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Geochemical evolution of a sublacustrine hydrothermal vent system: Temporal constraints imposed by reactive transport modeling
Geochimica et Cosmochimica Acta ( IF 4.5 ) Pub Date : 2022-06-07 , DOI: 10.1016/j.gca.2022.06.003
Liheng Wang , Yanhui Dong , Amanda Tudor , Chunyang Tan , William E. Seyfried

Studies of heat and mass transport in hydrothermal systems are challenging owing to the complex feedback that exists between chemical and physical processes. Taking full advantage of the existing geochemical framework recently recognized for sublacustrine vent fluids in the Stevenson Island Deep Hole, Yellowstone Lake, here we apply a multiphase reactive transport model, coupling hydraulic and thermal effects, to simulate time series changes in mineralization associated with venting of vapor-dominated hydrothermal fluids. This distinctive region of the lake floor is characterized by a series of overlapping depressions hosting sites of active venting. Model results show that the addition of high enthalpy steam enriched in CO2 and H2S, creates acidic and reducing conditions, while heating entrained lake water and coexisting sediment to temperatures in excess of 174 °C. The diatomaceous silica-rich substrate is predicted to dissolve, being replaced largely by pyrite, quartz, and kaolinite, in good agreement with the observed vent mineralization and fluid chemistry. Data suggest that vent-related mineral dissolution and transformation processes occur rapidly, on the order of 1 ka for the spatial scale of the modeled-up flow zone considered. The accuracy of time series changes predicted however, is explicitly linked to a number of physical and chemical factors imposed on the model, including source fluid, flow rate and gas enrichment, and sediment thermal conductivity, permeability, and reactive surface area, as well as mineral reaction rate data for primary and secondary alteration phases. When combined with robust field observations, as is the case here, reactive transport models can elucidate important, if not fundamental, controls on the temporal and spatial evolution of the geochemistry of modeled system, challenging chemical, and physical conditions notwithstanding.



中文翻译:

湖底热液喷口系统的地球化学演化:反应输运模型施加的时间约束

由于化学和物理过程之间存在复杂的反馈,对热液系统中的热量和质量传输的研究具有挑战性。充分利用最近公认的黄石湖史蒂文森岛深孔湖底喷口流体的现有地球化学框架,在这里我们应用多相反应输运模型,耦合水力和热效应,模拟与喷口相关的矿化时间序列变化以蒸汽为主的热液。湖底这一独特区域的特点是一系列重叠的洼地,这些洼地拥有活跃的通风点。模型结果表明,添加富含CO 2和H 2的高焓蒸汽S,创造酸性和还原条件,同时将夹带的湖水和共存的沉积物加热到超过 174 °C 的温度。预计富含硅藻硅的基质会溶解,主要被黄铁矿、石英和高岭石取代,这与观察到的喷口矿化和流体化学非常吻合。数据表明,与喷口相关的矿物溶解和转化过程发生得很快,所考虑的模拟流动区的空间尺度约为 1 ka。然而,预测的时间序列变化的准确性与施加在模型上的许多物理和化学因素明确相关,包括源流体、流速和气体富集,以及沉积物热导率、渗透率和反应表面积,以及初级和次级蚀变阶段的矿物反应速率数据。当与可靠的现场观测相结合时,反应传输模型可以阐明对建模系统的地球化学的时间和空间演化的重要(如果不是基本)控制,尽管具有挑战性的化学和物理条件。

更新日期:2022-06-07
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