Dating mineral formation during mid-ocean ridge flank hydrothermal circulation: Evidence from the Juan de Fuca Ridge, IODP Expedition 327

大洋中脊侧翼热液循环期间矿物形成的年代测定：来自胡安德富卡海脊的证据，IODP 327 号探险队

• 批准号: NE/L000032/1
• 负责人: Damon Teagle
• 金额: $ 4.56万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FL000032%2F1
• 关键词: Dating; mineral; formation; during; mid

New ocean crust is formed from volcanic eruptions along a chain of volcanoes under the oceans called mid ocean ridges. This chain of volcanoes represents the tectonic boundary where two oceanic plates diverge away from each other. This process represents the major mechanism for the exchange of heat from the mantle to the crust. The ocean crust covers ~60% of the Earth's surface and all formed during the past 180 million years. After new ocean crust has formed, seawater percolates down into ocean crust and reacts with the rocks. Near the ridge axis the heat from the magma chamber that formed the crust drives the circulation of the seawater, and results in the heating and chemical modification of seawater that then exit the ocean crust from black smoker chimneys as focused high temperature hydrothermal fluids (~400 deg C metal rich fluids). The percolation of seawater into the ocean crust continues beyond the ridge axis onto the ridge flank region for tens of millions of years. In the ridge flank region, the circulation of seawater occurs at much lower temperatures (a few 10's deg C) and is driven by the cooling of the oceanic plate as it ages. The volume of seawater that circulates in the ridge flank region is far greater than in the axial region and has more impact on the chemistry of the oceans for some elements and is thus important for understanding global geochemical cycles.The inaccessibility and difficulty in locating and sampling hydrothermal fluids as they exit the ocean crust in the ridge flank region has resulted in limited direct observations of this important hydrogeologic reservoir. An alternative to direct sampling of the fluids is to sample hydrothermal veins; these are fractures in the ocean crust that have been filled with secondary minerals that are precipitated as the fluid migrates and reacts with the ocean crust. The distribution, composition and relative timing of these hydrothermal veins provide the only direct insight into the processes operating in the subsurface during the circulation of seawater.This project will investigate the Juan de Fuca plate located in the NE Pacific, where ocean crust formed at 30 mm/yr. This area is characterised by lava flows overlain by sediments, abyssal hill topography, high angle faulting and basement outcrops. This regions experiences high sedimentation rates because of the abundant supply of young glacial sediments derived from the North American continental margin that bury relatively young oceanic crust. This creates hydrologically and thermally isolated young (1 Ma) ocean crust with strong lateral pressure and temperature gradients, ideal for the study of ridge flank hydrothermal processes. The Juan de Fuca Ridge Flank has been the focus of a decadal long program of ODP/IODP drilling, where the recent completion of IODP Expedition 327 took the total to 12 ODP/IODP drill sites located along both ridge perpendicular and ridge parallel transects, ranging from 0.6 to 3.6 Ma. Volcanic rocks recovered during Exp 327 from Hole U1362A, one of the deeper boreholes in this region (496 metres below seafloor), contains over 1200 hydrothermal veins. A range of mineral compositions is present within these veins that are dominated by clay minerals and oxidised iron minerals. Calcium carbonate veins are also present. For the first time in this region hydrothermal minerals characteristic of higher temperatures and mixing of fluids were also recovered.By documenting the distribution and relationships between different vein types, insight into the pathways of fluid flow can be achieved. Chemical analyses of the vein minerals themselves will document the chemical composition and evolution of the fluids they formed from, that in turn reflect the extent of reaction between the fluid and the ocean crust. Dating of the different secondary minerals will provide direct constraints on the timing of hydrothermal ridge flank fluids.

新的洋壳是由沿着海底的一系列火山（称为大洋中脊）的火山喷发形成的。这条火山链代表了两个海洋板块彼此分开的构造边界。这个过程代表了从地幔到地壳热量交换的主要机制。洋壳覆盖了地球表面约 60% 的面积，全部形成于过去 1.8 亿年。新的洋壳形成后，海水渗入洋壳并与岩石发生反应。在洋脊轴附近，来自形成地壳的岩浆室的热量驱动海水循环，导致海水被加热和化学改性，然后海水以集中高温热液的形式从黑烟囱排出洋地壳（~400摄氏度富含金属的流体）。海水渗入洋壳的过程持续了数千万年，超出了山脊轴线，到达了山脊侧面区域。在山脊侧翼区域，海水循环发生在低得多的温度（几十摄氏度）下，并且是由海洋板块随着老化而冷却所驱动的。洋脊侧翼区域循环的海水量远大于轴心区域，对海洋中某些元素的化学影响更大，因此对于了解全球地球化学循环具有重要意义。 定位和采样的难处和困难热液从洋脊侧翼区域的洋壳流出时，导致对这一重要水文地质储层的直接观测有限。直接对流体取样的另一种方法是对热液脉进行取样；这些是海洋地壳中的裂缝，其中充满了次生矿物，这些矿物是在流体迁移并与海洋地壳发生反应时沉淀出来的。这些热液脉的分布、成分和相对时间提供了对海水循环过程中地下运行过程的唯一直接了解。该项目将调查位于太平洋东北部的胡安德富卡板块，该板块的海洋地壳形成于 30毫米/年该地区的特点是熔岩流覆盖着沉积物、深海山地貌、高角度断层和基底露头。该地区的沉积速率很高，因为来自北美大陆边缘的年轻冰川沉积物供应充足，埋藏了相对年轻的洋壳。这创造了水文和热隔离的年轻（1 Ma）海洋地壳，具有强大的侧压力和温度梯度，非常适合研究脊侧热液过程。 Juan de Fuca 山脊侧翼一直是长达十年的 ODP/IODP 钻探计划的重点，最近完成的 IODP Expedition 327 使沿着山脊垂直和山脊平行横断面的 ODP/IODP 钻探地点总数达到 12 个，范围从 0.6 到 3.6 Ma。 327 勘探期间从 U1362A 孔中回收的火山岩是该地区较深的钻孔之一（海底以下 496 米），包含 1200 多个热液脉。这些矿脉内存在一系列矿物成分，主要是粘土矿物和氧化铁矿物。还存在碳酸钙脉。该地区还首次发现了具有较高温度和流体混合特征的热液矿物。通过记录不同矿脉类型之间的分布和关系，可以深入了解流体流动的路径。对矿脉矿物本身的化学分析将记录其形成的流体的化学成分和演化，进而反映流体与洋壳之间的反应程度。不同次生矿物的年代测定将直接限制热液脊翼流体的出现时间。

项目成果

Controls on thallium uptake during hydrothermal alteration of the upper ocean crust

• DOI: 10.1016/j.gca.2014.09.001
• 发表时间: 2014-11
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: R. Coggon;M. Rehkämper;C. Atteck;D. Teagle;J. Alt;M. Cooper

Laser ablation MC-ICP-MS U/Pb geochronology of ocean basement calcium carbonate veins

海洋基底碳酸钙脉激光烧蚀 MC-ICP-MS U/Pb 年代学

• 发表时间: 2014
• 期刊: EOS Transactions of the American Geophysical Union
• 作者: Harris, M.

Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D

• DOI: 10.1016/j.epsl.2017.01.010
• 发表时间: 2017-03-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Harris, Michelle;Coggon, Rosalind M.;Teagle, Damon A. H.
• 通讯作者: Teagle, Damon A. H.

Channelling of hydrothermal fluids during the accretion and evolution of the upper oceanic crust: Sr isotope evidence from ODP Hole 1256D

• DOI: 10.1016/j.epsl.2015.01.042
• 发表时间: 2015-04
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: M. Harris;R. Coggon;C. Smith-Duque;M. Cooper;J. Milton;D. Teagle