Deformation and fluid flow of a major out-of-sequence thrust located at seismogenic depth in an accretionary complex: Nobeoka Thrust in the Shimanto Belt, Kyushu, Japan
Deformation and fluid flow of a major out-of-sequence thrust located at seismogenic depth in an accretionary complex: Nobeoka Thrust in the Shimanto Belt, Kyushu, Japan
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DOI：
10.1029/2004tc001655
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发表时间：
2005-11-23
期刊：
影响因子：
4.2
通讯作者：
Okamoto, S
中科院分区：
文献类型：
--
作者：
Kondo, H;Kimura, G;Okamoto, S
[1]对日本西南部九州的野冈逆冲断层进行了研究，以了解孕震的无序逆冲断层（OST）与增生棱柱体中流体流动之间的关系。野冈逆冲断层是一个在孕震深度处活动的断层。上盘表现出渗透性塑性变形，而一个脆的，catacquantummelange-like发生的下盘的特点，虽然他们都有相同的页岩和砂岩为主的原岩。镜质组反射率分析表明，上盘和下盘的最高温度分别约为320和250摄氏度。假设地热梯度为28 - 47摄氏度/公里，则跨越逆冲断层的热间隙相当于8.6 - 14.4公里的位移。逆冲断层的脆性破坏带是不对称的，上盘仅2 m，下盘100 m。三种类型的矿脉，石英和碳酸盐岩发育良好，特别是在损坏的下盘：张裂隙充填脉，断层充填脉和后混杂岩。第一个是与织物和谐，垂直于P面。流体包裹体温压测试表明，下盘强烈破坏带流体P-T值约为300 ℃，230 ~ 250 MPa，高于镜质体反射率值，表明热液流体流动与变形有关。下盘损伤带最低部位的同类型矿脉，其P-T流体含量低得多。这种差异表明，连续底侵造成的损坏区传播向下冷却和变浅，这不同于断层特征的剪切本地化，可能是唯一的含水OSR在增生复合体。
[1] Nobeoka Thrust in Kyushu, southwest Japan, was investigated to understand the relationship between the seismogenic out-of-sequence thrust (OST) and fluid flow in accretionary prisms. The Nobeoka Thrust is a fossilized OST, being active at seismogenic depth. The hanging wall exhibits a penetrative plastic deformation, while a brittle, cataclastic melange-like occurrence characterizes the footwall, although both of them have same shale and sandstone-dominant protolith. Vitrinite reflectance analyses indicate that the maximum temperatures of the hanging wall and footwall are approximately 320 and 250 degrees C, respectively. This thermal gap across the thrust corresponds to 8.6 - 14.4 km of displacement assuming a 28 - 47 degrees C/km geothermal gradient. The brittle damage zone of the thrust is asymmetric: only 2 m for hanging wall side and 100 m for footwall. Three types of mineral veins, quartz, and carbonate are well developed, especially in the damaged footwall: the tension crack-filling vein, the fault-filling vein, and postmelange one. The first is harmonious with fabric, perpendicular to the P surface. Fluid inclusion geothermobarometry indicates the P-T of fluid in the intensively damaged zone of the footwall is similar to 300 degrees C, 230 - 250 MPa, higher than that from vitrinite reflectance, which suggests that hydrothermal fluid flow is associated with deformation. The same type vein in the lowest portion of the footwall- damaged zone includes a much lower P-T fluid. This difference suggests that continuous underplating caused the damaged zone to propagate downward with cooling and shallowing, which differs from faults characterized by shear localization and might be unique to aquiferous OSR in accretionary complexes.