洋中脊构造型热液系统对微震簇的响应研究 -以龙旂热液区为例

Hydrothermal circulations at mid-ocean ridge are controlled by magmatic and tectonic processes. Magmatic intrusions or tectonic movements always induced earthquake swarm with intense earthquakes activity in a short time. The hydrothermal fluid response of the discharge zone to the swarm, such as temperature perturbation. Only several swarm-induced changes in hydrothermal system at global mid-ocean ridge are observed and all of them are occurred in magmatic-controlled hydrothermal field at fast-spreading rate ridge. These facts suggested that magmatic intrusion and migration is the main reason of the hydrothermal changes. However, no observation of swarm-induced hydrothermal changes in tectonic-controlled hydrothermal field. So the relationship of microearthquake and regional hydrothermal circulation is not clear. The first observation of swarm-induced perturbation of high-temperature and diffused flow in tectonic origin of Longqi field at Southwest Indian Ridge (SWIR) is conducted by “Jiaolong” human-occupied vehicle at 2015. This program will utilize swarm time-space characteristics and hydrothermal variation, and model swarm-induced hydrothermal perturbation numerically. We will make a breakthrough on the relationship of hydrothermal circulation and tectonic fracturing or magmatic movement, it is very significant to understand thermodynamics and hydrothermal exchanges in the tectonic-controlled hydrothermal field.

洋中脊热液区的热液循环受岩浆和构造活动的控制，由岩浆侵入或构造错动引发微震集中爆发的微震簇事件往往会造成热液系统释放区流体温度等环境参数的变化。全球洋中脊已观测到的数起微震簇诱发热液流体扰动事件都发生在岩浆活动主导的热液区，揭示了岩浆在运移和补给过程中对热液流体的扰动过程。然而对于构造控制型热液区尚未观测到此类事件。2015年“蛟龙号”载人潜水器在构造控制型的西南印度洋中脊龙旂热液区首次观测到了微震簇诱发高温喷口和弥散流温度变化事件。本项目将利用该观测事件开展微震簇时空分布特征与热液流体环境参数变化规律的研究，采用热液循环数值模拟方法建立热液流体扰动对微震簇响应机制模型。研究成果有望在构造控制型热液区深部岩浆或构造活动与热液循环之间的作用机制研究上取得突破，对理解构造控制型热液区的热动力学过程和热液流体热量与物质的交换模式有着重要的意义。

洋中脊热液区的热液循环受岩浆和构造活动的控制，由岩浆侵入或构造错动引发微震集中爆发的微震簇事件往往会造成热液系统释放区流体温度等环境参数的变化。全球洋中脊已观测到的数起微震簇诱发热液流体扰动事件都发生在岩浆活动主导的热液区，揭示了岩浆在运移和补给过程中对热液流体的扰动过程。然而对于构造控制型热液区尚未观测到此类事件。本项目利用2015年“蛟龙号”载人潜水器在构造控制型的西南印度洋中脊龙旂热液区首次观测到了微震簇诱发高温喷口和弥散流温度变化事件，开展微震簇时空分布特征与热液流体环境参数变化规律的研究，取得如下成果与认识：1)通过提取OBS台站间的背景噪声互相关函数（NCF）进行钟漂校正并基于水声测距和多波束地形的确定OBS坐底位置。2）采用绝对定位和相对定位双差定位方法获得了龙旂热液区的三维微震定位结果，并对结果进行构造解译。3）提出了一种地震簇事件使得拆离断层活动导致渗透率突然增加，增大了热流通量，导致了弥散流温度的短暂升高的构造型微震簇诱发热液扰动的机制，该机制为全球洋脊构造活动为主控因素的热液驱动机制为地震簇与热液扰动的耦合提出了新的思路。