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High pressure phases in ophiolites - products of electrical discharges?

蛇绿岩中的高压相 - 放电产物？

基本信息

批准号：
335612051
负责人：
Professor Dr. Christian Gerhard Ballhaus
金额：
--
依托单位：
Abteilung Geochemie/Petrologie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2022-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/335612051?language=en
关键词：
pressure phases ophiolites products electrical

项目摘要

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.

近年来，在蛇绿岩杂岩的岩性中发现了高压矿物。高压相包括金刚石、柯石英、柯石英之后的假柯石英和高压晶型的二氧化钛。它们与碳化硅、硅铁合金、金属钛、钛碳化物和氮化物等高度还原的相紧密共生。从表面上看，这些不同寻常的矿物组合有可能质疑蛇绿岩杂岩的成因和侵位历史的成熟模式。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。新的实验技术将被用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下来。当闪电击中岩石时，温度足以稳定等离子体，这些等离子体在冷却时可能会沉淀出看似高度还原的化合物，但在形成过程中并不反映还原条件。如果岩性在雷电的冲击下没有解体，热膨胀可以产生足够高的压力，使柯石英、辉石和钻石得到稳定。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，如碳化硅或硅铁钛合金，可能不能监测它们的氧化还原历史。