Impact structures: Effect of post-shock thermal conditions on mineral magnetism

撞击结构：震后热条件对矿物磁性的影响

• 批准号: 432762445
• 负责人: Privatdozentin Dr. Agnes Kontny
• 金额: --
• 依托单位: Abteilung Strukturgeologie und Tektonophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/432762445?language=en
• 关键词: Impact; structures; Effect; post; shock

Large impact structures on Earth like the Chicxulub in Mexico are characterized by magnetic highs but the magneto-mineralogical origin is still poorly constrained and impact-generated melt versus hydrothermal activity models are discussed. Shock features along with thermally activated processes are the most important driving forces for the creation or destruction of magnetic minerals causing magnetic anomaly signals over impact structures. The main goal of this research project is the investigation and characterization of heat treatment on shocked magnetite and pyrrhotite, the two main magnetic minerals in crustal rocks of the Earth. For this purpose, we plan to study rock magnetic properties and microstructural features from experimentally shocked and afterwards annealed material and compare it to magnetic minerals from impacted rocks. For comparison, the IODP-ICDP drill core M0077A from the Chicxulub impact crater and from the Nördlingen 1973 drill core are selected, because both structures show inner craters with impact-related magnetic anomalies. The difference is the size and it is hypothesized for the 200 km diameter Chicxulub that a long-living hydrothermal system was active, but not for the 25 km diameter Nördlingen impact structure. Temperature dependent magnetic susceptibility along with a series of microscopic (reflected light, scanning electron microscopy, magnetic force microscopy, transmission electron microscopy), x-ray diffraction techniques and magnetization experiments at room temperature and low-temperature will be used to characterize shocked and annealed samples. An understanding of the magnetic and microstructural features due to heating of shocked material and their distinction from new magnetic mineral formations are likely a key to explain magnetic anomaly pattern over large impact craters on Earth and other planetary bodies. Therefore, this proposal aims on the discrimination of different secondary processes leading to enhancement or destruction of magnetic signals over large impact structures.

地球上的大型撞击结构，如墨西哥的希克苏鲁布，其特征是磁高，但磁矿物学的起源仍然没有得到很好的限制，并讨论了撞击产生的熔体与热液活动模型。冲击特征沿着热激活过程是形成或破坏磁性矿物的最重要的驱动力，从而在冲击构造上产生磁异常信号。本研究项目的主要目的是对地壳岩石中的两种主要磁性矿物--冲击磁铁矿和磁黄铁矿进行热处理的研究和表征。为此，我们计划研究岩石的磁性和微观结构特征，从实验冲击和后来退火的材料，并比较它的磁性矿物从冲击岩石。为了进行比较，选择了来自希克苏鲁布撞击坑的IODP-ICDP岩心M0077 A和来自Nördlingen 1973年的岩心，因为这两个结构都显示了内部撞击坑与撞击有关的磁异常。不同之处在于大小，据推测，直径为200公里的希克苏鲁布是一个长期活动的热液系统，但直径为25公里的诺德林根撞击结构则不是。将使用温度相关磁化率沿着以及一系列显微镜（反射光、扫描电子显微镜、磁力显微镜、透射电子显微镜）、X射线衍射技术和室温和低温下的磁化实验来表征冲击和退火样品。了解由于受冲击物质加热而产生的磁性和微观结构特征及其与新磁性矿物形成的区别，可能是解释地球和其他行星上大型撞击坑磁异常模式的关键。因此，本建议的目的是对不同的次级过程的歧视，导致增强或破坏的磁信号在大的影响结构。