A near-bottom magnetic survey of the Mid-Atlantic Ridge axis at 26°N:: Implications for the tectonic evolution of the TAG segment -: art. no. 2277
A near-bottom magnetic survey of the Mid-Atlantic Ridge axis at 26°N:: Implications for the tectonic evolution of the TAG segment -: art. no. 2277
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DOI：
10.1029/2002jb001967
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发表时间：
2003-05-27
影响因子：
3.9
通讯作者：
Kleinrock, MC
中科院分区：
文献类型：
--
作者：
Tivey, MA;Schouten, H;Kleinrock, MC
[1]对中大西洋洋脊TAG脊段的广泛深拖磁测量揭示了磁异常场与TAG热液矿床之间关系的新信息。结果表明，最强磁化位于新火山轴上，不对称地向中央布伦什异常的西侧方向移动。在TAG段的东部裂谷壁上有一个明确的线性磁化低点。近底资料显示，这种地壳磁化强度低与热液矿床之间没有直接关系。磁化强度低的原因是沿正断层水平延伸4公里导致地壳变薄。先前的观测和取样表明，东部裂谷壁上有辉长岩和岩脉暴露，表明沿正断层的滑动暴露了该地壳。模拟表明，该断层自0.35±0.1 Ma以来一直处于活跃状态，水平滑动速率大约是22 km/Myr扩展速率的一半。TAG热液系统位于断层末端3 km范围内的断层上盘。在过去的几十万年里，拆离断层上的运动可能偶尔增加了上盘的渗透率，重新激活了上覆的热液系统。像TAG这样的重要通风口通常与海底扩张中心附近的长期剥离断层的上盘有关。这意味着与断层反复运动有关的上盘渗透率的重新激活控制了这些热液系统的寿命。
[1] An extensive deep-tow magnetic survey of the TAG ridge segment on the MidAtlantic Ridge reveals new information about the relationship between the magnetic anomaly field and the TAG hydrothermal deposits. Results show the strongest magnetization is located over the neovolcanic axis and asymmetrically toward the western side of the central Brunhes anomaly. A well-defined linear magnetization low is located over the eastern rift valley wall of the TAG segment. The near-bottom data show no direct correlation between this crustal magnetization low and the hydrothermal deposits. The magnetization low is explained by crustal thinning caused by 4 km of horizontal extension along a normal fault. Previous observations and sampling indicate exposures of gabbros and dikes in the eastern rift valley wall, suggesting slip along a normal fault has revealed this crust. Modeling suggests the fault has been active since 0.35 +/- 0.1 Ma at a horizontal slip rate of roughly half the spreading rate of 22 km/Myr. The TAG hydrothermal system is located on the hanging wall of this fault within 3 km of its termination. Over the past several hundred thousand years, movement on the detachment fault may have episodically increased the permeability of the hanging wall reactivating the overlying hydrothermal systems. Significant vents like TAG may be typically associated with hanging walls of long-term detachment faults near seafloor spreading centers. This would imply that it is the reactivation of permeability in the hanging wall related to repeated fault movement that controls the longevity of these hydrothermal systems.