西南印度洋洋脊轴外构造-岩浆过程及其热液成矿模式

The on-axis and off-axis mid-ocean ridge processes have a major control on the formation and evolution of the oceanic lithosphere. The on-axis mid-ocean ridge process has achieved remarkable achievements in revealing origin and evolution of the oceanic lithosphere, and abundant modern marine hydrothermal resources have been obtained along the mid-ocean ridge. The ridge flanks are located in the stable intraplate and buried by thick oceanic sediments, and progress is little on the off-axial process which records the evolution of the oceanic lithosphere. Extinct or fossil ridges and spreading centres and hotspot traces within plates have been reported. Pre-existing magmatic-hydrothermal activities are possible when extinct ridges or spreading centres were active in a tensile tectonic setting, or when hotspot-related magma were upwelling, leading to the formation of old hydrothermal resources. To investigate the off-axis process on the ridge flanks is important to scientific research and global resource exploration. RMBA reflects variations in crustal thickness, crustal and mantle densities. Four factors provide most important constraints on RMBA, including mantle depletion, mantle temperature, mantle porosity, and oceanic crust. Resulted asymmetric RMBA of the Southwest Indian Ocean reveals the off-axis mid-ocean ridge processes and its influencing factor, using the Euler Rotation model. Based on geological, geophysical, and geochemical data of the confirmed modern hydrothermal vents along the Southwest Indian Ridge, this project aims to analyze the favorable mineralization structures and mineralization mechanism, and to explore the old hydrothermal resources on the ridge flanks, especially along the extinct or fossil ridges .

洋中脊的轴内和轴外过程控制了大洋岩石圈的组成和演化。洋中脊轴内过程的研究成果显著，推动了现代型海底热液资源调查和研究；而对大洋岩石圈演化和深部地幔动力学制约的洋脊侧翼的轴外过程的研究进展不大。轴外洋底有被证实有石化洋脊等单元，这些单元在其活动时期可能发育热液系统，但现今不再活动，其资源量如何待发掘。故对轴外过程的研究愈发重要。剩余地幔布格重力异常（RMBA）反映了洋壳厚度、洋壳与地幔密度的变化，有地幔亏损程度、地幔温度、地幔孔隙度和洋壳厚度四个影响因素。本课题拟以RMBA为岩浆作用的参数，以西南印度洋为例，通过欧拉旋转和重力因素的定量化计算，获取反映轴外过程的非对称RMBA，分析其关键数值并分离其影响因素，从而探讨轴外过程及其对热液系统的制约。最终，综合对比分析现今活动洋脊已探明热液区的地质-地球物理-地球化学特征，预测有利成矿构造和成矿机制，探索轴外（尤其是石化洋脊）区域的热液资源。

洋中脊的轴内和轴外过程控制了大洋岩石圈的组成和演化。洋中脊轴内过程的研究成果显 著，推动了现代型海底热液资源调查和研究;而对大洋岩石圈演化和深部地幔动力学制约的洋 脊侧翼的轴外过程的研究进展不大。轴外洋底有被证实有石化洋脊等单元，这些单元在其活动 时期可能发育热液系统，但现今不再活动，其资源量如何待发掘。故对轴外过程的研究愈发重 要。剩余地幔布格重力异常(RMBA)反映了洋壳厚度、洋壳与地幔密度的变化，有地幔亏损程 度、地幔温度、地幔孔隙度和洋壳厚度四个影响因素。本课题拟以RMBA为岩浆作用的参数，以 西南印度洋为例，通过欧拉旋转和重力因素的定量化计算，获取反映轴外过程的非对称RMBA， 分析其关键数值并分离其影响因素，从而探讨轴外过程及其对热液系统的制约。最终，综合对 比分析现今活动洋脊已探明热液区的地质-地球物理-地球化学特征，预测有利成矿构造和成矿 机制，探索轴外(尤其是石化洋脊)区域的热液资源。