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首页> 外文期刊>Journal of geodynamics >One My scale subsidence of carbonate sedimentary bodies and the viscosity of the lower crust
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One My scale subsidence of carbonate sedimentary bodies and the viscosity of the lower crust

机译：碳酸盐沉积体和下地壳粘度的My My级沉降

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The possibility of flow of the lower crust under the load produced by carbonate sedimentary accumulations is investigated through the example of the Paris basin during the Middle Jurassic (i.e. Bathonian). Depositional geometries, water depths and sedimentary environments have been estimated and correlated for 164 sites spread over a surface of 380 per 220 km for three successive periods lasting each less than 0.8 My. A signal of relative vertical displacement has been extracted from water-depth and sedimentary thickness. Data have then been interpolated to produce maps of velocity of vertical displacement, sedimentation rate, water depth, and water-depth variation between two periods. The maps show that the western part of the basin is affected by faults which are independent of the sedimentation. The eastern part of the basin consists of a shallow carbonate platform affected by diffuse subsidence patches which are positively correlated with sedimentation. The patches of diffuse subsidence are elliptic in shape, with a radius of 20 km, a mean thickness of 40 m, and a maximum elevation of 10 m above the surrounding sea bottom. We suggest that the load of these patches induces the flow of the lower crust. The topography produced by these patches would be maintained at steady state by in situ carbonate production/accumulation combined with the lower crust flow. This model is tested by estimating the viscosity and the thickness of the flowing crust necessary to meet the geometric and kinematic conditions obtained from the patches. This model is valid for a lower crust viscosity of around 10~(21) Pa s. This value is higher by one order of magnitude than those inferred from other contexts but can be explained by the influence on viscosity of the load and temperature for a non-newtonian rock rheology.
机译：通过中侏罗纪（即巴东期）巴黎盆地的例子，研究了下地壳在碳酸盐沉积物所产生的载荷作用下流动的可能性。已评估了分布的几何形状，水深和沉积环境，并在三个连续的时期（每一个持续时间均小于0.8 My）的164个站点分布在每220 km的380个表面上。从水深和沉积厚度中提取出相对垂直位移的信号。然后对数据进行插值，以生成两个时期之间垂直位移速度，沉降速率，水深和水深变化的图。这些图表明，盆地西部受到断层的影响，而断层与沉积无关。盆地东部由一个浅碳酸盐台地组成，该碳酸盐台地受到与沉降成正相关的弥散性沉降片的影响。弥散性沉降片为椭圆形，半径为20 km，平均厚度为40 m，最大海拔高度为周围海底10 m。我们建议这些斑块的载荷引起下地壳的流动。这些地块产生的形貌将通过原位碳酸盐的生产/堆积和较低的地壳流量而保持在稳态。通过估算满足从贴片获得的几何和运动学条件所需的流动地壳的粘度和厚度来测试该模型。该模型适用于较低的地壳粘度约10〜（21）Pa s。该值比从其他情况推断的值高一个数量级，但可以通过非牛顿岩石流变学对载荷粘度和温度的影响来解释。

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