The origin of along‐rift variations in faulting and magmatism in the Ethiopian Rift
The origin of along‐rift variations in faulting and magmatism in the Ethiopian Rift
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埃塞俄比亚裂谷断层和岩浆作用沿裂谷变化的起源
DOI：
10.1002/2014tc003698
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发表时间：
2015
期刊：
影响因子：
4.2
通讯作者：
T. Rooney
中科院分区：
文献类型：
--
作者：
D. Keir;I. Bastow;G. Corti;F. Mazzarini;T. Rooney
世界范围内裂谷和边缘的地质记录经常揭示出，挤压和侵入的火成岩的体积沿沿着有相当大的变化。这些变化可能是软流圈不均匀性、速率变化和伸展时间的结果;或者，先前存在的板块结构和/或断裂期间伸展运动学的演变可能对岩浆活动产生一级控制。东非的埃塞俄比亚主裂谷（MER）为解决这一矛盾提供了一个极好的机会：它暴露了沿着走向的几个不同步裂谷发展的部分，从南部的大陆裂谷到北部的初始海洋扩张。在这里，我们进行研究的火山锥密度和裂谷的韧性沿着走向在MER。通过综合现有的地球物理，地球化学和岩石学的岩浆生成和侵位的限制，这些新的数据，我们能够区分构造和地幔地球动力学控制的地质记录新形成的岩浆裂谷边缘。裂谷扇区发展的时间、熔体的三维聚焦以及裂谷急剧变窄处羽流物质的积水，每一个都影响着沿着MER的火成岩侵入和火山活动。然而，裂谷热演化在雁列火山岩段下侵入地壳的局部化过程中起着重要作用。因此，在裂谷边缘发现的火成岩的体积和类型的沿着走向变化可能携带有关裂谷期间应变发展的信息，以及对流地幔在裂解时的物理状态。
The geological record at rifts and margins worldwide often reveals considerable along‐strike variations in volumes of extruded and intruded igneous rocks. These variations may be the result of asthenospheric heterogeneity, variations in rate, and timing of extension; alternatively, preexisting plate architecture and/or the evolving kinematics of extension during breakup may exert first‐order control on magmatism. The Main Ethiopian Rift (MER) in East Africa provides an excellent opportunity to address this dichotomy: it exposes, along strike, several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north. Here we perform studies of volcanic cone density and rift obliquity along strike in the MER. By synthesizing these new data in light of existing geophysical, geochemical, and petrological constraints on magma generation and emplacement, we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin. The timing of rift sector development, the three‐dimensional focusing of melt, and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the MER. However, rifting obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments. Along‐strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting, as well as the physical state of the convecting mantle at the time of breakup.