Crustal magnetization reveals subsurface structure of Juan de Fuca Ridge hydrothermal vent fields
Crustal magnetization reveals subsurface structure of Juan de Fuca Ridge hydrothermal vent fields
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地壳磁化揭示了胡安德富卡海岭热液喷口场的地下结构
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
H. Johnson
中科院分区：
文献类型：
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作者：
M. Tivey;H. Johnson
在Juan de Fuca Ridge北部的Endeavour部分进行的近底部地球物理调查表明，明确的低地壳磁化区域与活跃和已灭绝的海底热液喷口位置密切相关。特别是，在“奋进号”主场，我们发现与每一簇喷口相关的离散磁化低。磁化低区位于喷口簇的正下方，直径约为100 m，这意味着一个接近垂直的、狭窄的、管状的源区位于喷口结构的表面表达式的正下方。低气压之间的距离也只有200米，这进一步暗示了高度集中的区域。低磁化率也与不活跃和灭绝的通风口区有关，这表明地壳中磁性矿物的变化而不是（必然是暂时的）热退磁是低磁化率的主要原因。这些狭窄的管状体具有蛇绿岩蚀变管的高度特征，是热液上行流动带的标志。因此，每一个磁化低值可以定义一个单独的上升流区，具有不同的地下管道和热结构。地壳磁化模式对这些热液喷口系统地下管道的几何形状提供了重要的限制。在主奋进区，磁化低磁极沿裂谷趋势呈半规则模式分布，间隔约200米，表明向上流动可能沿裂谷轴线被划分为规则间隔。
A near-bottom geophysical survey on the Endeavour segment of the northern Juan de Fuca Ridge shows that regions of well-defined low crustal magnetization are strongly correlated with both active and extinct submarine hydrothermal vent sites. In particular, at the Main Endeavour Field, we find discrete magnetization lows associated with each cluster of vents. Magnetization lows are directly centered beneath the vent clusters and have diameters of ∼100 m, which implies a near-vertical, narrow, pipe-like source region located directly beneath the surface expression of the vent edifices. Lows are also separated from each other by only 200 m, which further implies highly focused zones. Magnetization lows are also associated with inactive and extinct vent areas, which indicates that alteration of the magnetic minerals in the crust rather than (necessarily temporary) thermal demagnetization is the primary process responsible for the low magnetization. These narrow pipe-like bodies are highly characteristic of alteration pipes found in ophiolites and are indicative of hydrothermal fluid up-flow zones. Thus, each magnetization low may define an individual upwelling zone, with distinct subsurface plumbing and thermal structure. The crustal-magnetization patterns provide important constraints on the geometry of the subsurface plumbing beneath these hydrothermal vent systems. At the Main Endeavour Field, magnetization lows are distributed along the trend of the rift valley in a semiregular pattern with a spacing of ∼200 m, arguing that upward flow may be partitioned into regularly spaced intervals along the axis of the rift valley.