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

最近的研究表明，一些夏威夷熔岩在1860 /188Os和187Os/188Os的耦合富集与夏威夷羽流源内核幔相互作用的假设是一致的。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。或者，这些数据可能与古代再循环地壳的夹带作用相一致，只要条件允许。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1860o / 188o和1870o / 188o数据。由于以下原因，这两个组对于后续测试核幔相互作用和古地壳再循环在羽流中产生放射性成因Os组成中的作用是理想的。地震证据表明，冰岛地幔柱起源于D”，正好在核心-地幔边界之上。它是一个高3He热点，在相对固定的位置有至少6000万年的活火山活动。综上所述，这些观测结果支持冰岛羽流的深层地幔起源，在那里可能发生核幔相互作用。一些南岛熔岩的187o / 188o含量太高，无法通过合理的模型将外核带入羽流源。因此，这些熔岩可以用来对古代地壳再循环在羽状熔岩中可能产生放射性成因186Os/188Os的作用进行严格的测试。本研究的最终结果将有助于更好地理解外核与地幔柱源之间化学交换的意义，地壳循环在地幔柱中产生Os同位素特征的作用，以及利用186Os/188Os和187Os/188Os的耦合富集来约束地幔柱的起源深度。

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.