Rotation of the Philippine Sea Plate (IODP Expedition 351)

菲律宾海板块的旋转（IODP 351 号探险队）

• 批准号: NE/M007367/1
• 负责人: Antony Morris
• 金额: $ 4.57万
• 依托单位: Plymouth University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FM007367%2F1
• 关键词: Rotation; Philippine; Sea; Plate; IODP

Tectonic (or lithospheric) plates are formed by seafloor spreading at mid-ocean ridges in the world's oceans and are recycled back into the Earth's interior at subduction zones. The formation and destruction of plates produces the most important surface features on Earth, and are the major drivers of the physical and chemical evolution of our planet. Although subduction zones are unique to Earth among the terrestrial planets, as yet we do not have a good understanding of how they form. We know that subduction relates to gravitational instability of dense, old ocean lithosphere with respect to the underlying mantle. However, it remains unclear whether subduction is triggered by horizontal forces acting on existing structures like mid-ocean ridges or initiates spontaneously from vertical gravitational forces. The key to advancing our understanding of this fundamental process is to examine changes in sedimentary rock sequences through time that have accumulated by deposition on a plate that has experienced subduction initiation, in order to examine changes in plate conditions. Such a sequence will be drilled and sampled by International Ocean Discovery Program Expedition 351 to the Philippine Sea Plate. Following subduction initiation 52 million years ago, this plate now sits above the major Izu-Bonin-Mariana (IBM) subduction zone system. A 1300 m thick sequence will be sampled that includes rocks formed prior to and after initiation of the IBM system. Analysis of magnetizations acquired by these rocks during their deposition will allow accurate dating of the sampled section, as the timing of changes in the geometry of the Earth's magnetic field (polarity reversals) during the geological past is well known. This will provide essential control on the timing of geological events associated with the tectonic history of the Philippines Sea Plate.Full understanding of the evolution of this system, however, requires the boundary conditions of the past motions of the Philippine Sea Plate to be known. This information can again be obtained using the magnetization of the sequence of rocks that overlie the igneous basement of the plate. The angle the magnetization of a rock sample makes with the horizontal (its inclination) provides a direct measure of the latitude at which it formed, as the inclination of the Earth's magnetic field is a simple function of latitude. Previous studies of rocks exposed on islands on the Philippine Sea Plate have suggested that it has drifted northwards by 25 degrees during its evolution. The palaeomagnetic data used in these interpretations, however, come from the tectonically complex margins of the plate and are widely distributed in time. In contrast, this project will yield near-continuous records of inclination through time that will resolve plate motion at a high resolution. In addition to northwards translation, existing palaeomagnetic data also suggest a 90 degree vertical axis rotation of the plate since it formed. To test this requires knowledge of changes in the azimuth (or declination) of magnetizations through time. Unfortunately, scientific ocean drilling samples are not oriented with respect to geographic north, so declinations cannot be acquired directly from the core materials recovered during Expedition 351. However, this information can be retrieved by matching geological features seen in unoriented cores with the same features seen on oriented images of the inside of the borehole wall. Alternatively, records of magnetization direction can be obtained indirectly by modeling of the disturbances to the present day geomagnetic field that result from variations in the ancient magnetizations of rocks downhole. Both of these approaches will be used in this project to obtain high-resolution records of the tectonic rotation of the Philippine Sea Plate, providing key information on the regional tectonic evolution that are required to understand subduction initiation processes.

构造(或岩石圈)板块是由海底在世界海洋的大洋中脊扩张形成的，并在俯冲带循环回到地球内部。板块的形成和破坏产生了地球上最重要的地表特征，是我们星球物理和化学演化的主要驱动力。虽然俯冲带是类地行星中地球独有的，但到目前为止，我们对它们的形成还没有很好的了解。我们知道俯冲与致密的古老海洋岩石圈相对于下伏地幔的重力不稳定有关。然而，目前尚不清楚俯冲是由作用在大洋中脊等现有结构上的水平力引发的，还是由垂直重力自发发起的。促进我们对这一基本过程的理解的关键是研究沉积岩序列随时间的变化，这些变化是由于经历了俯冲开始的板块上的沉积而积累的，以便研究板块条件的变化。这样的层序将由国际海洋发现计划351号远征菲律宾海板块进行钻探和取样。在5200万年前开始俯冲之后，这个板块现在位于主要的伊豆-博宁-马里亚纳(IBM)俯冲带系统之上。将对一个1300米厚的层序进行采样，其中包括在IBM系统启动之前和之后形成的岩石。对这些岩石在沉积过程中获得的磁化作用的分析将使采样剖面的准确测年成为可能，因为地质过去期间地球磁场几何形状的变化(极性反转)的时间是众所周知的。这将提供对与菲律宾海板块构造历史相关的地质事件的时间的基本控制。然而，要完全理解这个系统的演化，需要知道菲律宾海板块过去运动的边界条件。利用覆盖在板块火成岩基底之上的岩石序列的磁化作用，可以再次获得这一信息。由于地球磁场的倾斜度是纬度的简单函数，岩石样品的磁化程度与水平线的夹角(其倾角)提供了它形成时所在纬度的直接测量。此前对菲律宾海板块岛屿上暴露出的岩石的研究表明，在其演化过程中，它向北漂移了25度。然而，这些解释中使用的古地磁数据来自板块构造复杂的边缘，在时间上分布广泛。相比之下，该项目将产生随时间推移的几乎连续的倾斜记录，从而以高分辨率解决板块运动问题。除了向北平移外，现有的古地磁数据还表明，自板块形成以来，板块垂直轴旋转了90度。要测试这一点，需要知道磁化的方位角(或偏角)随时间的变化。不幸的是，科学的大洋钻探样品不是以地理上的北向为导向的，因此不能直接从351次探险中发现的岩心材料中获取倾角。然而，这种信息可以通过将未定向岩心中看到的地质特征与井壁内侧定向图像上看到的相同特征进行匹配来检索。另外，磁化方向的记录可以通过对井下岩石古老磁化作用的变化对现代地磁场的扰动进行模拟而间接获得。这两种方法都将用于该项目，以获得菲律宾海板块构造旋转的高分辨率记录，提供了解俯冲启动过程所需的区域构造演化的关键信息。

项目成果

Timing of Tectonic and Magmatic Events in the Philippine Sea Plate since 50 Ma from High-Resolution Magnetostratigraphy of IODP Site U1438

IODP 站点 U1438 高分辨率磁性地层学对 50 Ma 以来菲律宾海板块构造和岩浆事件的计时

• DOI: 10.1002/essoar.10509798.1
• 发表时间: 2021
• 作者: Maffione M

A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc

• DOI: 10.1038/ngeo2515
• 发表时间: 2015-09-01
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: Arculus, Richard J.;Ishizuka, Osamu;Zhang, Zhaohui
• 通讯作者: Zhang, Zhaohui

The onset of fabric development in deep marine sediments

深海沉积物中织物发育的开始

• DOI: 10.1016/j.epsl.2017.06.018
• 发表时间: 2017
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Maffione M