Thermal effects of pyroxenites on mantle melting below mid-ocean ridges
Thermal effects of pyroxenites on mantle melting below mid-ocean ridges
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DOI：
10.1038/s41561-018-0139-z
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发表时间：
2018-07-01
影响因子：
18.3
通讯作者：
Bonatti, Enrico
中科院分区：
文献类型：
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作者：
Brunelli, Daniele;Cipriani, Anna;Bonatti, Enrico
在地球内部旅行长达数十亿年后，回收的物质一旦注入俯冲带，就可以到达亚脊熔融区，成为分散在主橄榄岩地幔中的辉石岩。在这里，我们研究遗传相关的地壳玄武岩和地幔橄榄岩采样沿着一个上升的岩石圈部分创建的一段大西洋中脊通过26万年的时间间隔。低固相线物质进入熔融区，迫使残留橄榄岩和玄武岩的元素和同位素印记随时间而发散。我们发现，含辉石岩源进入subridge熔融区诱导过冷的主机橄榄岩地幔，由于扣除潜热熔融的低T-固相线辉石岩。地幔过冷，反过来，降低了热边界层，导致更深的熔化停止。其结果是减少了提取的熔体总量，从而减少了岩浆地壳的厚度。一个均一的橄榄岩地幔所经历的熔融程度高于同一橄榄岩但被辉石岩脉所包裹的熔融程度。这种效果，marble-cake-type橄榄岩-辉石岩混合源的预测，意味着对流地幔中再循环物质的不完全均匀化。
After travelling in Earth's interior for up to billions of years, recycled material once injected at subduction zones can reach a subridge melting region as pyroxenite dispersed in the host peridotitic mantle. Here we study genetically related crustal basalts and mantle peridotites sampled along an uplifted lithospheric section created at a segment of the Mid-Atlantic Ridge through a time interval of 26 million years. The arrival of low-solidus material into the melting region forces the elemental and isotopic imprint of the residual peridotites and of the basalts to diverge with time. We show that a pyroxenite-bearing source entering the subridge melting region induces undercooling of the host peridotitic mantle, due to subtraction of latent heat by melting of the low-T-solidus pyroxenite. Mantle undercooling, in turn, lowers the thermal boundary layer, leading to a deeper cessation of melting. A consequence is to decrease the total amount of extracted melt, and hence the magmatic crustal thickness. The degree of melting undergone by a homogeneous peridotitic mantle is higher than the degree of melting of the same peridotite but veined by pyroxenites. This effect, thermodynamically predicted for a marble-cake-type peridotite-pyroxenite mixed source, implies incomplete homogenization of recycled material in the convective mantle.