The remelting of hydrothermally altered peridotite at mid-ocean ridges by intruding mantle diapirs
The remelting of hydrothermally altered peridotite at mid-ocean ridges by intruding mantle diapirs
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DOI：
10.1038/990073
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发表时间：
1999-12
期刊：
影响因子：
64.8
通讯作者：
M. Benoit;G. Ceuleneer;M. Polvé
中科院分区：
文献类型：
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作者：
M. Benoit;G. Ceuleneer;M. Polvé
在大洋扩张中心发现的大多数辉长岩堆晶岩被认为是由洋中脊玄武岩（MORB）组成的熔体的分离结晶作用产生的。然而，也有例外，包括一些堆积物，这些堆积物似乎来自于比MORB含有更多二氧化硅的熔体，并且不相容元素（那些不容易替代成主要矿物相的元素）更贫乏。这些不寻常的岩石见证了相对较深的岩石学过程，这些过程无法通过研究海底喷发的熔体来获得，它们的起源仍然存在争议。幸运的是，同样的岩性可以在蛇绿岩（海洋地壳的部分增生到大陆）中进行详细研究。在阿曼蛇绿岩的地幔底辟化石中，我们观察到了一套“正常”的MORB型堆晶（“N-堆晶”）和一套富硅但不相容元素贫化熔体产生的堆晶（“D-堆晶”）之间相同的二分法。当N-堆晶在底辟内部结晶时，D-堆晶基本上以侵入体的形式出现在底辟周围。硅富集，极端亏损的不相容元素，海水同位素特征的组合表明，D-累积形成的水化残余橄榄岩后，在脊轴MORB提取在低压重熔。的分布的D-累积相对于N-累积表明，这种亏损熔体产生episodically在脊轴时，岩石圈地幔被重新加热的一个新的底辟脉冲。
Most gabbroic cumulates found at ocean spreading centres are thought to have been generated by the fractional crystallization of melts with the composition of mid-ocean ridge basalt (MORB). There are exceptions, however, including some cumulates which appear to have come from melts that contain more silica than MORB and are much more depleted in the incompatible elements (those elements that do not readily substitute into the main mineral phases). These unusual rocks bear witness to relatively deep petrological processes that are not accessible through the study of melts erupted on the sea floor, and their origin is still debated. Fortunately, the same lithologies can be studied in detail in ophiolites (sections of oceanic crust accreted to a continent). In a fossil mantle diapir of the Oman ophiolite,, we have observed the same dichotomy between a suite of ‘normal’, MORB-type, cumulates (‘N-cumulates’) and a suite of cumulates issued from silica-enriched but incompatible-element-depleted melts (‘D-cumulates’). While the N-cumulates crystallized inside the diapir, the D-cumulates occur essentially as intrusions surrounding the diapir. The combination of silica enrichment, extreme depletion in incompatible elements, and seawater isotopic signature indicates that the D-cumulates were formed by the remelting at low pressure of hydrated residual peridotites left after MORB extraction at the ridge axis. The distribution of the D-cumulates relative to the N-cumulates suggests that such depleted melts are produced episodically at ridge axes when the lithospheric mantle is reheated by a new diapiric pulse.