Characterization of the Cretaceous Normal Superchron

白垩纪正常超纪元的表征

• 批准号: 0511016
• 负责人: Xixi Zhao
• 金额: $ 47万
• 依托单位: University of California-Santa Cruz
• 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 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0511016&HistoricalAwards=false
• 关键词: Characterization; Cretaceous; Normal; Superchron

Numerical simulations have suggested that a stable (non-reversing) geodynamo may be more efficient at generating stronger dipole fields, and that this condition can arise from a favorable pattern of laterally varying heat flux across the core-mantle boundary. Thus it is important both for understanding how the geodynamo works and for inferring past lower-mantle conditions to find out whether or not the average field strength really was unusually high during the Cretaceous Normal Superchron (CNS), the span of time from around 121 to 83 Ma during which the geodynamo stopped reversing. The investigators propose a major effort to characterize the paleomagnetic field intensity and directional dispersion during CNS. They plan field work to collect lava samples in Madagascar, Korea, Costa Rica, N. Greenland, and Svalbard erupted during, just before, and just after the CNS. They will also collect basalt of mid-Miocene age (a time of high reversal rate) from the Columbia River Plateau. This research seeks answers to the following important questions that are still unresolved: (i) whether the average intensity during the CNS was unusually high, low or unexceptional, (ii) whether there were long-term intensity trends within the CNS, and (iii) whether the fluctuation of intensity on time scales of order 104 yr resembled that of the recent field or was distinctly different. An alternative conjecture for the occurrence of the CNS is that the geomagnetic field can switch abruptly into and out of a non-reversing state, simply by virtue of the highly nonlinear geodynamo processes operating in the core. The investigators will test this hypothesis by seeing whether there is an identifiable temporal trend in paleointensity or dispersion leading up to the beginning or end of the CNS. This international collaborative project includes bringing senior scientists, postdocs and students to work together and share their knowledge and ideas. The scientific results will be made available in the comprehensive paleomagnetic database currently under development with NSF support and will be disseminated in journal articles. The character of the geomagnetic field during the Cretaceous Normal Superchron also has societal relevance and interests a broad scientific community trying to understand mantle behavior and determine potential causal relationships between plumes, large igneous provinces formation and climatic changes.

数值模拟表明，稳定的（不转化）地球诺（Geodynamo）可能更有效地产生更强的偶极子场，并且这种情况可能是由于跨核心膜边界的横向变化热通量的有利模式引起的。因此，重要的是要了解地球人的工作原理以及推断过去的较低命中条件的工作方式，以找出在白垩纪正常超级纹理（CNS）期间平均场强度是否真的很高，这是从121 ma左右到83 mA的跨度，在此期间，Geodynamo停止了逆转。研究人员提出了一项重大努力，以表征CNS期间古磁场强度和方向性分散。他们计划在马达加斯加，韩国，哥斯达黎加，格陵兰岛，斯瓦尔巴德爆发中，在中枢神经系统之前和之后爆发了现场工作。他们还将从哥伦比亚河高原的中新世时代（高度逆转率）收集玄武岩。这项研究寻求尚未解决的以下重要问题的答案：（i）中枢神经系统中的平均强度异常高，低还是不可证实，（ii）中枢神经系统内是否存在长期强度趋势，以及（iii）104年阶段的强度上升的强度是否相差。 CNS发生的一种替代猜想是，仅凭高度非线性的Geodynamo流程，地磁场就可以突然进入和从非反向状态切换。研究人员将通过查看在中枢神经系统开始或结束之前是否存在可识别的时间趋势来检验这一假设。这个国际合作项目包括带高级科学家，博士后和学生一起工作并分享他们的知识和想法。该科学结果将在当前正在开发的NSF支持的综合性古磁数据库中提供，并将在期刊文章中传播。白垩纪正常超校长期间的地磁领域的特征也具有社会相关性，并具有一个广泛的科学界，试图理解地幔行为并确定羽毛，大火成岩省形成和气候变化之间的潜在因果关系。