FAST AND SLOW-SPREADING RIDGES - STRUCTURE AND HYDROTHERMAL ACTIVITY, ULTRAMAFIC TOPOGRAPHIC HIGHS, AND CH4 OUTPUT
FAST AND SLOW-SPREADING RIDGES - STRUCTURE AND HYDROTHERMAL ACTIVITY, ULTRAMAFIC TOPOGRAPHIC HIGHS, AND CH4 OUTPUT
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DOI：
10.1029/93jb00508
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发表时间：
1993-06-10
影响因子：
3.9
通讯作者：
SILANTIEV, S
中科院分区：
文献类型：
--
作者：
BOUGAULT, H;CHARLOU, JL;SILANTIEV, S
世界不同地区的山脊系统具有截然不同的形态，反映了不同的建造过程。各扩张中心的热液循环是大洋与新生洋壳之间重要的交换过程。这种热液循环可能因地貌和地壳组成而异，也可能影响海脊的构造过程。大西洋中脊（MAR）上的TAG（26度N）和Snake Pit（23度N）热液站点显示上覆海水中的Mn/CH4比率与非沉积的东太平洋隆起站点相似，即，约0.2mol/L。相比之下，大甲烷异常非常低的Mn/CH4比为0.005 mol/L与超镁铁地形高点附近15度N，接近轴和裂谷的超镁铁壁上。超镁铁质岩体与海水中CH4异常的组合指示了活跃的蛇纹石化过程。根据费托反应（Charlou et al.，1991年）。特别是深海钻探项目在远离断裂带的MAR上对许多超镁铁岩组合进行了取样。蛇纹岩化作用引起的增生板块边界带深部隆起物质力学性质和密度的变化，可能对缓慢扩张脊的形成起重要作用。
Different parts of the world ridge system have quite different morphologies, which reflect different constructional processes. It appears that hydrothermal circulation at all spreading centers is an important exchange process between the ocean and the newly formed oceanic crust. This hydrothermal circulation may vary according to morphology and crustal composition and may also affect ridge constructional processes. The TAG (26-degrees-N) and Snake Pit (23-degrees-N) hydrothermal sites on the Mid-Atlantic Ridge (MAR) display Mn/CH4 ratios in overlying seawater similar to those of nonsedimented East Pacific Rise sites, i.e., about 0.2 mol/L. In contrast, large methane anomalies with very low Mn/CH4 ratios of 0.005 mol/L are associated with ultramafic topographic highs near 15-degrees-N, close to the axis and on ultramafic walls of the rift valley. The association of ultramafic bodies and CH4 anomalies in seawater indicates active serpentinization processes. CH4 is produced during serpentinization according to the Fisher Tropsch reaction (Charlou et al., 1991). Many ultramafic rock assemblages have been sampled on the MAR away from fracture zones, in particular by the Deep Sea Drilling Project. Changes of mechanical properties and of density of uplifted deep material in the accreting plate boundary zone caused by serpentinization may play an important role in the construction of slow spreading ridges.