Magma Differentiation processes and volatile contents in Shatsky Rise oceanic Plateau basalts: constraints from mineral, glass and melt inclusion compositions combined with experimental and thermodynamic modeling

大洋高原是巨大的火山构造，其形成和存在与从地幔到岩石圈的巨大岩浆流动有关。这些大型火成岩省(LIP)可以作为地幔对流和地球动力学基本过程以及重大环境变化的重要指标，对增进对整个地球系统的了解至关重要。人们普遍认为，大洋高原是由于深部地幔热柱到达岩石圈而引发的大规模喷发。另一种假说认为，在快速扩张的海脊之下，异常可熔融的地幔发生了减压熔融。沙茨基隆起是一个独特的大洋高原，形成于晚侏罗世和早白垩世快速扩张的三重结合部，其特征可归因于任何一种形成模式。2009年进行的综合海洋钻探计划324探险的目标是取心沙茨基隆起的火成岩和上面的沉积物，以研究该隆起的年龄、物理火山学、地球化学和构造演化。在拟议的项目中，我们计划为确定岩浆储存条件和模拟沙茨基隆起大洋高原的分异过程做出贡献。这些信息可以从(1)回收的样品研究以确定天然矿物、玻璃和熔体包裹体的化学成分；(2)高压结晶实验和(3)热力学模拟(COMAGMAT)获得。沙茨基隆起也是研究唇状玄武岩中原始喷发前挥发性丰度的理想地区，因为它不受大陆岩石圈的污染。有关沙茨基隆起玄武岩岩浆的挥发分收支、成分、氧逸度和挥发分释放的定量信息将通过结合天然玻璃和熔体包裹体的分析、受控氧逸度的相关系和挥发分活动的研究而获得。这是量化地幔热柱产生的熔体的脱气和地球历史上可能产生的气候影响的先决条件信息。

Oceanic plateaus are giant volcanic constructs whose formation and existence is related to the enormous magma flux from mantle to lithosphere. These Large Igneous Provinces (LIPs) can be important indicators of fundamental processes of mantle convection and geodynamics, as well as major environmental changes and are crucial for advancing understanding of the whole Earth system. It is widely thought that oceanic plateaus arise from massive eruptions resulting from the arrival of a deep mantle plume head at the lithosphere. An alternative hypothesis invokes decompression melting of unusually fusible mantle beneath fast-spreading ridges. Shatsky Rise is a unique oceanic plateau, formed during the Late Jurassic and Early Cretaceous at a rapidly spreading triple junction, with characteristics that could be attributed to either model of formation. The goal of Integrated Oceanic Drilling Program Expedition 324 conducted in 2009 was to core the igneous rocks of Shatsky Rise and the sediments above to examine the age, physical volcanology, geochemistry, and tectonic evolution of the rise. In the proposed project we plan to contribute to the determination of magma storage conditions and to the simulation of differentiation processes in Shatsky Rise oceanic plateau. This information can be gained from (1) the study of recovered samples to determine chemical compositions of natural minerals, glasses and melt inclusions; (2) high pressure crystallization experiments and (3) thermodynamic modelling (COMAGMAT). The Shatsky Rise is also an ideal region to study pristine pre-eruptive volatile abundances in LIP basalts, due to the lack of contamination with continental lithosphere. The quantitative information on volatile budget, composition, oxygen fugacity, and volatile release in Shatsky Rise basaltic magmas will be obtained from a complementary approach combining analysis of natural glasses and melt inclusions, investigation of phase relationships at controlled oxygen fugacity and volatile activities. This is a prerequisite information to quantify the degassing of mantle plume derived melts and the possible climatic impact in Earth’s history.