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

基本信息

批准号：
1927851
负责人：
Francis Macdonald
金额：
$ 7.79万
依托单位：
University of California-Santa Barbara
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-11-01 至 2021-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927851&HistoricalAwards=false
关键词：
COLLABORATIVE RESEARCH Testing proposed rapid

项目摘要

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.

在地质时期，地球板已经通过两个不同的机制移动。首先是地球板相对于彼此的运动，这是由于底层地幔的对流和板上的力平衡 - 我们称之为“板块构造”。第二个机制是所有板的运动，由于地球内部质量异常的转移以及相关的旋转不平衡，这可能会导致相对于地球旋转轴的重新定位。这种重新定向运动被称为真正的极地徘徊，而进步的速度取决于地球内部的粘度，地球内部的粘度受到今天和地球历史的约束。这项研究针对大约8亿年前的时间间隔，当时提议真正的极地徘徊比平常快得多 - 足够快，以至于地球表面的某些部分可能在100年内移动了足球场的距离。 PI试图追踪蒙古和中国的古老板块运动，以使用这个时代的岩石来检验这一假设。他们将使用保存在古代岩石中的磁性方向与U/PB放射性同位素日期相结合，以精确确定其年龄。这些数据将被使用限制板的移动速率和不同板的相对运动，以确定运动是否与快速的真实极性流浪一致。结果将向地球科学家提供有关此时明显板运动的驱动因素以及大陆的过去位置。该数据还具有通过时间来对地球内部粘度的约束来放置限制。它已提出，大规模的振荡性真实极性徘徊（TPW）发生在CA。 800 MA，与称为苦泉阶段的碳同位素间隔有关。最近的进步导致了苦泉阶段的时间量化框架，使该TPW假设能够在非碳酸盐岩性岩性中进行测试，例如一系列膨胀的火山。该项目旨在通过从蒙古和中国南部开发新的古磁和年代学数据来检验假设。该研究的目的是在地球历史的这一关键时期稳健地量化地球的旋转稳定性，并限制TPW的速率。苦泉TPW假设已成为大陆如何汇总到超大陆的模型的核心组成部分，对于地球地幔粘度的基本推论以及对雷神凸起和过度椭圆形的稳定效果，以及neoperoterocic roperoterocic环境环境变化的稳定效果。此外，Ca快速TPW的假设。 800 MA已成为超大型Rodinia配置模型的重要组成部分。该项目旨在通过在强大的地层环境中开发蒙古Zavkhan火山和中国南部Banxi集团的新的年代学和古磁数据来限制极点运动的速率。重要的是，这些继承含有：（1）含有锆石的丰富火山岩，可以从中获得高精度的U-PB化学磨蚀 - 稀释度 - 热质谱法（CA-ID-TIMS）日期，并且（2）表明普通磁化的古磁置信度测试。三年的现场工作，古磁分析和CA-ID-TIMS U-PB日期的发展将着重于为蒙古的Zavkhan Terrane和CA中的中国craton生产高质量的极路路径。 820至750 MA。这样的路径可用于进一步测试是否通过此间隔进行快速振荡TPW，如果是的，则以什么速率发生。在整个时间段内进行测试和限制这一假设对于在固体和表面的共同进化上的进展是必要的，并确定在前寒武纪中是否存在时间段，在这种情况下，可以鲁atsection表明TPW的速率高于Phanerozoic中分辨率的速率。拟议的研究的更广泛影响是四倍：（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）与该领域和PIS实验室中的蒙古学生的文化交流，以及（4）通过与哈佛大学自然历史博物馆（HMNH）结合建立教育展示模块，通过建立一个教育展示模块来有效地向K-12社区传达一组地球系统历史学习目标。该教育展览将集中在亚洲的地质记录上，并包括：（1）可以触及的大岩石样本；（2）现场探险的照片；（3）关于年代学和古磁主义的教育展示；（4）一视频解释了本研究中使用的地球物理技术。在HMNH的地球科学展览馆展出之后，展览模块将在加州大学伯克利分校的地球和行星科学系上展出，然后前往Ulaanbaatar的蒙古科学与技术大学。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。