Volatile Recycling at the Lesser Antilles Arc: Processes and Consequences

小安的列斯群岛弧的挥发性回收：过程和后果

基本信息

批准号：
NE/K010662/1
负责人：
Jonathan Blundy
金额：
$ 14万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK010662%2F1
关键词：
Volatile Recycling Lesser Antilles Arc

项目摘要

The Earth is unique in our solar system in having abundant liquid water, plate tectonics and life. These properties are not unconnected; The evolution of life has depended heavily on water, and water is pumped around the planet by the plate tectonic cycle. Plate tectonics in turn, and its capacity to generate the very continents on which we live, also depends on the existence of water.Subduction zones are the most important "valve" in the plate tectonic system. They form where tectonic plates sink back into the mantle. Here water, along with other volatiles such as carbon dioxide and sulphur, are returned to the deep interior. However, the return is not wholesale. As the sinking plate is subjected to heat and pressure, a large fraction of the incoming volatiles is "sweated off" and added to the overlying mantle where it causes melting. These melts feed volcanoes at subduction zones which are characteristically dangerously explosive. When considered with the earthquakes triggered by the plates scraping past each other and the consequent tsunamis and landslides, it is clear that subduction zones are the most hazardous places on Earth. Yet, these regions also have benefits: the cocktail of fluids travelling with magmas at subduction zones is responsible for transporting and emplacing valuable metal deposits into the crust, and the fine ash distributed by the explosive volcanoes produces nutrient-rich, fertile soils.The importance of cycling volatiles through subduction zones is self-evident. However we still don't really know how it works and what the budgets are of volatiles delivered to the subduction zone, versus those recycled into the lithosphere, hydrosphere and atmosphere compared with those sequestered back into the deep mantle.We propose an innovative multidisciplinary experiment to track volatiles at a subduction zone. Questions to be answered include: How do volatiles influence the types and amounts of magmas generated? How do they control where volcanoes, such as Mt Pinatubo and Montserrat are located and how explosive they are? How do volatiles dictate where ore deposits are formed? How do volatiles mediate the seismogenic behaviour of subduction zones - whether there are large "megathrust" earthquakes like Japan and Sumatra or whether slip is less violent?Our focus area is the Lesser Antilles Arc, which is a special case, because it is one of only two Atlantic subduction zones. Plate formation processes at the slowly-spreading mid-Atlantic ridge produce a much more pervasively hydrated plate than those in the extensively studied Pacific. Furthermore, a laterally varying capacity to carry water in the plate and sediments subducting below the Antillean arc are a likely culprit for the arc's highly variable style and intensity of seismic and volcanic activity. By mapping structural differences along the arc we will be able to pinpoint the effects of variable water input. We plan to use novel seismic approaches complemented by geochemical analyses and integrated using numerical models to identify and quantify where volatiles are in the downgoing plate, where they are released at depth, and how they are transported from the subducting plate through the mantle wedge to the arc. We will use a unique suite of rocks from deep in the crust which have been carried up in volcanoes to help us understand how magmas evolve, and what allows them to concentrate ore metals. Mapped water pathways will be compared with seismic and volcanic activity, as well as with those inferred at other subduction zones.This large research project will be "bookended' on the one hand by an enormous amount of resource; data, samples, expertise and results from previous studies that will provide excellent value for money, and on the other hand a special focus on the societal benefits; informing natural hazard planning, and a better appreciation of how and where economic deposits form.

地球在太阳系中是独一无二的，它拥有丰富的液态水、板块构造和生命。这些属性并不是没有联系的；生命的进化在很大程度上依赖于水，而水通过板块构造循环被泵送到地球周围。反过来，板块构造及其形成我们所生活的大陆的能力也取决于水的存在。俯冲带是板块构造系统中最重要的“阀门”。它们形成于构造板块沉入地幔的地方。在这里，水与二氧化碳和硫等其他挥发物一起返回到内部深处。但退货不批发。当下沉的板块受到热量和压力时，大部分进入的挥发物被“汗出”并添加到上覆的地幔中，导致熔化。这些熔体为俯冲带的火山提供燃料，这些火山具有危险的爆炸性。考虑到板块相互刮擦引发的地震以及随之而来的海啸和山体滑坡，俯冲带显然是地球上最危险的地方。然而，这些地区也有好处：在俯冲带与岩浆一起流动的流体混合物负责将有价值的金属矿床输送并安置到地壳中，而爆发性火山喷发的细灰可产生营养丰富、肥沃的土壤。通过俯冲带循环挥发物的过程是不言而喻的。然而，我们仍然不知道它是如何工作的，以及输送到俯冲带的挥发物的预算是多少，与回收到岩石圈、水圈和大气中的挥发物相比，与那些被隔离回地幔深处的挥发物相比。我们提出了一项创新的多学科实验追踪俯冲带的挥发物。需要回答的问题包括：挥发物如何影响产生的岩浆的类型和数量？他们如何控制皮纳图博山和蒙特塞拉特火山等火山的位置以及它们的爆炸性？挥发物如何决定矿床的形成位置？挥发物如何调节俯冲带的孕震行为——是否存在像日本和苏门答腊岛这样的大型“逆冲断层”地震，或者滑动是否不那么剧烈？我们的重点区域是小安的列斯群岛弧，这是一个特例，因为它是只有两个大西洋俯冲带。与广泛研究的太平洋地区相比，缓慢扩张的大西洋中脊的板块形成过程产生了更普遍的水合板块。此外，板块载水能力的横向变化以及俯冲到安的列斯岛弧以下的沉积物可能是该岛弧的地震和火山活动的类型和强度高度变化的罪魁祸首。通过绘制沿弧线的结构差异，我们将能够查明可变水输入的影响。我们计划使用新的地震方法，辅之以地球化学分析，并使用数值模型进行集成，以识别和量化挥发物在下降板块中的位置、挥发物在深处的释放位置，以及它们如何从俯冲板块通过地幔楔输送到地幔楔。弧。我们将使用一套来自地壳深处、被火山携带的独特岩石来帮助我们了解岩浆如何演化，以及是什么让它们能够浓缩矿石金属。绘制的水路径将与地震和火山活动以及其他俯冲带推断的水路径进行比较。这一大型研究项目一方面将通过大量资源“预订”：数据、样本、专业知识和结果以前的研究将提供卓越的资金价值，另一方面特别关注社会效益；为自然灾害规划提供信息，并更好地了解经济存款的形成方式和地点。