THE EFFECTIVE ELASTIC THICKNESS (T-E) OF CONTINENTAL LITHOSPHERE - WHAT DOES IT REALLY MEAN
THE EFFECTIVE ELASTIC THICKNESS (T-E) OF CONTINENTAL LITHOSPHERE - WHAT DOES IT REALLY MEAN
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DOI：
10.1029/94jb02770
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发表时间：
1995-03-10
影响因子：
3.9
通讯作者：
DIAMENT, M
中科院分区：
文献类型：
--
作者：
BUROV, EB;DIAMENT, M
岩石圈在地质时间和空间尺度上表现出非零的力学强度是公认的，这与非岩石静（偏）应力的存在有关。表征岩石圈表观强度的参数是抗弯刚度D，通常通过岩石圈的有效弹性厚度（T-e）表示。海洋岩石圈的T-e估计值大致遵循深度到一个特定的等温线（类似于600摄氏度），这标志着机械岩石圈的基础。大陆有效弹性厚度的物理意义和重要性仍然是个谜，因为大陆岩石圈的T-e估计与特定的地质或物理边界关系不大。虽然观测到的高T-e值（介子为70-90 km）可以部分地用现今的温度梯度来解释，但低T-e值（10-20 km）一般不能解释。此外，弹性板模型是自相矛盾的，因为它们大多预测板内应力高到足以导致非弹性（脆性或韧性）变形，根据岩石力学数据。为了提供一个物理上一致的统一解释的大陆和海洋岩石圈的T-e的观测变化的基础上，我们开发了一个分析和数值方法，允许直接治疗的T-e岩石圈流变学，热结构，应变/应力分布。我们的技术是基于找到真正的非弹性和等效（有效）弹性的岩石圈与现实的脆弹韧性流变变形的问题的解决方案。我们表明，岩石圈的热状态（热构造年龄）是至少三个同样重要的属性，确定表观值的T-E之一。这些其他的属性是壳幔界面的状态（地壳和地幔的解耦），厚度和比例的机械能力的地壳和地幔，和局部曲率的板块，这是直接相关的弯曲应力。机械能力地壳的厚度和耦合或去耦的程度通常由上地壳和下地壳的成分、地壳的总厚度和地壳地热控制。Lf去耦发生，它允许多达50%的减少T-e，与T-e暗示从传统的热分布相比。理论预测的T-E与不同地区的推断值的比较表明，大多数大陆板块的下地壳具有低温活化流变学（如石英），允许壳幔解耦。板的曲率取决于流变结构和施加到板上的外部载荷的分布（例如，表面地形、沉积物填充和板块边界力）。主要山脉带产生的弯曲应力大到足以引起下面板块的非弹性变形（脆性破坏和韧性流动），这反过来又导致这些带下面的T-e降低30%至80%，而相邻区域下面的T-e降低更少。边界闹剧和时刻（例如，由于板拉力等）导致T-e的更局部但甚至更强的降低（例如，俯冲带的板块颈缩）。我们的方法提供了一个反馈之间的“观察”的T-E和神学，允许限制岩石圈结构的估计T-E。
It is well accepted that the lithosphere may exhibit nonzero mechanical strength over geological time and space scales, associated with the existence of non-lithostatic (deviatoric) stress. The parameter that characterizes the apparent strength of the lithosphere is the flexural rigidity D, which is commonly expressed through the effective elastic thickness (T-e) of the lithosphere. Estimates of T-e for oceanic lithosphere approximately follow the depth to a specific isotherm (similar to 600 degrees C), which marks the base of the mechanical lithosphere. The physical meaning and significance of the effective elastic thickness for continents are still enigmatic, because for continental lithosphere estimates of T-e bear little relation to specific geological or physical boundaries. Although high observed values of T-e (70-90 km for cratons) can be partly explained by the present-day temperature gradients, the low values (10-20 km), in general, cannot. In addition, the elastic plate models are self-inconsistent in that they mostly predict intraplate stresses high enough to lead to inelastic (brittle or ductile) deformation, according to data of rock mechanics. To provide a basis for a physically consistent unified interpretation of the observed variations of T-e for continental and oceanic lithosphere, we developed an analytical and numerical approach that allows direct treatment of T-e in terms of the lithospheric theology, thermal structure, and strain/stress distribution. Our technique is based on finding true inelastic and equivalent (effective) elastic solutions for the problem of deformation of the lithosphere with realistic brittle-elasto-ductile theology. We show that the thermal state (thermotectonic age) of the lithosphere is only one of at least three equally important properties that determine apparent values of T-e. These other properties are the state of the crust-mantle interface (decoupling of crust and mantle), the thickness and proportions of the mechanically competent crust and mantle, and the local curvature of the plate, which is directly related to the bending stresses. The thickness of the mechanically competent crust and the degree of coupling or decoupling is generally controlled by composition of the upper and lower crust, total thickness of the crust, and by the crustal geotherm. Lf decoupling takes place, it permits as much as 50% decrease of T-e, compared with T-e implied from conventional thermal profiles. Comparison of the theoretically predicted T-e with inferred values for different regions suggests that the lower crust of most continental plates has a low-temperature activation theology (such as quartz) which permits crust and mantle decoupling. The curvature of the plate depends on the theological structure and on the distribution of external loads applied to the plate (e.g., surface topography, sediment fill, and plate-boundary forces). Bending stresses created by major mountain belts are large enough to cause inelastic deformation (brittle failure and a ductile flow) in the underlying plate, which, in turn, leads to a 30 to 80% decrease of T-e beneath such belts and less beneath the adjacent regions. The boundary farces and moments (e.g., due to the slab pull, etc.) lead to more localized but even stronger reductions in T-e (e.g., plate necking in subduction zones). Our approach provides a feedback between the ''observed'' T-e and theology, allowing to constrain the lithospheric structure from estimates of T-e.