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

在地质时代，地球的地壳板块通过两种不同的机制移动。第一个是地球板块之间的相对运动，这是由于底层地幔的对流和板块上的力平衡-我们称之为“板块构造”。第二种机制是由于地球内部的质量异常和相关的旋转不平衡而导致所有板块一起运动，这可能导致相对于地球自转轴的重新定向。这种重定向运动被称为真极移，其速度取决于地球内部的粘性，这在今天和地球历史上都受到很大的限制。这项研究的目标是大约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-快得足以让地球表面的一部分在大约100年内移动了足球场的距离。PI试图追踪蒙古和中国的古代板块运动，以使用这个年龄的岩石来验证这一假设。他们将使用保存在古代岩石中的磁性方向结合U/Pb放射性同位素年龄来精确确定它们的年龄。这些数据将用于限制板块移动的速率和不同板块的相对移动，以确定运动是否与快速的真实极移一致。这些结果将为地球科学家提供有关当时明显板块运动的驱动因素以及大陆过去位置的信息。这些数据也有可能限制地球内部的粘性随时间的变化。800马，与碳同位素间隔称为苦泉阶段。最近的进展为Bitter Springs阶段提供了一个时间量化框架，使TPW假设能够在非碳酸盐岩性（例如喷出火山岩的继承）中得到检验。该项目试图通过发展蒙古和中国南方的新的古地磁和年代学数据来检验这一假设。这项研究的目标是通过地球历史的这一关键时期来有力地量化地球的旋转稳定性，并允许限制TPW的速率。苦泉TPW假说已成为一个核心组成部分的模型如何大陆聚合成超大陆，为基本的推断到地球的地幔的粘度和稳定的影响，reversible凸起和过剩的椭圆率，和新元古代环境变化的行星背景。此外，快速TPW的假设在约。800 Ma已成为超大陆Rodinia构造模型的重要组成部分。该项目旨在通过在坚实的地层背景下开发蒙古扎夫汗火山和华南板溪群的新的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，这些序列包括：（1）丰富的火山岩含有锆石，从中可以获得高精度的U-Pb化学研磨-离子稀释-热质谱（CA-ID-TIMS）年龄和（2）古地磁置信度测试表明保留的原始磁化。为期三年的野外工作、古地磁分析和CA-ID-TIMS U-Pb定年的发展将集中于产生蒙古扎夫汗地体和华南克拉通约1000年以来的高质量极轨。820 ~ 750 Ma。这样的路径可以用于进一步测试快速振荡TPW是否在该间隔中发生，如果是，以什么速率发生。测试和约束这一假设是必要的固体地球和地表的共同演化的进展，通过时间段，并确定是否有时间段，在前寒武纪，它可以有力地表明，TPW的速率高于那些解决在中生代。拟议研究的更广泛影响是四方面的：（1）加州大学伯克利分校研究生的培训和发展;（2）本科生参与基础研究;（3）与蒙古学生在实地和两个PI实验室进行文化交流，（4）有效地向K传达一套地球系统历史学习目标，通过与哈佛自然历史博物馆（HMNH）合作建造一个教育展示模块，为12个社区提供服务。这次教育展览将侧重于亚洲的地质记录，包括：（1）可以触摸的大型岩石样本;（2）实地考察的照片;（3）关于地质年代学和古地磁学的教育展览;（4）解释本研究中使用的地球物理技术的录像。在HMNH的地球科学展览馆展出后，展览模块将前往加州大学伯克利分校的地球和行星科学系展出，然后前往乌兰巴托的蒙古科技大学。 这项工作包括广泛的国际合作，并由国际科学和工程办公室共同资助。

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.