Thermal effects of marine sedimentation in hydrothermally active areas
Thermal effects of marine sedimentation in hydrothermally active areas
复制标题
热液活动区海洋沉积的热效应
DOI：
10.1111/j.1365-246x.1992.tb00714.x
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发表时间：
1992
影响因子：
2.8
通讯作者：
E. Davis
中科院分区：
文献类型：
--
作者：
Kelin Wang;E. Davis
作为一个热液活跃的海洋盆地，在高渗透性的基底岩石中，强烈的热液循环使上覆沉积剖面底部的温度保持在接近恒定的水平。为了研究这种地质环境下沉积的热效应，我们开发了一个简单的一维有限元模型，并将其应用于东北太平洋的情况。该模型考虑了压实过程中流体和沉积物颗粒的微分运动，可用于任意孔隙度-深度函数。结果清楚地表明，积累沉积物部分的恒定基底温度，由基底的对流传热维持，导致该部分即使在非常高的积累速率下仍保持热接近稳定状态，特别是与基底通过传导传热的部分的估计条件相比。由于更新世后沉积物供应的严重减少，10年的热恢复期进一步大大减少了沉积的热效应。只有在积累速率超过每年10毫米和沉积物厚度超过1公里的极少数情况下，海底热流和深度温度才会显著降低。Juan de Fuca Ridge的中部山谷就是一个例子，在过去的200年中，该山谷的一部分积聚了超过2公里的沉积物。即使在这种极端情况下，估计热流也只比稳定状态低15%左右。虽然在中部山谷的其他部分和许多其他热液活跃地区，如瓜亚马斯盆地、埃斯卡纳巴槽和胡安·德·富卡山脊的东侧，积累速率也很高，但发现这些速率和积累的沉积物厚度不足以引起明显的热异常。
SUMMARY a hydrothermally active ocean basin, vigorous hydrothermal circulation in highly permeable basement rocks maintains a nearly constant temperature at the base of the overlying accumulating sediment section. To investigate the thermal effects of sedimentation in such geological settings, we have developed a simple onedimensional finite element model and applied it to cases in the northeast Pacific. The model accounts for differential motion of fluids and sediment grains during compaction, and can be used with any porosity-depth function. Results demonstrate clearly that the constant basal temperature of an accumulating sediment section, maintained by convective heat transfer in the basement, causes the section to remain thermally near steady state for even very high rates of accumulation, particularly when compared to conditions 'estimated for a section where heat is transported in the basement by conduction. A 10-kyr period of thermal recovery due to the highly diminished sediment supply during the post-Pleistocene further reduces the thermal effects of sedimentation by a significant amount. Only in rare cases where rates of accumulation exceed 10 mm yr-l and sediment thicknesses exceed 1 km are the sea-floor heat flow and temperatures at depth diminished significantly. An example is found in Middle Valley of the Juan de Fuca Ridge, in a part of which over 2 km of sediment has accumulated in the past 200 kyr. Even in this extreme case, the heat flow is estimated to be lower than that of the steady state by about only 15 per cent. While rates of accumulation are also high in other parts of Middle Valley and in many other hydrothermally active areas, such as Guayamas Basin, Escanaba Trough and the eastern flank of the Juan de Fuca Ridge, these rates and the accumulated sediment thicknesses are found to be insufficient to cause appreciable thermal anomalies.