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

[9815299lundstrom]这个项目是对外部熔融梯度对橄榄岩熔融行为影响的探索性研究。橄榄岩熔融实验将在1 GPa的活塞圆筒装置中进行，橄榄岩与硅不饱和熔体呈扩散接触（在某种意义上，模拟熔体导管-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，推断为MORB代残留物的深海橄榄岩记录了正辉石对熔融的贡献大于斜辉石，这与预测斜辉石主导熔融模式的实验结果不一致。其次，在橄榄岩捕虏体中观察到的熔体成分主要是富含二氧化硅（55-65%）的熔体，而不是由橄榄岩熔体实验预测的玄武岩熔体。如果外部熔融梯度能够影响橄榄岩的熔融方式，从而解释这些观察结果；这将深刻影响到实验熔体测定和地幔熔融数值模拟的未来方向。外部熔体梯度的潜在影响也将通过进一步分析橄榄岩捕虏体-熔体关系来评估，包括通过离子探针分析检查熔体和斜辉石之间的微量元素的原位分配。考虑到基于实验和观察的火成岩成因观念的迅速变化，这项探索性研究尤其及时。

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.