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

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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