Investigation of High Precision Os Measurements on Lavas From Iceland and the Austral Islands

最近的研究表明，一些夏威夷熔岩中186 Os/188 Os和187 Os/188 Os的耦合富集与夏威夷地幔柱源内核幔相互作用的假设一致。如果这是正确的，那么这些可能是迄今为止最可靠的地球化学数据，表明一些地幔柱起源于地幔最深处的D”区域。 或者，这些数据可能与古代再循环地壳的夹带相一致，前提是某些条件成立。 作为对这些假设的进一步检验，将获得冰岛和南极群岛熔岩的高精度186 Os/188 Os和187 Os/188 Os数据。这两个套房是理想的后续测试的作用，核幔相互作用和古地壳再循环产生放射性成因的Os组成的羽状，因为以下。 地震证据表明，冰岛热柱起源于核幔边界上方的D”。 它是一个高3 He热点，至少有6000万年的火山活动在相对固定的位置。 总之，这些意见支持深地幔起源的冰岛羽核-地幔相互作用可能发生。 一些南极群岛熔岩的187 Os/188 Os太高，无法通过合理的模型将外核夹带到羽流源中。 因此，这些熔岩可以用来进行严格的测试的作用，古地壳再循环的潜在生产放射性成因的186 Os/188 Os的地幔柱熔岩。 这项研究的最终结果将是提供一个更好的理解的意义之间的化学交换的外核和羽流源，地壳再循环的作用，以产生在羽流中的Os同位素签名，并使用耦合富集的186 Os/188 Os和187 Os/188 Os，以限制羽流的起源深度。

BrandonEAR-0000908Recent work has shown that coupled enrichments in 186Os/188Os and 187Os/188Os for some Hawaiian lavas is consistent with the hypothesis of core-mantle interaction within the Hawaiian plume source. If this is correct, then these are perhaps the most robust geochemical data to date, that show some plumes originate in the D" region of the deepest part of the mantle. Alternatively, these data could instead be consistent with entrainment of ancient recycled crust provided certain conditions hold. As a further test of these hypotheses, high precision 186Os/188Os and 187Os/188Os data for lavas from Iceland and the Austral Islands will be obtained. These two suites are ideal for subsequent testing of the roles of core-mantle interaction and ancient crustal recycling in generating radiogenic Os compositions in plumes because of the following. Seismic evidence suggests that Iceland plume originates from D" just above the core-mantle boundary. It is a high 3He hotspot with active volcanism in a relatively fixed position for at least 60 million years. Taken together, these observations support a deep mantle origin for the Iceland plume where core-mantle interaction may occur. Some Austral Islands lavas have 187Os/188Os that are too high to be produced by reasonable models for entrainment of outer core into plume sources. Therefore, the these lavas can be used to make a rigorous test of the role of ancient crustal recycling for potentially producing radiogenic 186Os/188Os in plume-derived lavas. The ultimate result of this study will be to provide a greater understanding of the significance of chemical exchange between the outer core and plume sources, the role of crustal recycling to produce Os isotopic signatures in plumes, and the use of coupled enrichments of 186Os/188Os and 187Os/188Os to constrain the depths of origin of plumes.