A mantle magma reservoir beneath an incipient mid-ocean ridge in Afar, Ethiopia
A mantle magma reservoir beneath an incipient mid-ocean ridge in Afar, Ethiopia
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DOI：
10.1038/ngeo1925
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发表时间：
2013-10-01
影响因子：
18.3
通讯作者：
Dawes, G. J. K.
中科院分区：
文献类型：
--
作者：
Desissa, M.;Johnson, N. E.;Dawes, G. J. K.
浅层岩浆储集层存在于火山和大洋中脊下方的地壳中，但没有报道称最上面的地幔内有广泛的岩浆体。事实上，岩浆的浮力应该会导致它侵入地壳，防止它在地幔下面积水。埃塞俄比亚阿法尔的达巴湖岩浆段标志着大陆裂谷的晚期。这一段自2005年以来一直活跃，并经历了多次岩浆侵入(1-6次)。在这里，我们使用大地电磁数据对其下方的岩浆体进行成像。我们确定了一个30公里宽的非常高电导率的区域，深入到大约35公里深。我们将这一地区解释为至少500公里(3)的大体积岩浆延伸到地幔，包含约13%的熔体分数。岩浆体积比典型裂谷事件期间侵入的岩浆体积大几个数量级，这意味着岩浆储集层持续了数万年。这与大洋中脊之下的情况形成鲜明对比，在那里，熔体供应被认为是断断续续的(7-11)。因此，地幔内的大型岩浆储集层可能是伴随着大陆解体的最后阶段的应变局部化的原因。
Shallow magma reservoirs exist in the crust beneath volcanoes and mid-ocean ridges, yet there are no reports of extensive magma bodies within the uppermost mantle. Indeed the buoyancy of magma should cause it to intrude into the crust, preventing it from ponding in the mantle below. The Dabbahu magmatic segment in Afar, Ethiopia, marks the late stages of continental rifting. This segment has been active since 2005 and has experienced repeated magma intrusions(1-6). Here we use magnetotelluric data to image magma bodies beneath it. We identify a 30-km-wide region of very high electrical conductivity that reaches down to about 35 km depth. We interpret this region as a large volume of magma of at least 500 km(3) that extends well into the mantle and contains about 13% melt fraction. The magma volume is orders of magnitude larger than that intruded during a typical rifting episode, implying that the magma reservoir persists for several tens of thousands of years. This is in marked contrast to the situation beneath mid-ocean ridges, where melt supply is thought to be episodic(7-11). Large magma reservoirs within the mantle may therefore be responsible for the localization of strain that accompanies the final stages of continental break-up.