Magnetostratigraphy and Polarity transitions studies of lavas of the island of Lanai, Hawaii

夏威夷拉奈岛熔岩的磁性地层学和极性转变研究

• 批准号: 1114065
• 负责人: Emilio Herrero-Bervera
• 金额: $ 16.5万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114065&HistoricalAwards=false
• 关键词: Magnetostratigraphy; Polarity; transitions; studies; lavas

Paleomagnetic data are the unique source of observations to understand the geomagnetic transitions and hence the geodynamo processes involved in field generation. However, because reversals and excursions occur over a few thousands years at most, it is a real challenge to acquire detailed paleomagnetic information about the reversing and the transitional field. In addition, due to the fact that there is a real need to obtain reversal records from long volcanic sequences in order to have a better understanding of the generation of the field, we propose to study in detail, a long volcanic sequence (about 320 meters) of lavas from the island of Lanai with the main objective of investigating the directional behavior (i.e. Declination and Inclination) as well as the geomagnetic field strength recorded before during and after several successive polarity transitions registered by the Lanai section. We have already identified a volcanic section on the island of Lanai (Hawaii) covering about 400,000 years of geomagnetic field changes that includes the possibility of studying the detailed records of the successive Gilsa, Gardar, Bjorn and Cobb Mountain Subchron and excursions, since the base of the section is 1.6 +/-0.08 Ma old according to Ar/Ar radiometric age determinations. We also propose to do additional high precision Ar/Ar radiometric dating of the reversal boundaries and the expected excursions of the Lanai lava sequences. It is clear that proper analysis of these observations requires documenting the total field vector and therefore conducting an exhaustive study of the directional changes and absolute paleointensity of the paleo-field recorded by the sequence of lava flows of the Lanai Volcano is proposed here. The objectives of this two year proposed study are primarily related to the knowledge of the field variations during periods like reversals and excursions but also related to the critical time intervals that precede and follow reversals that so far have only been documented from a few sedimentary sequences with conflicting observations, particularly for the interval between 1.6 to ~1.2 Million years that is still not very well defined in terms of the above mentioned reversals and excursions of the geomagnetic field. Reversal studies cannot be separated from the surrounding polarity intervals and most records published so far were not long enough to provide complete information. The Lanai sequence offers the first exceptional opportunity to study field changes over a time period that includes several polarity intervals and thus documents the paleofield behavior over various time constants. This is a basic condition to extract and bring up significant constraints for the theoretical and numerical modeling of the geodynamo. The principal investigator and three undergraduate student(s) will carry out the entire scientific research project proposed here. The involvement of undergraduate students will be a priority in this project, from fieldwork through lab work, analysis and publication. The project will help support a US scientist of an underrepresented ethnic group (the PI). Data will be disseminated through publication the web and community maintained paleomagnetic databases. This project will also provide the stimulus to maintain the paleomagnetics and petrofabrics operation at UH which is used by a diverse group of students and researchers from all over the world.

古地磁数据是唯一的观测来源，以了解地磁转换，因此，地球发电机过程中涉及的字段生成。然而，由于反转和偏移最多发生在几千年内，因此获取有关反转和过渡场的详细古地磁信息是一个真实的挑战。此外，由于有真实的需要从长火山层序中获得反转记录，以便更好地了解场的生成，我们建议进行详细的研究，一个漫长的火山序列（约320米）的熔岩从拉奈岛的主要目的是调查的方向行为（即下降和倾斜），以及地磁场强度记录之前，期间和之后的几个连续的极性转换登记的拉奈部分。 我们已经在拉奈岛（夏威夷）上确定了一个火山剖面，覆盖了大约40万年的地磁场变化，其中包括研究连续的吉尔萨、加达、比约恩和科布山亚时和远足的详细记录的可能性，因为根据Ar/Ar放射性年龄测定，该剖面的基底年龄为1.6 +/-0.08 Ma。我们还建议做额外的高精度Ar/Ar放射性测年的反转边界和预期的游览拉奈火山熔岩序列。很明显，这些意见的适当分析，需要记录的总场矢量，因此，进行详尽的研究的方向变化和绝对paleostrensity记录的拉奈火山熔岩流序列的古场在这里提出。这项为期两年的拟议研究的目标主要是了解反转和偏移期间的油田变化，但也涉及反转之前和之后的关键时间间隔，迄今为止，这些时间间隔仅记录在少数具有相互矛盾的观测结果的沉积序列中。特别是对于160万年到120万年之间的时间间隔，这仍然不能很好地根据上述地磁场的反转和偏移来定义。记录研究不能与周围的极性间隔分开，迄今为止发表的大多数记录都不够长，无法提供完整的信息。拉奈序列提供了第一个特殊的机会，研究领域的变化在一个时间段，包括几个极性的间隔，从而记录了古油田的行为在不同的时间常数。这是提取和提出地球发电机理论和数值模拟中重要约束条件的基本条件。主要研究者和三名本科生将执行这里提出的整个科学研究项目。本科生的参与将是本项目的优先事项，从实地考察到实验室工作，分析和出版。该项目将帮助支持一个代表性不足的种族（PI）的美国科学家。数据将通过出版物、网络和社区维护的古地磁数据库传播。该项目还将提供刺激，以维持UH的古地磁学和岩石组构操作，该操作由来自世界各地的不同学生和研究人员使用。