Collaborative Research: Geochemistry of the Source Regions of Southwest Pacific Volcanic Islands: An approach using Ultramafic xenoliths and host basalts

这是一个合作项目， 研究所和麻省理工学院的弗雷德·弗雷。 它是一种综合的质地， 超镁铁岩捕虏体的矿物学和地球化学研究， 它们的宿主熔岩来自萨摩亚群岛、社会群岛和马克萨斯群岛 在西南太平洋。 捕虏体存在于 矿物学和同位素的初步工作 表明它们与部分加工有关 融化和岩浆分化 岛链中含有一些最丰富的玄武岩 海洋盆地中的熔岩，假设它们是相关的 到一个区域性的，也许是半球性的， 地幔中的异常 捕虏体应该提供了 地幔源区成分的信息， 影响或改变源岩的交代作用 成分，以及熔体萃取和岩浆作用过程 洋岛源区及其附近分异 玄武岩 迄今为止的研究表明，残留（1型）和 “堆晶”（2型）捕虏体存在于所有三个岛屿 链，以及大量程度的部分熔融产生的 可能是拉斑玄武岩岩浆结晶了橄榄石-尖晶石- 从地幔中出来的辉石组合 这些熔岩可能 包括大量的，淹没的，但仍然是未知的 这些火山的一部分 捕虏体研究的主要技术有：1） 矿物相的电子探针显微分析; 3)矿物中痕量元素丰度的离子探针分析， 和4）质谱（常规固体- 源和ICP-MS）、XRF和仪器中子活化 全岩和矿物分离物的分析。 步骤1和2 将用于选择适当的样本范围， 详细的离子探针、同位素和微量元素研究。 散装 将进行化学、微量元素和同位素测量 这些都与火山岩的时间序列有关， 这些岛屿是已知的。 还将进行比较 大陆和夏威夷捕虏体的公开信息 套房

This is a collaborative project between James Natland of Scripps Institution, and Fred Frey of MIT. It is an integrated textural, mineralogical, and geochemical study of ultramafic xenoliths and their host lavas from the Samoan, Society, and Marquesas Islands in the southwest Pacific. The xenoliths are in existing collections, and preliminary mineralogical and isotopic work demonstrates that they are related to processed of partial melting and magmatic differentiation beneath these volcanoes. The island chains contain some of the most enriched basaltic lavas in the ocean basins, which are hypothesized to be related to a regionally widespread, perhaps hemispheric, geochemical anomaly in the mantle. Xenoliths should provide complementary information on the compositions of mantle sources, the action of metasomatic processes in influencing or modifying source compositions, and the processes of melt extraction and magmatic differentiation in and near the source regions of ocean-island basalts. Studies so far indicate that both residual (Type 1) and "cumulate" (Type 2) xenoliths are present in all three island chains, and that substantial degrees of partial melting produced possible tholeiitic magmas which crystallized olivine-spinel- pyroxene assemblages en route from the mantle. Such lavas may comprise much of the voluminous, submerged, but still unsamples portions of these volcanoes Principal techniques to be applied to the xenoliths will be 1) petrography; 2) electron-probe microanalysis of mineral phases; 3) ion-probe analysis of trace-element abundances in minerals, and 4) a combination of mass spectrometry (conventional solid- source and ICP-MS), XRF, and instrumental neutron-activation analysis for whole-rocks and mineral separates. Steps 1 and 2 will be used to select the appropriate range of samples for detailed ion-probe, isotope, and trace-element studies. Bulk chemical, trace-element, and isotopic measurements will be made on host lavas and these related to temporal successions on the islands, which are already known. Comparisons will also be made to published information on continental and Hawaiian xenolith suites.