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西南印度洋中脊热液区的岩浆活动与构造特征

, PP. 1834-1846

Keywords: 超慢速扩张洋中脊,A区热液喷口,剩余地幔布格重力异常,洋中脊-热点相互作用,拆离断层

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Abstract:

?A区热液喷口(37.78°S,49.65°E)是在西南印度洋中脊(SWIR)上发现的第一个活动热液喷口.热源及水循环通道是形成热液喷口的两个必要条件.沿SWIR49.3°~51.2°E区域,重力反演的地壳厚度最厚超过9.0km,远超过全球平均海洋地壳厚度,表明此区域存在丰富热源,可能受到了热点的影响.大尺度的地幔布格重力异常(RMBA)揭示了A区所在一级洋中脊段(Indomed-Gallieni转换断层,46.0°~52.0°E)和Marion-DelCano-Crozet区域之间的重力低值带,推断为热点-洋中脊相互作用的路径.去除正常热模型后的层析成像资料表明,与此路径对应的低速带在垂直距离上可以到达岩石圈底部.A区热液喷口区域扩张脊两侧地形和地壳厚度明显不对称.在扩张脊南侧,高地形对应着减薄的地壳厚度.剩余均衡地形异常显示A区处于明显的非均衡状态,与转换断层内角的特征极为类似.磁力剖面的正演表明,A区南侧磁性减薄区域与OBS揭示的隆起高速异常区相对应,推断为拆离断层的构造减薄作用.A区强烈的构造活动可以为热液喷口提供充分的水循环通道,可能形成较大的热液硫化物矿床.

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