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

IODP Exp 324沙茨基隆起的主要目标是研究海底沙茨基隆起高原的起源、时间和地球化学演化。沙茨基隆起高原是西北太平洋上的一个火成岩大省，位于日本以东约1500公里处。两个40Ar/39Ar高原年龄和古地磁资料表明，该高原主要形成于晚侏罗世至早白垩世。古地磁资料还可以重建原始构造环境，表明沙茨基隆起形成于海脊-海脊-海脊三重结合部。这项研究的目的有两个。首先，我们将测定青藏高原两个不同钻探地点每个主要岩性单元的最新火成岩基岩样品的锶(Sr)、钕(ND)、铅(Pb)和氢(Hf)同位素组成，以确定岩浆源区的组成(S)。限制岩浆源的地球化学成分(S)将有助于实现考察的主要目标：测试沙茨基隆起大洋高原形成的对比端元模型(烟柱头部或海脊控制模型)。其次，我们将利用斜长石斑晶的40Ar/39Ar阶梯加热技术测定两个地点样品的绝对年龄，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，常量和微量元素以及He、Os、B、O和V同位素数据)以及其他探险324参与者产生的其他钻探地点的数据结合起来，以产生尽可能全面的数据集，使我们能够评估地幔热柱是否参与了LIP的生成，如沙茨基隆起，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.