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首页> 外文期刊>Journal of Asian earth sciences >Fluid overpressure along an Oligocene out-of-sequence thrust in the Shimanto Belt, SW Japan
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Fluid overpressure along an Oligocene out-of-sequence thrust in the Shimanto Belt, SW Japan

机译：日本西南部Shimanto带中渐新世无序推力的流体超压

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Out-of-sequence thrusts (OSTs) exposed in ancient accretionary prisms are considered as fossil analogs of present-day megasplay faults in subduction margins and can provide direct information about the conditions of deformation during thrust activity. In modern as well as in ancient accretionary prisms, first-order megasplay faults or OSTs truncate or merge with faults of lesser importance called second-order OSTs. Structural analysis of the Makinokuchi fault, a branch of an Oligocene to lower Miocene second-order OST in the Tertiary Shimanto Belt of central Kyushu, SW Japan, brings information about the conditions of deformation at the time of thrusting. The studied exposure shows that the fault footwall and, to a much lesser extent, the fault hanging-wall, consist of quartz-cemented syntectonic dilatant hydraulic breccias testifying to pore fluid pressures larger than the least principal stress component. The footwall sandstones are crossed by several centimeters thick quartz veins that merge with the footwall breccias. The continuity between the veins and the breccias suggest that the veins acted as conduits which likely collected fluids from the footwall side sandstones upward and toward the fault. Fluid inclusions indicate that the quartz cementing the breccias and that filling the feeder veins crystallized from similar fluids and under similar pressure and temperature conditions (245-285 ℃ and 5-8 km depth). These similarities suggest that the fluids responsible for syn-tectonic hydraulic brecciation were collected from the footwall through the conduits. The fluid inclusion trapping temperatures are close to the temperatures expected to be reached along the seismogenic zone. Our analysis shows that fluid overpressures can play a key role in the growth and activity of second-order OSTs in accretionary prisms and suggests that fluids collected along second-order OSTs or splay faults may flow upward along first-order OSTs or megasplay faults.
机译：古代增生棱镜中暴露的乱序逆冲推力（OSTs）被认为是当今俯冲带巨震断层的化石类似物，并可提供有关推力活动过程中变形条件的直接信息。在现代以及古代的增生棱镜中，一阶兆张断层或OST都被截断或合并为次要重要性较低的二阶OST。对日本西南部九州中部第三纪四万十带中渐新世至下中新世二阶OST的一个分支-Makinokuchi断层的结构分析，提供了有关冲断时变形条件的信息。研究表明，断层下盘壁和断层上盘壁由石英胶结的构造扩张性水力角砾岩组成，其孔隙流体压力大于最小主应力分量。下盘砂岩与几厘米厚的石英脉相交，并与下盘角砾岩合并。静脉和角砾岩之间的连续性表明，这些静脉起着导管的作用，可能从底盘侧砂岩向上并向断层收集流体。流体包裹体表明石英胶结了角砾岩，充满了类似流体，并且在类似压力和温度条件下（245-285℃，深度为5-8 km）结晶了馈线。这些相似性表明，负责构造水力压裂的流体是通过导管从下壁收集的。流体夹杂物的捕集温度接近预期在地震发生带将达到的温度。我们的分析表明，流体超压在增生棱镜中对二阶OST的生长和活动起着关键作用，并表明沿二阶OST或张开断层收集的流体可能沿一阶OST或兆张断层向上流动。

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