Geological investigation of a lineated massif at the Kane Transform Fault: implications for oceanic core complexes
Geological investigation of a lineated massif at the Kane Transform Fault: implications for oceanic core complexes
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DOI：
10.1098/rsta.1999.0350
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发表时间：
1999-04-15
期刊：
影响因子：
5
通讯作者：
Karson, JA
中科院分区：
文献类型：
--
作者：
Karson, JA
最近关于大西洋中脊附近海底形态的新观点揭示了上表面有线纹的圆顶状海底生物的广泛发展。在形式和尺寸上，这些特征类似于在大规模伸展区域发育的大陆变质核杂岩，因此可能是“大洋核杂岩”。这些特征的优秀例子发生在凯恩转换断层以南，那里有来自侧视声纳、深拖摄像机和载人潜水器的高分辨率地质数据。来自两个不同地壳构造的地质数据，代表了不同类型的地壳结构，为这些洋核杂岩的发展提供了重要的制约因素。从这些直接的大洋核杂岩地质调查中得出的推论是理解这些特征在缓慢扩展的地壳中形成的过程的第一步，这些海脊和附近地区的特定关系表明，这些结构是在相当长的海脊轴（数十公里）上形成的，并不一定局限于任何特定的形态分割模式。在某些情况下，它们发育在厚的辉长岩地壳中，但在其他地方，它们形成在由蛇纹岩组成的地壳中，其中充满了辉长岩侵入体。这些部分的韧性拉伸和变薄记录在广泛的糜棱岩和剪切带。同构造辉长岩侵入体分布广泛，这与辉长岩在“岩浆扩展”间隔期间发育的观点相矛盾。辉长岩和蛇纹岩中的碎裂断层带在伸展地壳的抬升、冷却和水化过程中发育，可能是主要的拆离断层。稀疏的闪长岩脉和玄武质熔岩是这些地区最新的岩浆补充。众多的节理和陡倾角、小错距断层是观测到的最年轻的构造。在一个断层的部分顶面，小规模的断层似乎限制了断裂基岩的细长脊，形成了线状地形。因此，附近广泛的线理面不需要反映沿连续拆离断层面沿着的长时间位移。在沿着凯恩转换断层的圆顶状断层中形成的地质关系暗示了这些特征演化过程中涉及的一系列复杂过程，并提出了有关其起源和与大陆核杂岩类比的新问题。
Recently available new perspectives on the morphology of the sea-floor near the Mid-Atlantic Ridge reveal the widespread development of dome-like massifs with lineated upper surfaces. In form and dimensions, these features resemble continental metamorphic core complexes developed in regions of large-magnitude extension, and thus may be 'oceanic core complexes'. Excellent examples of these features occur south of the Kane Transform Fault where high-resolution geological data from side-looking sonar, deeply towed cameras, and manned submersibles are available. The geological data from two different massifs; representing somewhat different types of crustal structure, provide important constraints on the development of these oceanic core complexes. Inferences from these direct geological investigations of oceanic core complexes are a first step toward understanding the processes by which these features form in slow-spread crust.Specific relationships in these massifs and nearby areas suggest that these structures have formed over significant lengths of ridge axis (tens of kilometres) and are not necessarily confined to any specific setting with respect to morphologic segmentation patterns. In some cases they are developed in thick gabbroic crust, but elsewhere have formed in crust composed of serpentinite riddled with gabbroic intrusions. Ductile stretching and thinning of these sections is recorded in extensive mylonites and shear zones. Syntectonic gabbroic intrusions are widespread and contradict the notion that the massifs develop during intervals of 'amagmatic spreading'. Cataclastic fault zones in gabbros and serpentinites developed during uplift, cooling and hydration of the stretched crust and may have been localized as major detachment faults. Sparse diabase dikes and basaltic lavas are the latest magmatic additions to these areas. Numerous joints and steeply dipping, small-offset faults are the youngest observed structures. Across part of the top surface of one massif, small-scale faults appear to bound elongated ridges of fractured basement rocks creating the lineated terrain. Thus, the extensive lineated surfaces nearby need not reflect prolonged displacement along a continuous detachment fault surface.Geological relationships developed in the dome-like massifs along the Kane Transform Fault hint at a complex array of processes involved in the evolution of these features and raise new questions regarding their origin and analogies with continental core complexes.