Full Vector Studies of Polarity Transitions and Excursions Recorded in Long Sequences in the Koolau Volcano, O'ahu, Hawai'i.

夏威夷欧胡岛库劳火山长序列记录的极性转变和偏移的全矢量研究。

• 批准号: 0510061
• 负责人: Emilio Herrero-Bervera
• 金额: $ 23.22万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0510061&HistoricalAwards=false
• 关键词: Full; Vector; Studies; Polarity; Transitions

Paleomagnetic data are the unique source of observations to understand the geomagnetic transitions, and hence the geodynamo processes involved in field generation. However, because reversal and excursions occur over a few thousand years at most, it is a real challenge to acquire detailed paleomagnetic information about the reversing field. and the transitional field. There is a real need to obtain reversal records from long volcanic sequences to have a better understanding of the generation of the field. Therefore it is proposed here to study six long volcanic sequences varying in thickness from 300 to 800 meters that have registered several successive reversals and excursions of the paleofield recorded in the Koolau Volcano (O'ahu, Hawaii) covering about 0.7 Ma of geomagnetic field changes. These include detailed records of the successive Gauss-Matuyama (2.57 Ma), Cryptochron C2r.2r-l (ca. 2.42-2.44 Ma), Reunion(s), Huckleberry (2.137-2.086Ma) and Lower Olduvai (1.922 Ma) reversals. The objectives of this three year proposed study are primarily related to the knowledge of the field variations during periods like reversals and excursions but are also related to the critical time intervals that precede and follow reversals, particularly for the interval between 2.6 to 1.8 Ma years that is still not very well defined in terms of the Reunion(s) and the newly reported Huckleberry Ridge events. Reversal studies cannot be separated from the surrounding polarity intervals, and most records published so far were not long enough to provide complete information. These sequences offer the first exceptional opportunity to document field changes over a time period that includes several polarity intervals, thus documenting the field behavior over various time constants. This is a basic condition to extract and bring up significant constraints for theoretical and numerical modeling of the geodynamo.Intellectual merit of the proposed activity: The present proposal is focused on directional analyses and paleointensity studies in order to achieve determinations of the total field vector. The measurements will focus on the successive periods of polarity and their associated reversals as mentioned above. Preliminary experiments of paleointensity have been conducted on one sample per lava flow from several Koolau flows using a modified version of the Thellier-Coe technique. We have imposed a severe criteria to discard samples affected by magnetomineralogical transformations as well as magnetization components involving multidomain grains. Indeed it is important to deal with paleointensity values that rely on a minimum number of five to eight determinations per lava flow (as is the case for directions) in order to perform a suitable statistical treatment with appropriate error bars.Broader impacts of the proposed activity. The principal investigator and 4 undergraduate students will carry out the research project proposed here. The involvement of undergraduate students will be a priority in this project, from field work through lab work, analysis and publication. Data will be disseminated through publications, the web and community maintained paleomagnetic databases. This project will also provide stimulus to maintain the paleomagnetics and petrofabrics operation at UH which is used by a diverse group of students and researchers.--

古地磁资料是了解地磁转变的唯一观测资料来源，因此也有助于了解磁场产生过程中的地球动力学过程。然而，由于倒转和偏移最多发生在几千年的时间内，获取有关倒转场的详细古地磁信息是一项真正的挑战。以及过渡场。我们确实需要从长火山层序中获得反转记录，以便更好地了解磁场的形成。因此，本文拟研究6个厚度在300 ~ 800米之间的长火山序列，这些序列记录了夏威夷O’ahu的Koolau火山记录的古磁场的几次连续反转和偏移，覆盖了约0.7 Ma的地磁场变化。其中包括连续的高斯-松山（2.57 Ma）， Cryptochron C2r的详细记录。2r- 1（约2.42-2.44 Ma）、留尼旺（约5）、哈克贝利（2.137-2.086Ma）和下奥杜瓦伊（1.922 Ma）倒转。这项为期三年的拟议研究的目标主要与在像逆转和远足这样的时期的磁场变化的知识有关，但也与逆转之前和之后的关键时间间隔有关，特别是2.6至1.8 Ma年之间的间隔，这一间隔在留尼旺和新报道的哈克贝利岭事件方面仍然没有很好地定义。反转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。这些序列为记录一个时间段内（包括几个极性间隔）的场变化提供了第一个特殊的机会，从而记录了不同时间常数下的场行为。这是提取和提出地球动力学理论和数值模拟的重要约束的基本条件。建议活动的智力价值：目前的建议集中在定向分析和古强度研究上，以实现总场矢量的确定。如上所述，测量将集中于连续的极性周期及其相关的反转。利用改进版的Thellier-Coe技术，对几个库劳流的每个熔岩流的一个样本进行了古强度的初步实验。我们施加了一个严格的标准来丢弃受磁矿学转变影响的样品以及涉及多畴晶粒的磁化成分。事实上，处理古强度值是很重要的，因为古强度值依赖于每次熔岩流至少5到8次的测定（就像方向的情况一样），以便用适当的误差条进行适当的统计处理。拟议活动的更广泛影响。主要研究员和4名本科生将进行这里提出的研究项目。在这个项目中，本科生的参与将是一个优先事项，从实地工作到实验室工作，分析和出版。数据将通过出版物、网络和社区维持的古地磁数据库传播。该项目还将为维持休斯敦大学的古地磁和岩石结构操作提供刺激，该操作由不同群体的学生和研究人员使用