The interplay of hydrothermal and tectonic processes at (ultra)slow-spreading mid-ocean ridges

在大洋中部扩张中心形成的年轻大洋岩石圈受到岩浆、构造和热液作用的复杂网络的影响。除其他外，对水深测量、断层结构、微震分布和高温热液喷口区域位置的观察反映了这些过程的相互作用。在(超)缓慢扩张的海脊，许多山脊段由高角度正断层向长寿的滑脱断层过渡，使地壳和地幔岩石的大剪切面暴露在海底。沿这些可渗透断裂带的热液导流通过热、水力和化学作用削弱了变形岩石，从而控制了断裂带的演化，并解释了所观察到的断裂活动与热液活动之间的相关性。作为所有相关过程之间动态相互作用的结果，仅从观察的角度很难识别和量化单一的反馈机制。因此，该项目旨在利用数值模型系统地研究构造和热液过程之间的反馈机制以及流体-岩石-流体相互作用的影响，如水力压裂和蛇纹岩作用。这里最重要的问题是一个鸡或蛋的问题：构造断裂只是为热液流体流动提供了几何形状，还是热液循环改变了岩石圈的热和力学性质，从而在启动断层和/或延长其活动寿命方面发挥了重要作用？为了解决这些问题，我们将在现有的LaCoDe和HT2_SP程序的基础上开发一个新的水热力学模型。相关的反馈机制将在两个参数研究中进行调查和量化。最后，我们将在两个案例研究中验证我们的数值模型，以重建Logatchev(中大西洋海脊)和龙旗(西南印度洋海脊)热液油田的构造和热液演化。

The young oceanic lithosphere created at mid-ocean spreading centres is subject to a complex network of magmatic, tectonic and hydrothermal processes. Observations of, among others, bathymetry, fault structures, microearthquake distribution, and locations of high-temperature hydrothermal vent fields reflect the interplay of these processes. At (ultra)slow-spreading ridges, many ridge segments are dominated by a transition from high-angle normal faults to long-lived detachment faults exposing large shear planes of crust and mantle rocks to the seafloor. Channelling of hydrothermal fluids along these permeable fault zones weakens the deforming rocks through thermal, hydraulic, and chemical processes, thereby controlling the fault zone’s evolution and explaining the observed correlation between faulting and hydrothermal activity. Being the result of a dynamic interplay between all involved processes, it is hardly possible to identify and quantify single feedback mechanisms from the observational standpoint alone. This project therefore aims to systematically investigate feedback mechanisms between tectonic and hydrothermal processes together with the influence of fluid-rock-interactions like hydrofracturing and serpentinization using numerical models. The overarching question here is a chicken-or-egg problem: Does tectonic faulting simply provide the geometry for hydrothermal fluid flow or does hydrothermal circulation modify the thermal and mechanical properties of the lithosphere enough to play an important role in initiating faults and/or extending their active lifetime? To address these questions, we will develop a novel hydro-thermo-mechanical model based on the existing codes LaCoDe and HT2_SP. Relevant feedback mechanisms will be investigated and quantified in two parameter studies. We will finally test our numerical model in two case studies to reconstruct the tectonic and hydrothermal evolution of the Logatchev (Mid-Atlantic Ridge) and Longqi (South-West Indian Ridge) hydrothermal fields.