Magnetic properties and microfabrics of shocked minerals and their influence on the magnetic anomalies in the Ries, Vredefort and Manicouagan impact structures

冲击矿物的磁特性和微结构及其对 Ries、Vredefort 和 Manicouagan 冲击构造磁异常的影响

• 批准号: 433311356
• 负责人: Professor Dr. Stuart Alan Gilder
• 金额: --
• 依托单位: Department of Earth Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/433311356?language=en
• 关键词: Magnetic; properties; microfabrics; shocked; minerals

Impact-cratering subjects target rocks quasi-instantaneously to extremely high stresses, strain rates and temperatures that permanently modify the minerals within them. These shock effects bear heavily on the magnetic properties of ferrimagnetic minerals within impact structures, which in turn leads them to possess distinct magnetic field anomalies. However, the impact-related modifications of the magnetic minerals and their remanent magnetizations in the target rocks remain poorly understood. We therefore propose an integrated rock fabric and magneto-mineralogy study to understand the origin of the magnetic anomalies at three complex impact structures: Ries (Germany), Vredefort (South Africa) and Manicouagan (Canada). The chosen impact structures differ in diameter by an order of magnitude, offering a wide range in pressure and temperature conditions. They contain well-exposed outcrops of shocked crystalline basement and/or impact breccias with crystalline components that experienced a wide range of shock and post-shock conditions. Moreover, these impact structures possess magnetic anomalies whose origins are wholly or partially linked to shock processes. We have experience working in each of these structures and are familiar with their magnetic characteristics. The proposed integrated, field and laboratory-based, petrological, microstructural, paleomagnetic and rock magnetic analyses aim at a better understanding how shock metamorphism influences the magnetic remanence of shocked target rocks and how particular P-T conditions act to create magnetic field anomalies in impact structures. The following key questions will be addressed: (1) Can we equate shock effects in opaque ferrimagnets with established indicators of shock stages from non-opaque phases (e.g., PDFs in quartz)? (2) How are magnetic minerals affected/modified by the rapidly changing pressure and temperature conditions during shock loading and post-shock unloading? (3) Do specific microstructures arising from particular shock pressure and/or temperature conditions translate into specific responses in the remanent magnetization and magnetic properties of the ferrimagnets? (4) How does shock-induced remanent magnetization influence magnetic field anomalies including the case of shock demagnetization? Correlating shock effects to specific processes, P-T conditions and magnetic properties of the rocks is essential for the interpretation of magnetic anomalies in impact structures, which are among the most common morphologic features in our solar system.

撞击坑的目标是岩石，准瞬间达到极高的应力、应变率和温度，永久改变其中的矿物。这些冲击效应对撞击构造中亚铁磁性矿物的磁性产生了很大影响，从而使其具有明显的磁场异常。然而，与撞击有关的磁性矿物的改性及其在目标岩石中的再磁化仍然知之甚少。因此，我们提出了一个综合的岩石组构和磁性矿物学研究，以了解在三个复杂的影响结构的磁异常的起源：里斯（德国），Vredefort（南非）和Manicouagan（加拿大）。所选的冲击结构在直径上相差一个数量级，提供了广泛的压力和温度条件。它们包含了受冲击的结晶基底和/或具有结晶成分的冲击角砾岩的良好暴露的露头，这些结晶成分经历了广泛的冲击和冲击后条件。此外，这些撞击结构具有磁异常，其起源完全或部分与冲击过程有关。我们有在这些结构中工作的经验，并熟悉它们的磁特性。建议的综合，现场和实验室为基础的，岩石学，显微结构，古地磁和岩石磁性分析的目的是更好地了解如何冲击变质影响的剩磁的冲击目标岩石和特定的P-T条件下的行为，以创建磁场异常的影响结构。以下关键问题将得到解决：（1）我们是否可以将不透明亚铁磁体中的冲击效应等同于来自非不透明相的冲击阶段的既定指标（例如，PDF格式的石英）？(2)在冲击加载和冲击后卸载期间，磁性矿物如何受到快速变化的压力和温度条件的影响/修改？(3)由特定冲击压力和/或温度条件引起的特定微观结构是否会转化为亚铁磁体的回复磁化和磁性的特定响应？(4)冲击诱发的再磁化如何影响磁场异常，包括冲击退磁的情况？将冲击效应与特定的过程、P-T条件和岩石的磁性相关联，对于解释撞击结构中的磁异常是必不可少的，而撞击结构是我们太阳系中最常见的形态特征之一。