Upper mantle temperature and the onset of extension and break-up in Afar, Africa
Upper mantle temperature and the onset of extension and break-up in Afar, Africa
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DOI：
10.1016/j.epsl.2015.02.039
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发表时间：
2015-05-15
影响因子：
5.3
通讯作者：
Harmon, Nicholas
中科院分区：
文献类型：
--
作者：
Armitage, John J.;Ferguson, David J.;Harmon, Nicholas
地幔柱在大陆裂谷和最终分裂中发挥多大作用还存在争议。阿法尔位于现今最大和最活跃的大陆裂谷的北方末端，东非裂谷与红海和亚丁湾裂谷形成了一个三重连接点。它有一个羽活动的历史，但最近的研究得出了相互矛盾的结论，羽是否仍然有助于目前的阿法尔构造。一项地球化学研究得出结论，阿法尔是一个成熟的热裂谷，岩石圈厚达80公里，而地震数据则被解释为反映了一个年轻的海洋裂谷盆地的结构，位于正常温度的地幔之上。我们开发了一个自洽的地幔流的正演模型，包括熔体的产生和保留，以测试是否熔体化学，熔体体积和岩石圈软流圈地震结构的预测可以与观测相协调。埃尔塔阿勒、达巴胡和阿萨尔岩浆岩段镁铁质岩样品的稀土元素组成可作为裂谷过程的温度计和计时器。低的地震速度要求岩石圈减薄到50 km或更小。在裂谷下方50 ~ 70 km处的强正阻抗对比似乎与熔融带有关，但仅用各向同性地震速度不能再现。综合起来，最简单的解释是，阿法尔以下的地幔温度仍然在1450摄氏度，裂谷开始约22-23马，岩石圈已减薄100至50公里，允许显着的减压熔融。(C)2015年由Elsevier B. V.出版
It is debated to what extent mantle plumes play a role in continental rifting and eventual break-up. Afar lies at the northern end of the largest and most active present-day continental rift, where the East African Rift forms a triple junction with the Red Sea and Gulf of Aden rifts. It has a history of plume activity yet recent studies have reached conflicting conclusions on whether a plume still contributes to current Afar tectonics. A geochemical study concluded that Afar is a mature hot rift with 80 km thick lithosphere, while seismic data have been interpreted to reflect the structure of a young, oceanic rift basin above mantle of normal temperature. We develop a self-consistent forward model of mantle flow that incorporates melt generation and retention to test whether predictions of melt chemistry, melt volume and lithosphere-asthenosphere seismic structure can be reconciled with observations. The rare-earth element composition of mafic samples at the Erta Ale, Dabbahu and Asal magmatic segments can be used as both a thermometer and chronometer of the rifting process. Low seismic velocities require a lithosphere thinned to 50 km or less. A strong positive impedance contrast at 50 to 70 km below the rift seems linked to the melt zone, but is not reproduced by isotropic seismic velocity alone. Combined, the simplest interpretation is that mantle temperature below Afar is still elevated at 1450 degrees C, rifting started around 22-23 Ma, and the lithosphere has thinned from 100 to 50 km to allow significant decompressional melting. (C) 2015 Published by Elsevier B.V.