Immiscible sulphide liquids: Insights into chalcophile element fractionation processes in the oceanic crust

不混溶硫化物液体以岩浆硫化物球的形式保存在洋壳中，记录了其寄主岩浆系统中硫和亲铜元素的演化。最近的结果报告系统的变化，在矿物学和化学的岩浆硫化物球从收敛和发散板边缘，但这些差异的起源，和亲铜元素循环在大洋地壳的影响，是未知的。控制S在硅酸盐熔体中溶解度的参数包括：（1）温度，（2）压力，（3）氧逸度和（4）分馏程度。虽然上地幔熔融条件和岩浆分异在地壳洋中脊和俯冲带之间的不同，这些过程对硅酸盐熔体的S饱和极限和亲铜元素预算的影响仍然知之甚少。更好地约束岩浆系统中S和亲铜元素的演化，对于理解大洋岩石圈中亲铜元素的循环、海底热液硫化物的组成、大陆地壳的形成、火山气体的成分，以及可能的金属和准金属预算的一些陆上浅成热液-该项目旨在通过调查岩浆微量金属和准金属通量（例如，Co、Ni、Cu、Se、Ag、Te、PGE、Au、Bi）在洋中脊和大洋俯冲带的大洋岩石圈中的迁移。将采用最先进的分析技术，提出大洋岩石圈所有部分岩浆硫化物球的第一个全球微量元素数据集，涉及板块构造背景和岩浆系统的时间演变。样品反映了大陆分裂期间海洋扩张的开始和最近洋中脊的轴上火山活动，以及从海底最年轻到熔岩/岩墙过渡处最古老的熔岩堆的完整继承，记录了高时间分辨率的岩浆亲铜微量元素循环的演变。为了实现这些目标，需要从岩石圈上地幔到地壳最上层的连续样品光谱，这只能由钻探岩心提供，例如DSDP，ODP和IODP勘探期间回收的岩心。我们已经确定了合适的岩心，连同现代海底和古代海洋岩石圈（例如，Troodos蛇绿岩）提供了一个全面的样品集，包括上地幔橄榄岩，下地壳辉长岩，席状岩墙和熔岩从玄武岩到流纹岩组成。在许多这些样品中已经发现了岩浆硫化物球。拟议的项目将使我们能够开发第一个模型的岩浆亲铜微量元素循环通过整个海洋岩石圈在收敛和发散板块边缘。

Immiscible sulphide liquids preserved as magmatic sulphide globules in the oceanic crust record the S and chalcophile element evolution of their host magmatic systems. Recent results report systematic variations in the mineralogy and chemistry of magmatic sulphide globules from convergent and divergent plate margins, but the origin of these differences, and the implications for the chalcophile element cycle in the oceanic crust, are unknown. Parameters that control the solubility of S in silicate melts include: (1) temperature, (2) pressure, (3) oxygen fugacity and (4) the degree of fractionation. Although upper mantle melting conditions and magma differentiation in the crust differ between mid-ocean ridges and subduction zones, the effects of these processes on the S saturation limit of a silicate melt and its chalcophile element budget are still poorly understood. Better constraints on the S and chalcophile element evolution of magmatic systems are critical for understanding the chalcophile element cycle in the oceanic lithosphere, the composition of seafloor hydrothermal sulphides, the formation of the continental crust, the composition of volcanic gas and possibly the metal and metalloid budget of some subaerial epithermal-porphyry deposits.The project aims to address these questions by investigating the magmatic trace metal and metalloid flux (e.g., Co, Ni, Cu, Se, Ag, Te, PGE, Au, Bi) through the oceanic lithosphere at mid-ocean ridges and at oceanic subduction zones. State-of-the-art analytical techniques will be used to present the first global trace element data set of magmatic sulphide globules from all sections of the oceanic lithosphere, with respect to the plate-tectonic setting and the temporal evolution of the magmatic system. Samples reflecting the initiation of ocean spreading during continental break-up and recent on-axis volcanic activity at mid-ocean ridges together with a full succession of the lava pile from the youngest at the seafloor to the oldest at the lava/dyke transition record the evolution of the magmatic chalcophile trace element cycle at high temporal resolution. In order to address these objectives, a continuous sample spectrum from the upper lithospheric mantle to the uppermost crust is required, which can only be provided by drill cores, such as those recovered during DSDP, ODP and IODP expeditions. We have identified suitable cores, which together with samples from the modern seafloor and from ancient oceanic lithosphere (e.g., Troodos ophiolite) provide a comprehensive sample set including upper mantle peridotites, lower crustal gabbros, sheeted dykes and lavas from basaltic to rhyolitic composition. Magmatic sulphide globules have already been identified in many of these samples. The proposed project will allow us to develop the first models of the magmatic chalcophile trace element cycle through the entire oceanic lithosphere at both convergent and divergent plate margins.