Quantifying the thermal structure and hydrothermal fluid fluxes in the lower oceanic crust

量化下洋壳的热结构和热液流体通量

• 批准号: RGPIN-2016-04019
• 负责人: Gillis, Kathryn
• 金额: $ 2.91万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708955
• 关键词: Quantifying; thermal; structure; hydrothermal; fluid

New ocean crust is built along mid-ocean ridges by submarine volcanic activity. Seawater migrates down into this new permeable crust, and is progressively heated as it circulates due the presence of magma at depth. Seawater-derived fluids are chemically modified as they migrate through the crust because they react with the rocks through which they are passing. When these fluids exit the seafloor they are enriched in metals and H2S, leading to the formation of economically important volcanic hosted massive sulfide deposits and providing nutrients for unique biological ecosystems. The chemical exchange between the oceans and the ocean crust acts to modify the composition of both. Within the broader earth system this exchange plays an important role in regulating the composition of the ocean and the inputs into subduction zones, which influences the composition of arc volcanoes and contributes to heterogeneity in the mantle. A critical gap in our understanding of how the ocean crust is built and hydrothermally altered is related to the plutonic sequence that resides >2 km beneath the seafloor. At and near mid-ocean ridges, the interplay between magmatic intrusion and hydrothermal cooling and alteration controls the thermal and chemical evolution of the plutonic crust. To gain access to these critical rocks we take advantage of “tectonic windows,” where lower crustal exposures were unroofed by tectonic processes, thus bypassing the upper crust entirely. In the Pacific Ocean there are two such tectonic windows, Hess and Pito Deeps, and these are the only locations globally where these critical plutonic rocks have been mapped and sampled. Over the last 20+ years, I have participated in four submersible/ROV sampling cruises and led two international ocean drilling expeditions, leading to a globally unique sample suite for my proposed research. Over the next grant cycle, my research group will use this unique sample suite to test competing hypotheses for how crust is built at fast-spreading mid-ocean ridges by magmatic processes and subsequently cooled and altered by hydrothermal flow and reaction. We will also build a quantitative model for the magmatic and hydrothermal controls on the S and chalcophile element budget of the lower crust to expand our understanding of how the lower crust contributes to the global cycling of these elements.

海底火山活动使新的洋壳沿着大洋中脊形成。海水向下迁移到这个新的可渗透地壳中，由于深处岩浆的存在，海水在循环过程中逐渐被加热。海水衍生的流体在地壳中迁移时会发生化学变化，因为它们会与所经过的岩石发生反应。当这些流体离开海底时，它们富含金属和H2S，导致形成具有重要经济意义的火山岩块状硫化物矿床，并为独特的生物生态系统提供营养。 海洋和洋壳之间的化学交换改变了两者的组成。在更广泛的地球系统中，这种交换在调节海洋的组成和俯冲带的输入方面发挥着重要作用，这影响了弧火山的组成，并有助于地幔的不均匀性。 在我们对洋壳如何形成和热液蚀变的理解中，一个关键的空白与位于海底2公里以下的深成序列有关。在洋中脊及其附近，岩浆侵入与热液冷却和蚀变之间的相互作用控制着深成地壳的热演化和化学演化。为了接近这些关键的岩石，我们利用了“构造窗”，在那里，下地壳暴露被构造过程所取代，从而完全绕过了上地壳。在太平洋有两个这样的构造窗口，赫斯和皮托深，这是全球唯一的地方，这些关键的深成岩已被映射和采样。在过去的20多年里，我参加了四次潜水/潜水器采样巡航，并领导了两次国际海洋钻探探险，为我的研究提供了全球独一无二的样本套件。 在下一个资助周期，我的研究小组将使用这个独特的样本套件来测试相互竞争的假设，即地壳是如何通过岩浆过程在快速扩张的洋中脊形成的，随后又通过热液流和反应冷却和改变。我们还将建立一个定量模型的岩浆和热液控制下地壳的S和亲铜元素的预算，以扩大我们的理解下地壳如何有助于这些元素的全球循环。