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Testing the mantle plume hypothesis through IODP drilling on the Louisville Seamounts

通过路易斯维尔海山 IODP 钻探检验地幔柱假说

基本信息

批准号：
NE/I022205/1
负责人：
Godfrey Fitton
金额：
$ 1.79万
依托单位：
University of Edinburgh
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FI022205%2F1
关键词：
Testing mantle plume hypothesis through

项目摘要

Mantle plumes are solid-state convective mantle upwellings that provide the principal means by which heat and material are transferred from the deep Earth to the surface. They are responsible for much of the world's intraplate volcanism (e.g. Hawaii) and their initiation is accompanied by massive outpourings of magma on a scale not seen today. These massive volcanic episodes produce large igneous provinces (LIPs), two of the largest of which coincided with global mass-extinction events at the Permian-Triassic (Siberia) and Cretaceous-Palaeocene (Deccan) boundaries. The largest of all Earth's LIPs, the Ontong Java Plateau (OJP), was erupted entirely below sea level and consequently had only a limited environmental impact. Testing the mantle plume hypothesis and, if plumes do indeed exist, understanding their nature and origin, are first-order goals of the Earth Sciences, and have provided the motivation for several DSDP, ODP and IODP deep-sea drilling expeditions including IODP Expedition 330 which is the basis of the present proposal. One of the early predictions of the mantle plume hypothesis is that plumes remain fixed in the mantle for tens of millions of years and that their surface manifestation as hotspot trails (chains of ocean islands and seamounts) can be used to define absolute plate motions. This prediction was tested during ODP Leg 197 on the Hawaii-Emperor seamount chain (HESC) and shown to be invalid. Palaeomagnetic studies on the cores showed that the hotspot drifted about 15 degrees southwards between 81 and 47 Ma, implying motion of the early Hawaiian plume of about 40 mm/yr with respect to the Earth's rotation axis. Although this finding doesn't necessarily weaken the plume hypothesis, it does show that plumes aren't always fixed. One possible explanation for the motion is that it reflects a general southward mantle flow (mantle 'wind') over this period. IODP Expedition 330 is designed to test the mantle 'wind' hypothesis by carrying out a similar study on the part of the Louisville seamount chain (LSC) that formed over the same period. The LSC is located in the south Pacific Ocean, runs roughly parallel to the HESC, and is the only hotspot chain on which the hypothesis can be tested. My role in IODP Expedition 330 will be to study the petrology and geochemistry of the drill core, and I propose to test the mantle plume hypothesis in three ways. (1) I propose to use the major element composition of basalt to estimate the mantle temperature at the time of seamount formation and (2) trace element data to assess the composition of the mantle source. It has been proposed that the LSC were produced from a mantle plume whose initiation phase was responsible for the giant OJP LIP. Trace element data, coupled with isotope studies being carried out by other shipboard scientists, should be allow us to test this hypothesis. The OJP was drilled during ODP Leg 192, on which I served as Co-Chief Scientist. Finally (3) I propose to use helium-isotope data (obtained in collaboration with Dr Finlay Stuart at SUERC) to look for evidence of deep-mantle involvement in the formation of the LSC. High 3He/4He has been found in basalt from the HESC (and in other possibly plume-related basalts) and is thought to imply an input of primordial 3He, either from the deep mantle or possibly the core.

地幔柱是固态对流地幔隆起，提供了热量和物质从地球深部转移到地表的主要手段。它们是造成世界上许多板内火山活动的原因（例如夏威夷），它们的形成伴随着大量的岩浆涌出，其规模之大今天还未见。这些大规模的火山事件产生了大的火成岩省（LIPs），其中两个最大的与二叠纪-三叠纪（西伯利亚）和白垩纪-古新世（德干）边界的全球大规模灭绝事件相吻合。地球上最大的LIPs，Ontong Java Plateau（OJP），完全在海平面以下爆发，因此只有有限的环境影响。验证地幔柱假说，如果地幔柱确实存在，了解其性质和起源，是地球科学的首要目标，并为几次DSDP，ODP和IODP深海钻探探险提供了动力，包括IODP Expedition 330，这是本提案的基础。地幔柱假说的早期预测之一是，地幔柱在地幔中固定了数千万年，其表面表现为热点轨迹（海洋岛屿和海山链）可以用来定义绝对板块运动。这一预测在ODP第197航次期间在夏威夷-皇帝海山链上进行了测试，结果表明是无效的。对岩芯的古地磁研究表明，热点在81至47 Ma之间向南漂移了约15度，这意味着早期夏威夷羽流相对于地球自转轴的运动约为40 mm/年。虽然这一发现并不一定削弱羽流假说，但它确实表明羽流并不总是固定的。一个可能的解释是，它反映了一般向南地幔流（地幔“风”）在这一时期。IODP第330次考察的目的是通过对同一时期形成的路易斯维尔海山链进行类似的研究来检验地幔“风”假说。LSC位于南太平洋，与HESC大致平行，是唯一可以检验假设的热点链。我在IODP远征330中的角色将是研究岩心的岩石学和地球化学，我建议用三种方法来检验地幔柱假说。(1)笔者建议利用玄武岩的常量元素组成来估算海山形成时的地幔温度;（2）利用微量元素数据来估算地幔源区的组成。有人提出，LSC是由地幔柱产生的，其初始阶段是巨大的OJP LIP的原因。微量元素数据，加上其他船上科学家正在进行的同位素研究，应该可以让我们验证这一假设。OJP是在ODP第192航次期间钻探的，我担任该航次的联合首席科学家。最后（3）我建议使用氦同位素数据（与SUERC的Finlay Stuart博士合作获得）来寻找深地幔参与LSC形成的证据。在HESC玄武岩（以及其他可能与地幔柱有关的玄武岩）中发现了高的3 He/4 He，并认为这意味着原始3 He的输入，无论是来自深部地幔还是可能来自地核。