The character and distribution of mineralized fractures in the Kodiak Formation, Alaska: Implications for fluid flow in an underthrust sequence
The character and distribution of mineralized fractures in the Kodiak Formation, Alaska: Implications for fluid flow in an underthrust sequence
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阿拉斯加科迪亚克组矿化裂缝的特征和分布：对逆冲层序中流体流动的影响
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
T. Byrne
中科院分区：
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作者：
D. Fisher;T. Byrne
科迪亚克组是阿拉斯加西南部的一个增生板岩带，在晚白垩世-早第三纪经历了两次主要的断裂和成矿作用。这些事件的早期是有关的下推覆的沉积物下面的一个主要的滑脱（D1），而后来的情节是由褶皱和逆冲构造的发展和一个区域普遍的板状解理内的增生楔（D2）的标志。D1矿脉仅限于砂层，集中在科迪亚克组的最高构造层。最普遍的D1裂缝发生在混杂岩带内，其中Kodiak组被推压在较老的Uyak杂岩之下。混杂岩中的显微构造表明，这些矿脉是在变形的后期阶段形成的，该变形涉及层间平行剪切作用以及进行性岩化作用。D2矿脉切割砂和页岩层，集中在科迪亚克组的最低结构层。这些脉内的显微结构表明D2脉是水力压裂，其（1）沿裂纹长度沿着连续密封（例如，在最小的静脉（0.5厘米宽））。断裂正好与发展的板状解理在一个政权的渐进简单剪切。从最高到最低的结构水平，有一个逐渐增加的测量有限应变，突然出现的普遍D2静脉，和一个更大的非同轴应变东南向逆冲。这些观察结果表明，D2静脉上面形成的滑脱，是活跃的晚白垩世-早第三纪增生包的基础上。总的来说，D1和D2静脉建议大量的流体流动的古俯冲复合体，与发展的水力压裂首先在下盘，然后在从浅到深的结构层次的基底滑脱的上盘。
The Kodiak Formation, an accreted slate belt in southwest Alaska, experienced two major episodes of fracturing and mineralization in the Late Cretaceous-early Tertiary. The earlier of these episodes is related to underthrusting of sediments below a major decollement (D1), whereas a later episode is marked by development of fold and thrust structures and a regionally pervasive slaty cleavage within the accretionary wedge (D2). D1 veins are restricted to sand layers and are concentrated at the highest structural level of the Kodiak Formation. The most pervasive D1 fractures occur within a melange zone, where the Kodiak Formation is thrust beneath the older Uyak Complex. Microstructures in the melange suggest that these veins formed during the later stages of a deformation that involved layer parallel shear in conjunction with progressive lithification. D2 veins cut sand and shale layers and are concentrated at the lowest structural levels of the Kodiak Formation. Microstructures within these veins indicate that D2 veins are hydrofractures that were either (1) intermittentiy sealed along the length of the crack (e.g., in the smallest veins ( 0.5 cm width)). Fracturing coincided with development of a slaty cleavage in a regime of progressive simple shear. From highest to lowest structural levels, there is a gradual increase in measured finite strain, the abrupt appearance of pervasive D2 veins, and a greater noncoaxiality of strain related to southeast directed thrusting. These observations suggest that D2 veins formed above a decollement that was active at the base of a Late Cretaceous-early Tertiary accreted package. In total, the D1 and D2 veins suggest substantial fluid flow within an ancient subduction complex, with development of hydrofractures first in the footwall and then in the hanging wall of a basal decollement that stepped from shallow to deeper structural levels.