The composition of near-solidus partial melts of fertile peridotite at 1 and 1.5 GPa: Implications for the petrogenesis of MORB
The composition of near-solidus partial melts of fertile peridotite at 1 and 1.5 GPa: Implications for the petrogenesis of MORB
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DOI：
10.1093/petrology/egn009
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发表时间：
2008-04-01
影响因子：
3.9
通讯作者：
McNeill, Andrew W.
中科院分区：
文献类型：
--
作者：
Falloon, Trevor J.;Green, David H.;McNeill, Andrew W.
我们已经确定了橄榄岩 MM-3 的近固相线熔融成分，这是一种适合在 1 和 1 中心点 5 GPa 下通过减压部分熔融生产洋中脊玄武岩 (MORB) 的成分。在 1 GPa 下，MM-3 组合物具有含斜长石的亚固相线尖晶石二辉橄榄石组合，并且固相线接近 1270 摄氏度。仅在固相线以上约 5 摄氏度时，由于斜长石几乎完全熔化，存在 4% 的熔体。斜长石二辉橄榄石中的这种熔化行为是通过简单的系统和先前的实验工作预测的。斜长石的持久性 >0.8 GPa 很大程度上取决于块岩 CaO/Na(2)O 和橄榄岩中的标准斜长石含量。在 1 中心点 5 GPa 处，MM-3 成分具有亚固相线尖晶石二辉橄榄石组合，并且固相线类似于 1350 摄氏度。我们已经确定了近固相线熔体成分，在固相线的 10 摄氏度内有类似于 2% 的熔化。 1 和 15 GPa 下的近固相线熔体均为标准霞石，且标准透辉石含量较低；与较高程度的部分熔体相比，它们的TiO(2)、Al(2)O(3)和Na(2)O含量最高，而FeO和Cr(2)O(3)含量最低。这些近固相线熔体与原始 MORB 玻璃（其位于低压下仅橄榄石结晶场）的比较表明，涉及在 1 中心点 5 GPa 或更小的压力下熔化过程中形成的近分数熔体聚集的岩石成因模型不太可能是正确的。在这项研究中，我们使用了一种实验方法，利用烧结氧化物混合物起始材料和橄榄岩反应实验。我们还研究了一些最近的研究，使用另一种方法将熔体迁移到熔体陷阱（橄榄石、金刚石、玻璃碳）中并截留在其中，并讨论该方法的最佳程序。
We have determined the near-solidus melt compositions for peridotite MM-3, a suitable composition for the production of mid-ocean ridge basalt (MORB) by decompression partial melting, at 1 and 1 center dot 5 GPa. At 1 GPa the MM-3 composition has a subsolidus plagioclase-bearing spinel lherzolite assemblage, and a solidus at similar to 1270 degrees C. At only similar to 5 degrees C above the solidus, 4% melt is present as a result of almost complete melting of plagioclase. This melting behaviour in plagioclase lherzolite is predicted from simple systems and previous experimental work. The persistence of plagioclase to >0.8 GPa is strongly dependent on bulk-rock CaO/Na(2)O and normative plagioclase content in the peridotite. At 1 center dot 5 GPa the MM-3 composition has a subsolidus spinel lherzolite assemblage, and a solidus at similar to 1350 degrees C. We have determined a near-solidus melt composition at similar to 2% melting within 10 degrees C of the solidus. Near-solidus melts at both 1 and 15 GPa are nepheline normative, and have low normative diopside contents; also they have the highest TiO(2), Al(2)O(3) and Na(2)O, and the lowest FeO and Cr(2)O(3) contents compared with higher degree partial melts. Comparison of these near-solidus melts with primitive MORB glasses, which lie in the olivine-only field of crystallization at low pressure, indicate that petrogenetic models involving aggregation of near-fractional melts formed during melting at pressures of 1 center dot 5 GPa or less are unlikely to be correct. In this study we use an experimental approach that utilizes sintered oxide mix starting materials and peridotite reaction experiments. We also examine some recent studies using an alternative approach of melt migration into, and entrapment within melt traps (olivine, diamond, vitreous carbon) and discuss optimal procedures for this method.