Chalcophile elements in Shatsky Rise basalts as potential indicators of the mantle plume origin

火成岩海洋高原，如沙茨基隆起，代表了地球上最不了解的玄武岩岩浆活动类型之一。在沙茨基海隆的情况下，提出了两个主要的模型来解释它们的起源：（1）深源地幔柱头的熔融，（2）具有不寻常特征的中洋脊（莫尔）熔融（例如，榴辉岩的异常高动态或扩展引起的上涌）。2009年，综合大洋钻探计划第324远征队在早白垩世沙茨基海隆海洋高原取芯，以测试其羽流与非羽流起源。随后进行的巡航后岩石学和地球化学研究（包括岩石中Sr、Nd、Hf和He的同位素测定）证明，大多数沙茨基海隆岩浆来自略微富集的MORB型来源，并经历了类似MORB的晶体分馏。然而，这些数据并没有提供沙茨基海隆形成的两种主要假设之一（羽流与非羽流起源）的明确证据。一些热点相关的岩浆以前被认为具有高浓度的强亲铜元素（Cu，Au）相比，典型的MORB，提供了潜在的代理深地幔柱的起源。然而，目前的数据集可用于沙茨基隆起玄武岩只包括全岩铜含量，其升高的值在某些岩石类型也可以解释后岩浆硫化。在我们的新研究项目中，我们计划对沙茨基海隆玄武岩玻璃进行新的地球化学调查，重点是（1）原位分析原始玻璃中的强亲铜元素（Cu，Ag，Au，Se），以及（2）测定岩浆的氧化态。这些数据将用于测试沙茨基海隆海洋高原的羽流与非羽流起源。

Igneous oceanic plateaus, such as Shatsky Rise, represent one of the least understood types of basaltic magmatism on Earth. In the case of Shatsky Rise, two main models were proposed to explain their origin: (1) melting of deep-sourced mantle plume head, (2) melting at a mid oceanic ridge (MOR) with unusual characteristics (e.g., anomalously high dynamics or spreading-induced upwelling of eclogite) . In 2009, Integrated Ocean Drilling Program Expedition 324 has cored an early Cretaceous Shatsky Rise oceanic plateau to test its plume vs. non-plume origin. Consequent post-cruise petrological and geochemical studies including isotope determinations of Sr, Nd, Hf and He in the rocks testified that the majority of the Shatsky Rise magmas originated from a slightly enriched MORB-type source and underwent MORB-like crystal fractionation. The data did not, however, provide unequivocal evidence of the Shatsky Rise formation by one of the two main proposed scenarios (plume vs. non-plume origin). Some hotspot-related magmas were previously recognized to have elevated concentrations of strongly chalcophile elements (Cu, Au) compared to typical MORB, providing potential proxy for a deep mantle plume origin. However, the present dataset available for Shatsky Rise basalts includes only whole-rock Cu contents, whose elevated values in some rock types can also be explained by post-magmatic sulfidization. In the course of our new research project we plan to carry out new geochemical investigations of the Shatsky Rise basaltic glasses with the focus on (1) in-situ analysis of strongly chalcophile elements in pristine glasses (Cu, Ag, Au, Se), and (2) determination of the oxidation state of magmas. The data will be used to test plume vs. non-plume origin of the Shatsky Rise oceanic plateau.