Collaborative Research: Experimental and Theoretical Characterization of Rapid Jurassic True Polar Wander

合作研究：侏罗纪快速真实极地漂移的实验和理论表征

• 批准号: 1722529
• 负责人: Jessica Creveling
• 金额: $ 5.85万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-02-15 至 2023-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722529&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; Theoretical; Characterization

The motion of continents throughout the geologic history of the Earth strongly affects a vast number of processes on its surface. Among the effects of continental drift are the formation of mountain belts and volcanoes, the spread and extinction of biodiversity, and changes in climate at the local and global scales. Continents on Earth may move via one of two fundamentally different processes. The more familiar mechanism, known as plate tectonics, involves the differential motion of continents relative to each other. The second, less well-understood process is known as true polar wander (TPW), wherein the entire Earth rotates as a single unit such that the location of the present pole is transferred to a lower latitude. Theoretical studies show that TPW should have strong effects on the global environment, including regional sea-level changes of 100 m and drift of land surface across multiple, contrasting climate zones. However, the cause, rate, and even the existence of large-scale TPW events in Earth history have been controversial. Here we will measure the magnetism of rocks from the Late Jurassic (~165-150 million years before present) and pursue theoretical geodynamical computations to characterize the motion of the Earth during this most recent proposed episode of TPW. The results will have important implications for understanding the drivers of observed sea-level and climate changes throughout geologic time and for elucidating a fundamental process by which the global geography of the Earth evolves.This project is divided into two closely coupled parts that use complementary techniques to understand Jurassic TPW. First, the investigators will collect paleomagnetic rock samples from the La Negra Formation of Northern Chile and the Chon Aike province of Patagonian Argentina to quantify the position of continents during the 165-150 million year ago (Ma) interval, which has been identified by previous studies as the most recent time interval of potentially large amplitude (about 30 degrees) TPW. These rock units represent the most continuous deposits of igneous rocks from the candidate TPW interval, which implies the highest likelihood of recovering high precision paleogeographical information using paleomagnetic techniques. As part of this experimental component of this project, the team will collect samples for geochronological analysis using Ar-Ar and U-Pb in zircon techniques, which would provide more reliable rates of motion during this time span. Second, they will simulate the polar wander of the Earth using existing geodynamical code that accounts for the motion of mass anomalies in the mantle and lateral variations in the lithospheric strength of the Earth. A second, coupled geodynamical code will compute the expected changes in regional sea-level caused by the TPW motion. Combined with experimental data, these models will narrow the range of possible drivers of Late Jurassic TPW and evaluate its potential effect on records of climate and sea-level.

整个地球地质历史的大陆运动在其表面上强烈影响大量过程。大陆漂移的影响包括山带和火山的形成，生物多样性的扩散和灭绝以及当地和全球尺度上气候的变化。地球上的大洲可能通过两个根本不同的过程之一移动。更熟悉的机制（称为板块构造学）涉及大陆相对于彼此的差异运动。第二个，不太善良的过程被称为真正的极地徘徊（TPW），其中整个地球旋转为单个单元，因此将当前极的位置转移到较低的纬度。理论研究表明，TPW应该对全球环境产生强大的影响，包括100 m的区域海平面变化以及在多个对比的气候区域中陆地表面漂移。但是，地球历史上大规模TPW事件的原因，速度甚至存在引起了争议。在这里，我们将衡量侏罗纪晚期（在现在之前约有165-1.5亿年）的岩石磁性，并追求理论地球动力学计算，以表征地球在TPW的最新一集中表征地球的运动。该结果将对理解在整个地质时间内观察到的海平面和气候变化的驱动因素以及阐明地球全球地理发展的基本过程的驱动因素具有重要意义。该项目被分为两个使用互补技术来理解侏罗纪TPW的互补技术。首先，调查人员将从智利北部的La Negra形成和巴塔哥尼亚省阿根廷省的La Negra形成中收集古磁性岩石样品，以量化165-1.5亿年前（MA）间隔，这已被先前的研究确定为潜在的大型振幅的最新时间间隔（约30度）。这些岩石单元代表了候选TPW间隔中最连续的火成岩岩石沉积物，这意味着使用古磁技术恢复高精度古地理信息的可能性最高。作为该项目的实验组成部分的一部分，该团队将在锆石技术中使用AR-AR和U-PB收集样品，以进行地质学分析，这将在此时间跨度中提供更可靠的运动速率。其次，他们将使用现有的地球动力学代码来模拟地球的极地徘徊，这些密码解释了地幔中质量异常的运动和地球岩石圈强度中的横向变化。第二个，耦合的地球动力学代码将计算由TPW运动引起的区域海平面的预期变化。结合实验数据，这些模型将缩小侏罗纪晚期TPW的可能驱动因素的范围，并评估其对气候和海平面记录的潜在影响。