CSEDI: Collaborative Research: Development of Geochemical Tests for Detection of Core-Mantle Interaction

地球化学的一个基本问题是，在地球的冷却循环中，热量从地核到地幔的传递是否伴随着化学交换。以前有人提出，如果在源自地幔柱的熔岩中检测到186Os/188Os和187Os/188Os比值的某些耦合变化，则表明从外核到从核幔边界上升的地幔柱的少量质量转移。为了研究这个问题，将精确测量两个羽流衍生的海洋岛屿玄武岩系统的1860o / 188o和1870o / 188o比值。还有强有力的质量平衡证据表明，地核的182W/184W比大约比周围地幔低10000分之2。这个信号的一部分可以转移到羽流中，就像Os同位素一样。因此，将开发技术来检查相同的羽流衍生岩石的W同位素，其含量为百万分之5-15，这可能是检测核心成分所必需的。Os和W同位素作为岩心输入地幔柱的示踪剂的能力，需要对这些元素及其相关元素在高压条件下的金属/硅酸盐分配行为有很好的理解。因此，高压分区将被实验检验。最后，将考虑和评估地核金属向地幔转移的各种物理机制。

A basic question in geochemistry is whether or not there is chemical exchange accompanying the transfer of heat from the core to the mantle in the cooling cycle of the Earth. It has been previously proposed that minor mass transfer from the outer core to a mantle plume rising from the core-mantle boundary would be indicated if certain, coupled variations in 186Os/188Os and 187Os/188Os ratios are detected in lavas derived from the plume. To examine this issue, 186Os/188Os and 187Os/188Os ratios of rocks from two plume-derived, ocean island basalt systems will be precisely measured. There is also strong mass balance evidence that the core has a 182W/184W ratio that is approximately 2 parts in 10,000 lower than the ambient mantle. A portion of this signal could be transferred to a plume, as with the Os isotopes. Consequently, techniques will be developed to examine the same plume-derived rocks for W isotopes at the 5-15 parts per million level that will likely be necessary to detect a core component. The ability of Os and W isotopes to serve as tracers of core input to mantle plumes require a good understanding of metal/silicate partitioning behavior of these and allied elements, under high-pressure conditions. Consequently, high-pressure partitioning will be examined experimentally. Finally, a variety of physical mechanisms of the transfer of core metal into the mantle will be considered and evaluated.