Collaborative Research: An EARTHTIME Chronology for the Matuyama-Brunhes Geomagnetic Field Reversal

合作研究：松山-布伦赫斯地磁场反转的地球时间年表

• 批准号: 1250446
• 负责人: Bradley Singer
• 金额: $ 39.97万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-03-01 至 2017-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250446&HistoricalAwards=false
• 关键词: Collaborative; Research; EARTHTIME; Chronology; Matuyama

The Earth?s magnetic field is still useful for navigation, but perhaps more importantly today it forms a protective shield against cosmic radiation that otherwise would lead to further depletion of the ozone layer that protects us from UV radiation and interfere with the satellite communications so essential for society. The stronger the field, the greater the shielding. That the Earth?s magnetic field has weakened profoundly, reversed polarity hundreds of times, and attempted to do so on many other occasions, is one of the great enigmas of science. There are a variety of ways by which geoscientists advance our understanding of the magnetic field, which is widely thought to be generated by the flow of hot molten iron that swirls around in Earth?s liquid outer core to generate a magnetic dynamo. These include: (1) creation and study of analog dynamos made of molten sodium or other (dangerous) electrically conducting metals, (2) supercomputer modeling of dynamo processes that produce polarity reversals and field excursions, and (3) amassing and interpreting observations from natural rocks that record the magnetic fields of Earth?s past. This study falls into the latter category, and we have proposed to greatly expand the set of observations that bear on understanding the last reversal of Earth?s magnetic field that took place about 770 thousand years ago. This grant will permit a collaborative team of scientists to acquire new age determinations using the potassium-argon radio-isotope decay clock, as well as new information on the intensity and direction of the field, as recorded in sequences of lava flows that erupted during the last full polarity reversal of Earth?s magnetic field. The information we plan to collect will, in turn, provide fundamental data from the real Earth?s past that can help to inform and validate approaches that rely on analog or supercomputer simulations of this process. Reversals and excursions of Earth?s geomagnetic field create global marker horizons in sedimentary and volcanic rocks and polar ice. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to quantifying the timing and rates of climate change, surface processes, and biological evolution. Moreover, knowing the structural and temporal evolution of reversals and excursions is essential to understanding the geodynamic process by which reversals occur. Advances in rock magnetic measurement techniques in both sediments and lava flows, astrochronologic methods applied to sediment cores, and radio-isotopic dating of lava flows during the past two decades, using the 40Ar/39Ar variant of potassium-argon dating, has produced a number of paleomagnetic records of the most recent polarity transition from the Matuyama reversed chron to the Brunhes normal chron. Given the importance of an accurate and precise age for the the Matuyama-Brunhes reversal, our objectives are to: (1) Greatly enlarge the set of 40Ar/39Ar ages from lava flows that bear on the timing of this reversal while improving the precision and accuracy of these age determinations, (2) Test the hypothesis that the discrepancy between the astrochronologic age of 773,000 years before present recorded in sediment cores and the 40Ar/39Ar age of lava flows reflects the accuracy of the very limited 40Ar/39Ar data available from the lava flows, and (3) Determine the paleointensity of lavas that record directional changes associated with the MB reversal and its precursor on Maui and in Chile. This project is an international collaboration between scientists in Japan, the Netherlands, Denmark, and the USA. We will train undergraduate and graduate students in both state-of-the-art radio-isotopic geochronology and paleomagnetic methods in the labs at UW Madison and UC Santa Cruz, respectively. A geochronology summer short course will be held at UW for graduate and undergraduate students. Moreover, The PI will work with staff in the UW Geology museum to create a display that highlights how geologists tell time, including the use of 40Ar/39Ar dating and astrochronology.

地球的磁场仍然对导航有用，但也许今天更重要的是，它形成了针对宇宙辐射的保护屏蔽层，否则，否则将导致臭氧层进一步消耗，从而保护我们免受紫外线辐射的影响并干扰对社会至关重要的卫星通信。田地越强，屏蔽越大。地球的磁场已经深刻地减弱了，极性逆转了数百次，并试图在许多其他场合尝试这样做，这是科学的巨大谜之一。 地球科学家在多种方式上提高了我们对磁场的理解，人们认为这是由热熔融铁的流动产生的，这些热铁在地球液体外芯中旋转以产生磁发电机。 其中包括：（1）创建和研究由熔融钠或其他（危险的）电导电金属制成的模拟发电机，（2）产生极性逆转和田间偏移的发电机过程的超级计算机建模，以及（3）从自然岩石中进行了自然岩石的观察，这些岩石是记录了地球过去的磁场。 这项研究属于后一种类别，我们提议大大扩展一组观察结果，这些观察结果在理解大约7.7万年前发生的地球磁场的最后一次逆转。 该赠款将允许一支合作的科学家团队使用钾 - 阿尔贡钾的放射性异位衰减时钟获得新的年龄确定，以及有关该领域强度和方向的新信息，如在地球上最后一个完整的极性逆转磁场时爆发的一系列熔岩流中所记录的。 我们计划收集的信息又将提供来自真实地球过去的基本数据，这些数据可以帮助和验证依赖于该过程的模拟或超级计算机模拟的方法。地球地磁场的逆转和偏移在沉积物和火山岩和极地冰中创造了全球标记层。 这些地磁磁场不稳定性的准确和精确的年表对于量化气候变化，表面过程和生物学进化的时间和速率至关重要。此外，了解逆转和游览的结构和时间演变对于理解逆转发生的地球动力学过程至关重要。 在过去的二十年中，岩石和熔岩流中的岩石磁性测量技术的进步，适用于沉积物岩心的天体学方法以及熔岩流的放射性异位约会，使用了40AR/39AR的ARGON钾变体，从而产生了与最近期的Pallo tormation corn run to run cornertory corgry corteron corn run toserrone corl run corteron corteron corteron norder run corperon and to run。克隆。 鉴于准确和精确的年龄对于马u山 - 末日的逆转的重要性，我们的目标是：（1）大大扩大了40AR/39AR年龄的集合，从熔岩流中，这是在这种逆转时间表的时间内，同时又会在这些年龄确定的范围内提高了该假设的差异，（2）在这些年龄的准确性上，（2）2）（2）2）（2）2）（2）2）（2）2）熔岩流量非常有限的40AR/39AR数据的准确性，（3）确定了熔岩的古显微性，该熔岩的准确性非常有限，并且（3）确定了与MB反转及其在MAUI上的MB反转及其前体相关的定向变化。 该项目是日本，荷兰，丹麦和美国科学家之间的国际合作。 我们将分别在UW Madison和UC Santa Cruz的实验室分别培训本科和研究生的本科生和研究生。 夏季短期课程将在UW举行，以供研究生和本科生举行。 此外，PI将与UW地质博物馆的工作人员合作，以创建一个展示，以突出地质学家如何讲时间，包括使用40AR/39AR约会和星体照相学。