COLLABORATIVE RESEARCH: Testing proposed rapid true polar wander in the Neoproterozoic Zavkhan Volcanics of Mongolia and the Banxi Group of South China

合作研究：在蒙古新元古代扎夫汗火山和华南板西群中测试提出的快速真实极地漂移

• 批准号: 1547434
• 负责人: Nicholas Swanson-Hysell
• 金额: $ 28.63万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2021-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547434&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Testing; proposed; rapid

Through geological time, Earth's crustal plates have moved through two distinct mechanisms. The first is the motion of Earth's plates relative to one another due to convection of the underlying mantle and the force balance on the plate - we call this "plate tectonics". The second mechanism is motion of all of the plates together due to shifting mass anomalies within the Earth and associated rotational imbalance, which can cause reorientation relative to Earth's spin axis. This reorientation motion is referred to as true polar wander, and the rate at it proceeds is dependent on the viscosity of Earth's interior, which is poorly constrained both today and through Earth History. This research targets a particular interval of time around 800 million years ago when it has been proposed that true polar wander was much faster than usual -fast enough that parts of Earth's surface may have moved the distance of the length of football field in around 100 years. The PIs seek to track ancient plate movement in Mongolia and China to test this hypothesis using rocks of this age. They will do so using the magnetic directions preserved in the ancient rocks combined with U/Pb radiogenic isotope dates to precisely determine their age. These data will be used constrain both the rate that plates were moving and the relative movement of different plates in order to determine if the motion is consistent with rapid true polar wander. The results will inform Earth Scientists about the drivers of apparent plate motion at this time and the past position of the continents. The data also have the potential to place constraints on the viscosity of Earth's interior through time.It has been proposed that large-scale, oscillatory true polar wander (TPW) occurred at ca. 800 Ma, associated with a carbon isotope interval known as the Bitter Springs Stage. Recent advances have led to a temporally quantified framework for the Bitter Springs Stage that enables this TPW hypothesis to be tested in non-carbonate-bearing lithologies, such as successions of extrusive volcanics. This project seeks to test the hypothesis through the development of new paleomagnetic and geochronological data from Mongolia and South China. The goal of the research is to robustly quantify Earth's rotational stability through this critical period of Earth history and allow for rates of TPW to be constrained. The Bitter Springs TPW hypothesis has become a central component of models for how continents aggregate into supercontinents, for fundamental inferences into the viscosity of Earth's mantle and the stabilizing effect of the remanent bulge and excess ellipticity, and for the planetary context of Neoproterozoic environmental change. Furthermore, the hypothesis of rapid TPW at ca. 800 Ma has become a significant component of models for the configuration of the supercontinent Rodinia. This project seeks to constrain the rate of pole movement during this interval through the development of new geochronological and paleomagnetic data from the Zavkhan Volcanics of Mongolia and the Banxi Group of South China in robust stratigraphic context. Importantly, these successions contain: (1) abundant volcanic rocks containing zircon from which high-precision U-Pb chemical abrasion-ion dilution-thermal mass spectrometry (CA-ID-TIMS) dates can be obtained and (2) paleomagnetic confidence tests indicating preservation of primary magnetization. Three years of field work, paleomagnetic analysis, and the development of CA-ID-TIMS U-Pb dates will focus on producing high quality pole paths for the Zavkhan Terrane of Mongolia and the South China craton from ca. 820 to 750 Ma. Such paths can be used to further test whether rapid oscillatory TPW occurred through this interval and, if so, at what rates. Testing and constraining this hypothesis is necessary for progress on the co-evolution of the solid earth and the surface through the time period and determining whether there were time periods in the Precambrian where it can be robustly shown that rates of TPW were higher than those resolved in the Phanerozoic. The broader impacts of the proposed research are four-fold: (1) the training and development of a UC Berkeley graduate student; (2) engagement of undergraduate students in basic research; (3) cultural exchange with Mongolian students in the field and in both of the PIs labs and (4) effective communication of a set of Earth systems history learning goals to K-12 communities through the construction of an educational display module in conjunction with the Harvard Museum of Natural History (HMNH). This educational exhibit will be focused on the geological record of Asia and will include: (1) large rock samples that can be touched; (2) photographs from field expeditions; (3) educational displays about geochronology and paleomagnetism; and (4) a video explaining the geophysical techniques used in this study. Following display in the Earth Science exhibit galleries at HMNH, the exhibit module will travel for display in the Earth and Planetary Science Department at UC Berkeley and then to the Mongolia University for Science and Technology in Ulaanbaatar. This work includes extensive international collaboration, and is co-funded by the Office of International Science and Engineering.

在整个地质时期，地球的地壳板块经历了两种不同的机制。第一个是由于底层地幔的对流和板块上的力平衡而导致地球板块相对运动 - 我们称之为“板块构造”。第二种机制是由于地球内的质量异常移动和相关的旋转不平衡，所有板块一起运动，这可能导致相对于地球自转轴的重新定向。这种重新定向运动被称为真正的极地漂移，其进行的速率取决于地球内部的粘度，无论是在今天还是在地球历史上，这种粘度都受到很少的限制。这项研究针对的是大约 8 亿年前的一个特定时间间隔，当时有人提出，真正的极地漂移比平常快得多，快到地球表面的部分区域可能在大约 100 年内移动了一个足球场长度的距离。 PI 试图追踪蒙古和中国的古代板块运动，以利用这个时代的岩石来检验这一假设。他们将利用古代岩石中保存的磁场方向结合 U/Pb 放射性同位素年代来精确确定它们的年龄。这些数据将用于约束板块移动的速率和不同板块的相对运动，以确定运动是否与快速真实的极移一致。研究结果将为地球科学家提供有关此时明显板块运动的驱动因素以及大陆过去位置的信息。这些数据还有可能随着时间的推移对地球内部的粘度施加限制。有人提出，大规模的振荡真极漂移（TPW）发生在大约。 800 Ma，与称为苦泉阶段的碳同位素区间相关。最近的进展导致了苦泉阶段的时间量化框架，使该 TPW 假说能够在非碳酸盐岩岩性（例如喷发火山岩序列）中得到检验。该项目旨在通过开发来自蒙古和华南的新古地磁和地质年代学数据来检验这一假设。该研究的目标是在地球历史的这一关键时期强有力地量化地球的旋转稳定性，并限制 TPW 的速率。苦泉 TPW 假说已成为以下模型的核心组成部分：大陆如何聚集成超级大陆、地幔粘度的基本推论、残余隆起和过量椭圆率的稳定作用以及新元古代环境变化的行星背景。此外，快速 TPW 的假设在大约。 800 Ma 已成为罗迪尼亚超大陆构造模型的重要组成部分。该项目旨在通过在强大的地层背景下开发蒙古扎夫汗火山和华南板溪群的新地质年代学和古地磁数据来限制这一时期的极移速率。重要的是，这些序列包含：(1) 丰富的含有锆石的火山岩，从中可以获得高精度 U-Pb 化学磨损离子稀释热质谱 (CA-ID-TIMS) 数据；(2) 古地磁置信度测试表明保持初级磁化强度。为期三年的实地工作、古地磁分析以及 CA-ID-TIMS U-Pb 测年技术的开发将集中于为蒙古扎夫汗地体和华南克拉通生产高质量的极路径。 820 至 750 Ma。此类路径可用于进一步测试该时间间隔内是否发生快速振荡 TPW，如果发生，发生率是多少。测试和约束这一假设对于固体地球和地表在整个时期的共同演化方面取得进展是必要的，并确定前寒武纪是否存在可以强有力地表明 TPW 速率高于已解决的速率的时期。在显生宙。拟议研究的更广泛影响有四个方面：（1）加州大学伯克利分校研究生的培训和发展； （二）本科生从事基础研究的情况； (3) 在现场和两个 PI 实验室与蒙古学生进行文化交流，以及 (4) 通过与哈佛大学自然历史博物馆 (HMNH)。该教育展览将重点关注亚洲的地质记录，并将包括：（1）可触摸的大型岩石样本； （二）野外考察照片； （3）地质年代学和古地磁学的教育展示； (4) 解释本研究中使用的地球物理技术的视频。在 HMNH 的地球科学展厅展出后，该展览模块将在加州大学伯克利分校的地​​球与行星科学系展出，然后前往位于乌兰巴托的蒙古科技大学。 这项工作包括广泛的国际合作，并由国际科学与工程办公室共同资助。