Did Impact-Generated Fields Magnetize the Rocks of Vredefort?

撞击产生的磁场是否磁化了弗里德堡的岩石？

• 批准号: 0810244
• 负责人: Benjamin Weiss
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-02-01 至 2010-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0810244&HistoricalAwards=false
• 关键词: Did; Impact; Generated; Fields; Magnetize

A key unresolved question in planetary science is whether the magnetization observed in meteorites and lunar rocks was generated internally in the metallic cores of the parent bodies or was instead produced by an external source. In particular, the discovery of large crustal magnetic fields associated with craters on the Moon has led to the speculation that large impacts could generate magnetic fields. Subsequent experimental studies have shown that strong magnetic fields are produced by electric currents in plasma clouds. If we wish to use extraterrestrial samples to learn about internally generated fields and the evolution of metallic cores on other bodies, it is essential that we determine whether impact-magnetization is a common process in the solar system.One of the best ways to test whether impacts can generate fields is to examine rocks from impact craters on Earth. Members of the team have recently hypothesized that magnetization in the rocks of the 2.02 billion year old Vredefort crater in South Africa also originated from impact-produced plasmas (Carporzen et al. 2005). They found that magnetization in these rocks is extremely intense and heterogeneously oriented on spatial scales ranging from tens of kilometers down to less than a few centimeters. They will address three important unanswered questions:Question 1. Were magnetic fields generated by the Vredefort impact and if so what were their intensities?Question 2. What was the characteristic length scales of any impact-generated magnetic fields?Question 3. What is the dominant magnetic mineral that carries impact-generated magnetization?The answers to these questions have critical implications for the interior structures, bulk compositions, and thermal histories of the terrestrial planets.The investigators plan to drill four 10-m deep cores into the basement rocks and sediments of the Vredefort impact structure in order to obtain unaltered samples that are likely to record the impact event. Because these samples should be free of lightning remagnetization, the PIs can test a persistent criticism that magnetization in Vredefort rocks is not from the impact but rather from recent lightning strikes. Analysis of the drill cores will be conducted in the MIT Paleomagnetism Laboratory using a 2G Superconducting Rock Magnetometer (spatial resolution of ~10 mm) and the SQUID Microscope (spatial resolution of 0.1 mm). The broader impact of this grant is that it would support the postdoctoral training of Laurent Carporzen at MIT as well as fieldwork in South Africa with MIT graduate students and South African geologists.

行星科学中一个尚未解决的关键问题是，在陨石和月球岩石中观察到的磁化是在母体的金属核心内部产生的，还是由外部来源产生的。特别是，与月球上的陨石坑相关的巨大地壳磁场的发现，导致了人们的猜测，即大撞击可能会产生磁场。随后的实验研究表明，强磁场是由等离子体云中的电流产生的。如果我们希望利用地外样本来了解内部产生的磁场和其他天体上金属核心的演化，我们必须确定撞击磁化是否在太阳系中是一个常见的过程。测试撞击是否会产生磁场的最好方法之一是检查地球上撞击坑中的岩石。该研究小组的成员最近假设，南非有20.2亿年历史的Vredefort陨石坑岩石中的磁化也来自撞击产生的等离子体(Carporzen等人。2005)。他们发现，这些岩石中的磁化非常强烈，空间尺度上从几十公里到不到几厘米都有不均匀的取向。他们将回答三个重要的悬而未决的问题：问题1.Vredefort撞击产生的磁场吗？如果是的话，其强度是多少？问题2.任何撞击产生的磁场的特征长度尺度是什么？问题3.携带撞击产生的磁化的主要磁性矿物是什么？这些问题的答案对类地行星的内部结构、主体成分和热史具有重要影响。研究人员计划在Vredefort撞击结构的基岩和沉积物中钻入四个10米深的岩芯，以获取可能记录撞击事件的未经更改的样本。因为这些样品应该没有闪电再磁化，PI可以检验一个持续不断的批评，即Vredefort岩石中的磁化不是来自撞击，而是来自最近的雷击。麻省理工学院古地磁实验室将使用2G超导岩石磁强计(空间分辨率为~10毫米)和SQUID显微镜(空间分辨率为0.1毫米)对钻芯进行分析。这笔赠款的更广泛影响是，它将支持洛朗·卡波岑在麻省理工学院进行博士后培训，以及与麻省理工学院研究生和南非地质学家一起在南非进行实地考察。