Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB
Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB
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DOI：
10.1016/j.lithos.2016.05.001
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发表时间：
2016-09
期刊：
影响因子：
3.5
通讯作者：
L. Fischer;M. Erdmann;Paul Eric Wolff;E. Deloule;Chao Zhang;M. Godard;J. Koepke
中科院分区：
文献类型：
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作者：
L. Fischer;M. Erdmann;Paul Eric Wolff;E. Deloule;Chao Zhang;M. Godard;J. Koepke
在大洋扩张中心，岩浆和热液对流系统之间的相互作用会引发重大的物理、热和化学交换。在综合大洋钻探计划(IODP)1256点(赤道东太平洋)席状岩墙序列的底部发现的两个辉石角闪石被解释为下伏的轴向熔融透镜和水热冷却的席状岩墙之间的导电边界层。它们被许多细长英质矿脉切割，最近被解释为席状岩脉含水部分融化的产物。本文介绍了以IODP 1256点玄武岩和角闪石为原料的水合部分熔融实验的产物(熔体和残留物)的微量元素组成。在910摄氏度到970摄氏度之间产生的实验产品在常量和微量元素成分方面与1256遗址的自然岩性相匹配。深熔熔体的成分与长英质岩脉的成分相对应，而残留矿物的成分与二辉石角辉石的成分相匹配，证明了水合部分熔融是大洋中脊快速扩张的辉长岩/岩墙过渡过程中的一个重要岩浆过程。我们的结果补充了之前对发生在快速扩张的大洋中脊的岩浆室顶部的深熔过程的实验研究。此外，用实验的部分熔体作为污染物/同化物进行混合和同化分步结晶的计算表明，深熔熔体对污染过程的贡献很小。
At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.