Collaborative Research: Experimental and theoretical characterization of rapid Jurassic true polar wander

在整个地球地质历史中，大陆的运动强烈地影响着地球表面的许多过程。大陆漂移的影响包括形成山脉和火山，生物多样性的扩散和灭绝，以及地方和全球气候的变化。地球上的大陆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，涉及大陆相对于彼此的差异运动。第二个，不太好理解的过程被称为真极移（TPW），其中整个地球作为一个单一的单位旋转，使得当前极点的位置被转移到较低的纬度。理论研究表明，TPW应该对全球环境产生强烈的影响，包括100米的区域海平面变化和陆地表面在多个不同气候带的漂移。然而，地球历史上大规模TPW事件的成因、发生率甚至是否存在一直存在争议。在这里，我们将测量晚侏罗世（距今约1.65 - 1.5亿年）岩石的磁性，并进行理论地球动力学计算，以描述最近提出的TPW事件中地球的运动。这些结果将对理解整个地质时期观测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演变的基本过程产生重要影响。该项目分为两个紧密耦合的部分，使用互补技术来了解侏罗纪TPW。首先，研究人员将从智利北方的La Negra地层和阿根廷巴塔哥尼亚的Chon Aike省收集古地磁岩石样本，以量化1.65 - 1.5亿年前（Ma）间隔期间大陆的位置，以前的研究已将其确定为潜在大振幅（约30度）TPW的最近时间间隔。这些岩石单元代表了候选TPW间隔中最连续的火成岩沉积，这意味着使用古地磁技术恢复高精度古地理信息的可能性最大。作为该项目实验部分的一部分，该小组将收集样品，使用锆石技术中的Ar-Ar和U-Pb进行地质年代学分析，这将提供这一时间跨度内更可靠的运动速率。其次，他们将使用现有的地球动力学代码来模拟地球的极移，该代码解释了地幔中质量异常的运动和地球岩石圈强度的横向变化。第二，耦合地球动力学代码将计算预期的变化，在区域海平面所造成的TPW运动。结合实验数据，这些模型将缩小晚侏罗世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。

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.