SGER: Relating Observations to Experiments: Investigating the Effect of an External Melt Gradient on Melt Compositions Produced in Peridotite Melting Experiments

9815299 Lundstrom该项目是一项探索性研究，探讨外部熔体梯度对橄榄岩熔融行为的影响。 橄榄岩熔融实验将在1 GPa的活塞缸装置中进行，橄榄岩与二氧化硅不饱和熔体扩散接触（在某种意义上，模拟熔体熔体-橄榄岩界面）。这些实验的动机源于天然橄榄岩样品和实验结果之间的两个基本差异。 首先，深海橄榄岩，推断为残留物的MORB一代，记录斜方辉石贡献更多的熔融比单斜辉石，观察不一致的实验结果，预测单斜辉石占主导地位的熔融模式。第二，橄榄岩捕虏体内观察到的熔体成分主要是富硅（55-65%）熔体，而不是玄武岩熔体，如橄榄岩熔融实验所预测的。 如果外部熔体梯度能够影响橄榄岩如何熔化，从而解释这些观察结果，未来的方向在实验熔体测定和地幔熔融的数值模拟将受到深刻的影响。 外部熔体梯度的潜在影响也将通过橄榄岩捕虏体熔体关系的进一步分析，包括检查熔体和单斜辉石之间的微量元素的离子探针分析原位分区进行评估。 鉴于基于实验和观察的火成岩成因的想法迅速变化，这项探索性研究特别及时。

9815299LundstromThis project is an exploratory investigation of the effect of an external melt gradient on the behavior of peridotite melting. Peridotite melting experiments will be undertaken in a piston cylinder apparatus at 1 GPa with the peridotite in diffusive contact with a silica undersaturated melt (in a sense, simulating a melt conduit-peridotite interface). The motivation for these experiments stems from two fundamental discrepancies between natural peridotite samples and experimental results. First, abyssal peridotites, inferred to be residues of MORB generation, record that orthopyroxene contributes more to melting than clinopyroxene, an observation inconsistent with experimental results that predict clinopyroxene to dominate the melting mode. Second, melt compositions observed within peridotite xenoliths are dominated by silica rich (55-65%) melts, not basaltic melts as would be predicted by peridotite melting experiments. If an external melt gradient is able to influence how peridotite melts and thus explains these observations; future directions in experimental melt determinations and numerical modeling of mantle melting would be profoundly affected. The potential influence of external melt gradients also will be evaluated through further analyses of peridotite xenolith-melt relations including examining in-situ partitioning of trace elements between melt and clinopyroxene by ion probe analysis. This exploratory study is particularly timely given the rapidly changing state of ideas regarding the genesis of igneous rocks based on both experiments and observations.