Subduction Initiation Investigated by Drilling of the Izu-Bonin-Mariana (IBM) Forearc

通过伊豆-博南-马里亚纳 (IBM) 前弧钻探研究俯冲起始

• 批准号: NE/M012034/1
• 负责人: Julian Pearce
• 金额: $ 3.08万
• 依托单位: CARDIFF 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%2FM012034%2F1
• 关键词: Subduction; Initiation; Investigated; Drilling; Izu

The theory of plate tectonics has plates created at mid-ocean ridges and destroyed at subduction zones, above which lie chains of volcanoes known as island arcs. Subduction zones have been likened to a factory (the 'Subduction Factory') whereby materials (mantle, oceanic crust and sediment) are fed into the factory, processed within the factory (by dehydration and melting), and create range of products (magmas, ore deposits). There are many 'health and safety' issues, including earthquakes, tsunamis and explosive volcanoes. Because much of this 'Subduction Factory' is located underwater and sub-surface, the International Ocean Discovery Program (IODP) has put together three marine drilling Expeditions (350-352), each two months long, aimed at a better understanding of how the subduction factory works. These Expeditions are all located in the ocean south of Japan known as the IBM (Izu-Bonin-Mariana) region, which is a key natural laboratory for understanding subduction processes. Each Expedition has a particular goal and Expedition 352 (the focus of this proposal) has the remit to investigate how subduction starts (i.e. how the 'Factory' opens) and the products of this subduction initiation process. Julian Pearce, the PI of this proposal, is one of its two co-chief scientists.The rocks formed at the earliest stages of subduction are particularly well exposed in the inner walls of the deep ocean trenches south of Japan and it is here, in the Bonin Trench, that Expedition 352 plans to drill. Dredging has already demonstrated at the base is made up of an oceanic crust-like sequence with mantle rocks at its base, overlain by gabbros, and then by dykes and submarine lavas. These date back to c. 52Ma and are believed to represent the first stage of subduction initiation, when one plate sinks, peels back and creates a zone of extension. This is overlain by a set of geochemically-distinctive volcanic rocks which are believed to represent the transition from spreading to arc volcanism, and finally by more conventional island arc volcanic rocks marking the point at which true subduction starts, i.e. when the subducting plate has a horizontal as well as vertical component. Estimates indicate that it took about 8 m.y. between subduction initiation and the start of true subduction. Interpretations, and testing of hypotheses for subduction initiation, are however, limited by the fact that there is no reference section, and so we aim to obtain that by drilling of the full 1-1.5 km thick lava sequence.Many studies will be carried out on the drilling ship and in the laboratory. As co-chief scientist, the PI has joint responsibility for synthesising the results, in this case to provide the geological community with a type sequence of subduction initiation volcanism which can be used for comparison with inferred subduction initiation sequences in volcanic rocks now exposed in old geological sequences in mountain belts and elsewhere. In addition, he has specific responsibility for analyzing three isotopes (of Pb, Hf and Nd) for use as tracers of the subduction initiation process, and for interpreting the results. For this he aims to work with Rex Taylor (co-I), who has worked in the IBM region himself and also runs an isotope laboratory that not only analyses Hf and Nd isotopes but also specializes in high precision analyses of Pb isotope ratios. The subduction process is complicated, with elements having a number of potential sources: mantle above the subduction zone, subducted crust and various types of subducted sediment. Pb is a particularly good tracer of subducted sediment, while Hf-Nd are good tracers of the provenance of the mantle and temperature of the system. By analyzing these isotope ratios in samples taken from bottom to top of the lava sequence, we aim to document the how subduction variables change during the transition from subduction initiation to true subduction.

板块构造理论认为，板块在大洋中脊形成，在俯冲带被摧毁，俯冲带上方是被称为岛弧的火山链。俯冲带被比作工厂(“俯冲工厂”)，物质(地幔、洋壳和沉积物)被送入工厂，在工厂内加工(通过脱水和熔融)，并创造出一系列产品(岩浆、矿床)。有许多“健康和安全”问题，包括地震、海啸和火山爆发。由于“潜水工厂”的大部分位于水下和水下，国际海洋发现计划(IODP)组织了三次海洋钻探探险(350-352次)，每次为期两个月，旨在更好地了解潜水工厂是如何运作的。这些探险队都位于日本南部被称为IBM(伊豆-博宁-马里亚纳)地区的大洋上，这是了解俯冲过程的关键自然实验室。每一次探险都有一个特定的目标，而探险352(本提案的重点)有权调查俯冲是如何开始的(即“工厂”是如何打开的)以及这种俯冲启动过程的产物。朱利安·皮尔斯是该计划的两名联合首席科学家之一。在俯冲的最早阶段形成的岩石在日本南部深海海沟的内壁中暴露得特别好，正是在这里，博宁海沟，352探险队计划钻探。基地的疏浚已经证明是由洋壳状的层序组成的，底部有地幔岩石，上面覆盖着辉长岩，然后是堤坝和海底熔岩。它们可以追溯到约52 Ma，被认为是俯冲开始的第一阶段，当一个板块下沉、剥离并形成伸展带时。这被一组地球化学特征独特的火山岩所覆盖，这些火山岩被认为代表着从扩张火山作用向弧形火山作用的过渡，最后被更传统的岛弧火山岩覆盖，这些火山岩标志着真正俯冲的开始点，即俯冲板块具有水平和垂直分量的时候。据估计，它花了大约8英里。从俯冲开始到真正的俯冲开始。然而，对俯冲开始的假说的解释和测试受到这样一个事实的限制，即没有参考剖面，所以我们的目标是通过钻探完整的1-1.5公里厚的熔岩序列来获得参考剖面。许多研究将在钻探船上和实验室进行。作为联合首席科学家，PI共同负责综合结果，在这种情况下，为地质界提供俯冲启动火山作用的类型序列，可用于与现在暴露在山区和其他地方的旧地质序列中的火山岩中推断的俯冲启动序列进行比较。此外，他还专门负责分析用作俯冲启动过程示踪剂的三种同位素(铅、氢和钕)，并解释结果。为此，他的目标是与雷克斯·泰勒(Co-I)合作，后者本人曾在IBM地区工作，还经营着一家同位素实验室，不仅分析Hf和ND同位素，还专门从事高精度的铅同位素比率分析。俯冲过程是复杂的，具有许多潜在来源的元素：俯冲带上方的地幔、俯冲地壳和各种类型的俯冲沉积物。Pb是一种特别好的俯冲沉积物示踪剂，而Hf-ND是地幔来源和系统温度的良好示踪剂。通过分析从熔岩序列底部到顶部采集的样品中的这些同位素比率，我们的目标是记录从俯冲开始到真正俯冲的转变过程中俯冲变量的变化。

项目成果

Forearc ages reveal extensive short-lived and rapid seafloor spreading following subduction initiation

• DOI: 10.1016/j.epsl.2018.11.020
• 发表时间: 2019-01
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: M. Reagan;D. Heaton;M. Schmitz;J. Pearce;J. Shervais;A. Koppers

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

• DOI: 10.1130/ges01661.1
• 发表时间: 2019-06
• 期刊: Geosphere
• 影响因子: 2.5
• 作者: J. Pearce;M. Reagan

Subduction initiation as recorded in the Izu-Bonin-Mariana forearc

• DOI: 10.1016/j.earscirev.2023.104573
• 发表时间: 2023-10-03
• 期刊: EARTH-SCIENCE REVIEWS
• 影响因子: 12.1
• 作者: Reagan，Mark K.;Pearce，Julian A.;Christeson，Gail L.
• 通讯作者: Christeson，Gail L.

Subduction initiation and ophiolite crust: new insights from IODP drilling

• DOI: 10.1080/00206814.2016.1276482
• 发表时间: 2017-01
• 期刊: International Geology Review
• 影响因子: 2.6
• 作者: M. Reagan;J. Pearce;K. Petronotis;R. Almeev;Aaron Avery;C. Carvallo;T. Chapman;G. Christeson

Radiogenic isotopes document the start of subduction in the Western Pacific

• DOI: 10.1016/j.epsl.2019.04.041
• 发表时间: 2019-07
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Hongyang Li;R. Taylor;J. Prytulak;M. Kirchenbaur;J. Shervais;J. Ryan;M. Godard;M. Reagan