High pressure phases in ophiolites - products of electrical discharges?

近年来，在蛇绿岩复合体的岩性中发现了高压矿物。注意到的高压相包括金刚石、钴矿、钴矿的假晶和TiO2的高压多晶。它们与高度还原相如莫桑石SiC、Si-Fe合金、金属Ti、Ti碳化物和氮化物密切共生。从表面上看，这些不寻常的矿物组合有可能对蛇绿岩复合体的成因和就位历史的良好模型提出质疑。本文认为，这些组合既不能反映岩石的构造历史，也不能反映岩石的氧化还原状态。将采用新的实验技术来测试高压相和高度还原的矿物是否可以通过放电在局部稳定。当闪电击中岩石时，温度足以稳定等离子体，等离子体冷却后可能析出化合物，这些化合物看似高度还原，但并不反映其形成过程中的还原条件。如果岩性在雷电冲击下不崩解，热膨胀会产生足够高的压力，使钴矿、硅长石和金刚石稳定下来。积极的结果将具有重要的意义：(1)高压相不一定反映岩性的构造历史；(2)名义上高度还原的相，如SiC或Si-Fe-Ti合金，可能无法监测其氧化还原历史。

In recent times, high pressure minerals have been discovered in lithologies of ophiolite complexes. The high pressure phases noted include diamond, coesite, pseudomorphs of coesite after stishovite, and high pressure polymorphs of TiO2. They are intimately intergrown with highly reduced phases like moissanite SiC, Si-Fe alloys, metallic Ti, Ti carbides, and nitrides. Taken at face value, these unusual mineral assemblages have the potential to question well established models for the genesis and emplacement history of ophiolite complexes. It is proposed here that these assemblages neither reflect the tectonic history of the rocks nor their redox state. Novel experimental techniques will be employed to test if high pressure phases and highly reduced minerals can be stabilized locally by electric discharges. When a lightning bolt hits a rock, temperatures suffice to stabilize plasmas which, upon cooling, may precipitate compounds that are seemingly highly reduced but do not reflect reducing conditions during their formation. If lithologies do not disintegrate upon impact of a thunderbolt, thermal expansion can generate pressures sufficiently high that coesite, stishovite, and diamond may be stabilized. Positive results would have important implications: (1) high pressure phases do not necessarily reflect the tectonic history of the lithologies, and (2) nominally highly reduced phases like SiC or Si-Fe-Ti alloys may not monitor their redox histories.