Shatsky Rise: Ar/Ar Geochronology and geochemistry of igneous rock samples from the Shatsky Rise Plateau (northwest Pacific Ocean)

IODP Exp 324 Shatsky Rise的主要目标是研究海底Shatsky Rise高原的起源、时间和地球化学演化，该高原是位于日本以东约1500公里的西北太平洋的一个大型火成岩省（LIP）。两个40Ar/39Ar的高原年龄（在上覆沉积物中）和古地磁资料表明，该高原主要形成于晚侏罗世至早白垩世。古地磁资料也重建了原构造背景，表明沙茨基隆起形成于脊-脊-脊三联结。这项研究的目的是双重的。首先，我们将测定高原上两个不同钻孔点各主要岩性单元的最新火成岩基岩样品的锶（Sr）、钕（Nd）、铅（Pb）和铪（Hf）同位素组成，以确定岩浆源组成。限制岩浆源的地球化学成分将有助于实现这次考察的主要目标：测试沙斯基隆起海洋高原形成的不同端元模型（羽头或脊控模型）。其次，我们将利用40Ar/39Ar逐级加热技术对两个地点的斜长石斑晶进行绝对年龄测定，以进一步约束高原的时间和地球化学演化。最终，我们将把我们的结果与相同样品的数据（例如主要和微量元素以及He， Os， B， O和V同位素数据）以及其他324探险队参与者产生的其他钻探地点的数据相结合，以产生最全面的数据集，使我们能够评估地幔柱是否参与了像Shatsky隆起这样的LIP的产生，或者它们是否由其他过程形成。

The primary goal of IODP Exp 324 Shatsky Rise is to study the origin and temporal and geochemical evolution of the submarine Shatsky Rise Plateau, a large igneous province (LIP) in the northwest Pacific Ocean located ca. 1500 km east of Japan. Two 40Ar/39Ar plateau ages (on sills in the overlying sediments) and paleomagnetic data indicate that the plateau largely formed during the Late Jurassic to Early Cretaceous. The paleomagnetic data also allow the original tectonic setting to be reconstructed, indicating that the Shatsky Rise formed at a ridge-ridge-ridge triple junction. The purpose of this study is two-fold. First we will determine the strontium (Sr), neodymium (Nd), lead (Pb) and hafnium (Hf) isotopic compositions of the freshest igneous basement rock samples from each major lithological unit from two different drill sites on the plateau, in order to define the magmatic source composition(s). Constraining the geochemical composition of the magma source(s) will help achieve the primary objective of the expedition: testing contrasting endmember models of oceanic plateau formation at Shatsky Rise (plume head or ridge-controlled model). Second, we will determine the absolute age of samples from two sites using the 40Ar/39Ar step heating technique on plagioclase phenocrysts whenever available, in order to constrain further the temporal and geochemical evolution of the plateau. Ultimately we will combine our results with data on the same samples (e.g. major and trace element and He, Os, B, O and V isotope data) and from other drill sites generated by other Expedition 324 participants to produce the most comprehensive data set possible, enabling us to evaluate if mantle plumes are involved in the generation of LIP’s such as Shatsky Rise or if they are formed by other processes.