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

火成岩海洋高原，如沙斯基隆起，代表了地球上最不为人所知的玄武岩岩浆活动类型之一。对于沙茨基隆升的成因，提出了两种主要的解释模式：(1)深源地幔柱头熔融；(2)具有异常特征（如异常高动力学或扩张引起的榴辉岩上升流）的洋中脊熔融。2009年，综合海洋钻探计划远征324队对早白垩纪的Shatsky Rise海洋高原进行了取样，以测试其羽流与非羽流起源。随后的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，证明了沙茨基隆起的大部分岩浆起源于一个微富集的morb型源，并经历了morb型晶体分选。然而，这些数据并没有根据两种主要的假设（地幔柱与非地幔柱起源）提供沙斯基隆起形成的明确证据。与典型的MORB相比，一些热点相关的岩浆具有较高的强亲铜元素（Cu, Au）浓度，这为深部地幔柱起源提供了潜在的代理。然而，目前可用的沙斯基隆起玄武岩数据仅包括全岩铜含量，其在某些岩石类型中的升高也可以用岩浆后硫化作用来解释。在新的研究项目中，我们计划对沙斯基隆玄武岩玻璃进行新的地球化学研究，重点是(1)原位分析原始玻璃中强亲铜元素（Cu、Ag、Au、Se），(2)测定岩浆的氧化态。这些数据将用于测试沙斯基隆起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.