The geochemical evolution of Hawaiian magmatism: ODP Leg 197 drilling of the Emperor Seamounts

长寿的板块内(热点)岩浆作用，如发生在夏威夷，被认为是地幔热柱的表面表现：相对较热的物质柱从地幔深处升起。因此，对热点岩浆作用的地球化学研究可以深入了解地球深部的结构和组成，而这些结构和组成是无法直接采样的。我们计划对北太平洋皇帝海山的火山岩样品进行地球化学和同位素研究，这些样品将在ODP197航段(2001年7月至8月)钻探获得。皇帝海山是太平洋板块经过夏威夷热点时形成的，待分析的样品提供了该热点的独特的40 Ma(85-45 Ma前)的地球化学记录。这项研究将记录夏威夷岩浆活动在这一时期的地球化学演化。要讨论的具体问题是：(A)地幔热柱中地幔不均匀的性质、规模和来源，以及地幔成分的时间演化；(B)岩石圈混染、熔融和扩张脊相互作用等浅层过程对板内熔岩成分的影响；(C)屏蔽板内岩浆活动的起源和屏蔽板内岩浆作用后的板块内岩浆活动。

Long-lived, intra-plate (hotspot) magmatism, such as occurs on Hawaii, is thought to be the surface expression of mantle plumes: Columns of relatively hot material rising from deeper in the mantle. Geochemical studies of hotspot magmatism can thus give insights into the structure and composition of the Earth's deep interir, which cannot be directly sampled. We plan to carry out a geochemical and isotopic study of samples of volcanic rocks from the Emperor Seamounts, in the northern Pacific Ocean, which will be recovered by drilling on ODP Leg 197 (Juli - August, 2001). The Emperor Seamounts were creted when the Pacific Plate passed over the Hawaiian hotspot, and the samples to be analysed provide a unique, 40 Ma record (from 85 to 45 Ma ago) of the geochemistry of this hotspot. This study will document the geochemical evolution of Hawaiian magmatism over this period. Specific questions to be addressed are, (a) the nature, scale and origin of mantle heterogeneity in mantle plumes, and the temporal evolution of plume composition; (b) the influence of shallow-level processes such as lithospheric contamination, melting and spreading ridge interaction on the composition of intraplate lavas; (c) the origin of shield and post-shield intra-plate magmatism.