Magma-sediment mingling processes, control and longevity of related hydrothermal systems – Implications for the Earth’s Subseafloor Elements-, Plate-, Life-Cycles

岩浆-沉积物混合过程、相关热液系统的控制和寿命 â 对地球海底元素、板块、生命周期的影响

• 批准号: 447431016
• 负责人: Dr. Christophe Galerne
• 金额: --
• 依托单位: Fachgebiet Petrologie der Ozeankruste
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/447431016?language=en
• 关键词: Magma; sediment; mingling; processes; control

The longevity of hydrothermal systems powered by shallow off-axis sill intrusions emplaced in active marginal rift settings is poorly constrained. Yet, these systems power subseafloor element fluxes which may hold the key to answer fundamental questions related to the role of rift magmatism in the global elements cycles, and the evolution of deep microbial habitat. An important controlling process of such systems is the magma-sediment mingling that occurs during magma emplacement. The International Ocean Discovery Program Expedition 385 (Exp. 385) drilled through the shallow, soft, unconsolidated sediments of the Guaymas Basin (GB), Gulf of California. This young rifted margin is nested with shallow sill intrusions providing unprecedented access to an active setting to study and quantify the impact of the magma-sediment mingling. This proposal presents the preliminary results of a DFG-funded two-year research project led by the PI (Petrophysics team leader of the Exp. 385), and demonstrates the need for a third year of funding. We have chosen to study two IODP sites representing a syn- to post-cooling (moderate-temperature) hydrothermal system (U1547-U1548), and a post-cooling, extinct hydrothermal system (U1545-U1546). We have combined a petrological and geochemical approach, analyzing IODP samples, with a high-resolution X-ray μ-CT survey of the sill microfabric, paired with innovative laboratory experiments reproducing the uptake and fractionation of highly mobile fluid phases into the magma during magma-sediment mingling. Our preliminary results indicate that the unusually high primary porosity of the sills is a direct product of magma-sediment mingling. Our findings suggest that the resulting sill porosity could be a key factor in establishing longlasting, post-cooling hydrothermal system by channelling deeply sourced geothermal fluids along the established magma plumbing system. Here, we apply for a 12-months extension funding to perform specially designed laboratory experiments that will infer the in-situ permeability-porosity relation of the GB sediment which will be used in our numerical simulations. Moreover, we intend to simulate the liquefaction pipe formation process in cylinder tank experiments. Our preliminary results derived from numerical simulations indicate that heat transfer into the host sediment is inefficient to cause significant thermogenic degassing due to the petrophysical changes associated with the accelerated diagenetic phase transition of in the host sediment, which is rich in water and organic carbon. We estimate that, for equivalent initial TOC content, only a fraction of 1 to 4 % thermogenic gas is mobilized in case of shallow sill emplacement in soft, porous sediments compared to sill intrusion emplaced in hard sedimentary rocks. Our finding heralds a new paradigm that in the context of a young rift system, sill emplacement may power life instead of suppressing it.

热液系统的寿命动力浅离轴岩床侵入体侵位在活跃的边缘裂谷设置是不受约束。然而，这些系统为海底元素通量提供动力，这可能是回答与裂谷岩浆活动在全球元素循环中的作用以及深层微生物栖息地演变相关的基本问题的关键。岩浆侵位过程中的岩浆-沉积物混合作用是控制这类体系的重要因素。国际海洋探索计划385号探险队（International Ocean Discovery Program Expedition 385）385)在加州湾的瓜伊马斯盆地（GB）的浅、软、松散沉积物中钻探。这个年轻的裂谷边缘嵌套浅岩床侵入体提供了前所未有的访问到一个活跃的设置，研究和量化的岩浆沉积物混合的影响。该提案介绍了DFG资助的一个为期两年的研究项目的初步结果，该项目由PI（Exp. #38385;，并表示需要第三年的资金。我们选择了研究两个IODP网站，代表一个syn-后冷却（中温）热液系统（U1547-U1548），和后冷却，灭绝热液系统（U1545-U1546）。我们结合了岩石学和地球化学方法，分析IODP样品，高分辨率X射线μ-CT调查的岩床微组构，与创新的实验室实验再现的吸收和分馏的高度移动的流体相进入岩浆在岩浆-沉积物混合。我们的初步结果表明，异常高的原生孔隙度的岩床是一个直接产品的岩浆沉积物混合。我们的研究结果表明，由此产生的岩床孔隙度可能是一个关键因素，在建立持久的，后冷却热液系统的通道深源地热流体沿着已建立的岩浆管道系统。在这里，我们申请了12个月的延期资金，以进行专门设计的实验室实验，将推断出GB沉积物的原位渗透率-孔隙度关系，这将用于我们的数值模拟。此外，我们还打算在圆筒罐实验中模拟液化管的形成过程。我们的初步结果来自数值模拟表明，热传递到主机沉积物是低效的，导致显着的生热脱气由于岩石物理变化与加速成岩相变的主机沉积物，这是丰富的水和有机碳。我们估计，对于相同的初始TOC含量，只有一小部分的1%至4%的热成因气体被动员的情况下，浅岩床侵位在软，多孔沉积物相比，岩床侵入侵位在硬沉积岩。我们的发现预示着一个新的范例，在一个年轻的裂谷系统的背景下，岩床就位可能会为生命提供动力，而不是抑制它。