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

BrandonEAR-0000908最近的工作表明，一些夏威夷熔岩的186Os/188Os和187Os/188Os的耦合富集与夏威夷热柱源区内的核-地幔相互作用的假说是一致的。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，表明一些羽流起源于地幔最深处的D“区域。或者，如果某些条件保持不变，这些数据可能与古代回收壳的夹带作用一致。作为对这些假设的进一步检验，将获得冰岛和南岛熔岩的高精度186Os/188os和187os/188os数据。这两组是随后测试核-地幔相互作用和古代地壳再循环在羽流中产生放射性成因Os成分的作用的理想选择，原因如下。地震证据表明，冰岛热柱起源于地核-地幔边界上方的D“。它是一个高3He热点，活火山活动在一个相对固定的位置至少有6000万年。综上所述，这些观测结果支持冰岛热柱的深地幔起源，在那里可能发生核-地幔相互作用。一些澳大利亚群岛熔岩的187Os/188Os太高，不能通过合理的外核夹带到烟柱源的模型来产生。因此，这些熔岩可以用来严格测试古代地壳再循环在羽状熔岩中潜在产生放射性成因186Os/188Os的作用。这项研究的最终结果将使人们更好地了解外核和羽状源之间化学交换的重要性，地壳再循环在羽状物中产生Os同位素特征的作用，以及使用186Os/188Os和187Os/188Os的耦合浓缩来限制羽状物的起源深度。

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.