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）板块是由世界各大洋洋中脊的海底扩张形成的，并在俯冲带再循环回到地球内部。板块的形成和破坏产生了地球上最重要的表面特征，是地球物理和化学演变的主要驱动力。虽然俯冲带是地球在类地行星中所独有的，但我们对它们是如何形成的还没有很好的了解。我们知道，俯冲作用与致密、古老的海洋岩石圈相对于下伏地幔的重力不稳定性有关。然而，目前还不清楚俯冲是由作用在现有结构（如洋中脊）上的水平力引发的，还是由垂直重力自发引发的。推进我们对这一基本过程的理解的关键是检查沉积岩序列随时间的变化，这些变化是通过在经历俯冲开始的板块上沉积而积累的，以检查板块条件的变化。国际海洋发现计划351号考察队将对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-小笠原-马里亚纳（IBM）俯冲带系统之上。将对1300 m厚的层序进行取样，其中包括IBM系统启动前后形成的岩石。对这些岩石在沉积过程中获得的磁化进行分析，将能够对取样部分进行准确的年代测定，因为在地质历史期间地球磁场几何形状变化（极性反转）的时间是众所周知的。这将提供与菲律宾海板块构造历史相关的地质事件的时间控制，然而，要充分了解该系统的演化，需要知道菲律宾海板块过去运动的边界条件。这一信息也可以通过对覆盖在板块火成岩基底上的岩石序列进行磁化来获得。岩石样品的磁化强度与水平面的夹角（它的倾角）提供了它形成时纬度的直接测量，因为地球磁场的倾角是纬度的简单函数。先前对菲律宾海板块岛屿上暴露的岩石的研究表明，它在演化过程中向北漂移了25度。然而，这些解释中使用的古地磁数据来自构造复杂的板块边缘，并且在时间上分布广泛。相比之下，这个项目将产生近连续的倾斜记录，随着时间的推移，将解决板块运动在一个高分辨率。除了向北的平移，现有的古地磁数据还表明，自板块形成以来，该板块的垂直轴旋转了90度。为了检验这一点，需要了解磁化随时间的方位角（或衰减）变化。不幸的是，科学的海洋钻探样品并不是以地理上的北方为方向的，因此赤纬不能直接从351号考察期间回收的岩心材料中获得。然而，可以通过将在未定向岩心中看到的地质特征与在钻孔壁内部的定向图像上看到的相同特征进行匹配来检索该信息。或者，磁化方向的记录可以间接地通过模拟由井下岩石的古代磁化变化引起的对现今地磁场的干扰来获得。这两种方法都将用于本项目，以获得高分辨率的记录的菲律宾海板块的构造旋转，提供关键信息的区域构造演化，需要了解俯冲启动过程。

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