ИСТИНА

Выяснение факторов, ответственных за сульфидную ликвацию и геохимическую специфику сульфидного расплава. Мы планируем получить принципиально новые результаты по актуальной петролого-геохимической проблеме взаимодействия субдукционных расплавов и флюидов с надсубдукционным мантийным клином. Это важно потому, что такое взаимодействие не только понижает температуру солидуса перидотита и вызывает частичное плавление, но также вызывает перитектические реакции новообразованных расплавов с остаточными фазами, формированию новых минеральных ассоциаций, существенному перераспределению летучих и рудных элементов, и проявлению эффектов редокс-реакций в виде силикатно-сульфидной несмесимости и концентрированию хрома, никеля, меди и элементов платиновой группы.

Studies of the silicate-sulfide liquid immiscibility in oceanic and island-arc magmas of Kamchatka, carried out by our team within the framework of the RSF project No. 16-17-10145 (2016-2020), revealed the compositions and conditions for the formation of the most primitive sulfide melts in Nature. We have also found that the platinum group elements (PGE) are not only partitioned in the sulfide melt and the sulfide solid solution, but also form their own mineral phases and alloys, both in the sulfide and silicate melts. The most unexpected result of our previous studies was the similarity of sulfide melts of oceanic magmas (ophiolite of the Kamchatka Mys) and typical island-arc magmas (Tolbachik volcano) in terms of the major elements (Fe, Ni, Cu) and abundances of trace elements, including noble metals. Therefore, we are putting forward a project for the RSF grant competition. Our proposal aims to further constrain factors responsible for sulfide unmixing and the geochemical signature of the sulfide melt. We plan to get principally new results to resolve the long-standing petrological and geochemical problem of interaction of subduction melts and fluids with an overlying mantle wedge. This is important because this interaction not only reduces the solidus temperature of peridotite and causes partial melting, but is also responsible for peritectic reactions of newly formed melts with the restite mantle assemblage, the formation of new mineral associations, a significant redistribution of volatile and metal elements, and the manifestation of redox reactions in the form of silicate-sulfide immiscibility and concentration of chromium, nickel, copper, and platinum group elements. Our collections of mantle and mantle-derived rocks are unique and significant because they represent a sequence of reactions of the mantle wedge with fluids and melts of subduction origin. In particular, the use of existing and newly collected mantle xenoliths in the Kamchatka volcanic rocks will allow studying mantle metasomatic developments that are caused by the subduction derived melts and fluids. Petrographic and mineralogical studies will be instrumental in recognizing the main stages of modification of the mantle wedge, understanding the distribution of ore-forming elements (Cr, Ni, Cu, Fe) among silicate mineral phases, sulfides and oxide minerals. The speciation of sulfur (S2−, S0, S4+and S6+) in the mantle wedge will also be targeted, its main mineral phases (sulfides, sulfates) and their petrographic relationships will be identified. Additionally, the estimates of the redox conditions of metasomatic processes in the mantle will be evaluated via planned experimental studies.