Reappraising elastic thickness variation at oceanic trenches
Reappraising elastic thickness variation at oceanic trenches
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DOI：
10.1029/2005jb004190
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发表时间：
2007-08-18
影响因子：
3.9
通讯作者：
White, Nicky
中科院分区：
文献类型：
--
作者：
Bry, Madeleine;White, Nicky
我们使用垂直于海沟的测深和自由空气重力剖面全球数据库重新评估弹性厚度随岩石圈板块年龄的变化。与之前的许多研究一样，我们的出发点是众所周知的浮动弹性板模型。为了消除与岩石圈弯曲无关的短波长特征的影响，来自 10-Myr bin 的相邻剖面被堆叠在一起以构建具有标准偏差的平均剖面。然后通过两阶段程序反转每个平均轮廓。首先，对于任何给定的弹性厚度，使用奇异值分解来确定两个未知的弯曲参数，以及区域斜率和偏移量。对于一定范围的弹性厚度重复该过程。其次，将残余失配绘制为弹性厚度的函数，并确定了全局最小值。该两阶段过程没有预先假设载荷大小、弯矩大小或弹性板是否断裂/连续。我们在年龄范围为 0 - 150 Ma 的岩石圈测深和重力剖面中获得了理论与观测之间的良好拟合。残差失配函数的形状表明我们对弹性厚度估计的置信度。弹性厚度的下限通常是明确确定的，但上限通常很难约束。使用一系列剖面长度（250 - 300、500 和 700 公里）进行逆建模。一般来说，我们的估计表明弹性厚度随着板龄的变化而没有一致的增加。这一令人惊讶的结果与最近对海山下方弹性厚度的重新评估一致，并且意味着弹性厚度与板块年龄无关，或者弹性厚度无法以足够的精度测量来揭示这种关系。短自由空气重力剖面（250 - 300 km）的建模确实初步表明，弹性厚度在 0 到 20 Ma 之间从 5 公里线性增加到 10 km，在 20 到 150 Ma 之间从 10 到 15 km 线性增加。这种变化与 200 摄氏度等温线的深度大致匹配，该等温线对应于湿橄榄岩的同源温度 0.4。不幸的是，对于较长的轮廓长度，不存在时间依赖性，并且弹性厚度对于所有板龄来说变化很大。尽管不确定性更大，但测深剖面模型产生了类似的结果。
We reassess the variation of elastic thickness as a function of lithospheric plate age using a global database of bathymetric and free- air gravity profiles which are perpendicular to oceanic trenches. As in many previous studies, our starting point is the well- known floating elastic plate model. In order to remove the influence of short- wavelength features not associated with lithospheric bending, adjacent profiles from 10- Myr bins have been stacked together to construct average profiles with standard deviations. Each average profile was then inverted in a two- stage procedure. First, singular value decomposition was used to determine two unknown flexural parameters, together with a regional slope and offset, for any given elastic thickness. This procedure was repeated for a range of elastic thicknesses. Second, residual misfit was plotted as a function of elastic thickness, and the global minimum was identified. This two- stage procedure makes no prior assumptions about magnitude of the load, size of the bending moment, or whether the elastic plate is broken/ continuous. We obtained excellent fits between theory and observation for both bathymetric and gravity profiles from lithosphere with an age range of 0 - 150 Ma. The shape of the residual misfit function indicates the degree of confidence we have in our elastic thickness estimates. The lower limit of elastic thickness is usually well determined but upper limits are often poorly constrained. Inverse modeling was carried out using a range of profile lengths ( 250 - 300, 500, and 700 km). In general, our estimates show no consistent increase of elastic thickness as a function of plate age. This surprising result is consistent with recent reassessments of elastic thickness beneath seamounts and implies either that elastic thickness is independent of plate age or that elastic thickness cannot be measured with sufficient accuracy to reveal such a relationship. Modeling of short free- air gravity profiles ( 250 - 300 km) does tentatively suggest that elastic thickness increases linearly from 5 to 10 km between 0 and 20 Ma and from 10 to 15 km between 20 and 150 Ma. This variation roughly matches the depth to the 200 degrees C isotherm which corresponds to an homologous temperature of 0.4 for wet peridotite. Unfortunately, for longer profile lengths, there is no temporal dependence, and elastic thicknesses vary considerably for all plate ages. Bathymetric profile modeling yields similar results although uncertainties are larger.