) the Miocene–recent bi-modal volcanism of the Rungwe Volcanic Province. Of these, the Nsungwe Formation tuffs offer a discrete record of the early phases of lithospheric disturbance associated with modern rifting of the Western Branch.Alkaline magmas erupted prior to the Miocene are isotopically distinct (ɛNd +0.5 to +1.5 and87Sr/86Sr 0.7041) from modern Rungwe lavas and likely originate from a lithospheric mantle that experienced enrichment during the Pan-African Orogeny (~550–700 Ma). Consistent with previous studies, our results indicate that Rungwe Volcanic Province magmas were generated from a mixed, isotopically-enriched component of the lithospheric mantle that may have developed during the ca. 1.0 Ga Irumide Orogeny. The observed change in the source region of rift lavas though time is consistent with progressing melting of a compositionally layered lithosphere. Combined with existing geophysical and sedimentological data, we hypothesise that the lithosphere beneath the Rukwa-Malawi-Usangu junction of the Western Branch experienced an episode of destabilisation and foundering (lithospheric drip), during the early stages of East African Rift development.