Recycling of elements in subduction zones and formation of mineral deposits in magmatic arcs

岩浆弧中的火山释放出大量的挥发性元素。这些岩浆产生热液活动，可以浓缩金属矿物，如斑岩铜矿和贵金属矿脉。这些金属矿床与弧岩浆的联系表明两者之间存在成因联系。矿床的成分(金属、挥发物，包括水)在地表附近丰富，但在这些岩浆起源的地幔中含量极低。火山持续释放挥发性元素，以及在岩浆弧中形成矿藏，需要通过俯冲过程将这些组分从地表供应到地幔，在俯冲过程中，板块从地表下降到地幔，并将这些元素转移到地幔。一般的概念已经被广泛接受，但这种化学转移的机制还不是很清楚。我们早期的工作表明，赋存铜矿床的火成岩母岩岩浆被氧化并富含硫。一些火山弧，如菲律宾吕宋岛，蕴藏着丰富的斑岩铜矿，而日本则没有斑岩铜矿。不同类型金属矿床分布不均的原因尚不清楚。我计划研究两种类型的岩石：反映源地幔条件的原始镁铁质岩石，以及与浅成热液珍贵脉状矿床同时代的火成岩。要解决的问题包括：1.是什么控制了弧下地幔的条件？是什么控制着金属的流动性，将金属从板片转移到地幔，并转移到弧形岩浆？2.与贵金属矿床有关的岩浆有什么特征？它们与正常的弧岩浆和斑岩铜矿床有何不同？在该项目的第一阶段，我建议研究西太平洋的活动俯冲带，因为根据地震活动和断层图像，俯冲带的形状已经被很好地了解了。此外，该地区的大洋钻探计划显示了俯冲板块和沉积物的组成。然后，我计划将这些年轻弧线的信息应用到育空和纽芬兰的古老地体中，那里含有许多类似于活动弧线的贵金属矿藏。我的提议解决了基本的科学问题：元素是如何从地表循环到地幔，然后再循环到弧状岩浆的？除了这些学术问题外，拟议中的项目还有助于确保我们的生活水平。岩浆弧中的金属对我们的社会至关重要，例如用于电力传输的铜。此外，低碳社会呼唤替代能源。清洁能源需要许多金属，如太阳能电池板用的铟和银，这些金属是从岩浆弧的沉积物中提取的。建议的研究可以通过瞄准有利的岩浆弧和区域来帮助有效地勘探和发现这类金属矿床。

Volcanoes in magmatic arcs discharge large quantities of volatile elements. These magmas produce hydrothermal activity that can concentrate metallic minerals, such as porphyry copper deposits and precious metal veins. The association of these metallic deposits with arc magmas indicate a genetic link for the two. The constituents of deposits (metals, volatiles including water) are abundant near the surface, but extremely low in the mantle where these magmas originate. Continuous discharges of volatile elements from volcanoes, as well as the formation of mineral deposits in magmatic arcs, require these components to be supplied from the surface to the mantle via subduction processes where slabs descend from the surface into the mantle and transfer these elements to the mantle. The general concept is well accepted, but the mechanism of this chemical transfer is not well understood. Our earlier work showed that parental magmas of igneous rocks that host copper deposits are oxidized and sulphur-rich. Some volcanic arcs, such as Luzon, Philippines, contain abundant porphyry copper deposits, whereas there are no porphyry copper deposits in Japan. The causes of this uneven distribution of various types of metal deposits are not understood. I plan to examine two types of rocks; primitive mafic rocks that reflect the conditions of the source mantle, and igneous rocks contemporaneous with epithermal precious vein deposits. Questions to address include: 1. What controls the conditions of subarc mantle? What controls the mobility of metals to transfer metals from slabs to the mantle, and to arc magmas? 2. What characterizes magmas associated with precious metal deposits? How are they different from normal arc magmas and those responsible for porphyry copper deposits? In the first phase of the project, I propose to study active subduction zones in the western Pacific, since the configuration of the subduction zones is well understood, based on seismic activity and tomographic images. In addition, ocean drilling programs in the areas show the compositions of subducting slabs and sediments. Then, I plan to apply the information from these young arcs to old terranes in Yukon and Newfoundland, which contain many precious metal deposits similar to active arcs. My proposal addresses fundamental scientific questions: how are elements recycled from the surface to the mantle, then to arc magmas? In addition to these academic questions, the proposed project contributes to securing our living standards. Metals from magmatic arcs are vital for our society, such as copper for electric transmission. In addition, a low-carbon society calls for alternative energy sources. Clean energy requires many metals, such as indium and silver for solar panels, which are extracted from deposits in magmatic arcs. The proposed research can assist the efficient exploration and discovery of such metal deposits by targeting favourable magmatic arcs and regions